Development of a low cost method to estimate the seismic signature of a geothermal field from ambient seismic noise analysis, Authors: Tibuleac, I. M., J. Iovenitti, S. Pullammanapallil, D. von Seggern, F.H. Ibser, D. Shaw and H. McLahlan

NASA Astrophysics Data System (ADS)

Tibuleac, I. M.; Iovenitti, J. L.; Pullammanappallil, S. K.; von Seggern, D. H.; Ibser, H.; Shaw, D.; McLachlan, H.

2015-12-01

A new, cost effective and non-invasive exploration method using ambient seismic noise has been tested at Soda Lake, NV, with promising results. Seismic interferometry was used to extract Green's Functions (P and surface waves) from 21 days of continuous ambient seismic noise. With the advantage of S-velocity models estimated from surface waves, an ambient noise seismic reflection survey along a line (named Line 2), although with lower resolution, reproduced the results of the active survey, when the ambient seismic noise was not contaminated by strong cultural noise. Ambient noise resolution was less at depth (below 1000m) compared to the active survey. Useful information could be recovered from ambient seismic noise, including dipping features and fault locations. Processing method tests were developed, with potential to improve the virtual reflection survey results. Through innovative signal processing techniques, periods not typically analyzed with high frequency sensors were used in this study to obtain seismic velocity model information to a depth of 1.4km. New seismic parameters such as Green's Function reflection component lateral variations, waveform entropy, stochastic parameters (Correlation Length and Hurst number) and spectral frequency content extracted from active and passive surveys showed potential to indicate geothermal favorability through their correlation with high temperature anomalies, and showed potential as fault indicators, thus reducing the uncertainty in fault identification. Geothermal favorability maps along ambient seismic Line 2 were generated considering temperature, lithology and the seismic parameters investigated in this study and compared to the active Line 2 results. Pseudo-favorability maps were also generated using only the seismic parameters analyzed in this study.

1D Seismic reflection technique to increase depth information in surface seismic investigations

NASA Astrophysics Data System (ADS)

Camilletti, Stefano; Fiera, Francesco; Umberto Pacini, Lando; Perini, Massimiliano; Prosperi, Andrea

2017-04-01

1D seismic methods, such as MASW Re.Mi. and HVSR, have been extensively used in engineering investigations, bedrock research, Vs profile and to some extent for hydrologic applications, during the past 20 years. Recent advances in equipment, sound sources and computer interpretation techniques, make 1D seismic methods highly effective in shallow subsoil modeling. Classical 1D seismic surveys allows economical collection of subsurface data however they fail to return accurate information for depths greater than 50 meters. Using a particular acquisition technique it is possible to collect data that can be quickly processed through reflection technique in order to obtain more accurate velocity information in depth. Furthermore, data processing returns a narrow stratigraphic section, alongside the 1D velocity model, where lithological boundaries are represented. This work will show how collect a single-CMP to determine: (1) depth of bedrock; (2) gravel layers in clayey domains; (3) accurate Vs profile. Seismic traces was processed by means a new software developed in collaboration with SARA electronics instruments S.r.l company, Perugia - ITALY. This software has the great advantage of being able to be used directly in the field in order to reduce the times elapsing between acquisition and processing.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Doug Blankenship

PDFs of seismic reflection profiles 101,110, 111 local to the West Flank FORGE site. 45 line kilometers of seismic reflection data are processed data collected in 2001 through the use of vibroseis trucks. The initial analysis and interpretation of these data was performed by Unruh et al. (2001). Optim processed these data by inverting the P-wave first arrivals to create a 2-D velocity structure. Kirchhoff images were then created for each line using velocity tomograms (Unruh et al., 2001).

Archive of digital boomer and CHIRP seismic reflection data collected during USGS cruise 06FSH03 offshore of Fort Lauderdale, Florida, September 2006

USGS Publications Warehouse

Harrison, Arnell S.; Dadisman, Shawn V.; Reich, Christopher D.; Wiese, Dana S.; Greenwood, Jason W.; Swarzenski, Peter W.

2007-01-01

In September of 2006, the U.S. Geological Survey conducted geophysical surveys offshore of Fort Lauderdale, FL. This report serves as an archive of unprocessed digital boomer and CHIRP seismic reflection data, trackline maps, navigation files, GIS information, Field Activity Collection System (FACS) logs, observer's logbook, and formal FGDC metadata. Filtered and gained digital images of the seismic profiles are also provided. The archived trace data are in standard Society of Exploration Geophysicists (SEG) SEG-Y format (Barry and others, 1975) and may be downloaded and processed with commercial or public domain software such as Seismic Unix (SU). Example SU processing scripts and USGS software for viewing the SEG-Y files (Zihlman, 1992) are also provided.

Time-Lapse Acoustic Impedance Inversion in CO2 Sequestration Study (Weyburn Field, Canada)

NASA Astrophysics Data System (ADS)

Wang, Y.; Morozov, I. B.

2016-12-01

Acoustic-impedance (AI) pseudo-logs are useful for characterising subtle variations of fluid content during seismic monitoring of reservoirs undergoing enhanced oil recovery and/or geologic CO2 sequestration. However, highly accurate AI images are required for time-lapse analysis, which may be difficult to achieve with conventional inversion approaches. In this study, two enhancements of time-lapse AI analysis are proposed. First, a well-known uncertainty of AI inversion is caused by the lack of low-frequency signal in reflection seismic data. To resolve this difficulty, we utilize an integrated AI inversion approach combining seismic data, acoustic well logs and seismic-processing velocities. The use of well logs helps stabilizing the recursive AI inverse, and seismic-processing velocities are used to complement the low-frequency information in seismic records. To derive the low-frequency AI from seismic-processing velocity data, an empirical relation is determined by using the available acoustic logs. This method is simple and does not require subjective choices of parameters and regularization schemes as in the more sophisticated joint inversion methods. The second improvement to accurate time-lapse AI imaging consists in time-variant calibration of reflectivity. Calibration corrections consist of time shifts, amplitude corrections, spectral shaping and phase rotations. Following the calibration, average and differential reflection amplitudes are calculated, from which the average and differential AI are obtained. The approaches are applied to a time-lapse 3-D 3-C dataset from Weyburn CO2 sequestration project in southern Saskatchewan, Canada. High quality time-lapse AI volumes are obtained. Comparisons with traditional recursive and colored AI inversions (obtained without using seismic-processing velocities) show that the new method gives a better representation of spatial AI variations. Although only early stages of monitoring seismic data are available, time-lapse AI variations mapped within and near the reservoir zone suggest correlations with CO2 injection. By extending this procedure to elastic impedances, additional constraints on the variations of physical properties within the reservoir can be obtained.

Seismic depth imaging of sequence boundaries beneath the New Jersey shelf

NASA Astrophysics Data System (ADS)

Riedel, M.; Reiche, S.; Aßhoff, K.; Buske, S.

2018-06-01

Numerical modelling of fluid flow and transport processes relies on a well-constrained geological model, which is usually provided by seismic reflection surveys. In the New Jersey shelf area a large number of 2D seismic profiles provide an extensive database for constructing a reliable geological model. However, for the purpose of modelling groundwater flow, the seismic data need to be depth-converted which is usually accomplished using complementary data from borehole logs. Due to the limited availability of such data in the New Jersey shelf, we propose a two-stage processing strategy with particular emphasis on reflection tomography and pre-stack depth imaging. We apply this workflow to a seismic section crossing the entire New Jersey shelf. Due to the tomography-based velocity modelling, the processing flow does not depend on the availability of borehole logging data. Nonetheless, we validate our results by comparing the migrated depths of selected geological horizons to borehole core data from the IODP expedition 313 drill sites, located at three positions along our seismic line. The comparison yields that in the top 450 m of the migrated section, most of the selected reflectors were positioned with an accuracy close to the seismic resolution limit (≈ 4 m) for that data. For deeper layers the accuracy still remains within one seismic wavelength for the majority of the tested horizons. These results demonstrate that the processed seismic data provide a reliable basis for constructing a hydrogeological model. Furthermore, the proposed workflow can be applied to other seismic profiles in the New Jersey shelf, which will lead to an even better constrained model.

Seismic Imaging of Circumpolar Deep Water Exchange across the Shelf Break of the Antarctic Peninsula

NASA Astrophysics Data System (ADS)

Gunn, K.; White, N.; Larter, R. D.; Falder, M.; Caulfield, C. C. P.

2016-02-01

The western Antarctic Peninsula is an area of recent extreme atmospheric warming. In the adjacent ocean, there is particular interest in on-shelf movement of Circumpolar Deep Water as a possible link to changing climate by affecting ice shelf processes. Here, we investigate on-shelf intrusions using two-dimensional seismic imaging of the water column which has vertical and horizontal resolutions of 10 m. 8 seismic profiles were acquired in February 2015 using the RRS James Clark Ross. These profiles traverse the shelf break and cross two bathymetric features, the Marguerite and Biscoe troughs, which may play a role in water exchange processes. Seismic data were acquired using two Generator-Injector air guns fired every 10 s with a pressure of 2000 psi. Reflections were recorded on a 2.4 km streamer of 192 receivers spaced every 12.5 m. Observed reflections in the processed records are caused by rapid changes of temperature ( 80%) and salinity ( 20%), delineating water masses of different properties. 13 XCTDs and XBTs plus a 38 kHz echo-sounder profile were simultaneously acquired along seismic profiles and used for calibration. Preliminary results show the top of the Winter Water layer as a bright reflection at 50-120 m depth across the entire survey, corresponding to temperatures ≤ -1°C. Curved, discontinuous, eddy-like reflections, also seen on echo-sounder profiles, are attributed to modified Upper Circumpolar Deep Water with temperatures ≥ 1.34°C. A warm core eddy, 11 km long and 220 m high, is visible 2 km inland of the shelf break. Pure Upper Circumpolar Deep Water of temperatures ≥ 1.80°C is aligned with weak but discernible, lens-shaped reflections. Eddy-like structures and the overall reflective morphology yield useful insights into shelf exchange processes, suggestive of three potential mechanisms: (i) topography controlled flow; (ii) an 'ice-pump' mechanism; and (iii) mesoscale eddies.

The Mohorovičić discontinuity beneath the continental crust: An overview of seismic constraints

NASA Astrophysics Data System (ADS)

Carbonell, Ramon; Levander, Alan; Kind, Rainer

2013-12-01

The seismic signature of the Moho from which geologic and tectonic evolution hypotheses are derived is to a large degree a result of the seismic methodology which has been used to obtain the image. Seismic data of different types, passive source (earthquake) broad-band recordings, and controlled source seismic refraction, densely recorded wide-angle deep seismic reflection, and normal incidence reflection (using VibroseisTM, explosives, or airguns), have contributed to the description of the Moho as a relatively complex transition zone. Of critical importance for the quality and resolution of the seismic image are the acquisition parameters, used in the imaging experiments. A variety of signatures have been obtained for the Moho at different scales generally dependent upon bandwidth of the seismic source. This variety prevents the development of a single universally applicable interpretation. In this way source frequency content, and source and sensor spacing determine the vertical and lateral resolution of the images, respectively. In most cases the different seismic probes provide complementary data that gives a fuller picture of the physical structure of the Moho, and its relationship to a petrologic crust-mantle transition. In regional seismic studies carried out using passive source recordings the Moho is a relatively well defined structure with marked lateral continuity. The characteristics of this boundary change depending on the geology and tectonic evolution of the targeted area. Refraction and wide-angle studies suggest the Moho to be often a relatively sharp velocity contrast, whereas the Moho in coincident high quality seismic reflection images is often seen as the abrupt downward decrease in seismic reflectivity. The origin of the Moho and its relation to the crust-mantle boundary is probably better constrained by careful analysis of its internal details, which can be complex and geographically varied. Unlike the oceanic Moho which is formed in a relatively simple, well understood process, the continental Moho can be subject to an extensive variety of tectonic processes, making overarching conclusions about the continental Moho difficult. Speaking very broadly: 1) In orogenic belts still undergoing compression and active continental volcanic arcs, the Moho evolves with the mountain belt, 2) In collapsed Phanerozoic orogenic belts the Moho under the collapse structure was formed during the collapse, often by a combination of processes. 3) In regions having experienced widespread basaltic volcanism, the Moho can result from underplated basalt and basaltic residuum. In Precambrian terranes the Moho may be as ancient as the formation of the crust, in others Precambrian tectonic and magmatic processes have reset it. We note that seismic reflection data in Phanerosoic orogens as well as from Precambrian cratonic terranes often show thrust type structures extending as deep as the Moho, and suggest that even where crust and mantle xenoliths provide similar age of formation dates, the crust may be semi-allochothonous.

Seismic Evidence And Complex Trace Attributes Of Shallow Gas Structures In The Sea Of Marmara

NASA Astrophysics Data System (ADS)

Aydemir, Seval; Okay, Seda; Cifci, Gunay; Dondurur, Derman; Sorlien, Christopher; Cormier, Marie-Helene

2015-04-01

Analysis of multi-channel seismic reflection, sparker and chirp data from Marmara Sea observed various shallow gas indicators including seismic chimneys, bright spots, mud diapirs, pockmarks, and acoustic blanking related to gas accumulations along North Anatolian Fault (NAF) system which branches out towards the west into the in Marmara Sea. Middle branch of the (NAF) is the place where distinct amount of seismic activity has occurred and gas deposits have been observed. This study is also devoted to evaluate the gas related structures with seismic attributes of multichannel seismic reflection data which have been collected at South Marmara shelf. The dataset was collected in September 2013 and July 2014 including nearly 1000 km high Resolution Multichannel Seismic and Chirp data and 967 km Sparker data in the frame of a bilateral TÜBİTAK Project onboard R/V K. Piri Reis. The streamer has 168 or 144 channel and group interval was 6.25 m. The source was 45+45 inch GI gun fired every 12.5 or 25 m producing high-resolution seismic signal between 10-250 Hz frequency bands. The Chirp data was collected with a transducer, which produced acoustic signal between 2.75-6.75 kHz. The source of sparker system was used to 1000 J. The data have been processed using a conventional data processing flow. In addition attributes were applied to final migration sections and than was tried to find gas accumulations with Reflection strength section, instantaneous frequency section and apparent polarity. Reflection strength section has strong reflections (bright spot). Also instantaneous frequency section has low-frequency zone depending on absorption where gas accumulations are expected. Apparent polarity section has negative polarity anamoly due to low acoustic impedance where gas accumulations are expected in sediments. In addition, attributes were coincided with sparker and chirp data where expected shallow gas accumulations.

Wave equation datuming applied to S-wave reflection seismic data

NASA Astrophysics Data System (ADS)

Tinivella, U.; Giustiniani, M.; Nicolich, R.

2018-05-01

S-wave high-resolution reflection seismic data was processed using Wave Equation Datuming technique in order to improve signal/noise ratio, attenuating coherent noise, and seismic resolution and to solve static corrections problems. The application of this algorithm allowed obtaining a good image of the shallow subsurface geological features. Wave Equation Datuming moves shots and receivers from a surface to another datum (the datum plane), removing time shifts originated by elevation variation and/or velocity changes in the shallow subsoil. This algorithm has been developed and currently applied to P wave, but it reveals the capacity to highlight S-waves images when used to resolve thin layers in high-resolution prospecting. A good S-wave image facilitates correlation with well stratigraphies, optimizing cost/benefit ratio of any drilling. The application of Wave Equation Datuming requires a reliable velocity field, so refraction tomography was adopted. The new seismic image highlights the details of the subsoil reflectors and allows an easier integration with borehole information and geological surveys than the seismic section obtained by conventional CMP reflection processing. In conclusion, the analysis of S-wave let to characterize the shallow subsurface recognizing levels with limited thickness once we have clearly attenuated ground roll, wind and environmental noise.

Geometry and slip rates of active blind thrusts in a reactivated back-arc rift using shallow seismic imaging: Toyama basin, central Japan

NASA Astrophysics Data System (ADS)

Ishiyama, Tatsuya; Kato, Naoko; Sato, Hiroshi; Koshiya, Shin; Toda, Shigeru; Kobayashi, Kenta

2017-10-01

Active blind thrust faults, which can be a major seismic hazard in urbanized areas, are commonly difficult to image with seismic reflection surveys. To address these challenges in coastal plains, we collected about 8 km-long onshore high-resolution two-dimensional (2D) seismic reflection data using a dense array of 800 geophones across compressionally reactivated normal faults within a failed rift system located along the southwestern extension of the Toyama trough in the Sea of Japan. The processing of the seismic reflection data illuminated their detailed subsurface structures to depths of about 3 km. The interpreted depth-converted section, correlated with nearby Neogene stratigraphy, indicated the presence of and along-strike variation of previously unrecognized complex thrust-related structures composed of active fault-bend folds coupled with pairs of flexural slip faults within the forelimb and newly identified frontal active blind thrusts beneath the alluvial plain. In addition, growth strata and fold scarps that deform lower to upper Pleistocene units record the recent history of their structural growth and fault activity. This case shows that shallow seismic reflection imaging with densely spaced seismic recorders is a useful tool in defining locations, recent fault activity, and complex geometry of otherwise inaccessible active blind thrust faults.

Archive of digital and digitized analog boomer seismic reflection data collected during USGS cruise 96CCT02 in Copano, Corpus Christi, and Nueces Bays and Corpus Christi Bayou, Texas, July 1996

USGS Publications Warehouse

Harrison, Arnell S.; Dadisman, Shawn V.; Kindinger, Jack G.; Morton, Robert A.; Blum, Mike D.; Wiese, Dana S.; Subiño, Janice A.

2007-01-01

In June of 1996, the U.S. Geological Survey conducted geophysical surveys from Nueces to Copano Bays, Texas. This report serves as an archive of unprocessed digital boomer seismic reflection data, trackline maps, navigation files, GIS information, cruise log, and formal FGDC metadata. Filtered and gained digital images of the seismic profiles and high resolution scanned TIFF images of the original paper printouts are also provided. The archived trace data are in standard Society of Exploration Geophysicists (SEG) SEG-Y format (Barry and others, 1975) and may be downloaded and processed with commercial or public domain software such as Seismic Unix (SU). Example SU processing scripts and USGS software for viewing the SEG-Y files (Zihlman, 1992) are also provided.

Archive of Digital Boomer Seismic Reflection Data Collected During USGS Field Activity 08LCA04 in Lakes Cherry, Helen, Hiawassee, Louisa, and Prevatt, Central Florida, September 2008

USGS Publications Warehouse

Harrison, Arnell S.; Dadisman, Shawn V.; Davis, Jeffrey B.; Flocks, James G.; Wiese, Dana S.

2009-01-01

From September 2 through 4, 2008, the U.S. Geological Survey and St. Johns River Water Management District (SJRWMD) conducted geophysical surveys in Lakes Cherry, Helen, Hiawassee, Louisa, and Prevatt, central Florida. This report serves as an archive of unprocessed digital boomer seismic reflection data, trackline maps, navigation files, GIS information, FACS logs, and formal FGDC metadata. Filtered and gained digital images of the seismic profiles are also provided. The archived trace data are in standard Society of Exploration Geophysicists (SEG) SEG-Y format (Barry and others, 1975) and may be downloaded and processed with commercial or public domain software such as Seismic Unix (SU). Example SU processing scripts and USGS software for viewing the SEG-Y files (Zihlman, 1992) are also provided.

Seismic Linear Noise Attenuation with Use of Radial Transform

NASA Astrophysics Data System (ADS)

Szymańska-Małysa, Żaneta

2018-03-01

One of the goals of seismic data processing is to attenuate the recorded noise in order to enable correct interpretation of the image. Radial transform has been used as a very effective tool in the attenuation of various types of linear noise, both numerical and real (such as ground roll, direct waves, head waves, guided waves etc). The result of transformation from offset - time (X - T) domain into apparent velocity - time (R - T) domain is frequency separation between reflections and linear events. In this article synthetic and real seismic shot gathers were examined. One example was targeted at far offset area of dataset where reflections and noise had similar apparent velocities and frequency bands. Another example was a result of elastic modelling where linear artefacts were produced. Bandpass filtering and scaling operation executed in radial domain attenuated all discussed types of linear noise very effectively. After noise reduction all further processing steps reveal better results, especially velocity analysis, migration and stacking. In all presented cases signal-to-noise ratio was significantly increased and reflections covered previously by noise were revealed. Power spectra of filtered seismic records preserved real dynamics of reflections.

High-resolution lithospheric imaging with seismic interferometry

NASA Astrophysics Data System (ADS)

Ruigrok, Elmer; Campman, Xander; Draganov, Deyan; Wapenaar, Kees

2010-10-01

In recent years, there has been an increase in the deployment of relatively dense arrays of seismic stations. The availability of spatially densely sampled global and regional seismic data has stimulated the adoption of industry-style imaging algorithms applied to converted- and scattered-wave energy from distant earthquakes, leading to relatively high-resolution images of the lower crust and upper mantle. We use seismic interferometry to extract reflection responses from the coda of transmitted energy from distant earthquakes. In theory, higher-resolution images can be obtained when migrating reflections obtained with seismic interferometry rather than with conversions, traditionally used in lithospheric imaging methods. Moreover, reflection data allow the straightforward application of algorithms previously developed in exploration seismology. In particular, the availability of reflection data allows us to extract from it a velocity model using standard multichannel data-processing methods. However, the success of our approach relies mainly on a favourable distribution of earthquakes. In this paper, we investigate how the quality of the reflection response obtained with interferometry is influenced by the distribution of earthquakes and the complexity of the transmitted wavefields. Our analysis shows that a reasonable reflection response could be extracted if (1) the array is approximately aligned with an active zone of earthquakes, (2) different phase responses are used to gather adequate angular illumination of the array and (3) the illumination directions are properly accounted for during processing. We illustrate our analysis using a synthetic data set with similar illumination and source-side reverberation characteristics as field data recorded during the 2000-2001 Laramie broad-band experiment. Finally, we apply our method to the Laramie data, retrieving reflection data. We extract a 2-D velocity model from the reflections and use this model to migrate the data. On the final reflectivity image, we observe a discontinuity in the reflections. We interpret this discontinuity as the Cheyenne Belt, a suture zone between Archean and Proterozoic terranes.

New insights on shallow and deep crustal geological structures of BABEL line 7 marine reflection seismic data revealed from reprocessing

NASA Astrophysics Data System (ADS)

Shahrokhi, H.; Malehmir, A.; Sopher, D.

2012-04-01

The BABEL project (Baltic And Bothnian Echoes from the Lithosphere) was a collaboration among British, Danish, Finnish, German and Swedish geoscientists to collect deep-crustal reflection and wide-angle refraction profiles in Baltic Shield and Gulf of Bothnia. The acquisition of 2,268km of deep marine reflection seismic data was carried out in 1989. The BABEL line 7 runs in E-W direction in the Bothnian Sea, north of the Åland islands and east of the city of Gävle. Several authors presented the seismic results but with a main focus of imaging and interpreting deep crustal geological structures and the nature and the depth of Moho discontinuity along line 7. Based on this seismic data, several publications about velocity distributions within the crust, the depth and texture of Moho discontinuity and seismic reflectivity patterns in the crust were presented. Some evidence from the reflection seismic data was also presented to suggest Early Proterozoic plate tectonics in the Baltic Shield. Previous seismic images of the BABEL line 7 reflection data show a dramatic change in the reflectivity pattern from weakly reflective lower crust in the west to a more reflective lower crust in the east, which was attributed to a change from a rigid crust to a plastic crust from the west to the east. The BABEL line 7 reflection data were acquired with a total profile length of 174km, a set of 48 airguns towed at 7.5m depth, and 3000m long streamer with 60 channels spaced with 50m intervals and towed at 15m depth. Seismic data were recorded for 25s using 4ms sampling interval and 75m shot interval. Seismic data is characterized by strong source-generated noise at shallow travel times and strong but randomly distributed spurious spikes at later arrival times. In this study, we have recovered and reprocessed the seismic data along BABEL line 7. Using modern processing and imaging techniques, which were not available at the time, and with a focus on the shallow parts of the seismic data, we have managed to reveal reflections as shallow as 1s in the data. Some of these reflections appear to be a continuation of deeper reflections but now they appear to reach to the surface, allowing correlation with the near-surface geology. At least two major moderately dipping shear zones are visible in the reprocessed data in comparison with the previous results. Deeper reflections are also improved which together with the improvements in the shallow parts of the data should allow small-scale geological structures encounter along the BABEL line 7 to be refined.

Hydrogeologic structure underlying a recharge pond delineated with shear-wave seismic reflection and cone penetrometer data

USGS Publications Warehouse

Haines, S.S.; Pidlisecky, Adam; Knight, R.

2009-01-01

With the goal of improving the understanding of the subsurface structure beneath the Harkins Slough recharge pond in Pajaro Valley, California, USA, we have undertaken a multimodal approach to develop a robust velocity model to yield an accurate seismic reflection section. Our shear-wave reflection section helps us identify and map an important and previously unknown flow barrier at depth; it also helps us map other relevant structure within the surficial aquifer. Development of an accurate velocity model is essential for depth conversion and interpretation of the reflection section. We incorporate information provided by shear-wave seismic methods along with cone penetrometer testing and seismic cone penetrometer testing measurements. One velocity model is based on reflected and refracted arrivals and provides reliable velocity estimates for the full depth range of interest when anchored on interface depths determined from cone data and borehole drillers' logs. A second velocity model is based on seismic cone penetrometer testing data that provide higher-resolution ID velocity columns with error estimates within the depth range of the cone penetrometer testing. Comparison of the reflection/refraction model with the seismic cone penetrometer testing model also suggests that the mass of the cone truck can influence velocity with the equivalent effect of approximately one metre of extra overburden stress. Together, these velocity models and the depth-converted reflection section result in a better constrained hydrologic model of the subsurface and illustrate the pivotal role that cone data can provide in the reflection processing workflow. ?? 2009 European Association of Geoscientists & Engineers.

Seismic reflection and refraction data acquired in Canada Basin, Northwind Ridge and Northwind Basin, Arctic Ocean in 1988, 1992 and 1993

USGS Publications Warehouse

Grantz, Arthur; Hart, Patrick E.; May, Steven D.

2004-01-01

Seismic reflection and refraction data were collected in generally ice-covered waters of the Canada Basin and the eastern part of the Chukchi Continental Borderland of the Amerasia Basin, Arctic Ocean, during the late summers of 1988, 1992, and 1993. The data were acquired from a Polar class icebreaker, the U.S. Coast Guard Cutter Polar Star, using a seismic reflection system designed by the U.S. Geological Survey (USGS). The northernmost data extend to 78? 48' N latitude. In 1988, 155 km of reflection data were acquired with a prototype system consisting of a single 195 cubic inch air gun seismic source and a two-channel hydrophone streamer with a 150-m active section. In 1992 and 1993, 500 and 1,900 km, respectively, of seismic reflection profile data were acquired with an improved six air gun, 674 to 1303 cubic inch tuned seismic source array and the same two-channel streamer. In 1993, a 12-channel streamer with a 150-m active section was used to record five of the reflection lines and one line was acquired using a three air gun, 3,000 cubic inch source. All data were recorded with a DFS-V digital seismic recorder. Processed sections feature high quality vertical incidence images to more than 6 km of sub-bottom penetration in the Canada Basin. Refraction data were acquired with U.S. Navy sonobuoys recorded simultaneously with the seismic reflection profiles. In 1988 eight refraction profiles were recorded with the single air gun, and in 1992 and 1993 a total of 47 refraction profiles were recorded with the six air gun array. The sonobuoy refraction records, with offsets up to 35 km, provide acoustic velocity information to complement the short-offset reflection data. The report includes trackline maps showing the location of the data, as well as both digital data files (SEG-Y) and images of all of the profiles.

Seismic reflection images of shallow faulting, northernmost Mississippi embayment, north of the New Madrid seismic zone

USGS Publications Warehouse

McBride, J.H.; Nelson, W.J.

2001-01-01

High-resolution seismic reflection surveys document tectonic faults that displace Pleistocene and older strata just beyond the northeast termination of the New Madrid seismic zone, at the northernmost extent of the Mississippi embayment. These faults, which are part of the Fluorspar Area fault complex in southeastern Illinois, are directly in line with the northeast-trending seismic zone. The reflection data were acquired using an elastic weight-drop source recorded to 500 msec by a 48-geophone array (24-fold) with a 10-ft (??3.0m) station interval. Recognizable reflections were recorded to about 200 msec (100-150 m). The effects of multiple reflections, numerous diffractions, low apparent velocity (i.e., steeply dipping) noise, and the relatively low-frequency content of the recorded signal provided challenges for data processing and interpreting subtle fault offsets. Data processing steps that were critical to the detection of faults included residual statics, post-stack migration, deconvolution, and noise-reduction filtering. Seismic migration was crucial for detecting and mitigating complex fault-related diffraction patterns, which produced an apparent 'folding' of reflectors on unmigrated sections. Detected individual offsets of shallow reflectors range from 5 to 10 m for the top of Paleozoic bedrock and younger strata. The migrated sections generally indicate vertical to steeply dipping normal and reverse faults, which in places outline small horsts and/or grabens. Tilting or folding of stratal reflectors associated with faulting is also locally observed. At one site, the observed faulting is superimposed over a prominent antiformal structure, which may itself be a product of the Quaternary deformation that produced the steep normal and reverse faults. Our results suggest that faulting of the Paleozoic bedrock and younger sediments of the northern Mississippi embayment is more pervasive and less localized than previously thought.

Structural and Tectonic Map Along the Pacific-North America Plate Boundary in Northern Gulf of California, Sonora Desert and Valle de Mexicali, Mexico, from Seismic Reflection Evidence

NASA Astrophysics Data System (ADS)

Gonzalez-Escobar, M.; Suarez-Vidal, F.; Mendoza-Borunda, R.; Martin Barajas, A.; Pacheco-Romero, M.; Arregui-Estrada, S.; Gallardo-Mata, C.; Sanchez-Garcia, C.; Chanes-Martinez, J.

2012-12-01

Between 1978 and 1983, Petróleos Mexicanos (PEMEX) carried on an intense exploration program in the northern Gulf of California, the Sonora Desert and the southern part of the Mexicali Valley. This program was supported by a seismic reflection field operation. The collected seismic data was 2D, with travel time of 6 s recording, in 48 channels, and the source energy was: dynamite, vibroseis and air guns. Since 2007 to present time, the existing seismic data has been re-processing and ire-interpreting as part of a collaboration project between the PEMEX's Subdirección de Exploración (PEMEX) and CICESE. The study area is located along a large portion of the Pacific-North America plate boundary in the northern Gulf of California and the Southern part of the Salton Trough tectonic province (Mexicali Valley). We present the result of the processes reflection seismic lines. Many of the previous reported known faults were identify along with the first time described located within the study region. We identified regions with different degree of tectonic activity. In structural map it can see the location of many of these known active faults and their associated seismic activity, as well as other structures with no associated seismicity. Where some faults are mist placed they were deleted or relocated based on new information. We included historical seismicity for the region. We present six reflection lines that cross the aftershocks zone of the El Mayor-Cucapah earthquake of April 4, 2010 (Mw7.2). The epicenter of this earthquake and most of the aftershocks are located in a region where pervious to this earthquake no major earthquakes are been reported. A major result of this study is to demonstrate that there are many buried faults that increase the seismic hazard.

3D Seismic Experimentation and Advanced Processing/Inversion Development for Investigations of the Shallow Subsurface

DOE Office of Scientific and Technical Information (OSTI.GOV)

Levander, Alan Richard; Zelt, Colin A.

2015-03-17

The work plan for this project was to develop and apply advanced seismic reflection and wide-angle processing and inversion techniques to high resolution seismic data for the shallow subsurface to seismically characterize the shallow subsurface at hazardous waste sites as an aid to containment and cleanup activities. We proposed to continue work on seismic data that we had already acquired under a previous DoE grant, as well as to acquire additional new datasets for analysis. The project successfully developed and/or implemented the use of 3D reflection seismology algorithms, waveform tomography and finite-frequency tomography using compressional and shear waves for highmore » resolution characterization of the shallow subsurface at two waste sites. These two sites have markedly different near-surface structures, groundwater flow patterns, and hazardous waste problems. This is documented in the list of refereed documents, conference proceedings, and Rice graduate theses, listed below.« less

Updated mapping and seismic reflection data processing along the Queen Charlotte fault system, southeast Alaska

NASA Astrophysics Data System (ADS)

Walton, M. A. L.; Gulick, S. P. S.; Haeussler, P. J.; Rohr, K.; Roland, E. C.; Trehu, A. M.

2014-12-01

The Queen Charlotte Fault (QCF) is an obliquely convergent strike-slip system that accommodates offset between the Pacific and North America plates in southeast Alaska and western Canada. Two recent earthquakes, including a M7.8 thrust event near Haida Gwaii on 28 October 2012, have sparked renewed interest in the margin and led to further study of how convergent stress is accommodated along the fault. Recent studies have looked in detail at offshore structure, concluding that a change in strike of the QCF at ~53.2 degrees north has led to significant differences in stress and the style of strain accommodation along-strike. We provide updated fault mapping and seismic images to supplement and support these results. One of the highest-quality seismic reflection surveys along the Queen Charlotte system to date, EW9412, was shot aboard the R/V Maurice Ewing in 1994. The survey was last processed to post-stack time migration for a 1999 publication. Due to heightened interest in high-quality imaging along the fault, we have completed updated processing of the EW9412 seismic reflection data and provide prestack migrations with water-bottom multiple reduction. Our new imaging better resolves fault and basement surfaces at depth, as well as the highly deformed sediments within the Queen Charlotte Terrace. In addition to re-processing the EW9412 seismic reflection data, we have compiled and re-analyzed a series of publicly available USGS seismic reflection data that obliquely cross the QCF. Using these data, we are able to provide updated maps of the Queen Charlotte fault system, adding considerable detail along the northernmost QCF where it links up with the Chatham Strait and Transition fault systems. Our results support conclusions that the changing geometry of the QCF leads to fundamentally different convergent stress accommodation north and south of ~53.2 degrees; namely, reactivated splay faults to the north vs. thickening of sediments and the upper crust to the south. We also highlight areas where additional data are needed and would be ideal targets for future study.

Imaging the Ferron Member of the Mancos Shale formation using reprocessed high-resolution 2-D seismic reflection data: Emery County, Utah

USGS Publications Warehouse

Taylor, D.J.

2003-01-01

Late in 1982 and early in 1983, Arco Exploration contracted with Rocky Mountain Geophysical to acquired four high-resolution 2-D multichannel seismic reflection lines in Emery County, Utah. The primary goal in acquiring this data was an attempt to image the Ferron Member of the Upper Cretaceous Mancos Shale. Design of the high-resolution 2-D seismic reflection data acquisition used both a short geophone group interval and a short sample interval. An explosive energy source was used which provided an input pulse with broad frequency content and higher frequencies than typical non-explosive Vibroseis?? sources. Reflections produced by using this high-frequency energy source when sampled at a short interval are usually able to resolve shallow horizons that are relatively thin compared to those that can be resolved using more typical oil and gas exploration seismic reflection methods.The U.S. Geological Survey-Energy Resources Program, Geophysical Processing Group used the processing sequence originally applied by Arco in 1984 as a guide and experimented with processing steps applied in a different order using slightly different parameters in an effort to improve imaging the Ferron Member horizon. As with the Arco processed data there are sections along all four seismic lines where the data quality cannot be improved upon, and in fact the data quality is so poor that the Ferron horizon cannot be imaged at all.Interpretation of the seismic and core hole data indicates that the Ferron Member in the study area represent a deltaic sequence including delta front, lower delta plain, and upper delta plain environments. Correlating the depositional environments for the Ferron Member as indicated in the core holes with the thickness of Ferron Member suggests the presence of a delta lobe running from the northwest to the southeast through the study area. The presence of a deltaic channel system within the delta lobe complex might prove to be an interesting conventional exploration target along with the coal-bed methane production already proven in the area. ?? 2003 Elsevier B.V. All rights reserved.

Near-Surface and High Resolution Seismic Imaging of the Bennett Thrust Fault in the Indio Mountains of West Texas

NASA Astrophysics Data System (ADS)

Vennemann, Alan

My research investigates the structure of the Indio Mountains in southwest Texas, 34 kilometers southwest of Van Horn, at the UTEP (University of Texas at El Paso) Field Station using newly acquired active-source seismic data. The area is underlain by deformed Cretaceous sedimentary rocks that represent a transgressive sequence nearly 2 km in total stratigraphic thickness. The rocks were deposited in mid Cretaceous extensional basins and later contracted into fold-thrust structures during Laramide orogenesis. The stratigraphic sequence is an analog for similar areas that are ideal for pre-salt petroleum reservoirs, such as reservoirs off the coasts of Brazil and Angola (Li, 2014; Fox, 2016; Kattah, 2017). The 1-km-long 2-D shallow seismic reflection survey that I planned and led during May 2016 was the first at the UTEP Field Station, providing critical subsurface information that was previously lacking. The data were processed with Landmark ProMAX seismic processing software to create a seismic reflection image of the Bennett Thrust Fault and additional imbricate faulting not expressed at the surface. Along the 1-km line, reflection data were recorded with 200 4.5 Hz geophones, using 100 150-gram explosive charges and 490 sledge-hammer blows for sources. A seismic reflection profile was produced using the lower frequency explosive dataset, which was used in the identification of the Bennett Thrust Fault and additional faulting and folding in the subsurface. This dataset provides three possible interpretations for the subsurface geometries of the faulting and folding present. However, producing a seismic reflection image with the higher frequency sledge-hammer sourced dataset for interpretation proved more challenging. While there are no petroleum plays in the Indio Mountains region, imaging and understanding subsurface structural and lithological geometries and how that geometry directs potential fluid flow has implications for other regions with petroleum plays.

Experience from the ECORS program in regions of complex geology

NASA Astrophysics Data System (ADS)

Damotte, B.

1993-04-01

The French ECORS program was launched in 1983 by a cooperation agreement between universities and petroleum companies. Crustal surveys have tried to find explanations for the formation of geological features, such as rifts, mountains ranges or subsidence in sedimentary basins. Several seismic surveys were carried out, some across areas with complex geological structures. The seismic techniques and equipment used were those developed by petroleum geophysicists, adapted to the depth aimed at (30-50 km) and to various physical constraints encountered in the field. In France, ECORS has recorded 850 km of deep seismic lines onshore across plains and mountains, on various kinds of geological formations. Different variations of the seismic method (reflection, refraction, long-offset seismic) were used, often simultaneously. Multiple coverage profiling constitutes the essential part of this data acquisition. Vibrators and dynamite shots were employed with a spread generally 15 km long, but sometimes 100 km long. Some typical seismic examples show that obtaining crustal reflections essentialy depends on two factors: (1) the type and structure of shallow formations, and (2) the sources used. Thus, when seismic energy is strongly absorbed across the first kilometers in shallow formations, or when these formations are highly structured, standard multiple-coverage profiling is not able to provide results beyond a few seconds. In this case, it is recommended to simultaneously carry out long-offset seismic in low multiple coverage. Other more methodological examples show: how the impact on the crust of a surface fault may be evaluated according to the seismic method implemented ( VIBROSEIS 96-fold coverage or single dynamite shot); that vibrators make it possible to implement wide-angle seismic surveying with an offset 80 km long; how to implement the seismic reflection method on complex formations in high mountains. All data were processed using industrial seismic software, which was not always appropriate for records at least 20 s long. Therefore, a specific procedure adapted to deep seismic surveys was developed for several processing steps. The long duration of the VIBROSEIS sweeps often makes it impossible to perform correlation and stack in the recording truck in the field. Such field records were first preprocessed, in order to be later correlated and stacked in the processing center. Because of the long duration of the recordings and the great length of the spread, several types of final sections were replayed, such as: (1) detailed surface sections (0-5 s), (2) entire sections (0-20 s) after data compression, (3) near-trace sections and far-trace sections, which often yield complementary information. Standard methods of reflection migration gave unsatisfactory results. Velocities in depth are inaccurate, the many diffractions do not all come from the vertical plane of the line, and the migration software is poorly adapted to deep crustal reflections. Therefore, migration is often performed graphically from arrivals picked in the time section. Some line-drawings of various onshore lines, especially those across the Alps and the Pyrenees, enable to judge the results obtained by ECORS.

Local spatiotemporal time-frequency peak filtering method for seismic random noise reduction

NASA Astrophysics Data System (ADS)

Liu, Yanping; Dang, Bo; Li, Yue; Lin, Hongbo

2014-12-01

To achieve a higher level of seismic random noise suppression, the Radon transform has been adopted to implement spatiotemporal time-frequency peak filtering (TFPF) in our previous studies. Those studies involved performing TFPF in full-aperture Radon domain, including linear Radon and parabolic Radon. Although the superiority of this method to the conventional TFPF has been tested through processing on synthetic seismic models and field seismic data, there are still some limitations in the method. Both full-aperture linear Radon and parabolic Radon are applicable and effective for some relatively simple situations (e.g., curve reflection events with regular geometry) but inapplicable for complicated situations such as reflection events with irregular shapes, or interlaced events with quite different slope or curvature parameters. Therefore, a localized approach to the application of the Radon transform must be applied. It would serve the filter method better by adapting the transform to the local character of the data variations. In this article, we propose an idea that adopts the local Radon transform referred to as piecewise full-aperture Radon to realize spatiotemporal TFPF, called local spatiotemporal TFPF. Through experiments on synthetic seismic models and field seismic data, this study demonstrates the advantage of our method in seismic random noise reduction and reflection event recovery for relatively complicated situations of seismic data.

Improved 3D seismic images of dynamic deformation in the Nankai Trough off Kumano

NASA Astrophysics Data System (ADS)

Shiraishi, K.; Moore, G. F.; Yamada, Y.; Kinoshita, M.; Sanada, Y.; Kimura, G.

2016-12-01

In order to improve the seismic reflection image of dynamic deformation and seismogenic faults in the Nankai trough, the 2006 Kumano 3D seismic dataset was reprocessed from the original field records by applying advanced technologies a decade after the data acquisition and initial processing. The 3D seismic survey revealed the geometry of megasplay fault system. However, there were still unclear regions in the accretionary prism beneath from Kumano basin to the outer ridge, because of sea floor multiple reflections and noise caused by the Kuroshio current. For the next stage of deep scientific drilling into the Nankai trough seismogenic zone, it is essential to know exactly the shape and depth of the megasplay, and fine structures around the drilling site. Three important improvements were achieved in data processing before imaging. First, full deghosting and optimized zero phasing techniques could recover broadband signals, especially in low frequency, by compensating for ghost effects at both source and receiver, and removing source bubbles. Second, the multiple reflections better attenuated by applying advanced techniques in combination, and the strong noise caused by the Kuroshio were attenuated carefully. Third, data regularization by means of the optimized 4D trace interpolation was effective both to mitigate non-uniform fold distribution and to improve data quality. Further imaging processes led to obvious improvement from previous results by applying PSTM with higher order correction of VTI anisotropy, and PSDM based on the velocity model built by reflection tomography with TTI anisotropy. Final reflection images show new geological aspects, such as clear steep dip faults around the "notch", and fine scale faults related to main thrusts in frontal thrust zone. The improved images will highly contribute to understanding the deformation process in the old accretionary prism and seismogenic features related to the megasplay faults.

Seismic reflection constraints on the glacial dynamics of Johnsons Glacier, Antarctica

NASA Astrophysics Data System (ADS)

Benjumea, Beatriz; Teixidó, Teresa

2001-01-01

During two Antarctic summers (1996-1997 and 1997-1998), five seismic refraction and two reflection profiles were acquired on the Johnsons Glacier (Livingston Island, Antarctica) in order to obtain information about the structure of the ice, characteristics of the ice-bed contact and basement topography. An innovative technique has been used for the acquisition of reflection data to optimise the field survey schedule. Different shallow seismic sources were used during each field season: Seismic Impulse Source System (SISSY) for the first field survey and low-energy explosives (pyrotechnic noisemakers) during the second one. A comparison between these two shallow seismic sources has been performed, showing that the use of the explosives is a better seismic source in this ice environment. This is one of the first studies where this type of source has been used. The analysis of seismic data corresponding to one of the reflection profiles (L3) allows us to delineate sectors with different glacier structure (accumulation and ablation zones) without using glaciological data. Moreover, vertical discontinuities were detected by the presence of back-scattered energy and the abrupt change in frequency content of first arrivals shown in shot records. After the raw data analysis, standard processing led us to a clear seismic image of the underlying bed topography, which can be correlated with the ice flow velocity anomalies. The information obtained from seismic data on the internal structure of the glacier, location of fracture zones and the topography of the ice-bed interface constrains the glacial dynamics of Johnsons Glacier.

High Resolution Vertical Seismic Profile from the Chicxulub IODP/ICDP Expedition 364 Borehole: Wave Speeds and Seismic Reflectivity.

NASA Astrophysics Data System (ADS)

Nixon, C.; Kofman, R.; Schmitt, D. R.; Lofi, J.; Gulick, S. P. S.; Christeson, G. L.; Saustrup, S., Sr.; Morgan, J. V.

2017-12-01

We acquired a closely-spaced vertical seismic profile (VSP) in the Chicxulub K-Pg Impact Crater drilling program borehole to calibrate the existing surface seismic profiles and provide complementary measurements of in situ seismic wave speeds. Downhole seismic records were obtained at spacings ranging from 1.25 m to 5 m along the borehole from 47.5 m to 1325 mwsf (meters wireline below sea floor) (Fig 1a) using a Sercel SlimwaveTM geophone chain (University of Alberta). The seismic source was a 30/30ci Sercel Mini GI airgun (University of Texas), fired a minimum of 5 times per station. Seismic data processing used a combination of a commercial processing package (Schlumberger's VISTA) and MatlabTM codes. The VSP displays detailed reflectivity (Fig. 1a) with the strongest reflection seen at 600 mwsf (280 ms one-way time), geologically corresponding to the sharp contact between the post-impact sediments and the target peak ring rock, thus confirming the pre-drilling interpretations of the seismic profiles. A two-way time trace extracted from the separated up-going wavefield matches the major reflection both in travel time and character. In the granitic rocks that form the peak ring of the Chicxulub impact crater, we observe P-wave velocities of 4000-4500 m/s which are significantly less than the expected values of granitoids ( 6000 m/s) (Fig. 1b). The VSP measured wave speeds are confirmed against downhole sonic logging and in laboratory velocimetry measurements; these data provide additional evidence that the crustal material displaced by the impact experienced a significant amount of damage. Samples and data provided by IODP. Samples can be requested at http://web.iodp.tamu.edu/sdrm after 19 October 2017. Expedition 364 was jointly funded by ECORD, ICDP, and IODP with contributions and logistical support from the Yucatan State Government and UNAM. The downhole seismic chain and wireline system is funded by grants to DRS from the Canada Foundation for Innovation and the Alberta Enterprise and Advanced Education Grants Program.

Tectonic history in the Fort Worth Basin, north Texas, derived from well-log integration with multiple 3D seismic reflection surveys: implications for paleo and present-day seismicity in the basin

NASA Astrophysics Data System (ADS)

Magnani, M. B.; Hornbach, M. J.

2016-12-01

Oil and gas exploration and production in the Fort Worth Basin (FWB) in north Texas have accelerated in the last 10 years due to the success of unconventional gas production. Here, hydraulic fracturing wastewater is disposed via re-injection into deep wells that penetrate Ordovician carbonate formations. The rise in wastewater injection has coincided with a marked rise in earthquake rates, suggesting a causal relationship between industry practices and seismicity. Most studies addressing this relationship in intraplate regions like the FWB focus on current seismicity, which provides an a-posteriori assessment of the processes involved. 3D seismic reflection data contribute complementary information on the existence, distribution, orientation and long-term deformation history of faults that can potentially become reactivated by the injection process. Here we present new insights into the tectonic evolution of faults in the FWB using multiple 3D seismic reflection surveys in the basin, west of the Dallas Fort-Worth Metroplex, where high-volume wastewater injection wells have increased most significantly in number in the past few years. The datasets image with remarkable clarity the 3,300 m-thick sedimentary rocks of the basin, from the crystalline basement to the Cretaceous cover, with particular detail of the Paleozoic section. The data, interpreted using coincident and nearby wells to correlate seismic reflections with stratigraphic markers, allow us to identify faults, extract their orientation, length and displacements at several geologic time intervals, and therefore, reconstruct the long-term deformation history. Throughout the basin, the data show that all seismically detectable faults were active during the Mississippian and Pennsylvanian, but that displacement amounts drop below data resolution ( 7 m) in the post-Pennsylvanian deposits. These results indicate that faults have been inactive for at least the past 300 Ma, until the recent 2008 surge in seismicity. The results are consistent with previous studies, and inconsistent with a suggested sustained, significant Mesozoic and Cenozoic activity in the basin. Rather, the results strongly suggest that the recent seismicity in the FWB is highly anomalous, and therefore, more likely induced than natural.

Seismic reflection imaging of shallow oceanographic structures

NASA Astrophysics Data System (ADS)

Piété, Helen; Marié, Louis; Marsset, Bruno; Thomas, Yannick; Gutscher, Marc-André

2013-05-01

Multichannel seismic (MCS) reflection profiling can provide high lateral resolution images of deep ocean thermohaline fine structure. However, the shallowest layers of the water column (z < 150 m) have remained unexplored by this technique until recently. In order to explore the feasibility of shallow seismic oceanography (SO), we reprocessed and analyzed four multichannel seismic reflection sections featuring reflectors at depths between 10 and 150 m. The influence of the acquisition parameters was quantified. Seismic data processing dedicated to SO was also investigated. Conventional seismic acquisition systems were found to be ill-suited to the imaging of shallow oceanographic structures, because of a high antenna filter effect induced by large offsets and seismic trace lengths, and sources that typically cannot provide both a high level of emission and fine vertical resolution. We considered a test case, the imagery of the seasonal thermocline on the western Brittany continental shelf. New oceanographic data acquired in this area allowed simulation of the seismic acquisition. Sea trials of a specifically designed system were performed during the ASPEX survey, conducted in early summer 2012. The seismic device featured: (i) four seismic streamers, each consisting of six traces of 1.80 m; (ii) a 1000 J SIG sparker source, providing a 400 Hz signal with a level of emission of 205 dB re 1 μPa @ 1 m. This survey captured the 15 m thick, 30 m deep seasonal thermocline in unprecedented detail, showing images of vertical displacements most probably induced by internal waves.

Deep seismic reflection evidence for ancient subduction and collision zones within the continental lithosphere of northwestern Europe

NASA Astrophysics Data System (ADS)

Balling, N.

2000-12-01

Deep seismic profiling experiments in the region of NW Europe (including BABEL in the Gulf of Bothnia and the Baltic Sea, Mobil Search in the Skagerrak and MONA LISA in the North Sea) have demonstrated the existence of seismic reflectors in the mantle lithosphere beneath the Baltic Shield, the Tornquist Zone and the North Sea basins. Different sets of reflectors are observed, notably dipping and sub-horizontal. Dipping, distinct reflectivity, which may be followed from Moho/Moho offsets into the deeper parts of the continental lithosphere, is of special interest because of its tectonic and geodynamic significance. Such reflectivity, observed in several places, dipping 15-35° and covering a depth range of 30-90 km, constrained by surface geological information and radiometric age data, is interpreted to represent fossil, ancient subduction and collison zones. Subduction slabs with remnant oceanic basaltic crust transformed into eclogite is assumed, in particular, to generate deep seismic reflectivity. Deep seismic evidence is presented for subduction, crustal accretion and collision processes with inferred ages from 1.9 to 1.1 Ga from the main structural provinces within the Baltic Shield including Svecofennian, Transscandinavian Igneous Belt, Gothian and Sveconorwegian. Along the southwestern border of Baltica (in the southeastern North Sea) south-dipping crustal and sub-crustal reflectivity is observed down to a depth of about 90 km, close to the lithosphere-asthenosphere boundary. These structures are interpreted to reveal a lithosphere-scale Caledonian (ca. 440 Ma) suture zone resulting from the closure of the Tornquist Sea/Thor Ocean and the amalgamation of Baltica and Eastern Avalonia. These results demonstrate that deep structures within the continental lithosphere, originating from early crust-forming plate tectonic processes, may survive for a very long time and form seismic marker reflectivity of great value in geotectonic interpretation and reconstructions. Furthermore, the depth of dipping reflectivity from ancient structures, such as subduction slabs, significantly contributes information about the thickness of the coherent lithosphere. The seismic observations and our interpretations support plate tectonic and structural models, suggesting crustal growth and amalgamation of tectonic units in the Baltic Shield and along its southwestern margin generally from the northeast (in present-day orientation) towards the southwest and west, likely to result in regional deep structural and tectonic age zonations.

First Results from the Multi-beam Bathymetry and Multi-channel Seismic Reflection Data offshore Cide-Sinop, Southern Black Sea shelf

NASA Astrophysics Data System (ADS)

Alp, Y. I.; Ocakoglu, N.; Kılıc, F.; Ozel, A. O.

2016-12-01

The morphological and seismic features offshore Cide-Sinop at the Southern Black Sea shelf area were first time investigated by multi-beam bathymetric and multi-channel seismic reflection data under the Research Project of The Scientific and Technological Research Council of Turkey (TUBİTAK-ÇAYDAG-114Y057). Multi-beam bathymetric data were collected between 2002-2008 from onboard the research vessels TCG Çubuklu and TCG Çeşme run by the Turkish Navy, Department of Navigation, Hydrography and Oceanography (TN-DNHO) with the system an Elac-Nautic 1050D. Multi-channel seismic reflection data were collected by Turkish Petroleum Corporation (TPAO) Company in 1991. Multi-beam measurements cover 2.59 km2 areas and depths change from -1 to -500 m. Elevation data were digitized from contour lines of 1/25K topo-maps of General Command of Mapping, with the contour interval of 10 m and supplementary 5 m contours in areas of low relief. Contour and shore lines, multi-beam points were interpolated into DEMs of pixel size 10 m and 5 m respectively, using Annudem algorithm. The Geographic Information System (GIS) software was used to analyse and visualize the two data sets. Seismic reflection data were processed by conventional methods under `Echos' seismic data processing software and time migrated seismic sections were produced. DEMs were combined with seismic reflection sections to understand the morphological and morphodynamic character of the study area. First results indicate that offshore Cide-Sinop is characterised by a quite smooth and large shelf plain with an approx. 25 km wide and the water depth of about -100 m. The bathymetry gently deepens from inner shelf toward shelf break at -120 m isobath. Slope angles from 0 to 1 degrees at the shelf plain, increases about to 10 degrees beyond the shelf edge. The large shelf plain is widely characterized by sand dunes with an average height of 10 meters form E-W oriented belts of 500-1000 m in width. Toward offshore İnebolu, an eroded anticline was observed in NW-SE orientation. This erosional surface was also observed on the time-migrated seismic sections. In addition, there are some active strike-slip faults were interpreted in the study area.

CMP reflection imaging via interferometry of distributed subsurface sources

NASA Astrophysics Data System (ADS)

Kim, D.; Brown, L. D.; Quiros, D. A.

2015-12-01

The theoretical foundations of recovering body wave energy via seismic interferometry are well established. However in practice, such recovery remains problematic. Here, synthetic seismograms computed for subsurface sources are used to evaluate the geometrical combinations of realistic ambient source and receiver distributions that result in useful recovery of virtual body waves. This study illustrates how surface receiver arrays that span a limited distribution suite of sources, can be processed to reproduce virtual shot gathers that result in CMP gathers which can be effectively stacked with traditional normal moveout corrections. To verify the feasibility of the approach in practice, seismic recordings of 50 aftershocks following the magnitude of 5.8 Virginia earthquake occurred in August, 2011 have been processed using seismic interferometry to produce seismic reflection images of the crustal structure above and beneath the aftershock cluster. Although monotonic noise proved to be problematic by significantly reducing the number of usable recordings, the edited dataset resulted in stacked seismic sections characterized by coherent reflections that resemble those seen on a nearby conventional reflection survey. In particular, "virtual" reflections at travel times of 3 to 4 seconds suggest reflector sat approximately 7 to 12 km depth that would seem to correspond to imbricate thrust structures formed during the Appalachian orogeny. The approach described here represents a promising new means of body wave imaging of 3D structure that can be applied to a wide array of geologic and energy problems. Unlike other imaging techniques using natural sources, this technique does not require precise source locations or times. It can thus exploit aftershocks too small for conventional analyses. This method can be applied to any type of microseismic cloud, whether tectonic, volcanic or man-made.

Homogenization of Electromagnetic and Seismic Wavefields for Joint Inverse Modeling

NASA Astrophysics Data System (ADS)

Newman, G. A.; Commer, M.; Petrov, P.; Um, E. S.

2011-12-01

A significant obstacle in developing a robust joint imaging technology exploiting seismic and electromagnetic (EM) wave fields is the resolution at which these different geophysical measurements sense the subsurface. Imaging of seismic reflection data is an order of magnitude finer in resolution and scale compared to images produced with EM data. A consistent joint image of the subsurface geophysical attributes (velocity, electrical conductivity) requires/demands the different geophysical data types be similar in their resolution of the subsurface. The superior resolution of seismic data results from the fact that the energy propagates as a wave, while propagation of EM energy is diffusive and attenuates with distance. On the other hand, the complexity of the seismic wave field can be a significant problem due to high reflectivity of the subsurface and the generation of multiple scattering events. While seismic wave fields have been very useful in mapping the subsurface for energy resources, too much scattering and too many reflections can lead to difficulties in imaging and interpreting seismic data. To overcome these obstacles a formulation for joint imaging of seismic and EM wave fields is introduced, where each data type is matched in resolution. In order to accomplish this, seismic data are first transformed into the Laplace-Fourier Domain, which changes the modeling of the seismic wave field from wave propagation to diffusion. Though high frequency information (reflectivity) is lost with this transformation, several benefits follow: (1) seismic and EM data can be easily matched in resolution, governed by the same physics of diffusion, (2) standard least squares inversion works well with diffusive type problems including both transformed seismic and EM, (3) joint imaging of seismic and EM data may produce better starting velocity models critical for successful reverse time migration or full waveform imaging of seismic data (non transformed) and (4) possibilities to image across multiple scale lengths, incorporating different types of geophysical data and attributes in the process. Important numerical details of 3D seismic wave field simulation in the Laplace-Fourier domain for both acoustic and elastic cases will also be discussed.

Full Waveform Modelling for Subsurface Characterization with Converted-Wave Seismic Reflection

NASA Astrophysics Data System (ADS)

Triyoso, Wahyu; Oktariena, Madaniya; Sinaga, Edycakra; Syaifuddin, Firman

2017-04-01

While a large number of reservoirs have been explored using P-waves seismic data, P-wave seismic survey ceases to provide adequate result in seismically and geologically challenging areas, like gas cloud, shallow drilling hazards, strong multiples, highly fractured, anisotropy. Most of these reservoir problems can be addressed using P and PS seismic data combination. Multicomponent seismic survey records both P-wave and S-wave unlike conventional survey that only records compressional P-wave. Under certain conditions, conventional energy source can be used to record P and PS data using the fact that compressional wave energy partly converts into shear waves at the reflector. Shear component can be recorded using down going P-wave and upcoming S-wave by placing a horizontal component geophone on the ocean floor. A synthetic model is created based on real data to analyze the effect of gas cloud existence to PP and PS wave reflections which has a similar characteristic to Sub-Volcanic imaging. The challenge within the multicomponent seismic is the different travel time between P-wave and S-wave, therefore the converted-wave seismic data should be processed with different approach. This research will provide a method to determine an optimum converted point known as Common Conversion Point (CCP) that can solve the Asymmetrical Conversion Point of PS data. The value of γ (Vp/Vs) is essential to estimate the right CCP that will be used in converted-wave seismic processing. This research will also continue to the advanced processing method of converted-wave seismic by applying Joint Inversion to PP&PS seismic. Joint Inversion is a simultaneous model-based inversion that estimates the P&S-wave impedance which are consistent with the PP&PS amplitude data. The result reveals a more complex structure mirrored in PS data below the gas cloud area. Through estimated γ section resulted from Joint Inversion, we receive a better imaging improvement below gas cloud area tribute to the converted-wave seismic as additional constrain.

Breakup magmatism on the Vøring Margin, mid-Norway: New insight from interpretation of high-quality 2D and 3D seismic reflection data

NASA Astrophysics Data System (ADS)

Abdelmalak, M. M.; Planke, S.; Millett, J.; Jerram, D. A.; Maharjan, D.; Zastrozhnov, D.; Schmid, D. W.; Faleide, J. I.; Svensen, H.; Myklebust, R.

2017-12-01

The Vøring Margin offshore mid-Norway is a classic volcanic rifted margin, characterized by voluminous Paleogene igneous rocks present on both sides of the continent-ocean boundary. The margin displays (1) thickened transitional crust with a well-defined lower crustal high-velocity body and prominent deep crustal reflections, the so-called T-Reflection, (2) seaward dipping reflector (SDR) wedges and a prominent northeast-trending escarpment on the Vøring Marginal High, and (3) extensive sill complexes in the adjacent Cretaceous Vøring Basin. During the last decade, new 2D and 3D industry seismic data along with improved processing techniques, such as broadband processing and noise reduction processing sequences, have made it possible to image and map the breakup igneous complex in much greater detail than previously possible. Our interpretation includes a combination of (1) seismic horizon picking, (2) integrated seismic-gravity-magnetic (SGM) interpretation, (3) seismic volcanostratigraphy, and (4) igneous seismic geomorphology. The results are integrated with published wide-angle seismic data, re-analyzed borehole data including new geochronology, and new geodynamic modeling of the effects of magmatism on the thermal history and subsidence of the margin. The extensive sill complexes and associated hydrothermal vent complexes in the Vøring Basin have a Paleocene-Eocene boundary age based on high-precision U/Pb dating combined with seismic mapping constraints. On the marginal high, our results show a highly variable crustal structure, with a pre-breakup configuration consisting of large-scale structural highs and sedimentary basins. These structures were in-filled and covered by basalt flows and volcanogenic sediments during the early stages of continental breakup in the earliest Eocene. Subsequently, rift basins developed along the continent-ocean boundary and where infilled by up to ca. 6 km thick basalt sequences, currently imaged as SDRs fed by a dike swarm imaged on seismic data. The addition of magma within the crust had a prominent effect on the thermal history and hydrocarbon maturation of the sedimentary basin, causing uplift, delayed subsidence, and possibly contributing to the triggering of global warming during the Paleocene-Eocene Thermal Maximum (PETM).

Frequency-dependent processing and interpretation (FDPI) of seismic data for identifying, imaging and monitoring fluid-saturated underground reservoirs

DOEpatents

Goloshubin, Gennady M.; Korneev, Valeri A.

2006-11-14

A method for identifying, imaging and monitoring dry or fluid-saturated underground reservoirs using seismic waves reflected from target porous or fractured layers is set forth. Seismic imaging the porous or fractured layer occurs by low pass filtering of the windowed reflections from the target porous or fractured layers leaving frequencies below low-most corner (or full width at half maximum) of a recorded frequency spectra. Additionally, the ratio of image amplitudes is shown to be approximately proportional to reservoir permeability, viscosity of fluid, and the fluid saturation of the porous or fractured layers.

Frequency-dependent processing and interpretation (FDPI) of seismic data for identifying, imaging and monitoring fluid-saturated underground reservoirs

DOEpatents

Goloshubin, Gennady M.; Korneev, Valeri A.

2005-09-06

A method for identifying, imaging and monitoring dry or fluid-saturated underground reservoirs using seismic waves reflected from target porous or fractured layers is set forth. Seismic imaging the porous or fractured layer occurs by low pass filtering of the windowed reflections from the target porous or fractured layers leaving frequencies below low-most corner (or full width at half maximum) of a recorded frequency spectra. Additionally, the ratio of image amplitudes is shown to be approximately proportional to reservoir permeability, viscosity of fluid, and the fluid saturation of the porous or fractured layers.

The use of vertical seismic profiles in seismic investigations of the earth

USGS Publications Warehouse

Balch, Alfred H.; Lee, M.W.; Miller, J.J.; Ryder, Robert T.

1982-01-01

During the past 8 years, the U.S. Geological Survey has conducted an extensive investigation on the use of vertical seismic profiles (VSP) in a variety of seismic exploration applications. Seismic sources used were surface air guns, vibrators, explosives, marine air guns, and downhole air guns. Source offsets have ranged from 100 to 7800 ft. Well depths have been from 1200 to over 10,000 ft. We have found three specific ways in which VSPs can be applied to seismic exploration. First, seismic events observed at the surface of the ground can be traced, level by level, to their point of origin within the earth. Thus, one can tie a surface profile to a well log with an extraordinarily high degree of confidence. Second, one can establish the detectability of a target horizon, such as a porous zone. One can determine (either before or after surface profiling) whether or not a given horizon or layered sequence returns a detectable reflection to the surface. The amplitude and character of the reflection can also be observed. Third, acoustic properties of a stratigraphic sequence can be measured and sometimes correlated to important exploration parameters. For example, sometimes a relationship between apparent attenuation and sand percentage can be established. The technique shows additional promise of aiding surface exploration indirectly through studies of the evolution of the seismic pulse, studies of ghosts and multiples, and studies of seismic trace inversion techniques. Nearly all current seismic data‐processing techniques are adaptable to the processing of VSP data, such as normal moveout (NMO) corrections, stacking, single‐and multiple‐channel filtering, deconvolution, and wavelet shaping.

Fallon, Nevada FORGE Seismic Reflection Profiles

DOE Data Explorer

Blankenship, Doug; Faulds, James; Queen, John; Fortuna, Mark

2018-02-01

Newly reprocessed Naval Air Station Fallon (1994) seismic lines: pre-stack depth migrations, with interpretations to support the Fallon FORGE (Phase 2B) 3D Geologic model. Data along seven profiles (>100 km of total profile length) through and adjacent to the Fallon site were re-processed. The most up-to-date, industry-tested seismic processing techniques were utilized to improve the signal strength and coherency in the sedimentary, volcanic, and Mesozoic crystalline basement sections, in conjunction with fault diffractions in order to improve the identification and definition of faults within the study area.

Attributes and origins of ancient submarine slides and filled embayments: examples from the Gulf Coast basin

USGS Publications Warehouse

Morton, Robert

1993-01-01

Submarine slides exhibit landward-dipping, wavy, mounded, and chaotic seismic reflections that are manifestations of slump blocks and other mass transport material. Composition of these internally derived slide deposits depends on the composition of the preexisting shelf margin. Embayment fill above the slide consists mostly of externally derived mudstones and sandstones deposited by various disorganized slope processes, as well as more organized submarine channel-levee systems. Thickest slope sandstones, which are potential hydrocarbon reservoirs, commonly occur above the basal slide mudstones where seismic reflections change from chaotic patterns to overlying wavy or subhorizontal reflections.

Detecting lower-mantle slabs beneath Asia and the Aleutians

NASA Astrophysics Data System (ADS)

Schumacher, L.; Thomas, C.

2016-06-01

To investigate the descend of subducted slabs we search for and analyse seismic arrivals that reflected off the surface of the slab. In order to distinguish between such arrivals and other seismic phases, we search for waves that reach a seismic array with a backazimuth deviating from the theoretical backazimuth of the earthquake. Source-receiver combinations are chosen in a way that their great circle paths do not intersect the slab region, hence the direct arrivals can serve as reference. We focus on the North and Northwest Pacific region by using earthquakes from Japan, the Philippines and the Hindu Kush area recorded at North American networks (e.g. USArray, Alaska and Canada). Using seismic array techniques for analysing the data and record information on slowness, backazimuth and traveltime of the observed out-of-plane arrivals we use these measurements to trace the wave back through a 1-D velocity model to its scattering/reflection location. We find a number of out-of-plane reflections. Assuming only single scattering, most out-of-plane signals have to travel as P-to-P phases and only a few as S-to-P phases, due to the length of the seismograms we processed. The located reflection points present a view of the 3-D structures within the mantle. In the upper mantle and the transition zone they correlate well with the edges of fast velocity regions in tomographic images. We also find reflection points in the mid- and lower mantle and their locations generally agree with fast velocities mapped by seismic tomography models suggesting that in the subduction regions we map, slabs enter the lower mantle. To validate our approach, we calculate and process synthetic seismograms for 3-D wave field propagation through a model containing a slab-like heterogeneity. We show, that depending on the source-receiver geometry relative to the reflection plane, it is indeed possible to observe and back-trace out-of-plane signals.

Diffraction Seismic Imaging of the Chalk Group Reservoir Rocks

NASA Astrophysics Data System (ADS)

Montazeri, M.; Fomel, S.; Nielsen, L.

2016-12-01

In this study we investigate seismic diffracted waves instead of seismic reflected waves, which are usually much stronger and carry most of the information regarding subsurface structures. The goal of this study is to improve imaging of small subsurface features such as faults and fractures. Moreover, we focus on the Chalk Group, which contains important groundwater resources onshore and oil and gas reservoirs in the Danish sector of the North Sea. Finding optimum seismic velocity models for the Chalk Group and estimating high-quality stacked sections with conventional processing methods are challenging tasks. Here, we try to filter out as much as possible of undesired arrivals before stacking the seismic data. Further, a plane-wave destruction method is applied on the seismic stack in order to dampen the reflection events and thereby enhance the visibility of the diffraction events. After this initial processing, we estimate the optimum migration velocity using diffraction events in order to obtain a better resolution stack. The results from this study demonstrate how diffraction imaging can be used as an additional tool for improving the images of small-scale features in the Chalk Group reservoir, in particular faults and fractures. Moreover, we discuss the potential of applying this approach in future studies focused on such reservoirs.

NON-INVASIVE DETERMINATION OF THE LOCATION AND DISTRIBUTION OF FREE-PHASE DENSE NONAQUEOUS PHASE LIQUIDS (DNAPL) BY SEISMIC REFLECTION TECHNIQUES

DOE Office of Scientific and Technical Information (OSTI.GOV)

Michael G. Waddell; William J. Domoracki; Tom J. Temples

2001-12-01

This annual technical progress report is for part of Task 4 (site evaluation), Task 5 (2D seismic design, acquisition, and processing), and Task 6 (2D seismic reflection, interpretation, and AVO analysis) on DOE contact number DE-AR26-98FT40369. The project had planned one additional deployment to another site other than Savannah River Site (SRS) or DOE Hanford Site. After the SUBCON midyear review in Albuquerque, NM, it was decided that two additional deployments would be performed. The first deployment is to test the feasibility of using non-invasive seismic reflection and AVO analysis as a monitoring tool to assist in determining the effectivenessmore » of Dynamic Underground Stripping (DUS) in removal of DNAPL. The second deployment is to the Department of Defense (DOD) Charleston Naval Weapons Station Solid Waste Management Unit 12 (SWMU-12), Charleston, SC to further test the technique to detect high concentrations of DNAPL. The Charleston Naval Weapons Station SWMU-12 site was selected in consultation with National Energy Technology Laboratory (NETL) and DOD Naval Facilities Engineering Command Southern Division (NAVFAC) personnel. Based upon the review of existing data and due to the shallow target depth, the project team collected three Vertical Seismic Profiles (VSP) and an experimental P-wave seismic reflection line. After preliminary data analysis of the VSP data and the experimental reflection line data, it was decided to proceed with Task 5 and Task 6. Three high resolution P-wave reflection profiles were collected with two objectives; (1) design the reflection survey to image a target depth of 20 feet below land surface to assist in determining the geologic controls on the DNAPL plume geometry, and (2) apply AVO analysis to the seismic data to locate the zone of high concentration of DNAPL. Based upon the results of the data processing and interpretation of the seismic data, the project team was able to map the channel that is controlling the DNAPL plume geometry. The AVO analysis located a major amplitude anomaly, which was tested using a Geoprobe{trademark} direct push system. The Geoprobe{trademark} was equipped with a membrane interface probe (MIP) that was interfaced with a sorbent trap/gas chromatograph (GC) system. Both the Photo Ionization Detector (PID) and Electron Capture Detector (ECD) on the GC exceeded the maximum measurement values through the anomaly. A well was installed to collect a water sample. The concentration of chlorinated solvents in the water sample was in excess of 500 ppm. Other amplitude anomalies located directly under an asphalt road were also tested. Both the PID and ECD were zero. It appears that editing of poor quality near-offset traces during data processing caused these anomalies. Not having the full range of source to receiver offset traces in those areas resulted in a false anomaly during AVO analysis. This phenomenon was also observed at the beginning and end of each seismic profile also for the same reason. Based upon the water samples and MIP probes, it appears that surface seismic and AVO analysis were able to detect the area of highest concentration of DNAPL.« less

3D imaging of geological structures by R-VSP utilizing vibrations caused by shaft excavations at the Mizunami Underground Research Laboratory in Japan

NASA Astrophysics Data System (ADS)

Matsuoka, T.; Hodotsuka, Y.; Ishigaki, K.; Lee, C.

2009-12-01

Japan Atomic Energy Agency is now conducting the Mizunami Underground Research Laboratory (MIU) project. The MIU consists of two shafts (main shaft: 6.5m, ventilation shaft: 4.5m diameter) and horizontal research galleries, in sedimentary and granitic rocks at Mizunami City, Central Japan. The MIU project is a broad scientific study of the deep geological environment providing the basis for research and development for geological disposal of high level radioactive waste. One of the main goals is to establish techniques for investigation, analysis and assessment of the deep geological environment in fractured crystalline rock. As a part of the MIU project, we carried out the Reverse-Vertical Seismic Profile (R-VSP) using vibrations from the blasting for the shaft excavations and drilling of boreholes in the horizontal research galleries and examined the applicability of this method to imaging of geological structures around underground facilities, such as the unconformity between the sedimentary rocks and the basal granite, and faults and fracture zones in the granite. R-VSP method is a seismic method utilizing the receiver arrays on surface and seismic sources underground (e.g. in boreholes). This method is advantageous in that planning of 3-dimensional surveys is easy compared with reflection seismic surveying and conventional VSP because seismic source arrays that are major constraint for conducting surveys on surface are unnecessary. The receiver arrays consist of six radial lines on surface with a central focus on the main shaft. Seven blast rounds for the main shaft excavation from GL-52.8m to GL-250m and the borehole drilling in the GL-200m horizontal research gallery were observed. Three types of data processing, conventional VSP data processing (VSP-CDP transform and VSP migration), Reflection data processing utilizing Seismic interferometry method (“Seismic interferometry”) and Reflection mapping utilizing Image Point transform method (“IP transform”), were performed to obtain reflection images from heterogeneous geological structure. As the results, the reflective events that seemed to correspond with sedimentary layers, the unconformity between sedimentary rocks and granite, and fracture zones in granite could be detected by reflection profiles using “conventional VSP data processing” and “Seismic interferometry”. However, it is difficult to identify the faults around the MIU because they are generally at a high-angle. “IP transform” is one type of Radon transform which change common shot gather to IP domain. Image Points are defined through geometries of sources and reflectors. Reflection signals in time domain can be accumulated and enhanced in IP domain by “IP transform” on the condition of the right angle to a fault. So, by a search of the direction that reflection signals are enhanced using “IP transform”, the locations of faults can be inferred. By this method, the distribution of faults that correspond with faults in the current geological model constructed from investigation data in the MIU project could be detected.

Seismic velocity uncertainties and their effect on geothermal predictions: A case study

NASA Astrophysics Data System (ADS)

Rabbel, Wolfgang; Köhn, Daniel; Bahadur Motra, Hem; Niederau, Jan; Thorwart, Martin; Wuttke, Frank; Descramble Working Group

2017-04-01

Geothermal exploration relies in large parts on geophysical subsurface models derived from seismic reflection profiling. These models are the framework of hydro-geothermal modeling, which further requires estimating thermal and hydraulic parameters to be attributed to the seismic strata. All petrophysical and structural properties involved in this process can be determined only with limited accuracy and thus impose uncertainties onto the resulting model predictions of temperature-depth profiles and hydraulic flow, too. In the present study we analyze sources and effects of uncertainties of the seismic velocity field, which translate directly into depth uncertainties of the hydraulically and thermally relevant horizons. Geological sources of these uncertainties are subsurface heterogeneity and seismic anisotropy, methodical sources are limitations in spread length and physical resolution. We demonstrate these effects using data of the EU-Horizon 2020 project DESCRAMBLE investigating a shallow super-critical geothermal reservoir in the Larderello area. The study is based on 2D- and 3D seismic reflection data and laboratory measurements on representative rock samples under simulated in-situ conditions. The rock samples consistently show P-wave anisotropy values of 10-20% order of magnitude. However, the uncertainty of layer depths induced by anisotropy is likely to be lower depending on the accuracy, with which the spatial orientation of bedding planes can be determined from the seismic reflection images.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mellors, R J

The Comprehensive Nuclear Test Ban Treaty (CTBT) includes provisions for an on-site inspection (OSI), which allows the use of specific techniques to detect underground anomalies including cavities and rubble zones. One permitted technique is active seismic surveys such as seismic refraction or reflection. The purpose of this report is to conduct some simple modeling to evaluate the potential use of seismic reflection in detecting cavities and to test the use of open-source software in modeling possible scenarios. It should be noted that OSI inspections are conducted under specific constraints regarding duration and logistics. These constraints are likely to significantly impactmore » active seismic surveying, as a seismic survey typically requires considerable equipment, effort, and expertise. For the purposes of this study, which is a first-order feasibility study, these issues will not be considered. This report provides a brief description of the seismic reflection method along with some commonly used software packages. This is followed by an outline of a simple processing stream based on a synthetic model, along with results from a set of models representing underground cavities. A set of scripts used to generate the models are presented in an appendix. We do not consider detection of underground facilities in this work and the geologic setting used in these tests is an extremely simple one.« less

Reflection and refraction seismic on the great Ancona landslide

NASA Astrophysics Data System (ADS)

Stucchi, E.; Mazzotti, A.

2003-04-01

The Adriatic coast in Italy is characterised by the occurrence of several landslide bodies, some of which of huge extension. Here we present the results of seismic refraction and reflection studies recently carried out on the Ancona Landslide, which is located immediately westward of the harbour city of Ancona, and interests an area of about 3.5 km^2 with a landslide front of 2 km. The acquired seismic profile crosses the entire landslide body and was performed employing land and marine sources and receivers. Thus it allows the simultaneous acquisition of marine-marine, marine-land, land-marine and land-land data. The most significant acquisition parameters are: nominal maximum source-receiver offset 600 m, receiver group interval 5 m, single airgun and small explosive charges as energy sources, profile length 1.5 km, average reflection coverage on land 4000% and at sea 20000%. Notwithstanding the significant noise contamination due to intense human activities (road, naval and railway traffic) in the area, the data shows good first breaks and reflections which we use for refraction and reflection processing. The refraction study makes use of GRM and other techniques (Lawton) and it leads to a good definition of the shallower landslide bodies but it is not able to depict the deeper decollement surface. It is also very useful in providing a detailed near surface velocity model that is crucial for the determination of accurate static corrections for the reflection data. High quality subsurface images are achieved by applying different processing sequences to the different sets (marine, land or land-marine) of reflection seismic data. The processing steps that turned out as more effective to the achievement of such a quality were the noise removal by means of FX and SVD filtering, the attenuation of the bubble effect for the marine source data, the ground roll attenuation and the computation of accurate statics. The outcomes of the refraction and reflection investigations are greatly useful in evidencing the geometry of the huge landslide body, its maximum depth and the location, close to the sea shore, of the landslide foot. Moreover, together with other kind of data (a grid of high-resolution marine seismic lines acquired 200 m offshore, several marine and land lines acquired by ENI-AGIP for hydrocarbon exploration), these results clearly evidence the general structural setting of the area which likely plays a role in the landslide dynamic. Ongoing works include the estimation of an optimal velocity model by means of refraction/reflection tomography and pre-post stack depth migration.

Archive of digital Boomer seismic reflection data collected during USGS Cruises 94CCT01 and 95CCT01, eastern Texas and western Louisiana, 1994 and 1995

USGS Publications Warehouse

Calderon, Karynna; Dadisman, Shawn V.; Kindinger, Jack G.; Flocks, James G.; Morton, Robert A.; Wiese, Dana S.

2004-01-01

In June of 1994 and August and September of 1995, the U.S. Geological Survey, in cooperation with the University of Texas Bureau of Economic Geology, conducted geophysical surveys of the Sabine and Calcasieu Lake areas and the Gulf of Mexico offshore eastern Texas and western Louisiana. This report serves as an archive of unprocessed digital boomer seismic reflection data, trackline maps, navigation files, observers' logbooks, GIS information, and formal FGDC metadata. In addition, a filtered and gained GIF image of each seismic profile is provided. The archived trace data are in standard Society of Exploration Geophysicists (SEG) SEG-Y format (Barry and others, 1975) and may be downloaded and processed with commercial or public domain software such as Seismic Unix (SU). Examples of SU processing scripts and in-house (USGS) software for viewing SEG-Y files (Zihlman, 1992) are also provided. Processed profile images, trackline maps, navigation files, and formal metadata may be viewed with a web browser. Scanned handwritten logbooks and Field Activity Collection System (FACS) logs may be viewed with Adobe Reader.

Archive of digital Boomer and Chirp seismic reflection data collected during USGS Cruises 01RCE05 and 02RCE01 in the Lower Atchafalaya River, Mississippi River Delta, and offshore southeastern Louisiana, October 23-30, 2001, and August 18-19, 2002

USGS Publications Warehouse

Calderon, Karynna; Dadisman, Shawn V.; Kindinger, Jack G.; Flocks, James G.; Ferina, Nicholas F.; Wiese, Dana S.

2004-01-01

In October of 2001 and August of 2002, the U.S. Geological Survey conducted geophysical surveys of the Lower Atchafalaya River, the Mississippi River Delta, Barataria Bay, and the Gulf of Mexico south of East Timbalier Island, Louisiana. This report serves as an archive of unprocessed digital marine seismic reflection data, trackline maps, navigation files, observers' logbooks, GIS information, and formal FGDC metadata. In addition, a filtered and gained GIF image of each seismic profile is provided. The archived trace data are in standard Society of Exploration Geophysicists (SEG) SEG-Y format (Barry and othes, 1975) and may be downloaded and processed with commercial or public domain software such as Seismic Unix (SU). Examples of SU processing scripts and in-house (USGS) software for viewing SEG-Y files (Zihlman, 1992) are also provided. Processed profile images, trackline maps, navigation files, and formal metadata may be viewed with a web browser. Scanned handwritten logbooks and Field Activity Collection System (FACS) logs may be viewed with Adobe Reader.

Reply to “Comment on ‘Near-surface location, geometry, and velocities of the Santa Monica fault zone, Los Angeles, California’ by R. D. Catchings, G. Gandhok, M. R. Goldman, D. Okaya, M. J. Rymer, and G. W. Bawden” by T. L. Pratt and J. F. Dolan

USGS Publications Warehouse

Catchings, Rufus D.; Rymer, Michael J.; Goldman, Mark R.; Bawden, Gerald W.

2010-01-01

In a comment on our 2008 paper (Catchings, Gandhok, et al., 2008) on the Santa Monica fault in Los Angeles, California, Pratt and Dolan (2010) (herein referred to as P&D) cite numerous objections to our work, inferring that our study is flawed. However, as shown in our reply, their objections contradict their own published works, published works of others, and proven seismic methodologies. Rather than responding to each repeated invalid objection, we address their objections by topic in the subsequent sections.In Catchings, Gandhok, et al. (2008), we presented high-resolution seismic-reflection images that showed two near-surface faults in the upper 50 m beneath the grounds of the Wadsworth Veterans Administration Hospital (WVAH). Although P&D suggest we effectively duplicated their seismic acquisition, our survey was not a duplication of their efforts. Rather, we conducted a seismic-imaging survey over a similar profile as Pratt et al. (1998) but used a different data acquisition system and different data processing methods to evaluate methods of seismically imaging blind faults in the wake of the 17 January 1994 M 6.7 Northridge earthquake. We used an acquisition method that provides both tomographic seismic velocities and reflection images. Our combined-data approach allowed for shallower imaging (∼2.5 m minimum) than the ∼20-m minimum of Pratt et al. (1998), clearer images of the fault zone, and more accurate depth determinations (rather than time images). In processing the reflection images, we used prestack depth migration, which is generally accepted as the only proper imaging method for imaging subsurface structures with strong lateral velocity variations (Versteeg, 1993), a condition shown to exist at the WVAH site. We correlated our reflection images with refraction tomography images, borehole lithology, and velocity data, Interferometric Synthetic Aperture Radar images, and changes in groundwater depths. Except for some minor differences, our seismic-reflection images coincide with previously published seismic-reflection images by Dolan and Pratt (1997) and Pratt et al. (1998), and a paleoseismic study by Dolan et al. (2000). Principal differences among our interpretations and those of Pratt et al. (1998) relate to the upper 20 m and the south side of the fault, which Pratt et al. (1998) did not clearly image. In contrast, our seismic images included structures on both sides of the fault zone from about 2.5 m depth to about 100 m depth at WVAH, allowing us to interpret more details.

High resolution seismic reflection profiling at Aberdeen Proving Grounds, Maryland

DOE Office of Scientific and Technical Information (OSTI.GOV)

Miller, R.D.; Xia, Jianghai; Swartzel, S.

1996-11-01

The effectiveness of shallow high resolution seismic reflection (i.e., resolution potential) to image geologic interfaces between about 70 and 750 ft at the Aberdeen Proving Grounds, Maryland (APG), appears to vary locally with the geometric complexity of the unconsolidated sediments that overlay crystalline bedrock. The bedrock surface (which represents the primary geologic target of this study) was imaged at each of three test areas on walkaway noise tests and CDP (common depth point) stacked data. Proven high resolution techniques were used to design and acquire data on this survey. Feasibility of the technique and minimum acquisition requirements were determined throughmore » evaluation and correlation of walkaway noise tests, CDP survey lines, and a downhole velocity check shot survey. Data processing and analysis revealed several critical attributes of shallow seismic data from APG that need careful consideration and compensation on reflection data sets. This survey determined: (1) the feasibility of the technique, (2) the resolution potential (both horizontal and vertical) of the technique, (3) the optimum source for this site, (4) the optimum acquisition geometries, (5) general processing flow, and (6) a basic idea of the acoustic variability across this site. Source testing involved an accelerated weight drop, land air gun, downhole black powder charge, sledge hammer/plate, and high frequency vibrator. Shallow seismic reflection profiles provided for a more detailed picture of the geometric complexity and variability of the distinct clay sequences (aquatards), previously inferred from drilling to be present, based on sparse drill holes and basewide conceptual models. The seismic data also reveal a clear explanation for the difficulties previously noted in correlating individual, borehole-identified sand or clay units over even short distances.« less

Report of reprocessing of reflection seismic profile X-5 Waste Isolation Pilot Plant site, Eddy County, New Mexico

USGS Publications Warehouse

Miller, John J.

1983-01-01

Seismic reflection profile X-5 exhibits a 7,700 ft long anomalous zone of poor quality to nonexistent reflections between shotpoints 100 and 170, compared to the high-quality, flat-lying, coherent reflections on either side. Results from drill holes in the area suggest 'layer cake' geology with no detectable abnormalities such as faults present. In an attempt to determine whether the anomalous zone of the seismic profile is an artifact or actually indicates a geologic condition, the data were extensively reprocessed using state-of-the-art processing techniques and the following conclusions were made: 1. The field-recorded data in the anomalous zone are of poor quality due to surface conditions and recording parameters used. 2. Reprocessing shows reflectors throughout the anomalous zone at all levels. However, it cannot prove that the reflectors are continuous throughout the anomalous zone. 3. Significant improvement in data quality may be achieved if the line is reshot using carefully determined recording parameters.

Intraplate extensional tectonics of the eastern Basin-Range Inferencess on structural style from seismic reflection data, regional tectonics, and thermal-mechanical models of brittle-ductile deformation

NASA Technical Reports Server (NTRS)

Smith, R. B.; Bruhn, R. L.

1984-01-01

Using 1500 km of industry-released seismic reflection data, surface geology, velocity models from refraction data, and earthquake data, the large extensional structures in the crust of the eastern Basin-Range and its transition into the Middle Rocky Mountains and Colorado Plateau have been studied. It is suggested that the close spatial correlation between normal faults and thrust fault segmentation along the Wasatch Front reflects major east-trending structural and lithological boundaries inherited from tectonic processes associated with the evolution of the cordilleran miogeocline, which began in the Precambrian.

Study of a prehistoric landslide using seismic reflection methods integrated with geological data in the Wasatch Mountains, Utah, USA

USGS Publications Warehouse

Tingey, B.E.; McBride, J.H.; Thompson, T.J.; Stephenson, W.J.; South, J.V.; Bushman, M.

2007-01-01

An integration of geological and geophysical techniques characterizes the internal and basal structure of a landslide along the western margin of the Wasatch Mountains in northern Utah, USA. The study area is within a region of planned and continuing residential development. The Little Valley Landslide is a prehistoric landslide as old as 13??ka B.P. Drilling and trenching at the site indicate that the landslide consists of chaotic and disturbed weathered volcanic material derived from Tertiary age volcanic rocks that comprise a great portion of the Wasatch Range. Five short high-resolution common mid-point seismic reflection profiles over selected portions of the site examine the feasibility of using seismic reflection to study prehistoric landslides in the Wasatch Mountain region. Due to the expected complexity of the near-surface geology, we have pursued an experimental approach in the data processing, examining the effects of muting first arrivals, frequency filtering, model-based static corrections, and seismic migration. The results provide a framework for understanding the overall configuration of the landslide, its basal (failure) surface, and the structure immediately underlying this surface. A glide surface or de??collement is interpreted to underlie the landslide suggesting a large mass movement. The interpretation of a glide surface is based on the onset of coherent reflectivity, calibrated by information from a borehole located along one of the seismic profiles. The glide surface is deepest in the center portion of the landslide and shallows up slope, suggesting a trough-like feature. This study shows that seismic reflection techniques can be successfully used in complex alpine landslide regions to (1) provide a framework in which to link geological data and (2) reduce the need for an extensive trenching and drilling program. ?? 2007 Elsevier B.V. All rights reserved.

Seismic investigation of an ocean-continent transition zone in the northern South China Sea

NASA Astrophysics Data System (ADS)

Zhu, J.; Qiu, X.; Xu, H.; Zhan, W.; Sun, Z.

2011-12-01

Rifted continental margins and basins are mainly formed by the lithospheric extension. Thined lithosphere of passive continental margins results in decompression melt of magma and created oceanic crust and thined ocean-continent transition (OCT) zone. Two refraction profiles used ocean bottom seismometers deployed in the broad continental shelf and three multi-channel seismic reflection lines in the northern South China Sea, acquired by the ship "Shiyan 2" of the South China Sea Institute of Oceanology, Chinese Academy of Sciences in 2010, are processed and interpreted in this study. Seismic reflection lines cut through the Dongsha rise, Zhu-1 and Zhu-2 depression within a Tertiary basin, Pear River Mouth basin (called as Zhujiangkou basin). These tectonic features are clear imaged in the seismic reflection records. Numerous normal faults, cutted through the basement and related to the stretch of the northern South China Sea margin, are imaged and interpreted. Reflection characteristics of the ocean-continent transition (OCT) zone are summaried and outlined. The COT zone is mainly divided into the northern syn-rift subsidence zone, central volcano or buried volcano uplift zone and tilt faulted block near the South Chia Sea basin. Compared to the previous seismic reflection data and refraction velocity models, the segmentation range of the OCT zone is outlined, from width of about 225 km in the northeastern South China Sea , of 160 km in the central to of 110 km in the north-central South China Sea. Based on the epicenter distribution of sporadic and large than 6 magnitude earthquakes, it suggests the OCT zone in the northern South China Sea at present is still an active seismic zone.

Archive of digital boomer seismic reflection data collected during USGS field activities 95LCA03 and 96LCA02 in the Peace River of West-Central Florida, 1995 and 1996

USGS Publications Warehouse

Calderon, Karynna; Dadisman, Shawn V.; Tihansky, Ann B.; Lewelling, Bill R.; Flocks, James G.; Wiese, Dana S.; Kindinger, Jack G.; Harrison, Arnell S.

2006-01-01

In October and November of 1995 and February of 1996, the U.S. Geological Survey, in cooperation with the Southwest Florida Water Management District, conducted geophysical surveys of the Peace River in west-central Florida from east of Bartow to west of Arcadia. This report serves as an archive of unprocessed digital boomer seismic reflection data, trackline maps, navigation files, GIS files, Field Activity Collection System (FACS) logs, observers' logbooks, and formal FGDC metadata. Filtered and gained digital images of the seismic profiles are also provided. Refer to the Acronyms page for expansion of acronyms and abbreviations used in this report. The archived trace data are in standard Society of Exploration Geophysicists (SEG) SEG-Y format (Barry and others, 1975) and may be downloaded and processed with commercial or public domain software such as Seismic Unix (SU). Example SU processing scripts and USGS software for viewing the SEG-Y files (Zihlman, 1992) are also provided.

Reprocessing of multi-channel seismic-reflection data collected in the Beaufort Sea

USGS Publications Warehouse

Agena, W.F.; Lee, Myung W.; Hart, P.E.

2000-01-01

Contained on this set of two CD-ROMs are stacked and migrated multi-channel seismic-reflection data for 65 lines recorded in the Beaufort Sea by the United States Geological Survey in 1977. All data were reprocessed by the USGS using updated processing methods resulting in improved interpretability. Each of the two CD-ROMs contains the following files: 1) 65 files containing the digital seismic data in standard, SEG-Y format; 2) 1 file containing navigation data for the 65 lines in standard SEG-P1 format; 3) an ASCII text file with cross-reference information for relating the sequential trace numbers on each line to cdp numbers and shotpoint numbers; 4) 2 small scale graphic images (stacked and migrated) of a segment of line 722 in Adobe Acrobat (R) PDF format; 5) a graphic image of the location map, generated from the navigation file; 6) PlotSeis, an MS-DOS Application that allows PC users to interactively view the SEG-Y files; 7) a PlotSeis documentation file; and 8) an explanation of the processing used to create the final seismic sections (this document).

Along-strike variations in seismic structure of the locked-sliding transition on the plate boundary beneath the southern part of Kii Peninsula, southwestern Japan

NASA Astrophysics Data System (ADS)

Kurashimo, E.; Iidaka, T.; Iwasaki, T.; Saiga, A.; Umeyama, E.; Tsumura, N.; Sakai, S.; Hirata, N.

2013-12-01

The Nankai trough region, where the Philippine Sea Plate (PHS) subducts beneath the SW Japan arc, is a well-known seismogenic zone of interplate earthquakes. A narrow zone of nonvolcanic tremor has been found in the SW Japan fore-arc, along strike of the arc (Obara, 2002). The epicentral distribution of tremor corresponds to the locked-sliding transition estimated from thermal and deformation models (Hyndman et al., 1995). The spatial distribution of the tremor is not homogeneous in a narrow belt but is spatially clustered. Obara [2002] suggested fluids as a source for tremor because of the long duration and the mobility of the tremor activity. The behavior of fluids at the plate interface is a key factor in understanding fault slip processes. Seismic reflection characteristics and seismic velocity variations can provide important information on the fluid-related heterogeneity of structure around plate interface. However, little is known about the deeper part of the plate boundary, especially the transition zone on the subducting plate. To reveal the seismic structure of the transition zone, we conducted passive and active seismic experiments in the southern part of Kii Peninsula, SW Japan. Sixty 3-component portable seismographs were installed on a 60-km-long line (SM-line) nearly perpendicular to the direction of the subduction of the PHS with approximately 1 km spacing. To improve accuracy of hypocenter locations, we additionally deployed six 3-component seismic stations around the survey line. Waveforms were continuously recorded during a five-month period from December, 2009. In October of 2010, a deep seismic profiling was also conducted. 290 seismometers were deployed on the SM-line with about 200 m spacing, on which five explosives shots were fired as controlled seismic sources. Arrival times of local earthquakes and explosive shots were used in a joint inversion for earthquake locations and 3-D Vp and Vp/Vs structures, using the iterative damped least-squares algorithm, simul2000 (Thurber and Eberhart-Phillips, 1999). To obtain the detailed structure image of the transition zone on the subducting plate, the explosive shot data recorded on the SM-line were processed using the seismic reflection technique. Seismic reflection image shows the lateral variation of the reflectivity along the top of the PHS. A clear reflection band is present where the clustered tremors occurred. The depth section of Vp/Vs structure shows the lateral variation of the Vp/Vs values along the top of the PHS. Clustered tremors are located in and around the high Vp/Vs zone. These results suggest the occurrence of the tremors may be associated with fluids dehydrated from the subducted oceanic lithosphere.

Towards a more comprehensive usage of reflection seismic in near-surface characterization

NASA Astrophysics Data System (ADS)

Blouin, M.; Gloaguen, E.; Bellefleur, G.; Pugin, A.

2014-12-01

For more than a decade, research groups such as the Geological Survey of Canada built the interest for near-surface reflection seismic by proposing small vibrating sources and three components (3C) landstreamers. Developments in the instrumentation combined with extensive use of shear-wave profiling to image stratigraphy of unconsolidated environments at high resolution got this geophysical method more versatile, more accurate, increased cost effectiveness and allowed to cover greater distance per day. With those major upgrades as a starting point and in a context of regional aquifer characterization in St-Lawrence Lowlands in the province of Quebec, Canada, the present study propose a workflow to further enhance reflection seismic usage for near-surface characterization. First, as high resolution near surface surveys require small shot intervals and multiple channels on three axis, a lot of the acquisition information is received under a raw form yielding to unproductive quality control (QC). Hence, a tool was developed to process data "on the fly" and allow adequate real-time QC and on-site decision making. The algorithm was constructed in a Python environment and is accessible through a graphical user interface where the user is prompted for geometry parameters inputs and desired processing flow steps. Second, at the scale of seismic wavelengths, fine grain and poorly consolidated sediments such as marine clay of the St-Lawrence Lowlands can be viewed as a homogeneous medium presenting anisotropy. This section of the study showed that such geological settings yield to significant seismic velocity variations with angle of propagation that should not be ignore for normal move-out correction, migration or time to depth conversion. Finally, accurate delineation of stratigraphic horizons is an important task of any environmental or hydrogeological characterization study. A methodology was put forward to help integrate geophysical measurements with geological knowledge in the construction of stratigraphic maps. The approach accounts for reliability and resolution of the measurements, extracts statistical information from reflection seismic interpretations and can further serve as a tool for reinterpretation of the seismic data.

Structural variation of the oceanic Moho in the Pacific plate revealed by active-source seismic data

NASA Astrophysics Data System (ADS)

Ohira, Akane; Kodaira, Shuichi; Nakamura, Yasuyuki; Fujie, Gou; Arai, Ryuta; Miura, Seiichi

2017-10-01

The characteristics of the oceanic Moho are known to depend on various factors, such as seafloor spreading rate, crustal age, and accretionary processes at a ridge. However, the effect of local magmatic activities on the seismic signature of the Moho is poorly understood. Here an active-source reflection and refraction survey is used to investigate crustal structure and Moho characteristics along a >1000-km-long profile southeast of the Shatsky Rise in a Pacific Ocean basin formed from the Late Jurassic to Early Cretaceous and spanning the onset of Shatsky Rise volcanism. Although the seismic velocity structure estimated from the refraction data showed typical characteristics of the oceanic crust of the old Pacific plate, the appearance of the Moho reflections was spatially variable. We observed clear Moho reflections such as those to be expected where the spreading rate is fast to intermediate only at the southwestern end of the profile, whereas Moho reflections were diffuse, weak, or absent along other parts of the profile. The poor Moho reflections can be explained by the presence of a thick crust-mantle transition layer, which is temporally coincident with the formation of the Shatsky Rise. We inferred that the crust-mantle transition layer was formed by changes in on-axis accretion process or modification of the primary Moho by off-axis magmatism, induced by magmatic activity of the Shatsky Rise.

Seismological evidence for an along-axis hydrothermal flow at the Lucky Strike hydrothermal vents site

NASA Astrophysics Data System (ADS)

Rai, A.; Wang, H.; Singh, S. C.; Crawford, W. C.; Escartin, J.; Cannat, M.

2010-12-01

Hydrothermal circulation at ocean spreading centres plays fundamental role in crustal accretion process, heat extraction from the earth and helps to maintain very rich ecosystem in deep Ocean. Recently, it has been suggested that hydrothermal circulation is mainly along the ridge axis at fast spreading centres above along axis melt lens (AMC). Using a combination of micro-earthquake and seismic reflection data, we show that the hydrothermal circulation at the Lucky Strike segment of slow spreading Mid-Atlantic Ridge is also along axis in a narrow (~1 km) zone above a wide (2-3 km) AMC. We find that the seismicity mainly lies above the seismically imaged 3 km wide 7 km long melt lens at 3.2 km depth. We observe a vertical plume of seismicity above a weak AMC reflection just north of the hydrothermal vent fields that initiates just above the AMC and continues to the seafloor. This zone is collocated with active rifting of the seafloor in the neo-volcanic zone. Beneath the hydrothermal vents sites, where a strong melt lens is imaged, the seismicity initiates at 500 m above the AMC and continues to the seafloor. Just south of the hydrothermal field, where the AMC is widest and strongest, the seismicity band lies 500 m above the melt lens in a 800 m thick zone, which does not continue to the seafloor. The presence the weak melt lens reflection could be due to a cooled and crystallised AMC (mush) that permits the penetration of hydrothermal fluids down to the top of the AMC indicated by seismicity plume and might be the in-flow zone for hydrothermal circulation. The strong AMC reflection could be due to fresh supply of melt in the AMC (pure melt), which has pushed the cracking front 500 m above the AMC. Beneath the hydrothermal fields, the strong AMC reflection and seismicity 500 above the AMC to the seafloor could represent cracking along the up-flow zone. The 800 m thick zone of seismicity above the pure melt zone could be the zone of hydrothermal cracking zone. We do not observe any seismicity along the main bounding faults. These results suggest that the hydrothermal flow is mainly along the ridge axis in a narrow zone above the AMC, even when the AMC only 7 km long.

The Architecture of A Variscan Collisional Crust, As Revealed By The Iberseis Seismic Reflection Profile In Southwest Iberia

NASA Astrophysics Data System (ADS)

Simancas, F.; Carbonell, R.; Gonzalez-Lodeiro, F.; Perez-Estaun, A.; Ayarza, P.; Juhlin, C.; Azor, A.; Saez, R.; Martinez-Poyatos, D.; Pascual, E.

The recently acquired IBERSEIS Seismic Reflection Profile runs across major do- mains of the Variscan Orogen in SW Iberia. Geological studies indicate that the seis- mically surveyed region has been built up from three terranes, namely the South Por- tuguese Zone (SPZ), the Ossa-Morena Zone (OMZ) and the Central Iberian Zone (CIZ). These terranes became sutured after a complex, mainly transpressive (left- lateral), collisional history in Devonian-Carboniferous time. The deep seismic reflec- tion profile IBERSEIS has successfully imaged the sutures between these terranes as well as the structure of their crust. The following main features emerge from the pre- liminary integration of seismic and geological data: 1) The suture between the SPZ and OMZ terranes, marked by oceanic amphibolites, appears at present as a north- dipping left-lateral thrust merging in a mid-crustal detachment; the continuity of this suture-contact in the lower crust is not well defined in the seismic image. 2) The OMZ/CIZ suture, a shear zone with eclogites, is clearly imaged in the upper crust as a band of reflectivity dipping to the NE which, after a flat geometry in the middle crust, may continue downwards to the Moho as NE-dipping lower crustal reflections. 3) The SPZ upper crust has an imbricate structure merging into a mid-crustal detachment at constant depth in the surveyed profile. 4) The structure of the OMZ upper crust is dominated by large-scale recumbent folds affected by late upright folds, as fore- seen by geology and fully confirmed by the seismic image. 5) A general mid-crustal detachment exists in the whole surveyed area, whose geometry varies from a sharp detachment-level in the SPZ to a pinching and swelling horizontal band of reflectivity -a melting layer?- in the OMZ; in any case, a strong decoupling between upper and lower crust characterizes this transect of the Variscan orogen. 6) The lower crust of the SPZ has an intense seismic fabric, in accordance with the consideration of this ter- rane as an external orogenic domain with discrete shear bands preserved in the whole crust. 7) The lower crust of the OMZ is much less reflective than the lower crust of the SPZ. 8) The Moho is flat all along the surveyed area, which means that crustal 1 roots formed during the collisional processes were eliminated later on, probably in Late Carboniferous-Permian times. Despite the disturbance due to the generation of a post-orogenic flat Moho, the IBERSEIS seismic image seems to be a good snapshot of the Variscan collision, with very minor reworking by alpine processes. 2

Exploration and discovery in Yellowstone Lake: Results from high-resolution sonar imaging, seismic reflection profiling, and submersible studies

USGS Publications Warehouse

Morgan, L.A.; Shanks, Wayne C.; Lovalvo, D.A.; Johnson, S.Y.; Stephenson, W.J.; Pierce, K.L.; Harlan, S.S.; Finn, C.A.; Lee, G.; Webring, M.; Schulze, B.; Duhn, J.; Sweeney, R.; Balistrieri, L.

2003-01-01

Discoveries from multi-beam sonar mapping and seismic reflection surveys of the northern, central, and West Thumb basins of Yellowstone Lake provide new insight into the extent of post-collapse volcanism and active hydrothermal processes occurring in a large lake environment above a large magma chamber. Yellowstone Lake has an irregular bottom covered with dozens of features directly related to hydrothermal, tectonic, volcanic, and sedimentary processes. Detailed bathymetric, seismic reflection, and magnetic evidence reveals that rhyolitic lava flows underlie much of Yellowstone Lake and exert fundamental control on lake bathymetry and localization of hydrothermal activity. Many previously unknown features have been identified and include over 250 hydrothermal vents, several very large (>500 m diameter) hydrothermal explosion craters, many small hydrothermal vent craters (???1-200 m diameter), domed lacustrine sediments related to hydrothermal activity, elongate fissures cutting post-glacial sediments, siliceous hydrothermal spire structures, sublacustrine landslide deposits, submerged former shorelines, and a recently active graben. Sampling and observations with a submersible remotely operated vehicle confirm and extend our understanding of the identified features. Faults, fissures, hydrothermally inflated domal structures, hydrothermal explosion craters, and sublacustrine landslides constitute potentially significant geologic hazards. Toxic elements derived from hydrothermal processes also may significantly affect the Yellowstone ecosystem. Published by Elsevier Science B.V.

Near-Surface Geophysical Imaging of Deformation Associated with the Daytona Beach Sand Blow Deposits, Lee County, Arkansas

NASA Astrophysics Data System (ADS)

Rohrer, M.; Harris, J. B.; Cearley, C.; Teague, M.

2017-12-01

Within the past decade or so, paleoseismologic and geophysical studies at the Daytona Beach (DB) site in east-central Arkansas have reported earthquake-induced liquefaction (sand blows) along a prominent NW-trending lineament dated to approximately 5.5 ka. A recent compressional-wave (P-wave) seismic reflection survey acquired by the U. S. Geological Survey (USGS) along Highway 243 in Lee County, Arkansas, across the DB sand blow cluster, identified a previously unknown fault zone that is likely associated with the liquefaction. However, the USGS data were not able to image the Quaternary section (<60 m deep) and show a direct connection between the deeper faulting and the sand blows. In order to investigate the near-surface structure of the fault zone, we acquired an integrated geophysical data set consisting of 430-m-long shear-wave (S-wave) seismic reflection and ground penetrating radar (GPR) profiles above the deformation imaged on the USGS profile. The S-wave reflection data were collected using a 24-channel, towable landstreamer and the seismic energy was generated by a sledgehammer/I-beam source. The GPR data were collected with a cart-mounted 250-MHz system, using a 0.5-m antenna spacing and a 0.10-m step size. The processed seismic profile exhibits coherent reflection energy throughout the Quaternary section. Changes in reflection amplitude and coherency, offset reflections, and abundant diffractions suggest the presence of a complex zone of high-angle faults in the shallow subsurface coincident with the mapped lineament. Folded shallow reflections show that the deformation extends upward to within 10 m of the surface. Furthermore, the GPR profile images a distinct zone of deformation in the very near surface (<1.5 m deep) that is coincident with the upward projection of the deformation imaged on the S-wave seismic reflection profile.

Amplitude interpretation and visualization of three-dimensional reflection data

DOE Office of Scientific and Technical Information (OSTI.GOV)

Enachescu, M.E.

1994-07-01

Digital recording and processing of modern three-dimensional surveys allow for relative good preservation and correct spatial positioning of seismic reflection amplitude. A four-dimensional seismic reflection field matrix R (x,y,t,A), which can be computer visualized (i.e., real-time interactively rendered, edited, and animated), is now available to the interpreter. The amplitude contains encoded geological information indirectly related to lithologies and reservoir properties. The magnitude of the amplitude depends not only on the acoustic impedance contrast across a boundary, but is also strongly affected by the shape of the reflective boundary. This allows the interpreter to image subtle tectonic and structural elements notmore » obvious on time-structure maps. The use of modern workstations allows for appropriate color coding of the total available amplitude range, routine on-screen time/amplitude extraction, and late display of horizon amplitude maps (horizon slices) or complex amplitude-structure spatial visualization. Stratigraphic, structural, tectonic, fluid distribution, and paleogeographic information are commonly obtained by displaying the amplitude variation A = A(x,y,t) associated with a particular reflective surface or seismic interval. As illustrated with several case histories, traditional structural and stratigraphic interpretation combined with a detailed amplitude study generally greatly enhance extraction of subsurface geological information from a reflection data volume. In the context of three-dimensional seismic surveys, the horizon amplitude map (horizon slice), amplitude attachment to structure and [open quotes]bright clouds[close quotes] displays are very powerful tools available to the interpreter.« less

Submarine landslides in Arctic sedimentation: Canada Basin

USGS Publications Warehouse

Mosher, David C.; Shimeld, John; Hutchinson, Deborah R.; Lebedova-Ivanova, N; Chapman, C.

2016-01-01

Canada Basin of the Arctic Ocean is the least studied ocean basin in the World. Marine seismic field programs were conducted over the past 6 years using Canadian and American icebreakers. These expeditions acquired more than 14,000 line-km of multibeam bathymetric and multi-channel seismic reflection data over abyssal plain, continental rise and slope regions of Canada Basin; areas where little or no seismic reflection data existed previously. Canada Basin is a turbidite-filled basin with flat-lying reflections correlateable over 100s of km. For the upper half of the sedimentary succession, evidence of sedimentary processes other than turbidity current deposition is rare. The Canadian Archipelago and Beaufort Sea margins host stacked mass transport deposits from which many of these turbidites appear to derive. The stratigraphic succession of the MacKenzie River fan is dominated by mass transport deposits; one such complex is in excess of 132,000 km2 in area and underlies much of the southern abyssal plain. The modern seafloor is also scarred with escarpments and mass failure deposits; evidence that submarine landsliding is an ongoing process. In its latest phase of development, Canada Basin is geomorphologically confined with stable oceanographic structure, resulting in restricted depositional/reworking processes. The sedimentary record, therefore, underscores the significance of mass-transport processes in providing sediments to oceanic abyssal plains as few other basins are able to do.

Seismic stratigraphy and tomography in the outer shelf and slope of the Central Basin, Ross Sea, Antarctica

NASA Astrophysics Data System (ADS)

Kim, Sookwan; De Santis, Laura; Böhm, Gualtiero; Kuk Hong, Jong; Jin, Young Keun; Geletti, Riccardo; Wardell, Nigel; Petronio, Lorenzo; Colizza, Ester

2014-05-01

The Ross Sea, located between Victoria Land and Marie Byrd Land in Antarctica, is one of the main drainage of the Antarctic Ice Sheet (AIS). Reflection seismic data acquired by many countries during several decades have provided insights into the history of the Ross Sea and the AIS evolution. However the majority of the existing seismic data are concentrated in the shelf area, where hiatus formed by grounding ice sheet erosion multiple events prevent to reconstruct the entire sedimentary sequences depositional evolution. On the outer shelf and upper slope, the sedimentary sequences are relatively well preserved. The main purpose of this study is the investigation of the Cenozoic Antarctic Ice Sheet evolution through the seismic sequence analysis of the outer shelf and slope of the Central Basin, in the Ross Sea. The data used are the new multi-channel seismic data, KSL12, were acquired on the outer shelf and upper slope of the Central Bain in February 2013 by Korea Polar Research Institute. The reflection seismic data, previously collected by the Italian Antarctic Program (PNRA) and other data available from the Seismic Data Library System (SDLS) are also used for velocity tomography and seismic sequence mapping. The seismic data were processed by a conventional processing flow to produce the seismic profiles. Preliminary results show well-developed prograding wedges at the mouth of glacial troughs, eroded by a major glacial unconformity, the Ross Sea Unconformity 4 (RSU-4), correlated to a main event between early- and mid-Miocene. The velocity anomalies shown along KSL12-1 can be interpreted as showing the occurrence of gas and fluids, diagenetic horizons and sediment compactions. The isopach maps of each sequence show the variation of thickness of the sediments depocenter shift. The seismic sequence stratigraphy and acoustic facies analysis provide information about different phases of ice sheet's advance and retreat related to the AIS Cenozoic dynamics.

Seismic Imaging and Characterization of Bright Spots in the West Bohemia Seismic Zone (Germany and Czech Republic)

NASA Astrophysics Data System (ADS)

Alexandrakis, C.; Schreiter, L.; Hlousek, F.; Jusri, T.; Buske, S.

2017-12-01

In crystalline environments, imaging faults, layer boundaries and small scale structures is challenging due to the complex geometry of the structures themselves and the influence of the hardrock environment on the seismic wavefield. Optimally designed active seismic surveys and careful processing can produce a clear image of the subsurface structures. However, if little is known about the local geology and tectonic state of the area, the imaged reflections can be difficult to interpret. This is the case in the West Bohemia Seismic Zone, located along the border of Germany and Czech Republic. This geodynamically active area is spotted with springs and gas vents, and frequently experiences low magnitude seismic swarms. The most active region is located in the Cheb basin and coincides with the junction of a northwest trending fault with a north-south trending shear zone, making for a structurally complex hardrock setting. In the early 1990s, two long-offset reflection seismic profiles were collected along the boundary of the Cheb basin: MVE-90 along the northern edge, and 9HR-91 in the east. These profiles were recently reprocessed using Kirchhoff PreStack Depth Migration, revealing high amplitude reflections, or bright spots, that correlate to nearby seismicity. Several studies have hypothesized that the 9HR-91 bright spots image a fluid trap, where mantle-sourced fluids accumulate, thereby facilitating slip on the faults and triggering the swarms. However, the exact nature of the bright spots remains an open question. They may be a change in lithology and/or porosity, an infilled vein or an impermeable fault. We aim to answer this question by first using Coherency-Based PreStack Depth Migration to produce detailed images of the bright spots. We then forward model the waveforms guided by the reflection coefficients in order to derive rock-physical parameters. Finally, the best-fitting models are interpreted in terms of their possible relationship to the West Bohemia swarms.

SH-wave reflection seismic and VSP as tools for the investigation of sinkhole areas in Germany

NASA Astrophysics Data System (ADS)

Wadas, Sonja; Tschache, Saskia; Polom, Ulrich; Buness, Hermann; Krawczyk, Charlotte M.

2017-04-01

Sinkholes can lead to damage of buildings and infrastructure and they can cause life-threatening situations, if they occur in urban areas. The process behind this phenomenon is called subrosion. Subrosion is the underground leaching of soluble rocks, e.g. anhydrite and gypsum, due to the contact with ground- and meteoric water. Depending on the leached material, and especially the dissolution rate, different kinds of subrosion structures evolve in the subsurface. The two end members are collapse and depression structures. For a better understanding of the subrosion processes a detailed characterization of the resulting structures is necessary. In Germany sinkholes are a problem in many areas. In northern Germany salt and in central and southern Germany sulfate and carbonate deposits are affected by subrosion. The study areas described here are located in Thuringia in central Germany and the underground is characterized by soluble Permian deposits. The occurrence of 20 to 50 sinkholes is reported per year. Two regions, Bad Frankenhausen and Schmalkalden, are investigated, showing a leaning church tower and a sinkhole of 30 m diameter and 20 m depth, respectively. In Bad Frankenhausen four P-wave and 16 SH-wave reflection seismic profiles were carried out, supplemented by three zero-offset VSPs. In Schmalkalden five SH-wave reflection seismic profiles and one zero-offset VSP were acquired. The 2-D seismic sections, in particular the SH-wave profiles, showed known and unknown near-surface faults in the vicinity of sinkholes and depressions. For imaging the near-surface (< 100 m depth) high-resolution SH-waves are advantageous in order to detect subrosion structures at different stages. The reflection patterns of the 2-D seismic sections indicate a heterogeneous underground with lateral and vertical variations in forms of discontinuous reflectors, depressions, small-scale fractures and near-surface faults. Probably the faults and fractures serve as pathways for groundwater, forming cavities due to the increase in rock permeability. Besides these structures, anomalies of the seismic velocities and the attenuation of seismic waves are visible, especially in the SH-wave profiles. Low velocities < 200 m/s and high attenuation may indicate areas affected by subrosion. Other parameters characterizing the underground stability are the shear modulus, derived from shear-wave interval velocities and density, and the Vp-Vs ratio. The 1-D and the 2-D data revealed zones of low shear modulus < 100 MPa and high Vp-Vs ratios > 2,5, probably indicating unstable areas due to subrosion. We conclude, that SH-wave reflection seismic offer an important tool for the imaging and characterization of near-surface subrosion structures and the identification of unstable zones, especially in combination with P-wave reflection seismic and zero-offset VSP with P- and S-waves. Presumably there is a connection between the presence of large fluid pathways, like faults, and the occurrence of widespread subrosion.

Optimized suppression of coherent noise from seismic data using the Karhunen-Loève transform

NASA Astrophysics Data System (ADS)

Montagne, Raúl; Vasconcelos, Giovani L.

2006-07-01

Signals obtained in land seismic surveys are usually contaminated with coherent noise, among which the ground roll (Rayleigh surface waves) is of major concern for it can severely degrade the quality of the information obtained from the seismic record. This paper presents an optimized filter based on the Karhunen-Loève transform for processing seismic images contaminated with ground roll. In this method, the contaminated region of the seismic record, to be processed by the filter, is selected in such way as to correspond to the maximum of a properly defined coherence index. The main advantages of the method are that the ground roll is suppressed with negligible distortion of the remnant reflection signals and that the filtering procedure can be automated. The image processing technique described in this study should also be relevant for other applications where coherent structures embedded in a complex spatiotemporal pattern need to be identified in a more refined way. In particular, it is argued that the method is appropriate for processing optical coherence tomography images whose quality is often degraded by coherent noise (speckle).

NON-INVASIVE DETERMINATION OF THE LOCATION AND DISTRBUTION OF FREE-PHASE DENSE NONAQUEOUS PHASE LIQUIDS (DNAPL) BY SEISMIC REFLECTION TECHNIQUES

DOE Office of Scientific and Technical Information (OSTI.GOV)

Michael G. Waddell; William J. Domoracki; Jerome Eyer

2003-01-01

The Earth Sciences and Resources Institute, University of South Carolina is conducting a proof of concept study to determine the location and distribution of subsurface DNAPL carbon tetrachloride (CCl{sub 4}) contamination at the 216-Z-9 crib, 200 West area, DOE Hanford Site, Washington by use of two-dimensional high-resolution seismic reflection surveys and borehole geophysical data. The study makes use of recent advances in seismic reflection amplitude versus offset (AVO) technology to directly detect the presence of subsurface DNAPL. The techniques proposed are noninvasive means of site characterization and direct free-phase DNAPL detection. This final report covers the results of Tasks 1,more » 2, and 3. Task (1) contains site evaluation and seismic modeling studies. The site evaluation consists of identifying and collecting preexisting geological and geophysical information regarding subsurface structure and the presence and quantity of DNAPL. The seismic modeling studies were undertaken to determine the likelihood that an AVO response exists and its probable manifestation. Task (2) is the design and acquisition of 2-D seismic reflection data to image areas of probable high concentration of DNAPL. Task (3) is the processing and interpretation of the 2-D data. During the commission of these tasks four seismic reflection profiles were collected. Subsurface velocity information was obtained by vertical seismic profile surveys in three wells. The interpretation of these data is in two parts. Part one is the construction and interpretation of structural contour maps of the contact between the Hanford Fine unit and the underlying Plio/Pleistocene unit and of the contact between the Plio/Pleistocene unit and the underlying caliche layer. These two contacts were determined to be the most likely surfaces to contain the highest concentration CCl{sub 4}. Part two of the interpretation uses the results of the AVO modeling to locate any seismic amplitude anomalies that might be associated with the presence of high concentrations of CCl{sub 4}. Based on the modeling results three different methods of AVO analysis were preformed on the seismic data: enhanced amplitude stacks, offset range limited stacks, and gradient stacks. Seismic models indicate that the reflection from the contact between the Hanford Fine and the Plio/Pleistocene should exhibit amplitude variations where there are high concentrations of CCl{sub 4}. A series of different scenarios were modeled. The first scenario is the Hanford Fine pores are 100% saturated with CCl{sub 4} and the underlying Plio/Pleistocene pores are saturated with air. In this scenario the reflection coefficients are slightly negative at the small angles of incidence and become increasing more negative at the larger angles of incidence (dim-out). The second scenario is the Hanford Fine pores are saturated with air and Plio/Pleistocene pores are saturated with CCl{sub 4}. In this scenario the reflection coefficients are slightly positive at the small angles of incidence and become negative at the large angles of incidence (polarity reversal). Finally the third scenario is both the Hanford Fine and the Plio/Pleistocene pores are saturated CCl{sub 4}. In this scenario the reflection coefficients at the small angles of incidence are slightly positive, but much less than background response, and with increasing angle of incidence the reflection coefficients become slightly more positive. On the field data areas where extraction wells have high concentrations of CCl{sub 4} a corresponding dim-out and/or a polarity reversal is noted.« less

Geophysical Analysis of an Urban Region in Southwestern Pennsylvania

DOE Office of Scientific and Technical Information (OSTI.GOV)

Harbert, W.P.; Lipinski, B.A.; Kaminski, V.

2006-12-01

The goal of this project was to categorize the subsurface beneath an urban region of Southwestern Pennsylvania and to determine geological structure and attempt to image pathways for gas migration in this area. Natural gas had been commercially produced from this region at the turn of the century but this field, with more than 100 wells drilled, was closed approximately eighty years ago. There are surface expressions of gas migration visible in the study region. We applied geophysical methods to determine geological structure in this region, which included multi frequency electromagnetic survey performed using Geophex Gem-2 system, portable reflection seismicmore » and a System I/O-based reflection seismic survey. Processing and interpretation of EM data included filtering 10 raw channels (inphase and quadrature components measured at 5 frequencies), inverting the data for apparent conductivity using EM1DFM software by University of British Columbia, Canada and further interpretation in terms of nearsurface features at a maximum depth of up to 20 meters. Analysis of the collected seismic data included standard seismic processing and the use of the SurfSeis software package developed by the Kansas Geological Survey. Standard reflection processing of these data were completed using the LandMark ProMAX 2D/3D and Parallel Geoscience Corporations software. Final stacked sections were then imported into a Seismic Micro Technologies Kingdom Suite+ geodatabase for visualization and analysis. Interpretation of these data was successful in identifying and confirming a region of unmined Freeport coal, determining regional stratigraphic structure and identifying possible S-wave lower velocity anomalies in the shallow subsurface.« less

Uncertainty analysis of depth predictions from seismic reflection data using Bayesian statistics

NASA Astrophysics Data System (ADS)

Michelioudakis, Dimitrios G.; Hobbs, Richard W.; Caiado, Camila C. S.

2018-03-01

Estimating the depths of target horizons from seismic reflection data is an important task in exploration geophysics. To constrain these depths we need a reliable and accurate velocity model. Here, we build an optimum 2D seismic reflection data processing flow focused on pre - stack deghosting filters and velocity model building and apply Bayesian methods, including Gaussian process emulation and Bayesian History Matching (BHM), to estimate the uncertainties of the depths of key horizons near the borehole DSDP-258 located in the Mentelle Basin, south west of Australia, and compare the results with the drilled core from that well. Following this strategy, the tie between the modelled and observed depths from DSDP-258 core was in accordance with the ± 2σ posterior credibility intervals and predictions for depths to key horizons were made for the two new drill sites, adjacent the existing borehole of the area. The probabilistic analysis allowed us to generate multiple realizations of pre-stack depth migrated images, these can be directly used to better constrain interpretation and identify potential risk at drill sites. The method will be applied to constrain the drilling targets for the upcoming International Ocean Discovery Program (IODP), leg 369.

Uncertainty analysis of depth predictions from seismic reflection data using Bayesian statistics

NASA Astrophysics Data System (ADS)

Michelioudakis, Dimitrios G.; Hobbs, Richard W.; Caiado, Camila C. S.

2018-06-01

Estimating the depths of target horizons from seismic reflection data is an important task in exploration geophysics. To constrain these depths we need a reliable and accurate velocity model. Here, we build an optimum 2-D seismic reflection data processing flow focused on pre-stack deghosting filters and velocity model building and apply Bayesian methods, including Gaussian process emulation and Bayesian History Matching, to estimate the uncertainties of the depths of key horizons near the Deep Sea Drilling Project (DSDP) borehole 258 (DSDP-258) located in the Mentelle Basin, southwest of Australia, and compare the results with the drilled core from that well. Following this strategy, the tie between the modelled and observed depths from DSDP-258 core was in accordance with the ±2σ posterior credibility intervals and predictions for depths to key horizons were made for the two new drill sites, adjacent to the existing borehole of the area. The probabilistic analysis allowed us to generate multiple realizations of pre-stack depth migrated images, these can be directly used to better constrain interpretation and identify potential risk at drill sites. The method will be applied to constrain the drilling targets for the upcoming International Ocean Discovery Program, leg 369.

3D seismic data de-noising and reconstruction using Multichannel Time Slice Singular Spectrum Analysis

NASA Astrophysics Data System (ADS)

Rekapalli, Rajesh; Tiwari, R. K.; Sen, Mrinal K.; Vedanti, Nimisha

2017-05-01

Noises and data gaps complicate the seismic data processing and subsequently cause difficulties in the geological interpretation. We discuss a recent development and application of the Multi-channel Time Slice Singular Spectrum Analysis (MTSSSA) for 3D seismic data de-noising in time domain. In addition, L1 norm based simultaneous data gap filling of 3D seismic data using MTSSSA also discussed. We discriminated the noises from single individual time slices of 3D volumes by analyzing Eigen triplets of the trajectory matrix. We first tested the efficacy of the method on 3D synthetic seismic data contaminated with noise and then applied to the post stack seismic reflection data acquired from the Sleipner CO2 storage site (pre and post CO2 injection) from Norway. Our analysis suggests that the MTSSSA algorithm is efficient to enhance the S/N for better identification of amplitude anomalies along with simultaneous data gap filling. The bright spots identified in the de-noised data indicate upward migration of CO2 towards the top of the Utsira formation. The reflections identified applying MTSSSA to pre and post injection data correlate well with the geology of the Southern Viking Graben (SVG).

Processing of multichannel seismic reflection data acquired in 2013 for seismic investigations of gas hydrates in the Gulf of Mexico

USGS Publications Warehouse

Miller, John J.; Agena, Warren F.; Haines, Seth S.; Hart, Patrick E.

2016-04-13

As part of a cooperative effort among the U.S. Geological Survey (USGS), the U.S. Department of Energy, and the U.S. Department of the Interior Bureau of Ocean Energy Management, two grids of two-dimensional multichannel seismic reflection data were acquired in the Gulf of Mexico over lease blocks Green Canyon 955 and Walker Ridge 313 between April 18 and May 3, 2013. The purpose of the data acquisition was to fill knowledge gaps in an ongoing study of known gas hydrate accumulations in the area. These data were initially processed onboard the recording ship R/V Pelican for more quality control during the recording. The data were subsequently processed in detail by the U.S. Geological Survey in Denver, Colorado, in two phases. The first phase was to create a “kinematic” dataset that removed extensive noise present in the data but did not preserve relative amplitudes. The second phase was to create a true relative amplitude dataset that included noise removal and “wavelet” deconvolution that preserved the amplitude information. This report describes the processing techniques used to create both datasets.

Groundwater exploration in a Quaternary sediment body by shear-wave reflection seismics

NASA Astrophysics Data System (ADS)

Pirrung, M.; Polom, U.; Krawczyk, C. M.

2008-12-01

The detailed investigation of a shallow aquifer structure is the prerequisite for choosing a proper well location for groundwater exploration drilling for human drinking water supply and subsequent managing of the aquifer system. In the case of shallow aquifers of some 10 m in depth, this task is still a challenge for high-resolution geophysical methods, especially in populated areas. In areas of paved surfaces, shallow shear-wave reflection seismics is advantageous compared to conventional P-wave seismic methods. The sediment body of the Alfbach valley within the Vulkaneifel region in Germany, partly covered by the village Gillenfeld, was estimated to have a maximum thickness of nearly 60 m. It lies on top of a complicated basement structure, constituted by an incorporated lava flow near the basement. For the positioning of new well locations, a combination of a SH-wave land streamer receiver system and a small, wheelbarrow-mounted SH-wave source was used for the seismic investigations. This equipment can be easily applied also in residential areas without notable trouble for the inhabitants. The results of the 2.5D profiling show a clear image of the sediment body down to the bedrock with high resolution. Along a 1 km seismic profile, the sediment thickness varies between 20 to more than 60 m in the centre of the valley. The reflection behaviour from the bedrock surface corroborates the hypothesis of a basement structure with distinct topography, including strong dipping events from the flanks of the valley and strong diffractions from subsurface discontinuities. The reflection seismic imaging leads to an estimation of the former shape of the valley and a reconstruction of the flow conditions at the beginning of the sedimentation process.

Gravity and Seismic Investigations of the Northern Rio Grande Rift Area, New Mexico

NASA Astrophysics Data System (ADS)

Braile, L. W.; Deepak, A.; Helprin, O.; Kondas, S.; Maguire, H.; McCallister, B.; Orubu, A.; Rijfkogel, L.; Schumann, H.; Vannette, M.; Wanpiyarat, N.; Carchedi, C.; Ferguson, J. F.; McPhee, D.; Biehler, S.; Ralston, M. D.; Baldridge, W. S.

2017-12-01

Participants in the Summer of Applied Geophysical Experience (SAGE, a research and education program in applied geophysics for undergraduate and graduate students) program have studied the northern Rio Grande rift (RGR) area of New Mexico for the past thirty-five years. In recent years, the SAGE program has focused on the western edge of the Española basin and the transition into the Santo Domingo basin and the Valles caldera. During this time, we have collected about 50 km of seismic reflection and refraction data along approximately East-West profiles using a 120 channel data acquisition system with a 20 m station interval and a Vibroseis source. We also have access to several energy-industry seismic reflection record sections from the 1970s in the study area. During SAGE 2017, new gravity measurements north of the Jemez Mountains and a seismic reflection profile (Rio de Truchas Profile) in the Valarde graben adjacent to the eastern boundary of the RGR have added new constraints to a west-to-east transect in area of the northern RGR. The recorded near-vertical and wide-angle seismic refection data were processed to produce a CMP (common midpoint) stacked record section. Bandpass filtering, muting, deconvolution, and F-K velocity filtering were found to be effective in enhancing the seismic reflections. Modeling and interpretation of the northern RGR west-to-east geophysical profile indicates that the sedimentary rock fill in the Velarde graben is at least 3 km near the center of the graben. Gravity modeling also suggests the presence of a high-density intrusion at the top of the crystalline basement in an area to the north and west of Abiquiu, NM.

Recording and processing procedures for multi-channel seismic-reflection data collected in the western Ross Sea, Antarctica

USGS Publications Warehouse

Dadisman, Shawn V.; Ryan, Holly F.; Mann, Dennis M.

1987-01-01

During 1984, over 2300 km of multichannel seismic-reflection data were recorded by the U.S. Geological Survey in the western Ross Sea and Iselin Bank regions.  A temporary loss and sinking of the streamer led to increasing the streamer tow depth to 20 m, which resulted in some attenuation of frequencies in the 30-50 Hz range but no significant difference in resolution of the stacked data.  Severe water bottom multiples were encountered and removed by dip-filtering, weighted stacking, and severe post-NMO muting.

Combined Application of Shallow Seismic Reflection and High-resolution Refraction Exploration Approach to Active Fault Survey, Central Orogenic Belt, China

NASA Astrophysics Data System (ADS)

Lin, S.; Luo, D.; Yanlin, F.; Li, Y.

2016-12-01

Shallow Seismic Reflection (SSR) is a major geophysical exploration method with its exploration depth range, high-resolution in urban active fault exploration. In this paper, we carried out (SSR) and High-resolution refraction (HRR) test in the Liangyun Basin to explore a buried fault. We used NZ distributed 64 channel seismic instrument, 60HZ high sensitivity detector, Geode multi-channel portable acquisition system and hammer source. We selected single side hammer hit multiple overlay, 48 channels received and 12 times of coverage. As there are some coincidence measuring lines of SSR and HRR, we chose multi chase and encounter observation system. Based on the satellite positioning, we arranged 11 survey lines in our study area with total length for 8132 meters. GEOGIGA seismic reflection data processing software was used to deal with the SSR data. After repeated tests from the aspects of single shot record compilation, interference wave pressing, static correction, velocity parameter extraction, dynamic correction, eventually got the shallow seismic reflection profile images. Meanwhile, we used Canadian technology company good refraction and tomographic imaging software to deal with HRR seismic data, which is based on nonlinear first arrival wave travel time tomography. Combined with drilling geological profiles, we explained 11 measured seismic profiles. Results show 18 obvious fault feature breakpoints, including 4 normal faults of south-west, 7 reverse faults of south-west, one normal fault of north-east and 6 reverse faults of north-east. Breakpoints buried depth is 15-18 meters, and the inferred fault distance is 3-12 meters. Comprehensive analysis shows that the fault property is reverse fault with northeast incline section, and fewer branch normal faults presenting southwest incline section. Since good corresponding relationship between the seismic interpretation results, drilling data and SEM results on the property, occurrence, broken length of the fault, we considered the Liangyun fault to be an active fault which has strong activity during the Neogene Pliocene and early Pleistocene, Middle Pleistocene period. The combined application of SSR and HRR can provide more parameters to explain the seismic results, and improve the accuracy of the interpretation.

Use of Multibeam-Bathymetry and Seismic-Reflection Data to Investigate the Origin of Seafloor Depressions Along the Southeastern Carbonate Florida Platform

NASA Astrophysics Data System (ADS)

Cunningham, K. J.; Kluesner, J.; Westcott, R. L.; Ebuna, D. R.; Walker, C.

2016-12-01

Numerous large, semicircular, deep submarine depressions on the seafloor of the Miami Terrace (a bathymetric bench that interrupts the Atlantic continental slope on the southeastern carbonate Florida Platform) have been described as submarine sinkholes resulting from freshwater discharge at the seafloor and dissolution of carbonate rock. Multibeam-bathymetry and marine, high-resolution, multichannel 2D and 3D seismic-reflection data acquired over two of these depressions at water depths of about 250 m ("Miami sinkhole") and 336 m ("Key Biscayne sinkhole") indicate the depressions are pockmarks. Seafloor pockmarks are concave, crater-like depressions that form through the outburst or venting of fluid (gas, liquid) at the sea floor and are important seabed features that provide information about fluid flow on continental margins. Both the "Miami sinkhole" and "Key Biscayne sinkhole" (about 25 and 48m deep, respectively) have a seismic-chimney structure beneath them that indicates an origin related to seafloor fluid expulsion, as supported by multi-attribute analysis of the "Key Biscayne sinkhole". Further, there is no widening of the depressions with depth, as in the Fort Worth Basin, where downward widening of seismic, sub-circular, karst-collapse structures is common. However, hypogenic karst dissolution is not ruled out as part of the evolution of the two depressions. Indeed, a hypogenic karst pipe plausibly extends downward from the bottom of "Key Biscayne sinkhole", providing a passageway for focused upward flow of fluids to the seafloor. In "Key Biscayne sinkhole", the proposed karst pipe occurs above the underlying seismic chimney that contains flat bright spots (a hydrocarbon indicator) in the seismic data plausibly showing fluids are currently trapped beneath the pockmark within a tightly folded popup structure. The Miami Terrace depressions have seismic-reflection features similar to modern pockmarks imaged on the Maldives carbonate platform. The seismic-reflection data also show that ancient satellite expulsions formed buried pockmarks, slumps, and paleo-collapse structures in the carbonate sediments near the "Key Biscayne sinkhole". Additional processing of the 3D seismic data will aid in elucidation of the origin of these seafloor depressions.

Integration of seismic-reflection and well data to assess the potential impact of stratigraphic and structural features on sustainable water supply from the Floridan aquifer system, Broward County, Florida

USGS Publications Warehouse

Cunningham, Kevin J.

2014-01-01

The U.S. Geological Survey and Broward County water managers commenced a 3.5-year cooperative study in July 2012 to refine the geologic and hydrogeologic framework of the Floridan aquifer system (FAS) in Broward County. A lack of advanced stratigraphic knowledge of the physical system and structural geologic anomalies (faults and fractures originating from tectonics and karst-collapse structures) within the FAS pose a risk to the sustainable management of the resource. The principal objective of the study is to better define the regional stratigraphic and structural setting of the FAS in Broward County. The objective will be achieved through the acquisition, processing, and interpretation of new seismic-reflection data along several canals in Broward County. The interpretation includes integration of the new seismic-reflection data with existing seismic-reflection profiles along Hillsboro Canal in Broward County and within northeast Miami-Dade County, as well as with data from nearby FAS wellbores. The scope of the study includes mapping the geologic, hydrogeologic, and seismic-reflection framework of the FAS, and identifying stratigraphic and structural characteristics that could either facilitate or preclude the sustainable use of the FAS as an alternate water supply or a treated effluent repository. In addition, the investigation offers an opportunity to: (1) improve existing groundwater flow models, (2) enhance the understanding of the sensitivity of the groundwater system to well-field development and upconing of saline fluids, and (3) support site selection for future FAS projects, such as Class I wells that would inject treated effluent into the deep Boulder Zone.

Structure of the southern Juan de Fuca Ridge from seismic reflection records

USGS Publications Warehouse

Morton, Janet L.; Sleep, Norman H.; Normark, William R.; Tompkins, Donald H.

1987-01-01

Twenty-four-channel seismic reflection records were obtained from the axial region of the southern Juan de Fuca Ridge. Two profiles are normal to the strike of the spreading center and intersect the ridge at latitude 44°40′N and 45°05′N; a third profile extends south along the ridge axis from latitude 45°20′N and crosses the Blanco Fracture Zone. Processing of the axial portions of the cross-strike lines resolved a weak reflection centered beneath the axis. The reflector is at a depth similar to seismically detected magma chambers on the East Pacific Rise and a Lau Basin spreading center; we suggest that the reflector represents the top of an axial magma chamber. In the migrated sections the top of the probable magma chamber is relatively flat and 1–2 km wide, and the subbottom depth of the chamber is greater where the depth to the ridge axis is greater.

Improved images of crustal structures in the Bergslagen, central Sweden, through seismic reprocessing of BABEL lines 1, 6 and 7

NASA Astrophysics Data System (ADS)

Buntin, Sebastian; Malehmir, Alireza; Malinowski, Michał; Högdahl, Karin; Juhlin, Christopher; Buske, Stefan

2017-04-01

In a joint effort through the BABEL project, geoscientists from five countries acquired marine seismic data in the Baltic Sea with a total length of 2268 km in the year 1989. These consisted of near-vertical reflection and wide-angle refraction seismic data, providing insights into the subsurface down to the Moho and suggesting the existence of plate tectonics already during the Paleoproterozoic. The seismic data were acquired using a receiver group interval of 50 m and a total cable length of 3 km. In total, 60 groups of 64 hydrophones at 15 m depth were used. An airgun array consisting of six equal subarrays towed at 7.5 m depth was used to generate the seismic signal. The shot interval and the corresponding record lengths were different among the lines. A record length of 25 s and 75 m shot spacing for lines 1 and 7, respectively and 23 s and 62.5 m for line 6, respectively was used. The sampling rate was 4 ms for all three profiles. Lines 1, 6 and 7 are located at the boundary to the world-class and historical Bergslagen mineral district, and are being revisited in this study. Improved images can be used to refine previous interpretations, particularly at shallower depths (< 5 km). About 27 years after the acquisition, these data have been processed again in our study. Aside from the original processing steps, like spherical divergence correction, deconvolution and NMO corrections, additional processing steps such as DMO corrections or pre- and post-stack deconvolutions and coherency enhancements were applied. The reprocessing revealed reflections in the shallow part of the profiles, likely from major deformation (multi-phase) zones extending down to the lower crust, which were not present in the previous images. Also the images of the reflections in the deeper parts are remarkably improved. This also includes a few sub-Moho reflections. The three reprocessed profiles help constrain the nature of the northern boundary of Bergslagen and associated crustal structures. Furthermore they should assist in the planning of an onshore refraction and reflection profile, to be acquired in 2017, crossing the northern boundary of the Bergslagen district. Acknowledgments: This work is supported by the Swedish Research Council (VR) grant number 2015-05177 for which we are grateful. S. Buntin's PhD work is supported by the grant.

Wide-angle seismic recordings from the 1998 Seismic Hazards Investigation of Puget Sound (SHIPS), western Washington and British Columbia

USGS Publications Warehouse

Brocher, Thomas M.; Parsons, Tom; Creager, Ken C.; Crosson, Robert S.; Symons, Neill P.; Spence, George D.; Zelt, Barry C.; Hammer, Philip T.C.; Hyndman, Roy D.; Mosher, David C.; Tréhu, Anne M.; Miller, Kate C.; ten Brink, Uri S.; Fisher, Michael A.; Pratt, Thomas L.; Alvarez, Marcos G.; Beaudoin, Bruce C.; Louden, Keith E.; Weaver, Craig S.

1999-01-01

This report describes the acquisition and processing of deep-crustal wide-angle seismic reflection and refraction data obtained in the vicinity of Puget Lowland, the Strait of Juan de Fuca, and Georgia Strait, western Washington and southwestern British Columbia, in March 1998 during the Seismic Hazards Investigation of Puget Sound (SHIPS). As part of a larger initiative to better understand lateral variations in crustal structure along the Cascadia margin, SHIPS participants acquired 1000 km of deep-crustal multichannel seismic-reflection profiles and 1300 km of wideangle airgun shot lines in this region using the R/V Thompson and R/V Tully. The Tully was used to record airgun shots fired by the Thompson in two different geometries: (1) expanding spread profiles (ESPs) and (2) constant offset profiles (COPs). Prior to this reflection survey, we deployed 257 Reftek and 15 ocean-bottom seismic recorders to record the airgun signals at far offsets. All data were recorded digitally on large-capacity hard disks. Although most of these stations only recorded the vertical component of motion, 95 of these seismographs recorded signals from an oriented 3-component seismometer. By recording signals generated by the Thompson's marine air gun array, operated in two differing geometries having a total volume of 110 and 79 liters (6730 and 4838 cu. in.), respectively, the arrays of wide-angle recorders were designed to (1) image the crustal structure, particularly in the vicinity of crustal faults and Cenozoic sedimentary basins, (2) determine the geometry of the Moho, and (3) image the subducting Gorda and Juan de Fuca plates. Nearly 33,300 air gun shots were recorded along several seismic lines. In this report, we illustrate the expanding spread profiles acquired using the Thompson and Tully, describe the land and ocean-bottom recording of the air gun signals, discuss the processing of the land recorder data into common receiver gathers, and illustrate the processed wide-angle seismic data collected using the Refteks and ocean-bottom seismometers. We also describe the format and content of the archival tapes containing the SEGY-formated, common-receiver gathers for the Reftek data. Data quality is variable but SHIPS appears to have successfully obtained useful data from almost all the stations deployed to record the airgun shots. Several interesting arrivals were observed: including refractions from the sedimentary basin fill in several basins, refractions from basement rocks forming the upper crust, Pg, refractions from the upper mantle, Pn, as well as reflections from within the crust and from the top of the upper mantle, PmP. We separately archived more than 30 local earthquakes recorded by the Reftek array during our deployment.

Sub-metric Resolution FWI of Ultra-High-Frequency Marine Reflection Seismograms. A Remote Sensing Tool for the Characterisation of Shallow Marine Geohazard

NASA Astrophysics Data System (ADS)

Provenzano, G.; Vardy, M. E.; Henstock, T.; Zervos, A.

2017-12-01

A quantitative high-resolution physical model of the top 100 meters of the sub-seabed is of key importance for a wide range of shallow geohazard scenarios: identification of potential shallow landsliding, monitoring of gas storage sites, and assessment of offshore structures stability. Cur- rently, engineering-scale sediment characterisation relies heavily on direct sampling of the seabed and in-situ measurements. Such an approach is expensive and time-consuming, as well as liable to alter the sediment properties during the coring process. As opposed to reservoir-scale seismic exploration, ultra-high-frequency (UHF, 0.2-4.0 kHz) multi-channel marine reflection seismic data are most often limited to a to semi-quantitative interpretation of the reflection amplitudes and facies geometries, leaving largely unexploited its intrinsic value as a remote characterisation tool. In this work, we develop a seismic inversion methodology to obtain a robust sub-metric resolution elastic model from limited-offset, limited-bandwidth UHF seismic reflection data, with minimal pre-processing and limited a priori information. The Full Waveform Inversion is implemented as a stochastic optimiser based upon a Genetic Algorithm, modified in order to improve the robustness against inaccurate starting model populations. Multiple independent runs are used to create a robust posterior model distribution and quantify the uncertainties on the solution. The methodology has been applied to complex synthetic examples and to real datasets acquired in areas prone to shallow landsliding. The inverted elastic models show a satisfactory match with the ground-truths and a good sensitivity to relevant variations in the sediment texture and saturation state. We apply the methodology to a range of synthetic consolidating slopes under different loading conditions and sediment properties distributions. Our work demonstrates that the seismic inversion of UHF data has the potential to become an important practical tool for marine ground model building in spatially heterogeneous areas, reducing the reliance on expensive and time-consuming coring campaigns.

Combined interpretation of 3D seismic reflection attributes for geothermal exploration in the Polish Basin using self-organizing maps

NASA Astrophysics Data System (ADS)

Bauer, Klaus; Pussak, Marcin; Stiller, Manfred; Bujakowski, Wieslaw

2014-05-01

Self-organizing maps (SOM) are neural network techniques which can be used for the joint interpretation of multi-disciplinary data sets. In this investigation we apply SOM within a geothermal exploration project using 3D seismic reflection data. The study area is located in the central part of the Polish basin. Several sedimentary target horizons were identified at this location based on fluid flow rate measurements in the geothermal research well Kompina-2. The general objective is a seismic facies analysis and characterization of the major geothermal target reservoir. A 3D seismic reflection experiment with a sparse acquisition geometry was carried out around well Kompina-2. Conventional signal processing (amplitude corrections, filtering, spectral whitening, deconvolution, static corrections, muting) was followed by normal-moveout (NMO) stacking, and, alternatively, by common-reflection-surface (CRS) stacking. Different signal attributes were then derived from the stacked images including root-mean-square (RMS) amplitude, instantaneous frequency and coherency. Furthermore, spectral decomposition attributes were calculated based on the continuous wavelet transform. The resulting attribute maps along major target horizons appear noisy after the NMO stack and clearly structured after the CRS stack. Consequently, the following SOM-based multi-parameter signal attribute analysis was applied only to the CRS images. We applied our SOM work flow, which includes data preparation, unsupervised learning, segmentation of the trained SOM using image processing techniques, and final application of the learned knowledge. For the Lower Jurassic target horizon Ja1 we derived four different clusters with distinct seismic attribute signatures. As the most striking feature, a corridor parallel to a fault system was identified, which is characterized by decreased RMS amplitudes and low frequencies. In our interpretation we assume that this combination of signal properties can be explained by increased fracture porosity and enhanced fluid saturation within this part of the Lower Jurassic sandstone horizon. Hence, we suggest that a future drilling should be carried out within this compartment of the reservoir.

Near-vertical seismic reflection image using a novel acquisition technique across the Vrancea Zone and Foscani Basin, south-eastern Carpathians (Romania)

NASA Astrophysics Data System (ADS)

Panea, I.; Stephenson, R.; Knapp, C.; Mocanu, V.; Drijkoningen, G.; Matenco, L.; Knapp, J.; Prodehl, K.

2005-12-01

The DACIA PLAN (Danube and Carpathian Integrated Action on Process in the Lithosphere and Neotectonics) deep seismic sounding survey was performed in August-September 2001 in south-eastern Romania, at the same time as the regional deep refraction seismic survey VRANCEA 2001. The main goal of the experiment was to obtain new information on the deep structure of the external Carpathians nappes and the architecture of Tertiary/Quaternary basins developed within and adjacent to the seismically-active Vrancea zone, including the Focsani Basin. The seismic reflection line had a WNW-ESE orientation, running from internal East Carpathians units, across the mountainous south-eastern Carpathians, and the foreland Focsani Basin towards the Danube Delta. There were 131 shot points along the profile, with about 1 km spacing, and data were recorded with stand-alone RefTek-125s (also known as "Texans"), supplied by the University Texas at El Paso and the PASSCAL Institute. The entire line was recorded in three deployments, using about 340 receivers in the first deployment and 640 receivers in each of the other two deployments. The resulting deep seismic reflection stacks, processed to 20 s along the entire profile and to 10 s in the eastern Focsani Basin, are presented here. The regional architecture of the latter, interpreted in the context of abundant independent constraint from exploration seismic and subsurface data, is well imaged. Image quality within and beneath the thrust belt is of much poorer quality. Nevertheless, there is good evidence to suggest that a thick (˜10 km) sedimentary basin having the structure of a graben and of indeterminate age underlies the westernmost part of the Focsani Basin, in the depth range 10-25 km. Most of the crustal depth seismicity observed in the Vrancea zone (as opposed to the more intense upper mantle seismicity) appears to be associated with this sedimentary basin. The sedimentary successions within this basin and other horizons visible further to the west, beneath the Carpathian nappes, suggest that the geometry of the Neogene and recent uplift observed in the Vrancea zone, likely coupled with contemporaneous rapid subsidence in the foreland, is detached from deeper levels of the crust at about 10 km depth. The Moho lies at a depth of about 40 km along the profile, its poor expression in the reflection stack being strengthened by independent estimates from the refraction data. Given the apparent thickness of the (meta)sedimentary supracrustal units, the crystalline crust beneath this area is quite thin (< 20 km) supporting the hypothesis that there may have been delamination of (lower) continental crust in this area involved in the evolution of the seismic Vrancea zone.

Revised crustal architecture of the southeastern Carpathian foreland from active and passive seismic data

NASA Astrophysics Data System (ADS)

Enciu, Dana M.; Knapp, Camelia C.; Knapp, James H.

2009-08-01

Integration of active and passive source seismic data is employed in order to study the nature of the relationships between crustal seismicity and geologic structures in the southeastern (SE) Carpathian foreland of Romania and the possible connection with the Vrancea Seismogenic Zone (VSZ) of intermediate-depth seismicity, one of the most active earthquake-prone areas in Europe. Crustal epicenters and focal mechanisms are correlated with four deep industry seismic profiles, the reprocessed Danube and Carpathian Integrated Action on Process in the Lithosphere and Neotectonics (DACIA PLAN) profile and the Deep Reflection Acquisition Constraining Unusual Lithospheric Activity II and III (DRACULA) profiles in order to understand the link between neotectonic foreland deformation and Vrancea mantle seismicity. Projection of crustal foreland hypocenters onto deep seismic profiles identifies several active crustal faults in the SE Carpathian foreland and suggests a mechanical coupling between the mantle located VSZ and the overlying foreland crust. The coupled associated deformation appears to take place on the Trotus Fault, the Sinaia Fault, and the newly detected Ialomita Fault. Seismic reflection imaging reveals the absence of west dipping reflectors in the crystalline crust and a slightly east dipping to horizontal Moho in the proximity of the Vrancea area. These findings argue against previously purported mechanisms to generate mantle seismicity in the VSZ including oceanic lithosphere subduction in place and oceanic slab break off, furthermore suggesting that the Vrancea seismogenic body is undetached from the overlying crust in the foreland.

The damping of seismic waves and its determination from reflection seismograms

NASA Technical Reports Server (NTRS)

Engelhard, L.

1979-01-01

The damping in theoretical waveforms is described phenomenologically and a classification is proposed. A method for studying the Earth's crust was developed which includes this damping as derived from reflection seismograms. Seismic wave propagation by absorption, attenuation of seismic waves by scattering, and dispersion relations are considered. Absorption of seismic waves within the Earth as well as reflection and transmission of elastic waves seen through boundary layer absorption are also discussed.

Towards monitoring the englacial fracture state using virtual-reflector seismology

NASA Astrophysics Data System (ADS)

Lindner, F.; Weemstra, C.; Walter, F.; Hadziioannou, C.

2018-04-01

In seismology, coda wave interferometry (CWI) is an effective tool to monitor time-lapse changes using later arriving, multiply scattered coda waves. Typically, CWI relies on an estimate of the medium's impulse response. The latter is retrieved through simple time-averaging of receiver-receiver cross-correlations of the ambient field, i.e. seismic interferometry (SI). In general, the coda are induced by heterogeneities in the Earth. Being comparatively homogeneous, however, ice bodies such as glaciers and ice sheets exhibit little scattering. In addition, the temporal stability of the time-averaged cross-correlations suffers from temporal variations in the distribution and amplitude of the passive seismic sources. Consequently, application of CWI to ice bodies is currently limited. Nevertheless, fracturing and changes in the englacial macroscopic water content alter the bulk elastic properties of ice bodies, which can be monitored with cryoseismological measurements. To overcome the current limited applicability of CWI to ice bodies, we therefore introduce virtual-reflector seismology (VRS). VRS relies on a so-called multidimensional deconvolution (MDD) process of the time-averaged crosscorrelations. The technique results in the retrieval of a medium response that includes virtual reflections from a contour of receivers enclosing the region of interest (i.e., the region to be monitored). The virtual reflections can be interpreted as artificial coda replacing the (lacking) natural scattered coda. Hence, this artificial coda might be exploited for the purpose of CWI. From an implementation point of view, VRS is similar to SI by MDD, which, as its name suggests, also relies on a multidimensional deconvolution process. SI by MDD, however, does not generate additional virtual reflections. Advantageously, both techniques mitigate spurious coda changes associated with temporal variations in the distribution and amplitude of the passive seismic sources. In this work, we apply SI by MDD and VRS to synthetic and active seismic surface-wave data. The active seismic data were acquired on Glacier de la Plaine Morte, Switzerland. We successfully retrieve virtual reflections through the application of VRS to this active seismic data. In application to both synthetic and active seismic data, we show the potential of VRS to monitor time-lapse changes. In addition, we find that SI by MDD allows for a more accurate determination of phase velocity.

Exploration and discovery in Yellowstone Lake: results from high-resolution sonar imaging, seismic reflection profiling, and submersible studies

NASA Astrophysics Data System (ADS)

Morgan, L. A.; Shanks, W. C.; Lovalvo, D. A.; Johnson, S. Y.; Stephenson, W. J.; Pierce, K. L.; Harlan, S. S.; Finn, C. A.; Lee, G.; Webring, M.; Schulze, B.; Dühn, J.; Sweeney, R.; Balistrieri, L.

2003-04-01

'No portion of the American continent is perhaps so rich in wonders as the Yellow Stone' (F.V. Hayden, September 2, 1874) Discoveries from multi-beam sonar mapping and seismic reflection surveys of the northern, central, and West Thumb basins of Yellowstone Lake provide new insight into the extent of post-collapse volcanism and active hydrothermal processes occurring in a large lake environment above a large magma chamber. Yellowstone Lake has an irregular bottom covered with dozens of features directly related to hydrothermal, tectonic, volcanic, and sedimentary processes. Detailed bathymetric, seismic reflection, and magnetic evidence reveals that rhyolitic lava flows underlie much of Yellowstone Lake and exert fundamental control on lake bathymetry and localization of hydrothermal activity. Many previously unknown features have been identified and include over 250 hydrothermal vents, several very large (>500 m diameter) hydrothermal explosion craters, many small hydrothermal vent craters (˜1-200 m diameter), domed lacustrine sediments related to hydrothermal activity, elongate fissures cutting post-glacial sediments, siliceous hydrothermal spire structures, sublacustrine landslide deposits, submerged former shorelines, and a recently active graben. Sampling and observations with a submersible remotely operated vehicle confirm and extend our understanding of the identified features. Faults, fissures, hydrothermally inflated domal structures, hydrothermal explosion craters, and sublacustrine landslides constitute potentially significant geologic hazards. Toxic elements derived from hydrothermal processes also may significantly affect the Yellowstone ecosystem.

Detailed Crustal Geometry of the Continental Collision between India and Eurasia: Constraints from Deep Seismic Reflection Profiles across the Yarlung-Zangbo Suture, Tibet, at 88°E

NASA Astrophysics Data System (ADS)

Gao, R.; Li, W.; Guo, X.; Li, H.; Lu, Z.; He, R.; Zeng, L.; Klemperer, S. L.; Huang, X.

2016-12-01

The Tibetan plateau was created by continental collision between India and Eurasia and their ongoing convergence. The extent of subduction of Indian crust is central to our understanding the geodynamics of continental collision. However, owing to the lack of high-resolution data on the crustal-scale geometry of the Himalayan collision zone, the thickness of Indian crust subducting beneath the Yarlung-Zangbo Suture has been poorly known. Here we present two new deep seismic reflection profiles, respectively 100-km and 60-km long, across the central part of the Yarlung-Zangbo suture at c. 88°E (Figure 1). Seismic data processing used the CGG, ProMAX, and GeoEast systems. Processing included tomographic static correction, true-amplitude recovery, frequency analysis, filter-parameter tests, surface-consistent-amplitude corrections, surface-consistent deconvolution, coherent noise suppression, random noise attenuation, human-computer interactive velocity analysis, residual statics correction, Kirchhoff pre-stack time migration incorporating the rugged topography, and post-stack polynomial fitting to remove noise. Our two profiles both trace the Main Himalayan Thrust continuously from the mid-crust to deep beneath southern Tibet. Together with prominent Moho reflections at the base of the double-normal-thickness crust, the geometry of the subducting Indian crust is well defined. Both profiles image a limited extent of the Indian crust beneath southern Tibet and indicate that north-dipping Indian crust and south-dipping Lhasa crust converge beneath the Xietongmen region, above the remnant mantle suture. Figure 1. Geological map of the Xietongmen Region, south Tibet. The deep seismic reflection profile is shown as a solid red line, the location of big shots are shown as black stars.

Beyond seismic interferometry: imaging the earth's interior with virtual sources and receivers inside the earth

NASA Astrophysics Data System (ADS)

Wapenaar, C. P. A.; Van der Neut, J.; Thorbecke, J.; Broggini, F.; Slob, E. C.; Snieder, R.

2015-12-01

Imagine one could place seismic sources and receivers at any desired position inside the earth. Since the receivers would record the full wave field (direct waves, up- and downward reflections, multiples, etc.), this would give a wealth of information about the local structures, material properties and processes in the earth's interior. Although in reality one cannot place sources and receivers anywhere inside the earth, it appears to be possible to create virtual sources and receivers at any desired position, which accurately mimics the desired situation. The underlying method involves some major steps beyond standard seismic interferometry. With seismic interferometry, virtual sources can be created at the positions of physical receivers, assuming these receivers are illuminated isotropically. Our proposed method does not need physical receivers at the positions of the virtual sources; moreover, it does not require isotropic illumination. To create virtual sources and receivers anywhere inside the earth, it suffices to record the reflection response with physical sources and receivers at the earth's surface. We do not need detailed information about the medium parameters; it suffices to have an estimate of the direct waves between the virtual-source positions and the acquisition surface. With these prerequisites, our method can create virtual sources and receivers, anywhere inside the earth, which record the full wave field. The up- and downward reflections, multiples, etc. in the virtual responses are extracted directly from the reflection response at the surface. The retrieved virtual responses form an ideal starting point for accurate seismic imaging, characterization and monitoring.

Imaging a Fault Boundary System Using Controlled-Source Data Recorded on a Large-N Seismic Array

NASA Astrophysics Data System (ADS)

Paschall, O. C.; Chen, T.; Snelson, C. M.; Ralston, M. D.; Rowe, C. A.

2016-12-01

The Source Physics Experiment (SPE) is a series of chemical explosions conducted in southern Nevada with an objective of improving nuclear explosion monitoring. Five chemical explosions have occurred thus far in granite, the most recent being SPE-5 on April 26, 2016. The SPE series will improve our understanding of seismic wave propagation (primarily S-waves) due to explosions, and allow better discrimination of background seismicity such as earthquakes and explosions. The Large-N portion of the project consists of 996 receiver stations. Half of the stations were vertical component and the other half were three-component geophones. All receivers were deployed for 30 days and recorded the SPE-5 shot, earthquakes, noise, and an additional controlled-source: a large weight-drop, which is a 13,000 kg modified industrial pile driver. In this study, we undertake reflection processing of waveforms from the weight-drop, as recorded by a line of sensors extracted from the Large-N array. The profile is 1.2 km in length with 25 m station spacing and 100 m shot point spacing. This profile crosses the Boundary Fault that separates granite body and an alluvium basin, a strong acoustic impedance boundary that scatters seismic energy into S-waves and coda. The data were processed with traditional seismic reflection processing methods that include filtering, deconvolution, and stacking. The stack will be used to extract the location of the splays of the Boundary Fault and provide geologic constraints to the modeling and simulation teams within the SPE project.

Origin and Formation of Giant Mounds in Lake Ladoga (Russia) from High-Resolution Seismic Reflection Data

NASA Astrophysics Data System (ADS)

Gromig, R.; Lebas, E.; Krastel, S.; Averes, T.; Wagner, B.; Melles, M.; Fedorov, G.

2017-12-01

In the framework of the German-Russian project `PLOT - Paleolimnological Transect' (for an overview of the project see Gromig et al., this meeting), a pilot seismic survey was carried out in Lake Ladoga (Russia) in late summer 2013. In total, 1500 km of seismic reflection profiles have been acquired using a mini-GI gun and a 32-channel seismic streamer. The high-resolution of the seismic data allows us to document in detail the sedimentary processes that occurred in the lake during the preglacial and postglacial history. The seismic stratigraphic architecture of the lake shows, from top to bottom, acoustically well-stratified Holocene muds overlaying rather transparent postglacial varves. These sediment successions are usually bordered by a hard reflector underneath, which may represent coarse-grained sediments or a till. The nature of the material composing the uppermost units have been tied to coring information from core Co1309, which was retrieved during the same survey. Of particular interest, are the single to composite, giant (kilometer-scale) mounds directly overlying the hard reflector. Internal architecture of the mounds reveals a complex formation history, with mound types showing significant structural deformation of different degrees; and other mound types showing a central deformation area, which strongly contrasts with the titled reflections or undisturbed stratification visible at the edges. The deepest seismic unit underlying the mounds is characterized by well-bedded, tilted reflectors in the southeastern part of the lake, while clear synclines are identified in the northwestern part of the lake. An erosional truncation separates the deepest unit from the overlying ones. In the work presented here, we focus on the understanding of the origin and the formation of the giant mounds with respect to the glacial history of Lake Ladoga.

Geophysical Monitoring of Geodynamic Processes of Central Armenia Earth Crust

NASA Astrophysics Data System (ADS)

Avetyan, R.; Pashayan, R.

2016-12-01

The method of geophysical monitoring of earth crust was introduced. It allows by continuous supervision to track modern geodynamic processes of Armenia. Methodological practices of monitoring come down to allocation of a signal which reflects deformation of rocks. The indicators of deformations are not only deviations of geophysical indicators from certain background values, but also parameters of variations of these indicators. Data on changes of parameters of barometric efficiency and saw tooth oscillations of underground water level before seismic events were received. Low-amplitude periodic fluctuations of water level are the reflection of geodynamic processes taking place in upper levels of earth crust. There were recorded fluctuations of underground water level resulting from luni-solar tides and enabling to control the systems of borehole-bed in changes of voluminous deformations. The slow lowering (raising) of underground water level in the form of trend reflects long-period changes of stress-deformative state of environment. Application of method promotes identification of medium-term precursors on anomalous events of variations of geomagnetic field, change of content of subsoil radon, dynamics of level of underground water, geochemistry and water temperature. Increase of activity of geodynamic processes in Central Armenian tectonic complex is observed to change macro component Na+, Ca2+, Mg2-, CL-, SO42-, HCO3-, H4SiO4, pH and gas - CO2 structure of mineral water. Modern geodynamic movements of earth crust of Armenia are the result of seismic processes and active geodynamics of deep faults of longitudinal and transversal stretching. Key Words: monitoring, hydrogeodynamics, geomagnetic field, seismicity, deformation, earth crust

The Moho structure beneath the Yarlung Zangbo Suture and its implications: Evidence from 2000 kg large dynamite shots

NASA Astrophysics Data System (ADS)

Gao, R.; Li, H.; Li, W.; Lu, Z.; Guo, X.; WANG, Y.

2017-12-01

The YZS (Yarlung Zangbo Suture) is the collisional front between the Indian and Eurasian plates. The depth and geometry of the Moho thus provide first-order information for the restoration of complex geodynamic systems. Over the past three decades, numerous seismic experiments have been conducted across the YZS, including deep seismic reflection profiles, deep seismic soundings and broadband observation studies. However, there is strong disagreement concerning the character of the Moho along the YZS in Tibet. Hirn proposed an offset of more than 15 km along the Moho below the YZS according to wide-angle observations acquired by a Sino-French cooperative experiment. Jiang argued that the Moho exhibits a 20-km offset after analyzing multiple broadband seismic profiles across the YZS. Gao did not find any significant changes in the Moho depth using deep seismic reflection profile data across the western YZS. The above mentioned summary of previous findings shows that similar geophysical observations have yielded contrasting models. Due to the shortage of high-resolution geophysical data, the above controversial problems cannot currently be resolved effectively without improving the accuracy of available geophysical observations and consequently obtaining reliable evidence. The rapid development of the technology of deep seismic reflection profiling has provided an opportunity to resolve the above controversies. two deep seismic reflection profiles across the YZS(88°E) were deployed in 2015(Fig .1 -YZS-B). Four large dynamite shots with 2000 kg charges were employed to improve the signal-to-noise ratio (S/N) along the two transects(Fig .1 and Fig.2). The primary purpose of this experiment is to study images of the Moho both adjacent to and beneath the YZS using four large dynamite shots along two profiles. These four large shots were processed to combine two single-fold profiles. Our two single-fold profiles across the YZS clearly show the existence of a well-imaged Moho. The reflections from the Moho are clear with a narrow band of reflections that are typically <0.3 s between 21-25 s. The depth of the Moho is approximately 63-75 km across the entire profile (assuming an average crustal velocity of 6 km/s). A gap in the Moho is observed approximately 20 km north of the YZS, the amplitude of which is less than 6 km.

Seismic investigation of the Kunlun Fault: Analysis of the INDEPTH IV 2-D active-source seismic dataset

NASA Astrophysics Data System (ADS)

Seelig, William George

The Tibetan Plateau has experienced significant crustal thickening and deformation since the continental subduction and collision of the Asian and Indian plates in the Eocene. Deformation of the northern Tibetan Plateau is largely accommodated by strike-slip faulting. The Kunlun Fault is a 1000-km long strike-slip fault near the northern boundary of the Plateau that has experienced five magnitude 7.0 or greater earthquakes in the past 100 years and represents a major rheological boundary. Active-source, 2-D seismic reflection/refraction data, collected as part of project INDEPTH IV (International Deep Profiling of Tibet and the Himalaya, phase IV) in 2007, was used to examine the structure and the dip of the Kunlun fault. The INDEPTH IV data was acquired to better understand the tectonic evolution of the northeastern Tibetan Plateau, such as the far-field deformation associated with the continent-continent collision and the potential subduction of the Asian continent beneath northern Tibet. Seismic reflection common depth point (CDP) stacks were examined to look for reflectivity patterns that may be associated with faulting. A possible reflection from the buried North Kunlun Thrust (NKT) is identified at 18-21 km underneath the East Kunlun Mountains, with an estimated apparent dip of 15°S and thrusting to the north. Minimally-processed shot gathers were also inspected for reflections off near-vertical structures such as faults and information on first-order velocity structure. Shot offset and nearest receiver number to reflection was catalogued to increase confidence of picks. Reflections off the North Kunlun (NKF) and South Kunlun Faults (SKF) were identified and analyzed for apparent dip and subsurface geometry. Fault reflection analysis found that the North Kunlun Fault had an apparent dip of approximately 68ºS to an estimated depth of 5 km, while the South Kunlun Fault dipped at approximately 78ºN to an estimated 3.5 km depth. Constraints on apparent dip and geometry of the NKF/SKF and NKT provide information valuable for seismic hazard analysis.

Uniquely Acquired Vintage Seismic Reflection Data Reveal the Stratigraphic and Tectonic History of the Montana Disturbed Belt, USA

NASA Astrophysics Data System (ADS)

Speece, M. A.; Link, C. A.; Stickney, M.

2011-12-01

In 1983 and 1984 Techco of Denver, Colorado, acquired approximately 302 linear kilometers of two-dimensional (2D) seismic reflection data in Flathead and Lake Counties, Montana, USA, as part of an initiative to identify potential drilling targets beneath the Swan and Whitefish Mountain Ranges and adjacent basins of northwestern Montana. These seismic lines were collected in the Montana Disturbed Belt (MDB) or Montana thrust belt along the western edge of Glacier National Park in mountainous terrain with complicated subsurface structures including thrust faults and folds. These structures formed during the Laramide Orogeny as sedimentary rocks of the Precambrian Belt Supergroup were thrust eastward. Later, during the Cenozoic, high-angle normal faults produced prominent west-facing mountain scarps of the Mission, Swan and Whitefish mountains. The 1983 data set consisted of two profiles of 24-fold (96-channels) Vibroseis data and four profiles of 24-fold (96-channels) helicopter-assisted dynamite data. The dynamite data were collected using the Poulter Method in which explosives were placed on poles and air shots were recorded. The 1983 dynamite profiles extend from southwest to northeast across the Whitefish Mountain Range to the edge of Glacier National Park and the Vibroseis data were collected along nearby roadways. The 1984 data set consists of four profiles of 30-fold (120-channels) helicopter-assisted dynamite data that were also collected using the Poulter Method. The 1984 profiles cross the Swan Mountain Range between Flathead Lake and Glacier National Park. All of these data sets were recently donated to Montana Tech and subsequently recovered from nine-track tape. Conventionally processed seismic stacked sections from the 1980s of these data show evidence of a basement decollement that separates relatively undeformed basement from overlying structures of the MDB. Unfortunately, these data sets have not been processed using modern seismic processing techniques including linear noise suppression of the air wave and ground roll, refraction statics, and prestack migration. Reprocessing of these data using state-of-the-art seismic reflection processing techniques will provide a detailed picture of the stratigraphy and tectonic framework for this region. Moreover, extended correlations of the Vibroseis records to Moho depths might reveal new insights on crustal thickness and provide a framework for understanding crustal thickening during the Laramide Orogeny as well as later Cenozoic extension.

Multichannel seismic-reflection data collected in 1980 in the eastern Chukchi Sea

USGS Publications Warehouse

Grantz, Arthur; Mann, Dennis M.; May, Steven D.

1986-01-01

The U.S. Geological Survey (USGS) collected approximately 2,652 km of 24-channel seismic-reflection data in early September, 1980, over the continental shelf in the eastern Chukchi Sea (Fig. 1). The profiles were collected on the USGS Research Vessel S.P. Lee. The seismic energy source consisted of a tuned array of five airguns with a total volume of 1213 cubic inches of air compressed to approximately 1900 psi. The recording system consisted of a 24-channel, 2400 meter long streamer with a group interval of 100 m, and a GUS (Global Universal Science) model 4200 digital recording instrument. Shots were fired every 50 meters. Navigational control for the survey was provided by a Magnavox integrated navigation system using transit satellites and doppler-sonar augmented by Loran C (Rho-Rho). A 2-millisecond sampling rate was used in the field; the data were later desampled to 4-milliseconds during the demultiplexing process. 8 seconds data length was recorded. Processing was done at the USGS Pacific Marine Geology Multichannel Processing Center in Menlo Park, California, in the sequence: editing-demultiplexing, velocity analysis, CDP stacking, deconvolution-filtering, and plotting on an electrostatic plotter. Plate 1 is a trackline chart showing shotpoint navigation.

Estimating the location of baleen whale calls using dual streamers to support mitigation procedures in seismic reflection surveys.

PubMed

Abadi, Shima H; Tolstoy, Maya; Wilcock, William S D

2017-01-01

In order to mitigate against possible impacts of seismic surveys on baleen whales it is important to know as much as possible about the presence of whales within the vicinity of seismic operations. This study expands on previous work that analyzes single seismic streamer data to locate nearby calling baleen whales with a grid search method that utilizes the propagation angles and relative arrival times of received signals along the streamer. Three dimensional seismic reflection surveys use multiple towed hydrophone arrays for imaging the structure beneath the seafloor, providing an opportunity to significantly improve the uncertainty associated with streamer-generated call locations. All seismic surveys utilizing airguns conduct visual marine mammal monitoring surveys concurrent with the experiment, with powering-down of seismic source if a marine mammal is observed within the exposure zone. This study utilizes data from power-down periods of a seismic experiment conducted with two 8-km long seismic hydrophone arrays by the R/V Marcus G. Langseth near Alaska in summer 2011. Simulated and experiment data demonstrate that a single streamer can be utilized to resolve left-right ambiguity because the streamer is rarely perfectly straight in a field setting, but dual streamers provides significantly improved locations. Both methods represent a dramatic improvement over the existing Passive Acoustic Monitoring (PAM) system for detecting low frequency baleen whale calls, with ~60 calls detected utilizing the seismic streamers, zero of which were detected using the current R/V Langseth PAM system. Furthermore, this method has the potential to be utilized not only for improving mitigation processes, but also for studying baleen whale behavior within the vicinity of seismic operations.

Estimating the location of baleen whale calls using dual streamers to support mitigation procedures in seismic reflection surveys

PubMed Central

Abadi, Shima H.; Tolstoy, Maya; Wilcock, William S. D.

2017-01-01

In order to mitigate against possible impacts of seismic surveys on baleen whales it is important to know as much as possible about the presence of whales within the vicinity of seismic operations. This study expands on previous work that analyzes single seismic streamer data to locate nearby calling baleen whales with a grid search method that utilizes the propagation angles and relative arrival times of received signals along the streamer. Three dimensional seismic reflection surveys use multiple towed hydrophone arrays for imaging the structure beneath the seafloor, providing an opportunity to significantly improve the uncertainty associated with streamer-generated call locations. All seismic surveys utilizing airguns conduct visual marine mammal monitoring surveys concurrent with the experiment, with powering-down of seismic source if a marine mammal is observed within the exposure zone. This study utilizes data from power-down periods of a seismic experiment conducted with two 8-km long seismic hydrophone arrays by the R/V Marcus G. Langseth near Alaska in summer 2011. Simulated and experiment data demonstrate that a single streamer can be utilized to resolve left-right ambiguity because the streamer is rarely perfectly straight in a field setting, but dual streamers provides significantly improved locations. Both methods represent a dramatic improvement over the existing Passive Acoustic Monitoring (PAM) system for detecting low frequency baleen whale calls, with ~60 calls detected utilizing the seismic streamers, zero of which were detected using the current R/V Langseth PAM system. Furthermore, this method has the potential to be utilized not only for improving mitigation processes, but also for studying baleen whale behavior within the vicinity of seismic operations. PMID:28199400

Maps showing the change in modern sediment thickness on the Inner Continental Shelf offshore of Fire Island, New York, between 1996-97 and 2011

USGS Publications Warehouse

Schwab, William C.; Baldwin, Wayne E.; Denny, Jane F.

2015-01-01

The U.S. Geological Survey mapped approximately 336 square kilometers of the lower shoreface and inner continental shelf offshore of Fire Island, New York, in 1996 and 1997, using high-resolution sidescan-sonar and seismic-reflection systems, and again in 2011, using interferometric sonar and high-resolution chirp seismic-reflection systems. This report presents a comparison of sediment thickness and distribution as mapped during these two investigations. These spatial data support research on the Quaternary evolution of the Fire Island coastal system and provide baseline information for research on coastal processes along southern Long Island.

30 CFR 280.51 - What types of geophysical data and information must I submit to MMS?

Code of Federal Regulations, 2010 CFR

2010-07-01

..., shallow and deep subbottom profiles, bathymetry, sidescan sonar, gravity and magnetic surveys, and special... and of a quality suitable for processing; (c) Processed geophysical information derived from seismic... interpretive evaluation, reflecting state-of-the-art processing techniques; and (d) Other geophysical data...

Continuous monitoring of the lunar or Martian subsurface using on-board pattern recognition and neural processing of Rover geophysical data

NASA Technical Reports Server (NTRS)

Mcgill, J. W.; Glass, C. E.; Sternberg, B. K.

1990-01-01

The ultimate goal is to create an extraterrestrial unmanned system for subsurface mapping and exploration. Neural networks are to be used to recognize anomalies in the profiles that correspond to potentially exploitable subsurface features. The ground penetrating radar (GPR) techniques are likewise identical. Hence, the preliminary research focus on GPR systems will be directly applicable to seismic systems once such systems can be designed for continuous operation. The original GPR profile may be very complex due to electrical behavior of the background, targets, and antennas, much as the seismic record is made complex by multiple reflections, ghosting, and ringing. Because the format of the GPR data is similar to the format of seismic data, seismic processing software may be applied to GPR data to help enhance the data. A neural network may then be trained to more accurately identify anomalies from the processed record than from the original record.

AVO analysis of BSR to assess free gas within fine-grained sediments in the Shenhu area, South China Sea

NASA Astrophysics Data System (ADS)

Qian, Jin; Wang, Xiu-Juan; Wu, Shi-Guo; Wang, Zhen-zhen; Yang, Sheng-Xiong

2014-06-01

Gas hydrates have been identified from two-dimensional (2D) seismic data and logging data above bottom simulating reflector (BSR) during China's first gas hydrate drilling expedition in 2007. The multichannel reflection seismic data were processed to be preserved amplitudes for quantitatively analyzing amplitude variation with offset (AVO) at BSRs. Low P-wave velocity anomaly below BSR, coinciding with high amplitude reflections in 2D seismic data, indicates the presence of free gas. The absolute values of reflection coefficient versus incidence angles for BSR range from 0 to 0.12 at different CMPs near Site SH2. According to logging data and gas hydrate saturations estimated from resistivity of Site SH2, P-wave velocities calculated from effective media theory (EMT) fit the measured sonic velocities well and we choose EMT to calculate elastic velocities for AVO. The rock-physics modeling and AVO analysis were combined to quantitatively assess free gas saturations and distribution by the reflection coefficients variation of the BSRs in Shenhu area, South China Sea. AVO estimation indicates that free gas saturations immediately beneath BSRs may be about 0.2 % (uniform distribution) and up to about 10 % (patchy distribution) at Site SH2.

Seismic site survey investigations in urban environments: The case of the underground metro project in Copenhagen, Denmark.

NASA Astrophysics Data System (ADS)

Martínez, K.; Mendoza, J. A.; Colberg-Larsen, J.; Ploug, C.

2009-05-01

Near surface geophysics applications are gaining more widespread use in geotechnical and engineering projects. The development of data acquisition, processing tools and interpretation methods have optimized survey time, reduced logistics costs and increase results reliability of seismic surveys during the last decades. However, the use of wide-scale geophysical methods under urban environments continues to face great challenges due to multiple noise sources and obstacles inherent to cities. A seismic pre-investigation was conducted to investigate the feasibility of using seismic methods to obtain information about the subsurface layer locations and media properties in Copenhagen. Such information is needed for hydrological, geotechnical and groundwater modeling related to the Cityringen underground metro project. The pre-investigation objectives were to validate methods in an urban environment and optimize field survey procedures, processing and interpretation methods in urban settings in the event of further seismic investigations. The geological setting at the survey site is characterized by several interlaced layers of clay, till and sand. These layers are found unevenly distributed throughout the city and present varying thickness, overlaying several different unit types of limestone at shallow depths. Specific results objectives were to map the bedrock surface, ascertain a structural geological framework and investigate bedrock media properties relevant to the construction design. The seismic test consisted of a combined seismic reflection and refraction analyses of a profile line conducted along an approximately 1400 m section in the northern part of Copenhagen, along the projected metro city line. The data acquisition was carried out using a 192 channels array, receiver groups with 5 m spacing and a Vibroseis as a source at 10 m spacing. Complementarily, six vertical seismic profiles (VSP) were performed at boreholes located along the line. The reflection data underwent standard interpretation and the refraction included wavepath Eikonal traveltime tomography. The reflection results indicate the presence of horizontal reflectors with discontinuities likely related to deep lying structural features in deeper lying chalk layers. The refraction interpretation allowed the identification of the upper limestone surface, relevant to map for tunneling design. The VSP provided additional information regarding limestone quality and provided correlation data for improved refraction interpretation. In general, the pre-investigation results demonstrated that it is possible to image the limestone surface using the seismic method. The satisfactory results lead to the implementation of a 15 km survey planned during the spring 2009. The survey will combine reflection, refraction, walkaway-VSP and electrical resistivity tomography (ERT). The authors wish to acknowledge Metroselskabet I/S for permission in presenting the preliminary results and the Cityringen Joint Venture partners Arup and Systra.

Walker Ranch 3D seismic images

DOE Data Explorer

Robert J. Mellors

2016-03-01

Amplitude images (both vertical and depth slices) extracted from 3D seismic reflection survey over area of Walker Ranch area (adjacent to Raft River). Crossline spacing of 660 feet and inline of 165 feet using a Vibroseis source. Processing included depth migration. Micro-earthquake hypocenters on images. Stratigraphic information and nearby well tracks added to images. Images are embedded in a Microsoft Word document with additional information. Exact location and depth restricted for proprietary reasons. Data collection and processing funded by Agua Caliente. Original data remains property of Agua Caliente.

The T-Reflection and the Deep Crustal Structure of the Vøring Margin, Offshore mid-Norway

NASA Astrophysics Data System (ADS)

Abdelmalak, M. M.; Faleide, J. I.; Planke, S.; Gernigon, L.; Zastrozhnov, D.; Shephard, G. E.; Myklebust, R.

2017-11-01

Seismic reflection data along volcanic passive margins frequently provide imaging of strong and laterally continuous reflections in the middle and lower crust. We have completed a detailed 2-D seismic interpretation of the deep crustal structure of the Vøring Margin, offshore mid-Norway, where high-quality seismic data allow the identification of high-amplitude reflections, locally referred to as the T-Reflection. Using a dense seismic grid, we have mapped the geometry of the T-Reflection in order to compare it with filtered Bouguer gravity anomalies and seismic refraction data. The T-Reflection is identified between 7 and 10 s. Sometimes it consists of one single smooth reflection. However, it is frequently associated with a set of rough multiple reflections displaying discontinuous segments with varying geometries, amplitudes, and contact relationships. The T-Reflection seems to be connected to deep sill networks and is locally identified at the continuation of basement high structures or terminates over fractures and faults. The T-Reflection presents a low magnetic signal. The spatial correlation between the filtered positive Bouguer gravity anomalies and the deep dome-shaped reflections indicates that the latter represent a high-impedance boundary contrast associated with a high-density and high-velocity body. In 50% of the outer Vøring Margin, the depth of the mapped T-Reflection is found to correspond to the depth of the top of the Lower Crustal Body (LCB), which is characterized by high P wave velocities (>7 km/s). We present a tectonic scenario, where a large part of the deep crustal structure is composed of preserved upper continental crustal blocks and middle to lower crustal lenses of inherited high-grade metamorphic rocks. Deep intrusions into the faulted crustal blocks are responsible for the rough character of the T-Reflection, whereas intrusions into the ductile lower crust and detachment faults are likely responsible for its smoother character. Deep magma intrusions can be responsible for regional metamorphic processes leading to an increasing velocity of the lower crust to more than 7 km/s. The result is a heterogeneous LCB that likely represents a complex mixture of pre- to syn-breakup mafic and ultramafic rocks (cumulates and sills) and old metamorphic rocks such as granulites and eclogites. An increasing degree of melting toward the breakup axis is responsible for an increasing proportion of cumulates and sill intrusions in the lower crust.

76 FR 26255 - Takes of Marine Mammals Incidental to Specified Activities; Marine Geophysical Survey in the...

Federal Register 2010, 2011, 2012, 2013, 2014

2011-05-06

..., the R/V Marcus G. Langseth (Langseth) and a seismic airgun array to collect seismic reflection and... possible, depending on logistics and weather. The proposed seismic survey will collect seismic reflection... Shillington, Spahr Webb, and Mladen Nedimovic, all of L-DEO. The vessel will be self-contained, and the crew...

Synthetic Seismograms Derived from Oceanographic Data in the Campeche Canyon, Deepwater Gulf of Mexico

NASA Astrophysics Data System (ADS)

Gonzalez-Orduno, A.; Fucugauchi, J. U.; Monreal, M.; Perez-Cruz, G.; Salas de León, D. A.

2013-05-01

The seismic reflection method has been successfully applied worldwide to investigate subsurface conditions to support important business decisions in the oil industry. When applied in the marine environment, useful reflection information is limited to events on and below the sea floor; Information from the water column, if any, is disregarded. Seismic oceanography is emerging as a new technique that utilize the reflection information within the water column to infer thermal-density contrasts associated with oceanographic processes, such as cyclonic-anticyclonic eddies, ascending-descending water flows, and water flows related to rapid topographic changes on the sea floor. A seismic investigation to infer such oceanographic changes in one sector of the Campeche Canyon is in progress as a research matter at the Instituto de Ciencias del Mar y Limnologia from the University of Mexico (UNAM). First steps of the investigation consisted of creating synthetic seismograms based on oceanographic information (temperature and density) derived from direct observation on a series of close spaced depth points along vertical profiles. Details of the selected algorithms used for the transformation of the oceanographic data to acoustic impedances data sets and further construction of synthetic seismograms on each site and their representation as synthetic seismic sections, are presented in this work, as well as the road ahead in the investigation.

Crustal structure of Shatsky Rise from joint refraction and reflection seismic tomography

NASA Astrophysics Data System (ADS)

Korenaga, J.; Sager, W. W.

2011-12-01

Shatsky Rise in the western Pacific is one of a few gigantic oceanic plateaus in the world, with a surface area of ˜ 4.8 ± 105~km2 (about the same size as California). In contrast to other large oceanic plateaus formed during the Cretaceous Quite Period, Shatsky Rise formed during the frequent reversals of magnetic polarity, allowing its tectonic environment to be resolved in detail. It was formed at a rapidly spreading ridge-ridge-ridge triple junction, so the effect of lithospheric lid on magma migration is expected to be minimal, thereby facilitating the petrological interpretation of its seismic structure in terms of parental mantle processes. In the summer of 2010, a seismic refraction survey combined with multichannel seismic profiling was conducted across Shatsky Rise. Twenty eight ocean-bottom seismometers were deployed along two crossing perpendicular lines, and all of the instruments were recovered successfully, yielding a large volume of high-quality wide-angle refraction and reflection data, with the source-receiver distance often exceeding 200~km. In this contribution, we present the P-wave velocity structure of the Shatsky Rise crust, which is constructed by joint refraction and reflection travel time tomography, and also discuss its implications for the origin of Shatsky Rise.

Seismic imaging of post-glacial sediments - test study before Spitsbergen expedition

NASA Astrophysics Data System (ADS)

Szalas, Joanna; Grzyb, Jaroslaw; Majdanski, Mariusz

2017-04-01

This work presents results of the analysis of reflection seismic data acquired from testing area in central Poland. For this experiment we used total number of 147 vertical component seismic stations (DATA-CUBE and Reftek "Texan") with accelerated weight drop (PEG-40). The profile was 350 metres long. It is a part of pilot study for future research project on Spitsbergen. The purpose of the study is to recognise the characteristics of seismic response of post-glacial sediments in order to design the most adequate survey acquisition parameters and processing sequence for data from Spitsbergen. Multiple tests and comparisons have been performed to obtain the best possible quality of seismic image. In this research we examine the influence of receiver interval size, front mute application and surface wave attenuation attempts. Although seismic imaging is the main technique we are planning to support this analysis with additional data from traveltime tomography, MASW and other a priori information.

Coherent Waves in Seismic Researches

NASA Astrophysics Data System (ADS)

Emanov, A.; Seleznev, V. S.

2013-05-01

Development of digital processing algorithms of seismic wave fields for the purpose of useful event picking to study environment and other objects is the basis for the establishment of new seismic techniques. In the submitted paper a fundamental property of seismic wave field coherence is used. The authors extended conception of coherence types of observed wave fields and devised a technique of coherent component selection from observed wave field. Time coherence and space coherence are widely known. In this paper conception "parameter coherence" has been added. The parameter by which wave field is coherent can be the most manifold. The reason is that the wave field is a multivariate process described by a set of parameters. Coherence in the first place means independence of linear connection in wave field of parameter. In seismic wave fields, recorded in confined space, in building-blocks and stratified mediums time coherent standing waves are formed. In prospecting seismology at observation systems with multiple overlapping head waves are coherent by parallel correlation course or, in other words, by one measurement on generalized plane of observation system. For detail prospecting seismology at observation systems with multiple overlapping on basis of coherence property by one measurement of area algorithms have been developed, permitting seismic records to be converted to head wave time sections which have neither reflected nor other types of waves. Conversion in time section is executed on any specified observation base. Energy storage of head waves relative to noise on basis of multiplicity of observation system is realized within area of head wave recording. Conversion on base below the area of wave tracking is performed with lack of signal/noise ratio relative to maximum of this ratio, fit to observation system. Construction of head wave time section and dynamic plots a basis of automatic processing have been developed, similar to CDP procedure in method of reflected waves. With use of developed algorithms of head wave conversion in time sections a work of studying of refracting boundaries in Siberia have been executed. Except for the research by method of refracting waves, the conversion of head waves in time sections, applied to seismograms of reflected wave method, allows to obtain information about refracting horizons in upper part of section in addition to reflecting horizons data. Recovery method of wave field coherent components is the basis of the engineering seismology on the level of accuracy and detail. In seismic microzoning resonance frequency of the upper part of section are determined on the basis of this method. Maps of oscillation amplification and result accuracy are constructed for each of the frequencies. The same method makes it possible to study standing wave field in buildings and constructions with high accuracy and detail, realizing diagnostics of their physical state on set of natural frequencies and form of self-oscillations, examined with high detail. The method of standing waves permits to estimate a seismic stability of structure on new accuracy level.

Seismic Characterization and Continuity Analysis of Gas Hydrate Horizons Near the Mallik Research Wells, Mackenzie Delta, Canada

NASA Astrophysics Data System (ADS)

Bellefleur, G.; Riedel, M.; Brent, T.

2005-12-01

Gas hydrate deposits in arctic environment generally lack the BSR signature diagnostic of their presence in marine seismic data. The absence of the BSR signature complicates the estimation of the resources within or below the permafrost and the determination of their potential impact on future energy supplies, geohazard and climate change. We present results from a detailed seismic characterization of three gas hydrate horizons (A, B and C) intersected below the permafrost in five wells of the Mallik gas hydrate field located in the Mackenzie delta (Northwest Territories, Canada). The detailed seismic characterization included attribute analyses, synthetic modeling and acoustic impedance inversion and allowed estimation of the lateral continuity of the three horizons in the vicinity of the wells. Vertical Seismic Profiling (VSP) data, 3D and 2D industry seismic data and the 5L/2L-38 geophysical logs (density, P-wave sonic velocity) were used for this study. Synthetic modeling using the sonic and density logs reveals that the base of the lower gas hydrate horizons B and C can be identified on the industry 3D and 2D seismic sections as prominent isolated reflections. The uppermost gas hydrate occurrence (horizon A) and potentially other additional smaller-scale layers are identified only on the higher-resolution VSP data. The 3D industry seismic data set processed to preserve the relative true-amplitudes was used for attribute calculations and acoustic impedance inversion. The attribute maps defined areas of continuous reflectivity for horizons B and C and structural features disrupting them. Results from impedance inversion indicate that such continuous reflectivity around the wells is most likely attributable to gas hydrates. The middle gas hydrate occurrence (horizon B) covers an area of approximately 25 000m2. Horizon C, which marks the base of gas hydrate occurrence zone, extends over a larger area of approximately 120 000m2.

Regional seismic lines reprocessed using post-stack processing techniques; National Petroleum Reserve, Alaska

USGS Publications Warehouse

Miller, John J.; Agena, W.F.; Lee, M.W.; Zihlman, F.N.; Grow, J.A.; Taylor, D.J.; Killgore, Michele; Oliver, H.L.

2000-01-01

This CD-ROM contains stacked, migrated, 2-Dimensional seismic reflection data and associated support information for 22 regional seismic lines (3,470 line-miles) recorded in the National Petroleum Reserve ? Alaska (NPRA) from 1974 through 1981. Together, these lines constitute about one-quarter of the seismic data collected as part of the Federal Government?s program to evaluate the petroleum potential of the Reserve. The regional lines, which form a grid covering the entire NPRA, were created by combining various individual lines recorded in different years using different recording parameters. These data were reprocessed by the USGS using modern, post-stack processing techniques, to create a data set suitable for interpretation on interactive seismic interpretation computer workstations. Reprocessing was done in support of ongoing petroleum resource studies by the USGS Energy Program. The CD-ROM contains the following files: 1) 22 files containing the digital seismic data in standard, SEG-Y format; 2) 1 file containing navigation data for the 22 lines in standard SEG-P1 format; 3) 22 small scale graphic images of each seismic line in Adobe Acrobat? PDF format; 4) a graphic image of the location map, generated from the navigation file, with hyperlinks to the graphic images of the seismic lines; 5) an ASCII text file with cross-reference information for relating the sequential trace numbers on each regional line to the line number and shotpoint number of the original component lines; and 6) an explanation of the processing used to create the final seismic sections (this document). The SEG-Y format seismic files and SEG-P1 format navigation file contain all the information necessary for loading the data onto a seismic interpretation workstation.

Visualization of volumetric seismic data

NASA Astrophysics Data System (ADS)

Spickermann, Dela; Böttinger, Michael; Ashfaq Ahmed, Khawar; Gajewski, Dirk

2015-04-01

Mostly driven by demands of high quality subsurface imaging, highly specialized tools and methods have been developed to support the processing, visualization and interpretation of seismic data. 3D seismic data acquisition and 4D time-lapse seismic monitoring are well-established techniques in academia and industry, producing large amounts of data to be processed, visualized and interpreted. In this context, interactive 3D visualization methods proved to be valuable for the analysis of 3D seismic data cubes - especially for sedimentary environments with continuous horizons. In crystalline and hard rock environments, where hydraulic stimulation techniques may be applied to produce geothermal energy, interpretation of the seismic data is a more challenging problem. Instead of continuous reflection horizons, the imaging targets are often steep dipping faults, causing a lot of diffractions. Without further preprocessing these geological structures are often hidden behind the noise in the data. In this PICO presentation we will present a workflow consisting of data processing steps, which enhance the signal-to-noise ratio, followed by a visualization step based on the use the commercially available general purpose 3D visualization system Avizo. Specifically, we have used Avizo Earth, an extension to Avizo, which supports the import of seismic data in SEG-Y format and offers easy access to state-of-the-art 3D visualization methods at interactive frame rates, even for large seismic data cubes. In seismic interpretation using visualization, interactivity is a key requirement for understanding complex 3D structures. In order to enable an easy communication of the insights gained during the interactive visualization process, animations of the visualized data were created which support the spatial understanding of the data.

OpenFIRE - A Web GIS Service for Distributing the Finnish Reflection Experiment Datasets

NASA Astrophysics Data System (ADS)

Väkevä, Sakari; Aalto, Aleksi; Heinonen, Aku; Heikkinen, Pekka; Korja, Annakaisa

2017-04-01

The Finnish Reflection Experiment (FIRE) is a land-based deep seismic reflection survey conducted between 2001 and 2003 by a research consortium of the Universities of Helsinki and Oulu, the Geological Survey of Finland, and a Russian state-owned enterprise SpetsGeofysika. The dataset consists of 2100 kilometers of high-resolution profiles across the Archaean and Proterozoic nuclei of the Fennoscandian Shield. Although FIRE data have been available on request since 2009, the data have remained underused outside the original research consortium. The original FIRE data have been quality-controlled. The shot gathers have been cross-checked and comprehensive errata has been created. The brute stacks provided by the Russian seismic contractor have been reprocessed into seismic sections and replotted. A complete documentation of the intermediate processing steps is provided together with guidelines for setting up a computing environment and plotting the data. An open access web service "OpenFIRE" for the visualization and the downloading of FIRE data has been created. The service includes a mobile-responsive map application capable of enriching seismic sections with data from other sources such as open data from the National Land Survey and the Geological Survey of Finland. The AVAA team of the Finnish Open Science and Research Initiative has provided a tailored Liferay portal with necessary web components such as an API (Application Programming Interface) for download requests. INSPIRE (Infrastructure for Spatial Information in Europe) -compliant discovery metadata have been produced and geospatial data will be exposed as Open Geospatial Consortium standard services. The technical guidelines of the European Plate Observing System have been followed and the service could be considered as a reference application for sharing reflection seismic data. The OpenFIRE web service is available at www.seismo.helsinki.fi/openfire

Imaging the Danish Chalk Group with high resolution, 3-component seismics

NASA Astrophysics Data System (ADS)

Kammann, J.; Rasmussen, S. L.; Nielsen, L.; Malehmir, A.; Stemmerik, L.

2016-12-01

The Chalk Group in the Danish Basin forms important reservoirs to hydrocarbons as well as water resources, and it has been subject to several seismic studies to determine e.g. structural elements, deposition and burial history. This study focuses on the high quality seismic response of a survey acquired with an accelerated 45 kg weight drop and 3-component MEMS-based sensors and additional wireless vertical-type sensors. The 500 m long profile was acquired during one day close to a chalk quarry and chalk cliffs of the Stevns peninsula in eastern Denmark where the well-known K-T (Cretaceous-Tertiary) boundary and different chalk lithologies are well-exposed. With this simple and fast procedure we were able to achieve deep P-wave penetration to the base of the Chalk Group at about 900 m depth. Additionally, the CMP-processed seismic image of the vertical component stands out by its high resolution. Sedimentary features are imaged in the near-surface Danian, as well as in the deeper Maastrichtian and Upper Campanian parts of the Chalk Group. Integration with borehole data suggests that changes in composition, in particular clay content, correlate with changes in reflectivity of the seismic data set. While the pure chalk in the Maastrichtian deposits shows rather low reflectivity, succession enriched in clay appear to be more reflective. The integration of the mentioned methods gives the opportunity to connect changes in facies to the elastic response of the Chalk Group in its natural environmental conditions.

Seismic experiment ross ice shelf 1990/91: Characteristics of the seismic reflection data

USGS Publications Warehouse

1993-01-01

The Transantarctic Mountains, with a length of 3000-3500 km and elevations of up to 4500 m, are one of the major Cenozoic mountain ranges in the world and are by far the most striking example of rift-shoulder mountains. Over the 1990-1991 austral summer Seismic Experiment Ross Ice Shelf (SERIS) was carried out across the Transantarctic Mountain front, between latitudes 82 degrees to 83 degrees S, in order to investigate the transition zone between the rifted area of the Ross Embayment and the uplifted Transantarctic Mountains. This experiment involved a 140 km long seismic reflection profile together with a 96 km long coincident wide-angle reflection/refraction profile. Gravity and relative elevation (using barometric pressure) were also measured along the profile. The primary purpose was to examine the boundary between the rift system and the uplifted rift margin (represented by the Transantarctic Mountains) using modern multi-channel crustal reflection/refraction techniques. The results provide insight into crustal structure across the plate boundary. SERIS also represented one of the first large-scale and modern multi-channel seismic experiments in the remote interior of Antarctica. As such, the project was designed to test different seismic acquisition techniques which will be involved in future seismic exploration of the continent. This report describes the results from the analysis of the acquisition tests as well as detailing some of the characteristics of the reflection seismic data. (auths.)

Shear-wave reflection imaging using a MEMS-based 3C landstreamer and a vertical impact source - an esker study in SW Finland

NASA Astrophysics Data System (ADS)

Brodic, Bojan; Malehmir, Alireza; Maries, Georgiana; Ahokangas, Elina; Mäkinen, Joni; Pasanen, Antti

2017-04-01

Higher resolution of S-wave seismic data compared to the P-wave ones are attractive for the researches working with the seismic methods. This is particularly true for near-surface applications due to significantly lower shear-wave velocities of unconsolidated sediments. Shear-wave imaging, however, poses certain restrictions on both source and receiver selections and also processing strategies. With three component (3C) seismic receivers becoming more affordable and used, shear-wave imaging from vertical sources is attracting more attention for near-surface applications. Theoretically, a vertical impact source will always excite both P- and S-waves although the excited S-waves are radially polarized (SV). There is an exchange of seismic energy between the vertical and radial component of the seismic wavefield. Additionally, it is theoretically accepted that there is no energy conversion or exchange from vertical into the transverse (or SH) component of the seismic wavefield, and the SH-waves can only be generated using SH sources. With the objectives of imaging esker structure (glacial sediments), water table and depth to bedrock, we conducted a seismic survey in Virttaankangas, in southwestern Finland. A bobcat-mounted vertical drop hammer (500 kg) was used as the seismic source. To obtain better source coupling, a 75×75×1.5 cm steel plate was mounted at the bottom of the hammer casing and all the hits made on this plate after placing it firmly on the ground at every shot point. For the data recording, we used a state-of-the-art comprising of 100 units, 240 m-long, 3C MEMS (micro electro-mechanical system) based seismic landstreamer developed at Uppsala University. Although the focus of the study was on the vertical component data, careful inspection of the transverse (SH) component of the raw data revealed clear shear wave reflections (normal moveout velocities ranging from 280-350 m/s at 50 m depth) on several shot gathers. This indicated potential for their analysis, hence shear-wave reflection imaging was carried out. Results show an excellent correspondence between the drilled depth to bedrock and the one independently obtained using P-wave first arrivals traveltime tomography with a reflection imaged on the stacked section of the SH component data. Aside from this reflection that follows the undulating bedrock topography, additional reflections are also observed on the stacked section that might be related to the sedimentary structures at the site. The section shows much finer resolution compared to the P-wave stacked section processed independently and reported earlier this year. This study illustrates the importance of 3C data recording and shows the potential of the landstreamer in imaging shallow subsurface using both P- and SH-waves generated from a vertical impact source. Whether the strong SH-wave energy observed is generated immediately at the source-ground contact, possible sliding of the base plate on which the impacts were made, an effect of near-surface heterogeneities or other factors remains to be carefully investigated. Acknowledgments: A contribution from Trust 2.2 project (http://trust-geoinfra.se) sponsored by Formas, BeFo, SBUF, SGU, Skanska, Tyréns, FQM, and NGI. We thank Turku Water Company, GTK and University of Turku, Department of Geography and Geology for supporting the data acquisition.

Shallow Investigations of the Deep Seafloor: Quantitative Morphology in the Levant Basin, Eastern Mediterranean

NASA Astrophysics Data System (ADS)

Kanari, M.; Ketter, T.; Tibor, G.; Schattner, U.

2017-12-01

We aim to characterize the seafloor morphology and its shallow sub-surface structures and deformations in the deep part of the Levant basin (eastern Mediterranean) using recently acquired high-resolution shallow seismic reflection data and multibeam bathymetry, which allow quantitative analysis of morphology and structure. The Levant basin at the eastern Mediterranean is considered a passive continental margin, where most of the recent geological processes were related in literature to salt tectonics rooted at the Messinian deposits from 6Ma. We analyzed two sets of recently acquired high-resolution data from multibeam bathymetry and 3.5 kHz Chirp sub-bottom seismic reflection in the deep basin of the continental shelf offshore Israel (water depths up to 2100 m). Semi-automatic mapping of seafloor features and seismic data interpretation resulted in quantitative morphological analysis of the seafloor and its underlying sediment with penetration depth up to 60 m. The quantitative analysis and its interpretation are still in progress. Preliminary results reveal distinct morphologies of four major elements: channels, faults, folds and sediment waves, validated by seismic data. From the spatial distribution and orientation analyses of these phenomena, we identify two primary process types which dominate the formation of the seafloor in the Levant basin: structural and sedimentary. Characterization of the geological and geomorphological processes forming the seafloor helps to better understand the transport mechanisms and the relations between sediment transport and deposition in deep water and the shallower parts of the shelf and slope.

Bedrock mapping of buried valley networks using seismic reflection and airborne electromagnetic data

NASA Astrophysics Data System (ADS)

Oldenborger, G. A.; Logan, C. E.; Hinton, M. J.; Pugin, A. J.-M.; Sapia, V.; Sharpe, D. R.; Russell, H. A. J.

2016-05-01

In glaciated terrain, buried valleys often host aquifers that are significant groundwater resources. However, given the range of scales, spatial complexity and depth of burial, buried valleys often remain undetected or insufficiently mapped. Accurate and thorough mapping of bedrock topography is a crucial step in detecting and delineating buried valleys and understanding formative valley processes. We develop a bedrock mapping procedure supported by the combination of seismic reflection data and helicopter time-domain electromagnetic data with water well records for the Spiritwood buried valley aquifer system in Manitoba, Canada. The limited spatial density of water well bedrock observations precludes complete depiction of the buried valley bedrock topography and renders the water well records alone inadequate for accurate hydrogeological model building. Instead, we leverage the complementary strengths of seismic reflection and airborne electromagnetic data for accurate local detection of the sediment-bedrock interface and for spatially extensive coverage, respectively. Seismic reflection data are used to define buried valley morphology in cross-section beneath survey lines distributed over a regional area. A 3D model of electrical conductivity is derived from inversion of the airborne electromagnetic data and used to extrapolate buried valley morphology over the entire survey area. A spatially variable assignment of the electrical conductivity at the bedrock surface is applied to different features of the buried valley morphology identified in the seismic cross-sections. Electrical conductivity is then used to guide construction of buried valley shapes between seismic sections. The 3D locus of points defining each morphological valley feature is constructed using a path optimization routine that utilizes deviation from the assigned electrical conductivities as the cost function. Our resulting map represents a bedrock surface of unprecedented detail with more complexity than has been suggested by previous investigations. Our procedure is largely data-driven with an adaptable degree of expert user input that provides a clear protocol for incorporating different types of geophysical data into the bedrock mapping procedure.

Ground roll attenuation by synchrosqueezed curvelet transform

NASA Astrophysics Data System (ADS)

Liu, Zhao; Chen, Yangkang; Ma, Jianwei

2018-04-01

Ground roll is a type of coherent noise in land seismic data that has low frequency, low velocity and high amplitude. It damages reflection events that contain important information about subsurface structures, hence the removal of ground roll is a crucial step in seismic data processing. A suitable transform is needed for removal of ground roll. Curvelet transform is an effective sparse transform that optimally represents seismic events. In addition, the curvelets can provide a multiscale and multidirectional decomposition of the input data in time-frequency and angular domain, which can help distinguish between ground roll and useful signals. In this paper, we apply synchrosqueezed curvelet transform (SSCT) for ground roll attenuation. The synchrosqueezing technique in SSCT is used to precisely reallocate the energy of local wave vectors in order to separate ground roll from the original data with higher resolution and higher fidelity. Examples of synthetic and field seismic data reveal that SSCT performs well in the suppression of aliased and non-aliased ground roll while preserving reflection waves, in comparison with high-pass filtering, wavelet and curvelet methods.

Seismic reflection images of the accretionary wedge of Costa Rica

DOE Office of Scientific and Technical Information (OSTI.GOV)

Shipley, T.H.; Stoffa, P.L.; McIntosh, K.

The large-scale structure of modern accretionary wedges is known almost entirely from seismic reflection investigations using single or grids of two-dimensional profiles. The authors will report on the first three-dimensional seismic reflection data volume collected of a wedge. This data set covers a 9-km-wide {times} 22-km-long {times} 6-km-thick volume of the accretionary wedge just arcward of the Middle America Trench off Costa Rica. The three-dimensional processing has improved the imaging ability of the multichannel data, and the data volume allows mapping of structures from a few hundred meters to kilometers in size. These data illustrate the relationships between the basement,more » the wedge shape, and overlying slope sedimentary deposits. Reflections from within the wedge define the gross structural features and tectonic processes active along this particular convergent margin. So far, the analysis shows that the subdued basement relief (horst and graben structures seldom have relief of more than a few hundred meters off Costa Rica) does affect the larger scale through going structural features within the wedge. The distribution of mud volcanoes and amplitude anomalies associated with the large-scale wedge structures suggests that efficient fluid migration paths may extend from the top of the downgoing slab at the shelf edge out into the lower and middle slope region at a distance of 50-100 km. Offscraping of the uppermost (about 45 m) sediment occurs within 4 km of the trench, creating a small pile of sediments near the trench lower slope. Underplating of parts of the 400-m-thick subducted sedimentary section begins at a very shallow structural level, 4-10 km arcward of the trench. Volumetrically, the most important accretionary process is underplating.« less

Nonlinear Programming shallow tomography improves deep structure imaging

NASA Astrophysics Data System (ADS)

Li, J.; Morozov, I.

2004-05-01

In areas with strong variations in topography or near-surface lithology, conventional seismic data processing methods do not produce clear images, neither shallow nor deep. The conventional reflection data processing methods do not resolve stacking velocities at very shallow depth; however, refraction tomography can be used to obtain the near-surface velocities. We use Nonlinear Programming (NP) via known velocity and depth in points from shallow boreholes and outcrop as well as derivation of slowness as constraint conditions to gain accurate shallow velocities. We apply this method to a 2D reflection survey shot across the Flame Mountain, a typical mountain with high gas reserve volume in Western China, by PetroChina and BGP in 1990s. The area has a highly rugged topography with strong variations of lithology near the surface. Over its hillside, the quality of reflection data is very good, but on the mountain ridge, reflection quality is poorer. Because of strong noise, only the first breaks are clear in the records, with velocities varying by more than 3 times in the near offsets. Because this region contains a steep cliff and an overthrust fold, it is very difficult to find a standard refraction horizon, therefore, GLI refractive statics conventional field and residual statics do not result in a good image. Our processing approach includes: 1) The Herglotz-Wiechert method to derive a starting velocity model which is better than horizontal velocity model; 2) using shallow boreholes and geological data, construct smoothness constraints on the velocity field as well as; 3) perform tomographic velocity inversion by NP algorithm; 4) by using the resulting accurate shallow velocities, derive the statics to correct the seismic data for the complex near-surface velocity variations. The result indicates that shallow refraction tomography can greatly improve deep seismic images in complex surface conditions.

Contributions to a shallow aquifer study by reprocessed seismic sections from petroleum exploration surveys, eastern Abu Dhabi, United Arab Emirates

USGS Publications Warehouse

Woodward, D.

1994-01-01

The US Geological Survey, in cooperation with the National Drilling Company of Abu Dhabi, is conducting a 4-year study of the fresh and slightly saline groundwater resources of the eastern Abu Dhabi Emirate. Most of this water occurs in a shallow aquifer, generally less than 150 m deep, in the Al Ain area. A critical part of the Al Ain area coincides with a former petroleum concession area where about 2780 km of vibroseis data were collected along 94 seismic lines during 1981-1983. Field methods, acquistion parameters, and section processing were originally designed to enhance reflections expected at depths ranging from 5000 to 6000 m, and subsurface features directly associated with the shallow aquifer system were deleted from the original seismic sections. The original field tapes from the vibroseis survey were reprocessed in an attempt to extract shallow subsurface information (depths less than 550 m) for investigating the shallow aquifer. A unique sequence of reproccessing parameters was established after reviewing the results from many experimental tests. Many enhancements to the resolution of shallow seismic reflections resulted from: (1) application of a 20-Hz, low-cut filter; (2) recomputation of static corrections to a datum nearer the land surface; (3) intensive velocity analyses; and (4) near-trace muting analyses. The number, resolution, and lateral continuity of shallow reflections were greatly enhanced on the reprocessed sections, as was the delineation of shallow, major faults. Reflections on a synthetic seismogram, created from a borehole drilled to a depth of 786 m on seismic line IQS-11, matcheddprecisely with shallow reflections on the reprocessed section. The 33 reprocessed sections were instrumental in preparing a map showing the major structural features that affect the shallow aquifer system. Analysis of the map provides a better understanding of the effect of these shallow features on the regional occurrence, movement, and quality of groundwater in the concession area. Results from this study demonstrate that original seismic field tapes collected for deep petroleum exploration can be reprocessed to explore for groundwater. ?? 1994.

Archive of Digital Boomer Seismic Reflection Data Collected During USGS Field Activity 96LCA04 in Lakes Mabel and Starr, Central Florida, August 1996

USGS Publications Warehouse

Harrison, Arnell S.; Dadisman, Shawn V.; Swancar, Amy; Tihansky, Ann B.; Flocks, James G.; Wiese, Dana S.

2008-01-01

In August of 1996, the U.S. Geological Survey conducted geophysical surveys of Lakes Mabel and Starr, central Florida, as part of the Central Highlands Lakes project, which is part of a larger USGS Lakes and Coastal Aquifers (LCA) study. This report serves as an archive of unprocessed digital boomer seismic reflection data, trackline maps, navigation files, Geographic Information System (GIS) files, observer's logbook; and formal Federal Geographic Data Committee (FGDC) metadata. Filtered and gained (a relative increase in signal amplitude) digital images of the seismic profiles are also provided. Refer to the Acronyms page for expansions of acronyms and abbreviations used in this report. For detailed information about the hydrologic setting of Lake Starr and the interpretation of some of these seismic reflection data, see Swancar and others (2000) at http://fl.water.usgs.gov/publications/Abstracts/wri00_4030_swancar.html. The archived trace data are in standard Society of Exploration Geophysicists (SEG) SEG-Y format (Barry and others, 1975) and may be downloaded and processed with commercial or public domain software such as Seismic Unix (SU). Example SU processing scripts and USGS software for viewing the SEG-Y files (Zihlman, 1992) are also provided. The USGS Florida Integrated Science Center (FISC) - St. Petersburg assigns a unique identifier to each cruise or field activity. For example, 96LCA04 tells us the data were collected in 1996 for the Lakes and Coastal Aquifers (LCA) study and the data were collected during the fourth field activity for that project in that calendar year. Refer to http://walrus.wr.usgs.gov/infobank/programs/html/definition/activity.html for a detailed description of the method used to assign the field activity ID. The boomer plate is an acoustic energy source that consists of capacitors charged to a high voltage and discharged through a transducer in the water. The transducer is towed on a sled floating on the water surface and when discharged emits a short acoustic pulse, or shot, which propagates through the water and sediment column. The acoustic energy is reflected at density boundaries (such as the seafloor or sediment layers beneath the lake bottom), detected by the receiver (a hydrophone streamer), and recorded by a PC-based seismic acquisition system. This process is repeated at timed intervals (for example, 0.5 s) and recorded for specific intervals of time (for example, 100 ms). In this way, a two-dimensional (2-D) vertical image of the shallow geologic structure beneath the ship track is produced. Figure 1 displays the acquisition geometry. Refer to table 1 for a summary of acquisition parameters. Table 2 lists trackline statistics. Scanned images of the handwritten cruise logbook (1,020-KB PDF) is also provided as a PDF file. The unprocessed seismic data are stored in SEG-Y format (Barry and others, 1975). For a detailed description of the data format, refer to the SEG-Y Format page. See the How To Download SEG-Y Data page for download instructions. The printable profiles provided here are GIF images that were filtered and gained using Seismic Unix software. Refer to the Software page for details about the processing and examples of the processing scripts. The processed SEG-Y data were exported to Chesapeake Technology, Inc. (CTI) SonarWeb software to produce an interactive version of the seismic profile that allows the user to obtain a geographic location and depth from the profile for a curser position. This information is displayed in the status bar of the browser.

An active seismic experiment at Tenerife Island (Canary Island, Spain): Imaging an active volcano edifice

NASA Astrophysics Data System (ADS)

Garcia-Yeguas, A.; Ibañez, J. M.; Rietbrock, A.; Tom-Teidevs, G.

2008-12-01

An active seismic experiment to study the internal structure of Teide Volcano was carried out on Tenerife, a volcanic island in Spain's Canary Islands. The main objective of the TOM-TEIDEVS experiment is to obtain a 3-dimensional structural image of Teide Volcano using seismic tomography and seismic reflection/refraction imaging techniques. At present, knowledge of the deeper structure of Teide and Tenerife is very limited, with proposed structural models mainly based on sparse geophysical and geological data. This multinational experiment which involves institutes from Spain, Italy, the United Kingdom, Ireland, and Mexico will generate a unique high resolution structural image of the active volcano edifice and will further our understanding of volcanic processes.

Processing grounded-wire TEM signal in time-frequency-pseudo-seismic domain: A new paradigm

NASA Astrophysics Data System (ADS)

Khan, M. Y.; Xue, G. Q.; Chen, W.; Huasen, Z.

2017-12-01

Grounded-wire TEM has received great attention in mineral, hydrocarbon and hydrogeological investigations for the last several years. Conventionally, TEM soundings have been presented as apparent resistivity curves as function of time. With development of sophisticated computational algorithms, it became possible to extract more realistic geoelectric information by applying inversion programs to 1-D & 3-D problems. Here, we analyze grounded-wire TEM data by carrying out analysis in time, frequency and pseudo-seismic domain supported by borehole information. At first, H, K, A & Q type geoelectric models are processed using a proven inversion program (1-D Occam inversion). Second, time-to-frequency transformation is conducted from TEM ρa(t) curves to magneto telluric MT ρa(f) curves for the same models based on all-time apparent resistivity curves. Third, 1-D Bostick's algorithm was applied to the transformed resistivity. Finally, EM diffusion field is transformed into propagating wave field obeying the standard wave equation using wavelet transformation technique and constructed pseudo-seismic section. The transformed seismic-like wave indicates that some reflection and refraction phenomena appear when the EM wave field interacts with geoelectric interface at different depth intervals due to contrast in resistivity. The resolution of the transformed TEM data is significantly improved in comparison to apparent resistivity plots. A case study illustrates the successful hydrogeophysical application of proposed approach in recovering water-filled mined-out area in a coal field located in Ye county, Henan province, China. The results support the introduction of pseudo-seismic imaging technology in short-offset version of TEM which can also be an useful aid if integrated with seismic reflection technique to explore possibilities for high resolution EM imaging in future.

Feasibility of high resolution seismic reflection to improve accuracy of hydrogeologic models in a culturally noisy part of Ventura County, CA, USA

USGS Publications Warehouse

Miller, R.; Black, W.; Miele, M.; Morgan, T.; Ivanov, J.; Xia, J.; Peterie, S.

2011-01-01

A high-resolution seismic reflection investigation mapped reflectors and identified characteristics potentially influencing the interpretation of the hydrogeology underlying a portion of the Oxnard Plain in Ventura County, California. Design and implementation of this study was heavily influenced by high levels of cultural noise from vehicles, power lines, roads, manufacturing facilities, and underground utilities/vaults. Acquisition and processing flows were tailored to this noisy environment and relatively shallow target interval. Layering within both upper and lower aquifer systems was delineated at a vertical resolution potential of around 2.5 m at 350 m depth. ?? 2011 Society of Exploration Geophysicists.

Digital single-channel seismic-reflection data from western Santa Monica basin

USGS Publications Warehouse

Normark, William R.; Piper, David J.W.; Sliter, Ray W.; Triezenberg, Peter; Gutmacher, Christina E.

2006-01-01

During a collaborative project in 1992, Geological Survey of Canada and United States Geological Survey scientists obtained about 850 line-km of high-quality single-channel boomer and sleeve-gun seismic-reflection profiles across Hueneme, Mugu and Dume submarine fans, Santa Monica Basin, off southern California. The goals of this work were to better understand the processes that lead to the formation of sandy submarine fans and the role of sea-level changes in controlling fan development. This report includes a trackline map of the area surveyed, as well as images of the sleeve-gun profiles and the opportunity to download both images and digital data files (SEG-Y) of all the sleeve-gun profiles.

Seismic Characterization of Silica Diagenesis in the Northwestern Pacific

NASA Astrophysics Data System (ADS)

Greene, J. A.; Lizarralde, D.; Tominaga, M.; Tivey, M.

2017-12-01

We use seismic reflection data to investigate the silica diagenesis that converted siliceous ooze into the widespread chert/porcellanite layer in the northwestern Pacific. In particular, we investigate whether this process is currently ongoing in the oldest lithosphere of the Pacific. We present images of seismic reflection data collected during the R/V Thomas G. Thompson cruise TN272 and processed using a velocity model constructed from concurrently collected sonobuoy refraction data, applying a normal moveout correction and stack, post-stack Kirchhoff time migration, and predictive gap deconvolution. We compare our seismic observations of the chert/porcellanite layer with nearby drill holes and analogous studies of silica diagenesis around the world. In the processed seismic data, we identify a previously unobserved short-wavelength depth variation to a prominent reflector representing the top of the chert/porcellanite layer, with a vertical change in this horizon of 20 m. This short-wavelength character is in contrast to the flat, seafloor parallel character more typical of the regional chert/porcellanite reflector and may be indicative of the active transformation of siliceous ooze to chert/porcellanite. Drill results in the northwestern Pacific document little to no siliceous ooze above the chert/porcellanite layer; however, they have extremely low recovery rates that could have failed to sample this sediment. No folding or reflector offsets indicative of faulting are observed above or below the short-wave character of the chert/porcellanite reflector, suggesting a structural origin is unlikely, nor are the surrounding reflectors disturbed, as would be expected if these features were caused by fluid expulsion. Instead, the short-wavelength depth variation in the chert/porcellanite layer may be the result of differential advancement of the silica diagenetic front where the siliceous ooze to chert/porcellanite reaction locally occurs in shallower sediments, as has been seismically observed in settings around the world. This could indicate that silica diagenesis is currently ongoing in the northwestern Pacific, and that siliceous ooze remains present in the overlying sediment for conversion to chert/porcellanite.

Full waveform seismic AVAZ signatures of anisotropic shales by integrated rock physics and the reflectivity method

NASA Astrophysics Data System (ADS)

Liu, Xiwu; Guo, Zhiqi; Han, Xu

2018-06-01

A set of parallel vertical fractures embedded in a vertically transverse isotropy (VTI) background leads to orthorhombic anisotropy and corresponding azimuthal seismic responses. We conducted seismic modeling of full waveform amplitude variations versus azimuth (AVAZ) responses of anisotropic shale by integrating a rock physics model and a reflectivity method. The results indicate that the azimuthal variation of P-wave velocity tends to be more complicated for orthorhombic medium compared to the horizontally transverse isotropy (HTI) case, especially at high polar angles. Correspondingly, for the HTI layer in the theoretical model, the short axis of the azimuthal PP amplitudes at the top interface is parallel to the fracture strike, while the long axis at the bottom reflection directs the fracture strike. In contrast, the orthorhombic layer in the theoretical model shows distinct AVAZ responses in terms of PP reflections. Nevertheless, the azimuthal signatures of the R- and T-components of the mode-converted PS reflections show similar AVAZ features for the HTI and orthorhombic layers, which may imply that the PS responses are dominated by fractures. For the application to real data, a seismic-well tie based on upscaled data and a reflectivity method illustrate good agreement between the reference layers and the corresponding reflected events. Finally, the full waveform seismic AVAZ responses of the Longmaxi shale formation are computed for the cases of HTI and orthorhombic anisotropy for comparison. For the two cases, the azimuthal features represent differences mainly in amplitudes, while slightly in the phases of the reflected waveforms. Azimuth variations in the PP reflections from the reference layers show distinct behaviors for the HTI and orthorhombic cases, while the mode-converted PS reflections in terms of the R- and T-components show little differences in azimuthal features. It may suggest that the behaviors of the PS waves are dominated by vertically aligned fractures. This work provides further insight into the azimuthal seismic response of orthorhombic shales. The proposed method may help to improve the seismic-well tie, seismic interpretation, and inversion results using an azimuth anisotropy dataset.

Field test investigation of high sensitivity fiber optic seismic geophone

NASA Astrophysics Data System (ADS)

Wang, Meng; Min, Li; Zhang, Xiaolei; Zhang, Faxiang; Sun, Zhihui; Li, Shujuan; Wang, Chang; Zhao, Zhong; Hao, Guanghu

2017-10-01

Seismic reflection, whose measured signal is the artificial seismic waves ,is the most effective method and widely used in the geophysical prospecting. And this method can be used for exploration of oil, gas and coal. When a seismic wave travelling through the Earth encounters an interface between two materials with different acoustic impedances, some of the wave energy will reflect off the interface and some will refract through the interface. At its most basic, the seismic reflection technique consists of generating seismic waves and measuring the time taken for the waves to travel from the source, reflect off an interface and be detected by an array of geophones at the surface. Compared to traditional geophones such as electric, magnetic, mechanical and gas geophone, optical fiber geophones have many advantages. Optical fiber geophones can achieve sensing and signal transmission simultaneously. With the development of fiber grating sensor technology, fiber bragg grating (FBG) is being applied in seismic exploration and draws more and more attention to its advantage of anti-electromagnetic interference, high sensitivity and insensitivity to meteorological conditions. In this paper, we designed a high sensitivity geophone and tested its sensitivity, based on the theory of FBG sensing. The frequency response range is from 10 Hz to 100 Hz and the acceleration of the fiber optic seismic geophone is over 1000pm/g. sixteen-element fiber optic seismic geophone array system is presented and the field test is performed in Shengli oilfield of China. The field test shows that: (1) the fiber optic seismic geophone has a higher sensitivity than the traditional geophone between 1-100 Hz;(2) The low frequency reflection wave continuity of fiber Bragg grating geophone is better.

Attenuation of harmonic noise in vibroseis data using Simulated Annealing

NASA Astrophysics Data System (ADS)

Sharma, S. P.; Tildy, Peter; Iranpour, Kambiz; Scholtz, Peter

2009-04-01

Processing of high productivity vibroseis seismic data (such as slip-sweep acquisition records) suffers from the well known disadvantage of harmonic distortion. Harmonic distortions are observed after cross-correlation of the recorded seismic signal with the pilot sweep and affect the signals in negative time (before the actual strong reflection event). Weak reflection events of the earlier sweeps falling in the negative time window of the cross-correlation sequence are being masked by harmonic distortions. Though the amplitude of the harmonic distortion is small (up to 10-20 %) compared to the fundamental amplitude of the reflection events, but it is significant enough to mask weak reflected signals. Elimination of harmonic noise due to source signal distortion from the cross-correlated seismic trace is a challenging task since the application of vibratory sources started and it still needs improvement. An approach has been worked out that minimizes the level of harmonic distortion by designing the signal similar to the harmonic distortion. An arbitrary length filter is optimized using the Simulated Annealing global optimization approach to design a harmonic signal. The approach deals with the convolution of a ratio trace (ratio of the harmonics with respect to the fundamental sweep) with the correlated "positive time" recorded signal and an arbitrary filter. Synthetic data study has revealed that this procedure of designing a signal similar to the desired harmonics using convolution of a suitable filter with theoretical ratio of harmonics with fundamental sweep helps in reducing the problem of harmonic distortion. Once we generate a similar signal for a vibroseis source using an optimized filter, then, this filter could be used to generate harmonics, which can be subtracted from the main cross-correlated trace to get the better, undistorted image of the subsurface. Designing the predicted harmonics to reduce the energy in the trace by considering weak reflection and observed harmonics together yields the desired result (resolution of weak reflected signal from the harmonic distortion). As optimization steps proceeds forward it is possible to observe from the difference plots of desired and predicted harmonics how weak reflections evolved from the harmonic distortion gradually during later iterations of global optimization. The procedure is applied in resolving weak reflections from a number of traces considered together. For a more precise design of harmonics SA procedure needs longer computation time which is impractical to deal with voluminous seismic data. However, the objective of resolving weak reflection signal in the strong harmonic noise can be achieved with fast computation using faster cooling schedule and less number of iterations and number of moves in simulated annealing procedure. This process could help in reducing the harmonics distortion and achieving the objective of resolving the lost weak reflection events in the cross-correlated seismic traces. Acknowledgements: The research was supported under the European Marie Curie Host Fellowships for Transfer of Knowledge (TOK) Development Host Scheme (contract no. MTKD-CT-2006-042537).

On the recovery of missing low and high frequency information from bandlimited reflectivity data

NASA Astrophysics Data System (ADS)

Sacchi, M. D.; Ulrych, T. J.

2007-12-01

During the last two decades, an important effort in the seismic exploration community has been made to retrieve broad-band seismic data by means of deconvolution and inversion. In general, the problem can be stated as a spectral reconstruction problem. In other words, given limited spectral information about the earth's reflectivity sequence, one attempts to create a broadband estimate of the Fourier spectra of the unknown reflectivity. Techniques based on the principle of parsimony can be effectively used to retrieve a sparse spike sequence and, consequently, a broad band signal. Alternatively, continuation methods, e.g., autoregressive modeling, can be used to extrapolate the recorded bandwidth of the seismic signal. The goal of this paper is to examine under what conditions the recovery of low and high frequencies from band-limited and noisy signals is possible. At the heart of the methods we discuss, is the celebrated non-Gaussian assumption so important in many modern signal processing methods, such as ICA, for example. Spectral recovery from limited information tends to work when the reflectivity consist of a few well isolated events. Results degrade with the number of reflectors, decreasing SNR and decreasing bandwidth of the source wavelet. Constrains and information-based priors can be used to stabilize the recovery but, as in all inverse problems, the solution is nonunique and effort is required to understand the level of recovery that is achievable, always keeping the physics of the problem in mind. We provide in this paper, a survey of methods to recover broad-band reflectivity sequences and examine the role that these techniques can play in the processing and inversion as applied to exploration and global seismology.

Effects of salt-related mode conversions on subsalt prospecting

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ogilvie, J.S.; Purnell, G.W.

1996-03-01

Mode conversion of waves during seismic reflection surveys has generally been considered a small phenomenon that could be neglected in data processing and interpretation. However, in subsalt prospecting, the contrast in material properties at the salt/sediment interface is often great enough that significant P-to-S and/or S-to-P conversion occurs. The resulting converted waves can be both a help and a hindrance for subsalt prospecting. A case history from the Mississippi Canyon area of the Gulf of Mexico demonstrates strong converted-wave reflections from the base-of-salt that complicate the evaluation of a subsalt prospect using 3-D seismic data. Before and after stack, themore » converted-wave reflections are evident in 2-D and 3-D surveys across the prospect. Ray-tracing synthetic common midpoint (CMP) gathers provides some useful insights about the occurrence of these waves, but elastic-wave-equation modeling is even more useful. While the latter is more time-consuming, even in 2-D, it also provides a more realistic simulated seismic survey across the prospect, which helps to reveal how some converted waves survive the processes of CMP stack and migration, and thereby present possible pitfalls to an unwary interpreter. The insights gained from the synthetic-data suggest some simple techniques that can assist an interpreter in the 3-D interpretation of subsalt events.« less

High-resolution seismic-reflection data offshore of Dana Point, southern California borderland

USGS Publications Warehouse

Sliter, Ray W.; Ryan, Holly F.; Triezenberg, Peter J.

2010-01-01

The U.S. Geological Survey collected high-resolution shallow seismic-reflection profiles in September 2006 in the offshore area between Dana Point and San Mateo Point in southern Orange and northern San Diego Counties, California. Reflection profiles were located to image folds and reverse faults associated with the San Mateo fault zone and high-angle strike-slip faults near the shelf break (the Newport-Inglewood fault zone) and at the base of the slope. Interpretations of these data were used to update the USGS Quaternary fault database and in shaking hazard models for the State of California developed by the Working Group for California Earthquake Probabilities. This cruise was funded by the U.S. Geological Survey Coastal and Marine Catastrophic Hazards project. Seismic-reflection data were acquired aboard the R/V Sea Explorer, which is operated by the Ocean Institute at Dana Point. A SIG ELC820 minisparker seismic source and a SIG single-channel streamer were used. More than 420 km of seismic-reflection data were collected. This report includes maps of the seismic-survey sections, linked to Google Earth? software, and digital data files showing images of each transect in SEG-Y, JPEG, and TIFF formats.

Archive of Boomer and Chirp Seismic Reflection Data Collected During USGS Cruise 01RCE02, Southern Louisiana, April and May 2001

USGS Publications Warehouse

Calderon, Karynna; Dadisman, Shawn V.; Flocks, James G.; Wiese, Dana S.

2003-01-01

In April and May of 2001, the U.S. Geological Survey conducted a geophysical study of the Mississippi River Delta, Atchafalaya River Delta, and Shell Island Pass in southern Louisiana. This study was part of a larger USGS River Contaminant Evaluation (RCE) Project. This disc serves as an archive of unprocessed digital seismic reflection data, trackline navigation files, shotpoint navigation maps, observers' logbooks, GIS information, and formal Federal Geographic Data Committee (FGDC) metadata. In addition, a filtered and gained digital GIF-formatted image of each seismic profile is provided. For your convenience, a list of acronyms and abbreviations frequently used in this report has also been provided. This DVD (Digital Versatile Disc) document is readable on any computing platform that has standard DVD driver software installed. Documentation on this DVD was produced using Hyper Text Markup Language (HTML) utilized by the World Wide Web (WWW) and allows the user to access the information by using a web browser (i.e. Netscape or Internet Explorer). To access the information contained on this disc, open the file 'index.htm' located at the top level of the disc using your web browser. This report also contains WWW links to USGS collaborators and other agencies. These links are only accessible if access to the internet is available while viewing the DVD. The archived boomer and chirp seismic reflection data are in standard Society of Exploration Geophysicists (SEG) SEG-Y format (Barry et al., 1975) and may be downloaded for processing with public domain software such as Seismic Unix (SU), currently located at http://www.cwp.mines.edu/cwpcodes. Examples of SU processing scripts are provided in the boom.tar and chirp.tar files located in the SU subfolder of the SOFTWARE folder located at the top level of this DVD. In-house (USGS) DOS and Microsoft Windows compatible software for viewing SEG-Y headers - DUMPSEGY.EXE (Zilhman, 1992) - is provided in the USGS subfolder of the SOFTWARE folder. Processed profile images, shotpoint navigation maps, logbooks, and formal metadata may be viewed with your web browser.

Seismic-Reflection Technology Defines Potential Vertical Bypass in Hydrogeologic Confinement within Tertiary Carbonates of the Southeastern Florida Platform

NASA Astrophysics Data System (ADS)

Cunningham, K. J.; Walker, C.; Westcott, R. L.

2011-12-01

Continuous improvements in shallow-focused, high-resolution, marine seismic-reflection technology has provided the opportunity to evaluate geologic structures that breach confining units of the Floridan aquifer system within the southeastern Florida Platform. The Floridan aquifer system is comprised mostly of Tertiary platform carbonates. In southeastern Florida, hydrogeologic confinement is important to sustainable use of the Floridan aquifer system, where the saline lower part is used for injection of wastewater and the brackish upper part is an alternative source of drinking water. Between 2007 and 2011, approximately 275 km of 24- and 48-channel seismic-reflection profiles were acquired in canals of peninsular southeastern Florida, Biscayne Bay, present-day Florida shelf margin, and the deeply submerged Miami Terrace. Vertical to steeply dipping offsets in seismic reflections indicate faults, which range from Eocene to possible early Pliocene age. Most faults are associated with karst collapse structures; however, a few tectonic faults of early Miocene to early Pliocene age are present. The faults may serve as a pathway for vertical groundwater flow across relatively low-permeability carbonate strata that separate zones of regionally extensive high-permeability in the Floridan aquifer system. The faults may collectively produce a regional confinement bypass system. In early 2011, twenty seismic-reflection profiles were acquired near the Key Biscayne submarine sinkhole located on the seafloor of the Miami Terrace. Here the water depth is about 365 m. A steeply dipping (eastward) zone of mostly deteriorated quality of seismic-reflection data underlies the sinkhole. Correlation of coherent seismic reflections within and adjacent to the disturbed zone indicates a series of faults occur within the zone. It is hypothesized that upward movement of groundwater within the zone contributed to development of a hypogenic karst system and the resultant overlying sinkhole. Study of this modern seafloor sinkhole may provide clues to the genesis of the more deeply buried Tertiary karst collapse structures. Three-dimensional geomodeling of the seismic-reflection data from the Key Biscayne sinkhole further aids visualization of the seismic stratigraphy and structural system that underlies the sinkhole.

Preliminary Studies of the Structural Characteristics of the Lubao Fault using 2D High Resolution Shallow Seismic Reflection Profile

NASA Astrophysics Data System (ADS)

Bonus, A. A. B.; Lagmay, A. M. A.; Rodolfo, K. S.

2016-12-01

The Lubao fault, located in the province of Pampanga, Philippines, is part of the Bataan Volcanic Arc Complex (BVAC). Active faults within and around the BVAC include the East Zambales and Iba faults; according to the official active faults map of the Philippine Institute of Volcanology and Seismology (PHIVOLCS) there are no other existing active faults in the area. The Lubao Fault distinctly separates wetlands to the northeast and dry alluvial plains to the northwest of Manila Bay. Long term subsidence and high sedimentation rates were observed in the fault and over the past 1.5 thousand years, the northeastern block has dropped 3.5 meters. Along the southwest flank of Mount Natib, tectonic structures were identified using surface mapping and remote sensing. The Persistent Scattering Interferometric Synthetic Aperture Radar (PSInSAR) data results of Eco et al. in 2015 shows uplifts and subsidence in the BVAC area delineating the Lubao Fault. A 480-meter seismic reflection line was laid down perpendicular to the fault with a recording system consisting of 48 channels of Geometrics geophones spaced 10 meters apart. Acquired data were processed using the standard seismic reflection processing sequence by Yilmaz 2001. This preliminary study produced a high resolution subsurface profile of the Lubao fault in the village of San Rafael, Lubao where it is well manifested. The velocity model integrated by stratigraphic data of drilled core shows subsurface lithology. The depth converted profile reveals clear structures and dipping segments which indicates a history of movement along the Lubao fault. Discontinuity of reflectors, either offsets or breaks, are considered structures along the subsurface of the study area. Additional structural mapping and seismic lines along the projected fault are planned in the future to further detail the characteristics of the Lubao Fault. The surface observations made by other researchers coupled with the subsurface seismic profile mapping of this study hopes to clearly delineate and characterize the Lubao Fault.

A geophysical investigation of the northeastern rim of the St. Martin impact structure, Manitoba, Canada

NASA Astrophysics Data System (ADS)

Zivkovic, Vladimir B.

The St. Martin impact structure is a 40 Km diameter structure located in Manitoba, Canada lies in featureless, glaciated terrain lacking any surface expression of an impact structure. The age of the structure has been re-determined to range between 224.3 Ma to 241.4 Ma which nullified a previous hypothesis suggesting this impact was part of a multiple impact event. Within the proposed structural boundary two outcrops of Archean granite are present. The first outcrop is located in what has been identified as the central peak of the impact structure. The second outcrop lies along the northeastern boundary and is known locally as Big Rock. The purpose of this investigation was to determine the relationship of Big Rock, if any, to the impact event and to constrain a more accurate diameter of the structure. To accomplish this I conducted two geophysical surveys and used selected data from a previous survey. The two methods I conducted were: a magnetic survey and seismic reflection profiling. Selected data from a previous gravity survey was used to supplement survey results. The magnetic survey was conducted using the total field G-856 Memory-Mag proton precession magnetometer which measures local or regional field strength. The seismic reflection survey was conducted using three Geometrics Geode exploration seismographs. Due to the complexity of seismic data processing I retained an outside seismic data processing company. Previous gravity anomaly data were acquired using a LaCoste and Romberg Model G gravimeter. The results of this geophysical investigation reveal a shallowing of granitic basement rock with exposure near Big Rock. However, a suggested listric fault near Big Rock was not identified via seismic reflection profiling, but was suggested by both the gravity and magnetic surveys. Listric faults that are genetically related to impact structures are also indicative of the structure's outer boundary and therefore can confirm that the St. Martin impact structure is indeed 40 Km in diameter.

Active Magmatic Underplating in Western Eger Rift, Central Europe

NASA Astrophysics Data System (ADS)

Hrubcová, Pavla; Geissler, Wolfram H.; Bräuer, Karin; Vavryčuk, Václav; Tomek, Čestmír.; Kämpf, Horst

2017-12-01

The Eger Rift is an active element of the European Cenozoic Rift System associated with intense Cenozoic intraplate alkaline volcanism and system of sedimentary basins. The intracontinental Cheb Basin at its western part displays geodynamic activity with fluid emanations, persistent seismicity, Cenozoic volcanism, and neotectonic crustal movements at the intersections of major intraplate faults. In this paper, we study detailed geometry of the crust/mantle boundary and its possible origin in the western Eger Rift. We review existing seismic and seismological studies, provide new interpretation of the reflection profile 9HR, and supplement it by new results from local seismicity. We identify significant lateral variations of the high-velocity lower crust and relate them to the distribution and chemical status of mantle-derived fluids and to xenolith studies from corresponding depths. New interpretation based on combined seismic and isotope study points to a local-scale magmatic emplacement at the base of the continental crust within a new rift environment. This concept of magmatic underplating is supported by detecting two types of the lower crust: a high-velocity lower crust with pronounced reflectivity and a high-velocity reflection-free lower crust. The character of the underplated material enables to differentiate timing and tectonic setting of two episodes with different times of origin of underplating events. The lower crust with high reflectivity evidences magmatic underplating west of the Eger Rift of the Late Variscan age. The reflection-free lower crust together with a strong reflector at its top at depths of 28-30 km forms a magma body indicating magmatic underplating of the late Cenozoic (middle and upper Miocene) to recent. Spatial and temporal relations to recent geodynamic processes suggest active magmatic underplating in the intracontinental setting.

Seismic Reflection Transect across the Central Iberian Zone (Iberian Massif): The ALCUDIA project

NASA Astrophysics Data System (ADS)

Carbonell, R.; Simancas, F.; Martinez-Poyatos, D.; Ayarza, P.; Gonzalez, P.; Tejero, R.; Martín-Parra, L.; Matas, J.; Gonzalez-Lodeiro, F.; Pérez-Estaún, A.; García-Lobon, J.; Mansilla, L.; Palomeras, I.

2007-12-01

The lithosphere of the Central Iberian Zone (CIZ) differs from that of the southwestern Iberian Massif. They are limited by a suture zone. The seismic reflection profile IBERSEIS suggested that the activity of a Carboniferous mantle plume resulted in abundant intrusions of mafic magmas in the mid-to-lower crust which resulted in a singular crustal evolution. The current knowledge of the area based mostly in surface geological mapping suggests that basic magmatism continues further towards the north, indicating that the mantle plume may have affected a bigger area up to the Tajo depression. Furthermore, the existence of the Almadén mine, one of the largest mercury mine in the world within the CIZ, favour that the crust in this area is the result of anomalous lithospheric processes. Accordingly, the ALCUDIA project has been lauched aiming to study the structure and nature of the lithosphere of the CIZ. It includes the acquisition of a deep high resolution seismic reflection transect, detailed geological mapping, kinematic, petrologic and geochemical studies, and other geophysical studies (potential field methods). This new profile extends the previous IBERSEIS Transect towards the northeast, completing almost 600 km of deep seismic profiles, crossing the southern half of the Iberian Variscides. The transect crosses some important structures, such as the Toledo fault, Santa Elena Fault, Alcudia anticline, Almadén syncline, and some major magnetic anomalies. The preliminary results reveal that the crust is 30 km thick in average, with a horizontal Moho, a highly reflective mid-to-lower crust with a few mantle reflectors and well defined features in the upper crust with the indication of detachments zones that might link to the mid- crustal reflective zone.

Characteristics and processing of seismic data collected on thick, floating ice: Results from the Ross Ice Shelf, Antarctica

USGS Publications Warehouse

Beaudoin, Bruce C.; ten Brink, Uri S.; Stern, Tim A.

1992-01-01

Coincident reflection and refraction data, collected in the austral summer of 1988/89 by Stanford University and the Geophysical Division of the Department of Scientific and Industrial Research, New Zealand, imaged the crust beneath the Ross Ice Shelf, Antarctica. The Ross Ice Shelf is a unique acquisition environment for seismic reflection profiling because of its thick, floating ice cover. The ice shelf velocity structure is multilayered with a high velocity‐gradient firn layer constituting the upper 50 to 100 m. This near surface firn layer influences the data character by amplifying and frequency modulating the incoming wavefield. In addition, the ice‐water column introduces pervasive, high energy seafloor, intra‐ice, and intra‐water multiples that have moveout velocities similar to the expected subseafloor primary velocities. Successful removal of these high energy multiples relies on predictive deconvolution, inverse velocity stack filtering, and frequency filtering. Removal of the multiples reveals a faulted, sedimentary wedge which is truncated at or near the seafloor. Beneath this wedge the reflection character is diffractive to a two‐way traveltime of ∼7.2 s. At this time, a prominent reflection is evident on the southeast end of the reflection profile. This reflection is interpreted as Moho indicating that the crust is ∼21-km thick beneath the profile. These results provide seismic evidence that the extensional features observed in the Ross Sea region of the Ross Embayment extend beneath the Ross Ice Shelf.

Mobility Effect on Poroelastic Seismic Signatures in Partially Saturated Rocks With Applications in Time-Lapse Monitoring of a Heavy Oil Reservoir

NASA Astrophysics Data System (ADS)

Zhao, Luanxiao; Yuan, Hemin; Yang, Jingkang; Han, De-hua; Geng, Jianhua; Zhou, Rui; Li, Hui; Yao, Qiuliang

2017-11-01

Conventional seismic analysis in partially saturated rocks normally lays emphasis on estimating pore fluid content and saturation, typically ignoring the effect of mobility, which decides the ability of fluids moving in the porous rocks. Deformation resulting from a seismic wave in heterogeneous partially saturated media can cause pore fluid pressure relaxation at mesoscopic scale, thereby making the fluid mobility inherently associated with poroelastic reflectivity. For two typical gas-brine reservoir models, with the given rock and fluid properties, the numerical analysis suggests that variations of patchy fluid saturation, fluid compressibility contrast, and acoustic stiffness of rock frame collectively affect the seismic reflection dependence on mobility. In particular, the realistic compressibility contrast of fluid patches in shallow and deep reservoir environments plays an important role in determining the reflection sensitivity to mobility. We also use a time-lapse seismic data set from a Steam-Assisted Gravity Drainage producing heavy oil reservoir to demonstrate that mobility change coupled with patchy saturation possibly leads to seismic spectral energy shifting from the baseline to monitor line. Our workflow starts from performing seismic spectral analysis on the targeted reflectivity interface. Then, on the basis of mesoscopic fluid pressure diffusion between patches of steam and heavy oil, poroelastic reflectivity modeling is conducted to understand the shift of the central frequency toward low frequencies after the steam injection. The presented results open the possibility of monitoring mobility change of a partially saturated geological formation from dissipation-related seismic attributes.

NON-INVASIVE DETERMINATION OF THE LOCATION AND DISTRIBUTION OF FREE-PHASE DENSE NONAQUEOUS PHASE LIQUIDS (DNAPL) BY SEISMIC REFLECTION TECHNIQUES

DOE Office of Scientific and Technical Information (OSTI.GOV)

Michael G. Waddell; William J. Domoracki; Tom J. Temples

2001-05-01

This semi-annual technical progress report is for part of Task 4 (site evaluation), on DOE contact number DE-AR26-98FT40369. The project had planned one additional deployment to another site other than Savannah River Site (SRS) or DOE Hanford. After the SUBCON midyear review in Albuquerque, NM, it was decided that two additional deployments would be performed. The first deployment is to test the feasibility of using non-invasive seismic reflection and AVO analysis as monitoring to assist in determining the effectiveness of Dynamic Underground Stripping (DUS) in removal of DNAPL. The Second deployment site is the Department of Defense (DOD) Charleston Navymore » Weapons Station, Solid Waste Management Unit 12 (SWMU-12) Charleston, SC was selected in consultation with National Energy Technology Laboratory (NETL) and DOD Navy Facilities Engineering Command Southern Division (NAVFAC) personnel. Base upon the review of existing data and due to the shallow target depth the project team has collected three Vertical Seismic Profiles (VSP) and experimental reflection line. At the time of preparing this report VSP data and experimental reflection line data has been collected and has have preliminary processing on the data sets.« less

Mantle transition zone structure beneath India and Western China from migration of PP and SS precursors

NASA Astrophysics Data System (ADS)

Lessing, Stephan; Thomas, Christine; Rost, Sebastian; Cobden, Laura; Dobson, David P.

2014-04-01

We investigate the seismic structure of the upper-mantle and mantle transition zone beneath India and Western China using PP and SS underside reflections off seismic discontinuities, which arrive as precursors to the PP and SS arrival. We use high-resolution array seismic techniques to identify precursory energy and to map lateral variations of discontinuity depths. We find deep reflections off the 410 km discontinuity (P410P and S410S) beneath Tibet, Western China and India at depths of 410-440 km and elevated underside reflections of the 410 km discontinuity at 370-390 km depth beneath the Tien Shan region and Eastern Himalayas. These reflections likely correspond to the olivine to wadsleyite phase transition. The 410 km discontinuity appears to deepen in Central and Northern Tibet. We also find reflections off the 660 km discontinuity beneath Northern China at depths between 660 and 700 km (P660P and S660S) which could be attributed to the mineral transformation of ringwoodite to magnesiowuestite and perovskite. These observations could be consistent with the presence of cold material in the middle and lower part of the mantle transition zone in this region. We also find a deeper reflector between 700 and 740 km depth beneath Tibet which cannot be explained by a depressed 660 km discontinuity. This structure could, however, be explained by the segregation of oceanic crust and the formation of a neutrally buoyant garnet-rich layer beneath the mantle transition zone, due to subduction of oceanic crust of the Tethys Ocean. For several combinations of sources and receivers we do not detect arrivals of P660P and S660S although similar combinations of sources and receivers give well-developed P660P and S660S arrivals. Our thermodynamic modelling of seismic structure for a range of compositions and mantle geotherms shows that non-observations of P660P and S660S arrivals could be caused by the dependence of underside reflection coefficients on the incidence angle of the incoming seismic waves. Apart from reflections off the 410 and 660 km discontinuities, we observe intermittent reflectors at 300 and 520 km depth. The discontinuity structure of the study region likely reflects lateral thermal and chemical variations in the upper-mantle and mantle transition zone connected to past and present subduction and mantle convection processes.

Seismic multiple attenuation in the northern continent-ocean transition zone of the South China Sea

NASA Astrophysics Data System (ADS)

Chen, N.; Li, C. F.

2017-12-01

In seismic exploration, especially in marine oil and gas exploration, presence of multiple reflections lowers signal-to-noise ratio of seismic data and makes it difficult to analyze seismic velocity. In northern continent-ocean transition zone of the South China Sea (SCS), low-velocity Cenozoic strata cover sets of high-velocity carbonate strata directly, and over 1000 m thick of sediments were deposited on the igneous basement in the northwest SCS. These sedimentary boundaries generate quite strong impedance interfaces and strong internal multiples. Diffractions as a result of variation of seabed topography, coupled with the vibration, free surface multiples and refraction multiples, cause a variety of strong energy disturbances and missing of frequency component. In this study, we process four recently acquired multichannel reflection seismic profiles from the northern continent-ocean transition zone of the SCS with a new combination of demultiple techniques. There is a variety of strong multiples in the raw data, and the seabed multiple occurs between 9 to 11 seconds in two-way travel time (TWTT), and we apply Surface-related Multiple Elimination (SRME) to attenuate the free surface multiples. After SRME, we use high-resolution Radon transform (RAMUR) to attenuate deep multiples concentrating below 10 seconds in TWTT. Normal moveout correction (NMO) is necessary to flatten true reflections and turn multiples into a parabola before RAMUR, and we can attenuate the deep multiples in theτ-p domain. The seabed topography varies greatly in the continent-ocean transition zone, so the diffractions are well developed. However, SRME and RAMUR are not effective in attenuating diffractions and internal multiples. We select diffracted multiple attenuation (DIMAT) after many trials and detailed analysis. The diffractions are extracted in decomposed frequency bands. The internal multiples below 11 seconds in TWTT and high-amplitude noises are successfully suppressed while keeping the primary events. This combination of SRME, RAMUR and DIMAT in sequence demonstrates to be quite effective in attenuating these types of multiples on the continent-ocean transition zone. Keywords: Continent-ocean transition zone, seismic exploration, data processing, multiple attenuation

The forearc crustal evolution of Izu-Bonin (Ogasawara) region obtained by seismic reflection and refraction surveys

NASA Astrophysics Data System (ADS)

Yamashita, M.; Kodaira, S.; Takahashi, N.; Tatsumi, Y.; Kaneda, Y.

2009-12-01

The Izu-Bonin (Ogasawara)-Mariana (IBM) arc is known to the typical oceanic island arc, and it is the most suitable area to understand the growth process of island arc. By previous seismic survey and deep sea drilling, convex basements are distributed along North-South direction in present forearc region. The convex basements are reported to be formed during Oligocene and Eocene (Taylor, 1992). In IBM forearc region, the middle crust with 6 km/s is recognized by seismic survey using OBSs. In IBM region, four IODP drilling sites are proposed in order to understand comprehensive growth process of arc and continental crust evolution. Two of them are located in forearc region. Japan Agency for Marine-Earth Science and Technology (JAMSTEC) carried out multi-channel seismic reflection survey using 7,800/12,000 cu.in. air gun and 5-6 km streamer with 444/204 ch hydrophones in the IBM region since 2004. We investigate the crustal structure beneath the Izu-Bonin forearc region for contribution of IBM drilling site along five long survey lines, which are across from present volcanic front to forearc basin. Seismic refraction survey is also conducted across forearc region using 84 OBSs every 1 km interval. Shallow crustal structure can be classified four units including basement which compared between previous drilling results and obtained seismic profiles. In IBM forearc region, thick sedimentary basin distribute from east side of volcanic front. Two convex basement peaks are indicated in across profile of forearc region. These peaks are estimated the top of paleoarc (Oligocene and Eocene) by previous ODP drilling. The half graben structure with major displacement is identified from west side of present volcanic front to the top of Oligocene arc. On the other hand, there is no displacement of sediments between the Oligocene arc and Eocene arc. This result shows the same origin of basement between the present volcanic front and Oligocene arc. There is long time difference of tectonic activity of sediments between the west and east side of Oligocene paleoarc. We would present the crustal condition before rifting between present volcanic front and Oligocene paleoarc by comparison of reflection and velocity structure.

Seismic Fracture Characterization Methodologies for Enhanced Geothermal Systems

DOE Office of Scientific and Technical Information (OSTI.GOV)

Queen, John H.

2016-05-09

Executive Summary The overall objective of this work was the development of surface and borehole seismic methodologies using both compressional and shear waves for characterizing faults and fractures in Enhanced Geothermal Systems. We used both surface seismic and vertical seismic profile (VSP) methods. We adapted these methods to the unique conditions encountered in Enhanced Geothermal Systems (EGS) creation. These conditions include geological environments with volcanic cover, highly altered rocks, severe structure, extreme near surface velocity contrasts and lack of distinct velocity contrasts at depth. One of the objectives was the development of methods for identifying more appropriate seismic acquisition parametersmore » for overcoming problems associated with these geological factors. Because temperatures up to 300º C are often encountered in these systems, another objective was the testing of VSP borehole tools capable of operating at depths in excess of 1,000 m and at temperatures in excess of 200º C. A final objective was the development of new processing and interpretation techniques based on scattering and time-frequency analysis, as well as the application of modern seismic migration imaging algorithms to seismic data acquired over geothermal areas. The use of surface seismic reflection data at Brady's Hot Springs was found useful in building a geological model, but only when combined with other extensive geological and geophysical data. The use of fine source and geophone spacing was critical in producing useful images. The surface seismic reflection data gave no information about the internal structure (extent, thickness and filling) of faults and fractures, and modeling suggests that they are unlikely to do so. Time-frequency analysis was applied to these data, but was not found to be significantly useful in their interpretation. Modeling does indicate that VSP and other seismic methods with sensors located at depth in wells will be the most effective seismic tools for getting information on the internal structure of faults and fractures in support of fluid flow pathway management and EGS treatment. Scattered events similar to those expected from faults and fractures are seen in the VSP reported here. Unfortunately, the source offset and well depth coverage do not allow for detailed analysis of these events. This limited coverage also precluded the use of advanced migration and imaging algorithms. More extensive acquisition is needed to support fault and fracture characterization in the geothermal reservoir at Brady's Hot Springs. The VSP was effective in generating interval velocity estimates over the depths covered by the array. Upgoing reflection events are also visible in the VSP results at locations corresponding to reflection events in the surface seismic. Overall, the high temperature rated fiber optic sensors used in the VSP produced useful results. Modeling has been found useful in the interpretation of both surface reflection seismic and VSP data. It has helped identify possible near surface scattering in the surface seismic data. It has highlighted potential scattering events from deeper faults in the VSP data. Inclusion of more detailed fault and fracture specific stiffness parameters are needed to fully interpret fault and fracture scattered events for flow properties (Pyrak-Nolte and Morris, 2000, Zhu and Snieder, 2002). Shear wave methods were applied in both the surface seismic reflection and VSP work. They were not found to be effective in the Brady's Hot Springs area. This was due to the extreme attenuation of shear waves in the near surface at Brady's. This does not imply that they will be ineffective in general. In geothermal areas where good shear waves can be recorded, modeling suggests they should be very useful for characterizing faults and fractures.« less

The shallow structure of Solfatara Volcano, Italy, revealed by dense, wide-aperture seismic profiling.

PubMed

Bruno, Pier Paolo G; Maraio, Stefano; Festa, Gaetano

2017-12-12

Two active-source, high-resolution seismic profiles were acquired in the Solfatara tuff cone in May and November 2014, with dense, wide-aperture arrays. Common Receiver Surface processing was crucial in improving signal-to-noise ratio and reflector continuity. These surveys provide, for the first time, high-resolution seismic images of the Solfatara crater, depicting a ~400 m deep asymmetrical crater filled by volcanoclastic sediments and rocks and carved within an overall non-reflective pre-eruptive basement showing features consistent with the emplacement of shallow intrusive bodies. Seismic reflection data were interpreted using the trace complex attributes and clearly display several steep and segmented collapse faults, generally having normal kinematics and dipping toward the crater centre. Fault/fracture planes are imaged as sudden amplitude drops that generate narrow low-similarity and high-dip attributes. Uprising fluids degassed by a magmatic source are the most probable cause of the small-scale amplitude reduction. Seismic data also support the interpretation of the shallow structure of the Solfatara crater as a maar. Our results provides a solid framework to constrain the near-surface geological interpretation of such a complex area, which improves our understanding of the temporal changes of the structure in relation with other geophysical and geochemical measurements.

Moho depth across the Trans-European Suture Zone from ambient vibration autocorrelations

NASA Astrophysics Data System (ADS)

Becker, Gesa; Knapmeyer-Endrun, Brigitte

2017-04-01

In 2018 the InSight mission to Mars will deploy a seismic station on the planet. This seismic station will consist of a three-component very broadband seismic sensor and a collocated three-component short period seismometer. Single station methods are therefore needed to extract information from the data and learn more about the interior structure of Mars. One potential method is the extraction of reflected phases from autocorrelations. Here autocorrelations are derived from ambient seismic noise to make the most of the data expected, as seismicity on Mars is likely less abundant than on Earth. These autocorrelations are calculated using a phase autocorrelation algorithm and time-frequency domain phase-weighted stacking as the main processing steps in addition to smoothing the spectrum of the data with a short term-long term average algorithm. Afterward the obtained results are filtered and analyzed in the frequency range of 1-2 Hz. The developed processing scheme is applied to data from permanent seismic stations located in different geological provinces across Europe, i.e. the Upper Rhine Graben, Central European Platform, Bohemian Massif, Northern German and Polish Basin, and the East European Craton, with varying Moho depths between 25-50 km. These crustal thicknesses are comparable to various estimates for Mars, therefore providing a good reference and indication of resolvability for Moho depths that might be encountered at the landing site. Changes in reflectivity can be observed in the calculated autocorrelations. The lag times of these changes are converted into depths with the help of available velocity information (EPcrust and local models for Poland and the Czech Republic, respectively) and the results are compared to existing information on Moho depths, which show good agreement. The results are temporarily stable, but show a clear correlation with the existence of cultural noise. Based on the closely located broadband and short period stations of the GERESS-array, it is shown that the processing scheme is also applicable to short period stations. Subsequently it is applied to the mainly short period and temporary stations of the PASSEQ network along the seismic profile POLONAISE P4, running from Eastern Germany to Lithuania crossing the Trans-European Suture Zone.

The utility of petroleum seismic exploration data in delineating structural features within salt anticlines

USGS Publications Warehouse

Stockton, S.L.; Balch, Alfred H.

1978-01-01

The Salt Valley anticline, in the Paradox Basin of southeastern Utah, is under investigation for use as a location for storage of solid nuclear waste. Delineation of thin, nonsalt interbeds within the upper reaches of the salt body is extremely important because the nature and character of any such fluid- or gas-saturated horizons would be critical to the mode of emplacement of wastes into the structure. Analysis of 50 km of conventional seismic-reflection data, in the vicinity of the anticline, indicates that mapping of thin beds at shallow depths may well be possible using a specially designed adaptation of state-of-the-art seismic oil-exploration procedures. Computer ray-trace modeling of thin beds in salt reveals that the frequency and spatial resolution required to map the details of interbeds at shallow depths (less than 750 m) may be on the order of 500 Hz, with surface-spread lengths of less than 350 m. Consideration should be given to the burial of sources and receivers in order to attenuate surface noise and to record the desired high frequencies. Correlation of the seismic-reflection data with available well data and surface geology reveals the complex, structurally initiated diapir, whose upward flow was maintained by rapid contemporaneous deposition of continental clastic sediments on its flanks. Severe collapse faulting near the crests of these structures has distorted the seismic response. Evidence exists, however, that intrasalt thin beds of anhydrite, dolomite, and black shale are mappable on seismic record sections either as short, discontinuous reflected events or as amplitude anomalies that result from focusing of the reflected seismic energy by the thin beds; computer modeling of the folded interbeds confirms both of these as possible causes of seismic response from within the salt diapir. Prediction of the seismic signatures of the interbeds can be made from computer-model studies. Petroleum seismic-reflection data are unsatisfactory for mapping the thin beds because of the lack of sufficient resolution to provide direct evidence of the presence of the thin beds. However, indirect evidence, present in these data as discontinuous seismic events, suggests that two geophysical techniques designed for this specific problem would allow direct detection of the interbeds in salt. These techniques are vertical seismic profiling and shallow, short-offset, high-frequency, seismic-reflection recording.

Crustal investigations of the earthquake-prone Vrancea region in Romania - Part 2: Novel deep seismic reflection experiment in the southeastern Carpathian belt and its foreland basin - survey target, design, and first results

NASA Astrophysics Data System (ADS)

Mocanu, V. I.; Stephenson, R. A.; Diaconescu, C. C.; Knapp, J. H.; Matenco, L.; Dinu, C.; Harder, S.; Prodehl, C.; Hauser, F.; Raileanu, V.; Cloetingh, S. A.; Leever, K.

2001-12-01

Seismic studies of the outer Carpathian Orogen and its foreland (Focsani Basin) in the vicinity of the Vrancea Zone and Danube Delta (Romania) forms one component of a new multidisciplinary initiative of ISES (Netherlands Centre for Integrated Solid Earth Sciences) called DACIA PLAN ("Danube and Carpathian Integrated Action on Processes in the Lithosphere and Neotectonics"). The study area, at the margin of the European craton, constitutes one of the most active seismic zones in Europe, yet has remained a geological and geodynamic enigma within the Alpine-Himalayan orogenic system. Intermediate depth (50-220 km) mantle earthquakes of significant magnitude occur in a geographically restricted area in the south-east Carpathians bend. The adjacent, foreland Focsani Basin appears to exhibit recent extensional deformation in what is otherwise understood to be a zone of convergence. The deep seismic reflection component of DACIA PLAN comprises a ~140-km near-vertical profile across the Vrancea Zone and Focsani Basin. Data acquisition took place in August-September 2001, as part of the integrated refraction/reflection seismic field programme "Vrancea-2001" co-ordinated at Karlsruhe University (cf. Abstract, Part 1), utilising 640 independently deployed recorders provided by UTEP and IRIS/PASSCAL ("Texans"). Station spacing was every 100-m with shots every 1-km. These data are to be integrated with industry seismic as well as planned new medium-high resolution seismic reflection profiling across key neotectonically active structures in the Focsani Basin. Particular goals of DACIA PLAN include: (1) the architecture of the Tertiary/Quaternary basins developed within and adjacent to this zone, including the foreland Focsani Basin; (2) the presence and geometry of structural detachment(s) in relation with foreland basin development, including constraints for balanced cross-sections and geodynamic modelling of basin origin and evolution; (3) the relationship between crustal structures related to basin evolution, especially neotectonic structures, with deep (mantle) structure and seismicity; and, (4) integratration with complementary studies in the Carpathian-Transylvanian region for evaluation and validation of competing geodynamic models for the present-day development and neotectonic character of the Vrancea Zone-Focsani Basin-Danube Delta-Black Sea corridor.

Improving Vintage Seismic Data Quality through Implementation of Advance Processing Techniques

NASA Astrophysics Data System (ADS)

Latiff, A. H. Abdul; Boon Hong, P. G.; Jamaludin, S. N. F.

2017-10-01

It is essential in petroleum exploration to have high resolution subsurface images, both vertically and horizontally, in uncovering new geological and geophysical aspects of our subsurface. The lack of success may have been from the poor imaging quality which led to inaccurate analysis and interpretation. In this work, we re-processed the existing seismic dataset with an emphasis on two objectives. Firstly, to produce a better 3D seismic data quality with full retention of relative amplitudes and significantly reduce seismic and structural uncertainty. Secondly, to facilitate further prospect delineation through enhanced data resolution, fault definitions and events continuity, particularly in syn-rift section and basement cover contacts and in turn, better understand the geology of the subsurface especially in regard to the distribution of the fluvial and channel sands. By adding recent, state-of-the-art broadband processing techniques such as source and receiver de-ghosting, high density velocity analysis and shallow water de-multiple, the final results produced a better overall reflection detail and frequency in specific target zones, particularly in the deeper section.

Spectral element modelling of fault-plane reflections arising from fluid pressure distributions

USGS Publications Warehouse

Haney, M.; Snieder, R.; Ampuero, J.-P.; Hofmann, R.

2007-01-01

The presence of fault-plane reflections in seismic images, besides indicating the locations of faults, offers a possible source of information on the properties of these poorly understood zones. To better understand the physical mechanism giving rise to fault-plane reflections in compacting sedimentary basins, we numerically model the full elastic wavefield via the spectral element method (SEM) for several different fault models. Using well log data from the South Eugene Island field, offshore Louisiana, we derive empirical relationships between the elastic parameters (e.g. P-wave velocity and density) and the effective-stress along both normal compaction and unloading paths. These empirical relationships guide the numerical modelling and allow the investigation of how differences in fluid pressure modify the elastic wavefield. We choose to simulate the elastic wave equation via SEM since irregular model geometries can be accommodated and slip boundary conditions at an interface, such as a fault or fracture, are implemented naturally. The method we employ for including a slip interface retains the desirable qualities of SEM in that it is explicit in time and, therefore, does not require the inversion of a large matrix. We performa complete numerical study by forward modelling seismic shot gathers over a faulted earth model using SEM followed by seismic processing of the simulated data. With this procedure, we construct post-stack time-migrated images of the kind that are routinely interpreted in the seismic exploration industry. We dip filter the seismic images to highlight the fault-plane reflections prior to making amplitude maps along the fault plane. With these amplitude maps, we compare the reflectivity from the different fault models to diagnose which physical mechanism contributes most to observed fault reflectivity. To lend physical meaning to the properties of a locally weak fault zone characterized as a slip interface, we propose an equivalent-layer model under the assumption of weak scattering. This allows us to use the empirical relationships between density, velocity and effective stress from the South Eugene Island field to relate a slip interface to an amount of excess pore-pressure in a fault zone. ?? 2007 The Authors Journal compilation ?? 2007 RAS.

Continentward-dipping detachment fault system and asymmetric rift structure of the Baiyun Sag, northern South China Sea

NASA Astrophysics Data System (ADS)

Zhou, Zhichao; Mei, Lianfu; Liu, Jun; Zheng, Jinyun; Chen, Liang; Hao, Shihao

2018-02-01

The rift architecture and deep crustal structure of the distal margin at the mid-northern margin of the South China Sea have been previously investigated by using deep seismic reflection profiles. However, one fundamental recurring problem in the debate is the extensional fault system and rift structure of the hyperextended rift basins (Baiyun Sag and Liwan Sag) within the distal margin because of the limited amount of seismic data. Based on new 3D seismic survey data and 2D seismic reflection profiles, we observe an array of fault blocks in the Baiyun Sag, which were tilted towards the ocean by extensional faulting. The extensional faults consistently dip towards the continent. Beneath the tilted fault blocks and extensional faults, a low-angle, high-amplitude and continuous reflection has been interpreted as the master detachment surface that controls the extension process. During rifting, the continentward-dipping normal faults evolved in a sequence from south to north, generating the asymmetric rift structure of the Baiyun Sag. The Baiyun Sag is separated from the oceanic domain by a series of structural highs that were uplifted by magmatic activity in response to the continental breakup at 33 Ma and a ridge jump to the south at 26-24 Ma. Therefore, we propose that magmatism played a significant role in the continental extension and final breakup in the South China Sea.

Integration of P- and SH-wave high-resolution seismic reflection and micro-gravity techniques to improve interpretation of shallow subsurface structure: New Madrid seismic zone

USGS Publications Warehouse

Bexfield, C.E.; McBride, J.H.; Pugin, Andre J.M.; Ravat, D.; Biswas, S.; Nelson, W.J.; Larson, T.H.; Sargent, S.L.; Fillerup, M.A.; Tingey, B.E.; Wald, L.; Northcott, M.L.; South, J.V.; Okure, M.S.; Chandler, M.R.

2006-01-01

Shallow high-resolution seismic reflection surveys have traditionally been restricted to either compressional (P) or horizontally polarized shear (SH) waves in order to produce 2-D images of subsurface structure. The northernmost Mississippi embayment and coincident New Madrid seismic zone (NMSZ) provide an ideal laboratory to study the experimental use of integrating P- and SH-wave seismic profiles, integrated, where practicable, with micro-gravity data. In this area, the relation between "deeper" deformation of Paleozoic bedrock associated with the formation of the Reelfoot rift and NMSZ seismicity and "shallower" deformation of overlying sediments has remained elusive, but could be revealed using integrated P- and SH-wave reflection. Surface expressions of deformation are almost non-existent in this region, which makes seismic reflection surveying the only means of detecting structures that are possibly pertinent to seismic hazard assessment. Since P- and SH-waves respond differently to the rock and fluid properties and travel at dissimilar speeds, the resulting seismic profiles provide complementary views of the subsurface based on different levels of resolution and imaging capability. P-wave profiles acquired in southwestern Illinois and western Kentucky (USA) detect faulting of deep, Paleozoic bedrock and Cretaceous reflectors while coincident SH-wave surveys show that this deformation propagates higher into overlying Tertiary and Quaternary strata. Forward modeling of micro-gravity data acquired along one of the seismic profiles further supports an interpretation of faulting of bedrock and Cretaceous strata. The integration of the two seismic and the micro-gravity methods therefore increases the scope for investigating the relation between the older and younger deformation in an area of critical seismic hazard. ?? 2006 Elsevier B.V. All rights reserved.

Imaging near-subsurface subrosion structures and faults using SH-wave reflection seismics

NASA Astrophysics Data System (ADS)

Wadas, Sonja; Polom, Ulrich; Buness, Hermann; Krawczyk, Charlotte

2016-04-01

Subrosion is a term for underground leaching of soluble rocks and is a global phenomenon. It involves dissolution of evaporites due to the presence of unsaturated water, fractures and faults. Fractures and faults are pathways for water to circulate and to generate subsurface cavities. Depending on the leached material and the parameters of the generation process, especially the dissolution rate, different kinds of subrosion structures evolve in the subsurface. The two end members are collapse and depression structures. Subrosion is a natural process, but it can be enhanced by anthropogenic factors like manipulation of the aquifer system and groundwater flow and by e.g. extraction of saline water. The formation of sinkholes and depressions are a dangerous geohazard, especially if they occur in urban areas, which often leads to building and infrastructural damage and life-threatening situations. For this reason investigations of the processes that induce subrosion and a detailed analysis of the resulting structures are of importance. To develop a comprehensive model of near-subsurface subrosion structures, reflection seismics is one of the methods used by the Leibniz Institute for Applied Geophysics. The study area is located in the city of Bad Frankenhausen in northern Thuringia, Germany. Most of the geological underground of Thuringia is characterized by Permian deposits. Bad Frankenhausen is situated directly south of the Kyffhäuser mountain range at the Kyffhäuser Southern Margin Fault. This major fault is one of the main pathways for the circulating ground- and meteoric waters that leach the Permian deposits, especially the Leine-, Staßfurt- and Werra Formations. 2014 and 2015 eight shear wave reflection seismic profiles were carried out in the urban area of Bad Frankenhausen and three profiles in the countrified surroundings. Altogether ca. 3.6 km were surveyed using a landstreamer as receiver and an electro-dynamic vibrator as source. The surveys were adjusted in able to measure in the medieval center of Bad Frankenhausen. This required special equipment and configuration due to the densely built-up area, the differing ground conditions and the varying topography. The analysis of the seismic sections revealed structures associated with the continuing subrosion of the Permian deposits. The reflection patterns indicate heterogeneous near-surface geology of lateral and vertical variations in forms of discontinuous reflectors, small-scale fractures and faults. The fractures and faults also serve as additional pathways for the circulating water and the deposits are subsiding along these features, resulting in the formation of depression structures in the near-subsurface. Diffractions in the unmigrated sections indicate voids in the subsurface that develop due to the longtime subrosion processes. Besides these structures, variations of the traveltime, absorption and scattering of the seismic waves induced by the subrosion processes are visible.

Crustal structure in the Kiruna area, northern Sweden, based on seismic reflection profiling

NASA Astrophysics Data System (ADS)

Juhojuntti, Niklas; Bergman, Stefan; Olsson, Sverker

2013-04-01

Northernmost Sweden is currently one of the most active mining areas in Europe. In order to better understand the regional three-dimensional crustal structure and to support deep ore exploration, we have acquired a 74 km long seismic reflection profile in the Kiruna area. The upper crust in this area is largely composed of various supracrustal units, which are dominated by metabasalts, acidic metavolcanics and clastic metasedimentary rocks, resting on an Archaean metagranitoid complex. All of these units have been intruded by plutonic rocks, and to variable degrees folded, sheared and metamorphosed, during the Svecokarelian orogeny. The profile crosses several steep ductile shear zones, some of which extend for hundreds of kilometres along strike. Many of the lithological contacts and deformation zones are expected to be seismically reflective. The profile is located only a few kilometres from the world's largest underground iron-ore mine in Kiruna, and closer to the profile there are several known ore bodies, some of which are active exploration targets. For the seismic recording we used approximately 350 geophones in split-spread configuration, at a separation of 25 m. The main seismic source was the Vibsist system (an impact source), which normally was employed at every geophone station. We also fired explosive charges (8-16 kg) at a few locations distributed along the profile to image deeper structures, although at very low resolution. Wireless seismometers were placed along and to the side of the profile, mainly in order to achieve better velocity control and to study out-of-the-plane reflections. Some mining blasts in Kiruna were also recorded. The upper crust in the area is quite reflective, most clearly demonstrated by the dynamite shot records. Some of the reflections appear to originate from steeply dipping structures. The dynamite shot records show a set of reflections at 3-4 s twt, corresponding to a depth of roughly 10 km, the explanation for which is unknown at present. Many of the dynamite shot records also show reflections from deeper in the crust. The preliminary stacked sections based on the Vibsist data show reflections down to depths of at least 5 km, some of which have been tentatively interpreted to originate at the contacts between basalts and felsic metavolcanics. In the further data analysis, special focus is given to the processing of reflections from steeply dipping structures and to the integration of the low-fold dynamite and high-fold Vibsist data.

Preliminary Interpretations of Multi-Channel Seismic Reflection and Magnetic Data on North Anatolian Fault (NAF) in the Eastern Marmara Region, Turkey

NASA Astrophysics Data System (ADS)

Gözde Okut Toksoy, Nigar; Kurt, Hülya; İşseven, Turgay

2017-04-01

The North Anatolian Fault (NAF) is 1600 km long, right lateral strike-slip fault nearly E-W elongated between Karlıova in the east and Saros Gulf in the west. NAF splays into two major strands near the west of Bolu city as Northern and Southern strands. Northern strand passes Sapanca Lake and extends towards west and reaches Marmara Sea through the Gulf of Izmit. The area has high seismicity; 1999 Kocaeli (Mw=7.4) and 1999 Düzce (Mw=7.2) earthquakes caused approximately 150 km long surface rupture between the Gulf of Izmit and Bolu. The rupture has four distinct fault segments as Gölcük, Sapanca, Sakarya, and Karadere from west to east. In this study multi-channel seismic and magnetic data are collected for the first time on the Sapanca Segment to investigate the surficial and deeper geometry of the NAF. Previously, the NAF in the eastern Marmara region is investigated using by paleo-seismological data from trenches on the surface rupture of fault or the geomorphological data (Lettis et al., 2000; Dikbaş and Akyüz, 2010) which have shallower depth targets. Crustal structure and seismic velocities for Central Anatolia and eastern Marmara regions are obtained from deeper targeted refraction data (Gürbüz et al., 1992). However, their velocity models do not have the spatial resolution to determine details of the fault zone structure. Multi-channel seismic and magnetic data in this study were acquired on two N-S directed profiles crossing NAF perpendicularly near Kartepe on the western part of the Sapanca Lake in October 2016. The receiver interval is 5 m, shot interval is 5-10 m, and the total length of the profiles are approximately 1400 m. Buffalo Gun is used as a seismic source for deeper penetration. Conventional seismic reflection processing steps are applied to the data. These are geometry definition, editing, filtering, static correction, velocity analysis and deconvolution, stacking and migration. Echos seismic software package in Geophysical Department of Istanbul Technical University is used for processing. Proton magnetometer is used for measuring the magnetic field variations on the one of the profiles. Total magnetic field values are corrected using base readings from Bogazici University Kandilli Observatory, Iznik Earthquake Hazard Mitigation Center. Processed seismic and magnetic data are interpreted and compared to see effect of the NAF. Preliminary interpretations show vertical seismic discontinuities related to the fault figured out on the time-migrated seismic sections from surface to the about 1 s two-way travel time depth. Magnetic anomalies are also realized on the profile related to the NAF supporting the seismic data.

Fault zone characterization using P- and S-waves

NASA Astrophysics Data System (ADS)

Wawerzinek, Britta; Buness, Hermann; Polom, Ulrich; Tanner, David C.; Thomas, Rüdiger

2014-05-01

Although deep fault zones have high potential for geothermal energy extraction, their real usability depends on complex lithological and tectonic factors. Therefore a detailed fault zone exploration using P- and S-wave reflection seismic data is required. P- and S-wave reflection seismic surveys were carried out along and across the eastern border of the Leinetal Graben in Lower Saxony, Germany, to analyse the structural setting, different reflection characteristics and possible anisotropic effects. In both directions the P-wave reflection seismic measurements show a detailed and complex structure. This structure was developed during several tectonic phases and comprises both steeply- and shallowly-dipping faults. In a profile perpendicular to the graben, a strong P-wave reflector is interpreted as shallowly west-dipping fault that is traceable from the surface down to 500 m depth. It is also detectable along the graben. In contrast, the S-waves show different reflection characteristics: There is no indication of the strong P-wave reflector in the S-wave reflection seismic measurements - neither across nor along the graben. Only diffuse S-wave reflections are observable in this region. Due to the higher resolution of S-waves in the near-surface area it is possible to map structures which cannot be detected in P-wave reflection seismic, e.g the thinning of the uppermost Jurassic layer towards the south. In the next step a petrophysical analysis will be conducted by using seismic FD modelling to a) determine the cause (lithological, structural, or a combination of both) of the different reflection characteristics of P- and S-waves, b) characterize the fault zone, as well as c) analyse the influence of different fault zone properties on the seismic wave field. This work is part of the gebo collaborative research programme which is funded by the 'Niedersächsisches Ministerium für Wissenschaft und Kultur' and Baker Hughes.

Continuous seismic-reflection survey defining shallow sedimentary layers in the Charlotte Harbor and Venice areas, southwest Florida

USGS Publications Warehouse

Wolansky, R.M.; Haeni, F.P.; Sylvester, R.E.

1983-01-01

A continuous marine seismic-reflection survey system was used to define the configuration of shallow sedimentary layers underlying the Charlotte Harbor and Venice areas, southwest Florida. Seismic profiling was conducted over a distance of about 57 miles of Charlotte Harbor, the Peace and Myakka Rivers, and the Intracoastal Waterway near Venice using a high resolution energy source capable of penetrating 200 feet of sediments with a resolution of 1 to 3 feet. Five stratigraphic units defined from the seismic records includes sediments to Holocene to early Miocene age. All seismic-profile records are presented, along with geologic sections constructed from the records. Seismic reflection amplitude, frequency, continuity, configuration, external form, and areal association were utilized to interpret facies and depositional environments of the stratigraphic units. The despositional framework of the units ranges from shallow shelf to prograded slope. The stratigraphic units are correlated with the surficial aquifer and intermediate artesian aquifers, and permeable zones of the aquifers are related to the seismic records. (USGS)

Common features and peculiarities of the seismic activity at Phlegraean Fields, Long Valley, and Vesuvius

USGS Publications Warehouse

Marzocchi, W.; Vilardo, G.; Hill, D.P.; Ricciardi, G.P.; Ricco, C.

2001-01-01

We analyzed and compared the seismic activity that has occurred in the last two to three decades in three distinct volcanic areas: Phlegraean Fields, Italy; Vesuvius, Italy; and Long Valley, California. Our main goal is to identify and discuss common features and peculiarities in the temporal evolution of earthquake sequences that may reflect similarities and differences in the generating processes between these volcanic systems. In particular, we tried to characterize the time series of the number of events and of the seismic energy release in terms of stochastic, deterministic, and chaotic components. The time sequences from each area consist of thousands of earthquakes that allow a detailed quantitative analysis and comparison. The results obtained showed no evidence for either deterministic or chaotic components in the earthquake sequences in Long Valley caldera, which appears to be dominated by stochastic behavior. In contrast, earthquake sequences at Phlegrean Fields and Mount Vesuvius show a deterministic signal mainly consisting of a 24-hour periodicity. Our analysis suggests that the modulation in seismicity is in some way related to thermal diurnal processes, rather than luni-solar tidal effects. Independently from the process that generates these periodicities on the seismicity., it is suggested that the lack (or presence) of diurnal cycles is seismic swarms of volcanic areas could be closely linked to the presence (or lack) of magma motion.

Evaluation of seismic hazard of the Gökova bay in terms of seismotectonics

DOE Office of Scientific and Technical Information (OSTI.GOV)

Erkoç, Ebru Aktepe, E-mail: ebru.aktepe@deu.edu.tr; Uluğ, Atilla, E-mail: atilla.ulug@deu.edu.tr

While discovering the seismicity of our country, knowing the array of earthquake occurrence which reflects the characteristic tectonic features of each region makes vital contributions to the earthquakes that have occurred and to the pursuit of the processes which might occur in the future. When considering the region’s seismic activity, the presence of active faults that create earthquake within the bay is obvious. Many active fault parts in the Gulf of Gökova region continues their seismic activity with the opening effect that is generally prevailing in Western Anatolia. The region has generally been continuing its seismic activity under the controlmore » of normal faults. Considering the marine studies that are made and marine continuity of the faults which are on land in addition to the seismological and tectonic studies, the determination of seismic hazard in the Gulf of Gökova and its surroundings is also important in terms of introducing the earthquake scenarios with minimized errors.« less

Terrane accumulation and collapse in central Europe: seismic and rheological constraints

NASA Astrophysics Data System (ADS)

Meissner, R.

1999-05-01

An attempt is made to compare the tectonic units and their evolution in central Europe with the deep seismic velocity structure and patterns of reflectivity. Caledonian and Variscan terrane accretion and orogenic collapse dominate the tectonic development in central and western Europe and have left their marks in a distinct velocity structure and crustal thickness as well as in the various reflectivity patterns. Whereas the memory of old collisional structures is still preserved in the rigid upper crust, collapse processes have formed and modified the lower crust. They have generally created rejuvenated, thin crusts with shallow Mohos. In the Variscan internides, the center of collision and post-orogenic heat pulses, the lower crust developed strong and thick seismic lamellae, the (cooler) externides show a thrust and shear pattern in the whole crust, and the North German Basin experienced large mafic intrusions in the lower crust and developed a high-velocity structure with only very thin lamellae on top of the Moho. The various kinds of reflectivity patterns in the lithosphere can be explained by a thermo-rheological model from terrane collision, with crustal thickening to collapse in a hot, post-orogenic setting.

New Insights from Seismic Imaging over the Youanmi Terrane, Western Australia

NASA Astrophysics Data System (ADS)

Ahmadi, Omid; Juhlin, Christopher

2014-05-01

The Youanmi terrane is located in the central parts of the Yilgarn craton, Western Australia, an Archean granite-greenstone unit containing numerous mineral deposits such as gold, base metals, nickel, uranium and gemstones. The terrane is surrounded by the Kalgoorlie and Narryer terranes to the east and west, respectively. To the southwest it is bounded by the South West terrane. In order to study the transitions between the Youanmi terrane and the surrounding terranes, as well as identifying potential mineral rich areas, the Geological Survey of Western Australia acquired three deep crustal 2D seismic profiles with a total length of about 700 km in 2010. Correlated record lengths of 20 seconds allow the deep structure of the crust to be investigated with the data, down to Moho depths and greater. Initial processing using a conventional 2D flow show a highly reflective crust with several interesting features. We have now reprocessed the data following mainly the previous processing flow, but with a focus on the shallower crust, less than 10 seconds (about 27 km). Due to the complex geology in the region, 3D aspects of the structures need to be considered in the data processing. Therefore, we investigated the effect of cross-dip corrections to the data. The cross-dip correction has two advantages; (i) reflections are more coherent and enhanced after the correction and (ii) the orientation and dip angle of the geological structures of the corresponding reflections can be identified in the cross-line direction. Where the profiles intersect each other sparse 3D processing can be performed. First arrival travel-time tomography was also tested on parts of the dataset. Travel-time inversion may provide better velocity models at shallow depths than standard reflection seismic processing provides. Preliminary results show that the travel-time tomography has a depth of investigation of about 1 km, a depth that is of interest for mining purposes. Therefore, the tomography results in combination with the 3D processing of the Youanmi data set may be relevant to the mining industry active in the Youanmi terrane of Western Australia.

Chirp seismic-reflection data from the Baltimore, Washington, and Norfolk Canyons, U.S. mid-Atlantic margin

USGS Publications Warehouse

Obelcz, Jeffrey B.; Brothers, Daniel S.; ten Brink, Uri S.; Chaytor, Jason D.; Worley, Charles R.; Moore, Eric M.

2014-01-01

A large number of high-resolution geophysical surveys between Cape Hatteras and Georges Bank have been conducted by federal, state, and academic institutions since the turn of the century. A major goal of these surveys is providing a continuous view of bathymetry and shallow stratigraphy at the shelf edge in order to assess levels of geological activity during the current sea level highstand. In 2012, chirp seismic-reflection data was collected by the U.S. Geologial Survey aboard the motor vessel Tiki XIV near three United States mid-Atlantic margin submarine canyons. These data can be used to further our understanding of passive continental margin processes during the Holocene, as well as providing valuable information regarding potential submarine geohazards.

Seismic Wave Velocity in the Subducted Oceanic Crust from Autocorrelation of Tectonic Tremor Signals

NASA Astrophysics Data System (ADS)

Ducellier, A.; Creager, K.

2017-12-01

Hydration and dehydration of minerals in subduction zones play a key role in the geodynamic processes that generate seismicity and that allow tectonic plates to subduct. Detecting the presence of water in the subducted plate is thus crucial to better understand the seismogenesis and the consequent seismic hazard. A landward dipping, low velocity layer has been detected in most subduction zones. In Cascadia, this low velocity zone is characterized by a low S-wave velocity and a very high Poisson's ratio, which has been interpreted as high pore-fluid pressure in the upper half part of the subducted oceanic crust. Most previous studies were based on seismic reflection imaging, receiver function analysis, or body wave tomography, with seismic sources located far from the low velocity zone. In contrast, the sources of the tectonic tremors generated during Episodic Tremor and Slip (ETS) events are located on the plate boundary. As the sources of the tremors are much closer to the low velocity zone, seismic waves recorded during ETS events should illuminate the area with greater precision. Most methods to detect and locate tectonic tremors and low-frequency earthquakes are based on the cross correlation of seismic signals; either signals at the same station for different events, or the same event at different stations. We use the autocorrelation of the seismic signal recorded by eight arrays of stations, located in the Olympic Peninsula, Washington. Each tremor, assumed to be on the plate boundary, generates a direct wave and reflected and converted waves from both the strong shear-wave velocity contrast in the mid-oceanic crust, and from the Moho of the subducted oceanic crust. The time lag between the arrivals of these different waves at a seismic station corresponds to a peak of amplitude on the autocorrelation signals. Using the time lags observed for different locations of the tremor source, we intend to invert for the seismic wave velocity of the subducted oceanic crust under the arrays. Identifying zones with lower S-wave velocity and a high Poisson's ratio will then help detecting the presence of water in the subducted oceanic crust. Our ultimate goal is contributing to a better understanding of the mechanism of ETS and subduction zone processes.

The T-Reflection and the deep crustal structure of the Vøring Margin offshore Mid-Norway

NASA Astrophysics Data System (ADS)

Abdelmalak, M. M.; Faleide, J. I.; Planke, S.; Gernigon, L.; Zastrozhnov, D.; Shephard, G. E.; Myklebust, R.

2017-12-01

Volcanic passive margins are characterized by massive occurrence of mafic extrusive and intrusive rocks, before and during plate breakup, playing major role in determining the evolution pattern and the deep structure of magma-rich margins. Deep seismic reflection data frequently provide imaging of strong continuous reflections in the middle/lower crust. In this context, we have completed a detailed 2D seismic interpretation of the deep crustal structure of the Vøring volcanic margin, offshore mid-Norway, where high-quality seismic data allow the identification of high-amplitude reflections, locally referred to as the T-Reflection (TR). Using the dense seismic grid we have mapped the top of the TR in order to compare it with filtered Bouguer gravity anomalies and seismic refraction data. The TR is identified between 7 and 10 s. Sometimes it consists of one single smooth reflection. However, it is frequently associated with a set of rough multiple reflections displaying discontinuous segments with varying geometries, amplitude and contact relationships. The TR seems to be connected to deep sill networks and locally located at the continuation of basement high structures or terminates over fractures and faults. The spatial correlation between the filtered positive Bouguer gravity anomalies and the TR indicates that the latter represents a high impedance boundary contrast associated with a high-density/velocity body. Within an uncertainty of ± 2.5 km, the depth of the mapped TR is found to correspond to the depth of the top of the Lower Crustal Body (LCB), characterized by high P-wave velocities (>7 km/s), in 50% of the outer Vøring Margin areas, whereas different depths between the TR and the top LCB are estimated for the remaining areas. We present a tectonic scenario, where a large part of the deep structure could be composed of preserved upper continental basement and middle to lower crustal lenses of inherited and intruded high-grade metamorphic rocks. Deep intrusions into the faulted crustal blocks are responsible for the rough character of the TR, whereas intrusions into the lower crust and detachment faults are likely responsible for its smoother appearance. Deep magma intrusions can be responsible for metamorphic processes leading to an increased velocity of the lower crust of more than 7 km/s.

Crustal evolution of Eocene paleo arc around Ogasawara region obtained by seismic reflection survey

NASA Astrophysics Data System (ADS)

Yamashita, M.; Takahashi, N.; Kodaira, S.; Miura, S.; Ishizuka, O.; Tatsumi, Y.

2011-12-01

The Izu-Bonin (Ogasawara)-Mariana (IBM) arc is known to the typical oceanic island arc, and it is the most suitable area to understand the growth process of island arc. The existence of two paleo arc which consists of Oligocene and Eocene paleo age is known in IBM forearc region by geological and geophysical studies. The Ogasawara ridge is also known to locate the initial structure of arc evolution from geologic sampling of research submersible. In this region, IODP drilling site: IBM-2 is proposed in order to understand the temporal and spatial change in arc crust composition from 50 to 40Ma magmatism. Site IBM-2 consists of two offset drilling holes (BON-1, BON-2). BON-1 designed to first encounter forearc basalt and will reach the sheeted dykes. BON-2 will start in boninites and finish in fore arc basalts. The purpose of these drilling is sampling the full volcanic stratigraphy from gabbro to boninite. There is no seismic data around BON-1 and BON-2, therefore it is need to conduct the multi-channel seismic reflection survey. Japan Agency for Marine-Earth Science and Technology carried out multi-channel seismic reflection survey and wide-angle reflection survey using 7,800 cu.in. air gun, 5 km streamer with 444 ch hydrophones and 40 OBSs in March 2011. We obtained two seismic reflection profiles of lines KT06 and KT07 along the paleo arc around Ogasawara ridge. Line KT06 located the north side of Ogasawara ridge. Line KT07 located the trench side of Ogasawara ridge. Lines KT06 is also deployed the OBSs every 5 km interval. Thin sediments are covered with basement in both survey lines. There are some sediment filled in depression topography. The low-frequency reflection from the top of subducting Pacific plate is recognized in line KT06. The continuity of this reflection is not clear due to the complicated bathymetry. The displacement of basement in northern side of Ogasawara ridge is identified along the lineament of bathymetry in Line 06. This structure is estimated to relate the deformation in the Ogasawara Trough and lineament of paleo arc. We will discuss the relationship this lineament and deformation with regard to activity such as post volcanism.

Hybrid sparse blind deconvolution: an implementation of SOOT algorithm to real data

NASA Astrophysics Data System (ADS)

Pakmanesh, Parvaneh; Goudarzi, Alireza; Kourki, Meisam

2018-06-01

Getting information of seismic data depends on deconvolution as an important processing step; it provides the reflectivity series by signal compression. This compression can be obtained by removing the wavelet effects on the traces. The recently blind deconvolution has provided reliable performance for sparse signal recovery. In this study, two deconvolution methods have been implemented to the seismic data; the convolution of these methods provides a robust spiking deconvolution approach. This hybrid deconvolution is applied using the sparse deconvolution (MM algorithm) and the Smoothed-One-Over-Two algorithm (SOOT) in a chain. The MM algorithm is based on the minimization of the cost function defined by standards l1 and l2. After applying the two algorithms to the seismic data, the SOOT algorithm provided well-compressed data with a higher resolution than the MM algorithm. The SOOT algorithm requires initial values to be applied for real data, such as the wavelet coefficients and reflectivity series that can be achieved through the MM algorithm. The computational cost of the hybrid method is high, and it is necessary to be implemented on post-stack or pre-stack seismic data of complex structure regions.

Lithofacies and seismic-reflection interpretation of temperate glacimarine sedimentation in Tarr Inlet, Glacier Bay, Alaska

USGS Publications Warehouse

Cai, J.; Powell, R.D.; Cowan, E.A.; Carlson, P.R.

1997-01-01

High-resolution seismic-reflection profiles of sediment fill within Tart Inlet of Glacier Bay, Alaska, show seismic facies changes with increasing distance from the glacial termini. Five types of seismic facies are recognized from analysis of Huntec and minisparker records, and seven lithofacies are determined from detailed sedimentologic study of gravity-, vibro- and box-cores, and bottom grab samples. Lithofacies and seismic facies associations, and fjord-floor morphology allow us to divide the fjord into three sedimentary environments: ice-proximal, iceberg-zone and ice-distal. The ice-proximal environment, characterized by a morainal-bank depositional system, can be subdivided into bank-back, bank-core and bank-front subenvironments, each of which is characterized by a different depositional subsystem. A bank-back subsystem shows chaotic seismic facies with a mounded surface, which we infer consists mainly of unsorted diamicton and poorly sorted coarse-grained sediments. A bank-core depositional subsystem is a mixture of diamicton, rubble, gravel, sand and mud. Seismic-reflection records of this subsystem are characterized by chaotic seismic facies with abundant hyperbolic diffractions and a hummocky surface. A bank-front depositional subsystem consists of mainly stratified and massive sand, and is characterized by internal hummocky facies on seismic-reflection records with significant surface relief and sediment gravity flow channels. The depositional system formed in the iceberg-zone environment consists of rhythmically laminated mud interbedded with thin beds of weakly stratified diamicton and stratified or massive sand and silt. On seismic-reflection profiles, this depositional system is characterized by discontinuously stratified facies with multiple channels on the surface in the proximal zone and a single channel on the largely flat sediment surface in the distal zone. The depositional system formed in the ice-distal environment consists of interbedded homogeneous or laminated mud and massive or stratified sand and coarse silt. This depositional system shows continuously stratified seismic facies with smooth and flat surfaces on minisparker records, and continuously stratified seismic facies which are interlayered with thin weakly stratified facies on Huntec records.

Report for explosion and earthquake data acquired in the 1999 Seismic Hazards Investigation of Puget Sound (SHIPS), Washington

USGS Publications Warehouse

Brocher, Thomas M.; Pratt, Thomas L.; Miller, Kate C.; Tréhu, Anne M.; Snelson, Catherine M.; Weaver, Craig S.; Creager, Ken C.; Crosson, Robert S.; ten Brink, Uri S.; Alvarez, Marcos G.; Harder, Steven H.; Asudeh, Isa

2000-01-01

This report describes the acquisition, processing, and quality of seismic reflection and refraction data obtained in the Seattle basin, central Puget Lowland, western Washington, in September 1999 during the Seismic Hazards Investigation of Puget Sound (SHIPS). As a sequel to the 1998 SHIPS air gun experiment (also known as 'Wet SHIPS'), the 1999 experiment, nicknamed 'Dry SHIPS,' acquired a 112-km-long east-west trending multichannel seismic reflection and refraction line in the Seattle basin. One thousand and eight seismographs were deployed at a nominal spacing of 100 meters, and 29 shot points were detonated at approximately 4 km intervals along the seismic line. The wide-angle seismic profile was designed to (1) determine the E-W geometry of Seattle basin, (2) measure the seismic velocities within the basin, and (3) define the basement structure underlying the Seattle basin. In this report, we describe the acquisition of these data, discuss the processing and merging of the data into common shot gathers, and illustrate the acquired profiles. We also describe the format and content of the archival tapes containing the SEGY-formatted, common-shot gathers. Data quality is variable, but useful data were acquired from all 29 shot points fired along the Dry SHIPS seismic line. The data show pronounced travel time delays associated with the low velocity sedimentary rocks filling the Seattle basin. Thirty-five REFTEK stations, deployed at 4 km intervals along the Dry SHIPS line, recorded 26 regional earthquakes and blasts and 17 teleseismic events, including the main shock and several aftershocks of the Mw=7.6 Chi-Chi (Taiwan) earthquake of 9/20/1999. The teleseismic recordings of the Chi-Chi (Taiwan) mainshock provide useful signals down to 10 second periods. They document a significant (factor between 5 and 10) focusing of compressional- and shear-wave energy by the Seattle basin at periods between 1 and 2 seconds relative to 'bedrock' sites east and west of the basin. Signal durations in the Seattle basin were also substantially increased relative to 'bedrock' sites in the Olympic peninsula and Cascade foothills.

Development of Vertical Cable Seismic System

NASA Astrophysics Data System (ADS)

Asakawa, E.; Murakami, F.; Sekino, Y.; Okamoto, T.; Ishikawa, K.; Tsukahara, H.; Shimura, T.

2011-12-01

In 2009, Ministry of Education, Culture, Sports, Science and Technology(MEXT) started the survey system development for Hydrothermal deposit. We proposed the Vertical Cable Seismic (VCS), the reflection seismic survey with vertical cable above seabottom. VCS has the following advantages for hydrothermal deposit survey. (1) VCS is an efficient high-resolution 3D seismic survey in limited area. (2) It achieves high-resolution image because the sensors are closely located to the target. (3) It avoids the coupling problems between sensor and seabottom that cause serious damage of seismic data quality. (4) Because of autonomous recording system on sea floor, various types of marine source are applicable with VCS such as sea-surface source (GI gun etc.) , deep-towed or ocean bottom source. Our first experiment of 2D/3D VCS surveys has been carried out in Lake Biwa, JAPAN, in November 2009. The 2D VCS data processing follows the walk-away VSP, including wave field separation and depth migration. Seismic Interferometry technique is also applied. The results give much clearer image than the conventional surface seismic. Prestack depth migration is applied to 3D data to obtain good quality 3D depth volume. Seismic Interferometry technique is applied to obtain the high resolution image in the very shallow zone. Based on the feasibility study, we have developed the autonomous recording VCS system and carried out the trial experiment in actual ocean at the water depth of about 400m to establish the procedures of deployment/recovery and to examine the VC position or fluctuation at seabottom. The result shows that the VC position is estimated with sufficient accuracy and very little fluctuation is observed. Institute of Industrial Science, the University of Tokyo took the research cruise NT11-02 on JAMSTEC R/V Natsushima in February, 2011. In the cruise NT11-02, JGI carried out the second VCS survey using the autonomous VCS recording system with the deep towed source provided by Institute of Industrial Science, the University of Tokyo. It generates high frequency acoustic waves around 1kHz. The acquired VCS data clearly shows the reflections and currently being processed for imaging the subsurface structure.

Imaging the Alpine Fault: preliminary results from a detailed 3D-VSP experiment at the DFDP-2 drill site in Whataroa, New Zealand

NASA Astrophysics Data System (ADS)

Lay, Vera; Bodenburg, Sascha; Buske, Stefan; Townend, John; Kellett, Richard; Savage, Martha; Schmitt, Douglas; Constantinou, Alexis; Eccles, Jennifer; Lawton, Donald; Hall, Kevin; Bertram, Malcolm; Gorman, Andrew

2017-04-01

The plate-bounding Alpine Fault in New Zealand is an 850 km long transpressive continental fault zone that is late in its earthquake cycle. The Deep Fault Drilling Project (DFDP) aims to deliver insight into the geological structure of this fault zone and its evolution by drilling and sampling the Alpine Fault at depth. Previously analysed 2D reflection seismic data image the main Alpine Fault reflector at a depth of 1.5-2.2 km with a dip of approximately 48° to the southeast below the DFDP-2 borehole. Additionally, there are indications of a more complex 3D fault structure with several fault branches which have not yet been clearly imaged in detail. For that reason we acquired a 3D-VSP seismic data set at the DFDP-2 drill site in January 2016. A zero-offset VSP and a walk-away VSP survey were conducted using a Vibroseis source. Within the borehole, a permanently installed "Distributed Acoustic Fibre Optic Cable" (down to 893 m) and a 3C Sercel slimwave tool (down to 400 m) were used to record the seismic wavefield. In addition, an array of 160 three-component receivers with a spacing of 10 m perpendicular and 20 m parallel to the main strike of the Alpine Fault was set up and moved successively along the valley to record reflections from the main Alpine Fault zone over a broad depth range and to derive a detailed 3D tomographic velocity model in the hanging wall. We will show a detailed 3D velocity model derived from first-arrival traveltime tomography. Subsets of the whole data set were analysed separately to estimate the corresponding ray coverage and the reliability of the observed features in the obtained velocity model. By testing various inversion parameters and starting models, we derived a detailed near-surface velocity model that reveals the significance of the old glacial valley structures. Hence, this new 3D model improves the velocity model derived previously from a 2D seismic profile line in that area. Furthermore, processing of the dense 3C data shows clear reflections on both inline and crossline profiles. Correlating single reflection events enables us to identify the origin of reflections recorded in the data and reveal their 3D character. This array data gives strong evidence for reflections coming from the side, possibly from the steeply dipping valley flanks. Finally, the data will be processed using advanced seismic imaging methods to derive a detailed structural image of the valley and the fault zone at depth. Thus, the results will provide a detailed basis for a seismic site characterization at the DFDP-2 drill site, that will be of crucial importance for further structural and geological investigations of the architecture of the Alpine Fault in this area.

Interpretation of electrical resistivity data acquired at the Aurora plant site

DOT National Transportation Integrated Search

2008-02-01

MST proposes to acquire high-resolution reflection seismic data at the Knight Hawk Coal Company construction site. These geophysical data will be processed, analyzed and interpreted with the objective of locating and mapping any subsurface voids that...

Pulling the rug out from under California: Seismic images of the Mendocino Triple Junction region

USGS Publications Warehouse

Tréhu, Anne M.

1995-01-01

In 1993 and 1994 a network of large-aperture seismic profiles was collected to image the crustal and upper-mantle structure beneath northern California and the adjacent continental margin. The data include approximately 650 km of onshore seismic refraction/reflection data, 2000 km of off-shore multichannel seismic (MCS) reflection data, and simultaneous onshore and offshore recording of the MCS airgun source to yield large-aperture data. Scientists from more than 12 institutions were involved in data acquisition.

The crustal structure in the transition zone between the western and eastern Barents Sea

NASA Astrophysics Data System (ADS)

Shulgin, Alexey; Mjelde, Rolf; Faleide, Jan Inge; Høy, Tore; Flueh, Ernst; Thybo, Hans

2018-04-01

We present a crustal-scale seismic profile in the Barents Sea based on new data. Wide-angle seismic data were recorded along a 600 km long profile at 38 ocean bottom seismometer and 52 onshore station locations. The modeling uses the joint refraction/reflection tomography approach where co-located multi-channel seismic reflection data constrain the sedimentary structure. Further, forward gravity modeling is based on the seismic model. We also calculate net regional erosion based on the calculated shallow velocity structure.

Seismic signatures of carbonate caves affected by near-surface absorptions

NASA Astrophysics Data System (ADS)

Rao, Ying; Wang, Yanghua

2015-12-01

The near-surface absorption within a low-velocity zone generally has an exponential attenuation effect on seismic waves. But how does this absorption affect seismic signatures of karstic caves in deep carbonate reservoirs? Seismic simulation and analysis reveals that, although this near-surface absorption attenuates the wave energy of a continuous reflection, it does not alter the basic kinematic shape of bead-string reflections, a special seismic characteristic associated with carbonate caves in the Tarim Basin, China. Therefore, the bead-strings in seismic profiles can be utilized, with a great certainty, for interpreting the existence of caves within the deep carbonate reservoirs and for evaluating their pore spaces. Nevertheless, the difference between the central frequency and the peak frequency is increased along with the increment in the absorption. While the wave energy of bead-string reflections remains strong, due to the interference of seismic multiples generated by big impedance contrast between the infill materials of a cave and the surrounding carbonate rocks, the central frequency is shifted linearly with respect to the near-surface absorption. These two features can be exploited simultaneously, for a stable attenuation analysis of field seismic data.

Seismic imaging of esker structures from a combination of high-resolution broadband multicomponent streamer and wireless sensors, Turku-Finland

NASA Astrophysics Data System (ADS)

Maries, Georgiana; Ahokangas, Elina; Mäkinen, Joni; Pasanen, Antti; Malehmir, Alireza

2015-04-01

Eskers and glaciofluvial interlobate formations, mainly composed of sands and gravels and deposited in winding ridges, define the locations of glacial melt-water streams. These sediments, porous and permeable, form the most important aquifers in Finland and are often used as aggregates or for artificial aquifer recharge. The Virttaankangas interlobate suite and artificial aquifer recharge plant provides the entire water supply for the city of Turku and therefore an accurate delineation of the aquifer is critical for long term planning and sustainable use of these natural resources. The study area is part of the Säkylänharju-Virttaankangas Glaciofluvial esker-chain complex and lies on an igneous, crystalline basement rocks. To provide complementary information to existing boreholes and GPR studies at the site, such as identification of potential esker cores, planning for a water extraction, fractured bedrock and possible kettle holes, a new seismic investigation was designed and carried out during summer 2014. Two seismic profiles each about 1 km long were acquired using a newly developed 200 m long prototype, comprising of 80-3C MEMs-based, landstreamer system. To provide velocity information at larger depths (and longer offsets), fifty-two 10-Hz 1C wireless sensors spaced at about every 20 m were used. A Bobcat mounted drop-hammer source, generating three hits per source location, was used as the seismic source. This proved to be a good choice given the attenuative nature of the dry sediments down to about 20 m depth. One of the seismic lines overlaps an existing streamer survey and thus allows a comparison between the system used in this study and the one employed before. Except at a few places where the loose sands mixed with leaves affected the coupling, the data quality is excellent with several reflections identifiable in the raw shot gathers. First arrivals were easily identifiable in almost all the traces and shots and this allowed obtaining velocity information down to the bedrock, 50-80 m depth, using a diving-wave travel-time tomographic inversion method. The reflection data processing was challenging due to the large velocity contrasts between the dry sediments and the saturated ones. A careful velocity analysis was the key-processing step apart from filtering source-generated noise. The seismic refraction and reflection sections correlate well with the existing borehole information. Depth to the bedrock from the boreholes matches well the high velocity zones. A zone of low velocity associated with a flat reflection at about 20 m depth below the topography shows a good correspondence with the groundwater table. A major morphologically undetectable kettle hole (MUKH) is clearly observed in the reflection data as a concave reflectivity zone, with indication of normal faulting. The deposits show alternating coarse- and fine-grained sediments with channel structures representing subaqueous fans. An esker core is defined from a zone of reflectivity from coarser-grained materials overlaid by proximal fan sediments of the main aquifer. Acknowledgments: Formas (http://www.trust-geoinfra.se), Turku Region Water Ltd., University of Turku, GTK

Automatic Classification of volcano-seismic events based on Deep Neural Networks.

NASA Astrophysics Data System (ADS)

Titos Luzón, M.; Bueno Rodriguez, A.; Garcia Martinez, L.; Benitez, C.; Ibáñez, J. M.

2017-12-01

Seismic monitoring of active volcanoes is a popular remote sensing technique to detect seismic activity, often associated to energy exchanges between the volcano and the environment. As a result, seismographs register a wide range of volcano-seismic signals that reflect the nature and underlying physics of volcanic processes. Machine learning and signal processing techniques provide an appropriate framework to analyze such data. In this research, we propose a new classification framework for seismic events based on deep neural networks. Deep neural networks are composed by multiple processing layers, and can discover intrinsic patterns from the data itself. Internal parameters can be initialized using a greedy unsupervised pre-training stage, leading to an efficient training of fully connected architectures. We aim to determine the robustness of these architectures as classifiers of seven different types of seismic events recorded at "Volcán de Fuego" (Colima, Mexico). Two deep neural networks with different pre-training strategies are studied: stacked denoising autoencoder and deep belief networks. Results are compared to existing machine learning algorithms (SVM, Random Forest, Multilayer Perceptron). We used 5 LPC coefficients over three non-overlapping segments as training features in order to characterize temporal evolution, avoid redundancy and encode the signal, regardless of its duration. Experimental results show that deep architectures can classify seismic events with higher accuracy than classical algorithms, attaining up to 92% recognition accuracy. Pre-training initialization helps these models to detect events that occur simultaneously in time (such explosions and rockfalls), increase robustness against noisy inputs, and provide better generalization. These results demonstrate deep neural networks are robust classifiers, and can be deployed in real-environments to monitor the seismicity of restless volcanoes.

Improved 3D seismic attribute mapping by CRS stacking instead of NMO stacking: Application to a geothermal reservoir in the Polish Basin

NASA Astrophysics Data System (ADS)

Pussak, Marcin; Bauer, Klaus; Stiller, Manfred; Bujakowski, Wieslaw

2014-04-01

Within a seismic reflection processing work flow, the common-reflection-surface (CRS) stack can be applied as an alternative for the conventional normal moveout (NMO) or the dip moveout (DMO) stack. The advantages of the CRS stack include (1) data-driven automatic determination of stacking operator parameters, (2) imaging of arbitrarily curved geological boundaries, and (3) significant increase in signal-to-noise (S/N) ratio by stacking far more traces than used in a conventional stack. In this paper we applied both NMO and CRS stackings to process a sparse 3D seismic data set acquired within a geothermal exploration study in the Polish Basin. The stacked images show clear enhancements in quality achieved by the CRS stack in comparison with the conventional stack. While this was expected from previous studies, we also found remarkable improvements in the quality of seismic attributes when the CRS stack was applied instead of the conventional stack. For the major geothermal target reservoir (Lower Jurassic horizon Ja1), we present a comparison between both stacking methods for a number of common attributes, including root-mean-square (RMS) amplitudes, instantaneous frequencies, coherency, and spectral decomposition attributes derived from the continuous wavelet transform. The attribute maps appear noisy and highly fluctuating after the conventional stack, and are clearly structured after the CRS stack. A seismic facies analysis was finally carried out for the Ja1 horizon using the attributes derived from the CRS stack by using self-organizing map clustering techniques. A corridor parallel to a fault system was identified, which is characterized by decreased RMS amplitudes and decreased instantaneous frequencies. In our interpretation, this region represents a fractured, fluid-bearing compartment within the sandstone reservoir, which indicates favorable conditions for geothermal exploitation.

Data Processing Methods for 3D Seismic Imaging of Subsurface Volcanoes: Applications to the Tarim Flood Basalt.

PubMed

Wang, Lei; Tian, Wei; Shi, Yongmin

2017-08-07

The morphology and structure of plumbing systems can provide key information on the eruption rate and style of basalt lava fields. The most powerful way to study subsurface geo-bodies is to use industrial 3D reflection seismological imaging. However, strategies to image subsurface volcanoes are very different from that of oil and gas reservoirs. In this study, we process seismic data cubes from the Northern Tarim Basin, China, to illustrate how to visualize sills through opacity rendering techniques and how to image the conduits by time-slicing. In the first case, we isolated probes by the seismic horizons marking the contacts between sills and encasing strata, applying opacity rendering techniques to extract sills from the seismic cube. The resulting detailed sill morphology shows that the flow direction is from the dome center to the rim. In the second seismic cube, we use time-slices to image the conduits, which corresponds to marked discontinuities within the encasing rocks. A set of time-slices obtained at different depths show that the Tarim flood basalts erupted from central volcanoes, fed by separate pipe-like conduits.

Understanding the Evolution of an Oceanic Intraplate Volcano From Seismic Reflection Data: A New Model for La Réunion, Indian Ocean

NASA Astrophysics Data System (ADS)

Lebas, E.; Le Friant, A.; Deplus, C.; de Voogd, B.

2018-02-01

High-resolution seismic reflection profiles gathered in 2006 on La Réunion submarine flanks and surrounding abyssal plain, enabled characterization of the seismostratigraphy architecture of the volcaniclastic apron. Four seismic units are defined beyond the edifice base: (1) a basal unit, interpreted as pelagic sediment predating La Réunion volcanism; (2) a second unit showing low- to medium-amplitude reflections, related to La Réunion emergence including the submarine explosive phase; (3) a high-amplitude seismic unit, associated with subaerial volcanic activity (i.e., mature island stage); and (4) an acoustically transparent unit, ascribed to erosion that currently affects the volcanic complex. Two prominent horizons delineate the base of the units II and III marking, respectively, the onset of La Réunion seamount explosive activity and the Piton des Neiges volcanic activity. Related isopach maps demonstrate: (1) the existence of a large proto-Piton des Neiges volcano during the first building phase of the volcanic complex, and (2) the central role of the Piton des Neiges volcano during the second phase. Shield growth stage of the Piton de la Fournaise volcano is also captured in the upper part of the volcaniclastic apron, attesting to its recent contribution. Seismic facies identified in the apron highlight a prevalence of sedimentary and reworking processes since the onset of the volcanism compared to catastrophic flank collapses. We present here a new model of evolution for La Réunion volcanic complex since the onset of the volcanism and argue that a major proto Piton des Neiges-Piton des Neiges volcanic complex controls La Réunion present-day morphology.

Reflection processing of the large-N seismic data from the Source Physics Experiment (SPE)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Paschall, Olivia C.

2016-07-18

The purpose of the SPE is to develop a more physics-based model for nuclear explosion identification to understand the development of S-waves from explosion sources in order to enhance nuclear test ban treaty monitoring.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Burnison, Shaughn; Livers-Douglas, Amanda; Barajas-Olalde, Cesar

The scalable, automated, semipermanent seismic array (SASSA) project led and managed by the Energy & Environmental Research Center (EERC) was designed as a 3-year proof-of-concept study to evaluate and demonstrate an innovative application of the seismic method. The concept was to use a sparse surface array of 96 nodal seismic sensors paired with a single, remotely operated active seismic source at a fixed location to monitor for CO 2 saturation changes in a subsurface reservoir by processing the data for time-lapse changes at individual, strategically chosen reservoir reflection points. The combination of autonomous equipment and modern processing algorithms was usedmore » to apply the seismic method in a manner different from the normal paradigm of collecting a spatially dense data set to produce an image. It was used instead to monitor individual, strategically chosen reservoir reflection points for detectable signal character changes that could be attributed to the passing of a CO 2 saturation front or, possibly, changes in reservoir pressure. Data collection occurred over the course of 1 year at an oil field undergoing CO 2 injection for enhanced oil recovery (EOR) and focused on four overlapping “five-spot” EOR injector–producer patterns. Selection, procurement, configuration, installation, and testing of project equipment and collection of five baseline data sets were completed in advance of CO 2 injection within the study area. Weekly remote data collection produced 41 incremental time-lapse records for each of the 96 nodes. Validation was provided by two methods: 1) a conventional 2-D seismic line acquired through the center of the study area before injection started and again after the project ended and processed in a time-lapse manner and 2) by CO 2 saturation maps created from reservoir simulations based on injection and production history matching. Interpreted results were encouraging but mixed, with indications of changes likely due to the presence of CO 2 on some node reflection points where and when effects would be expected and noneffects where no CO 2 was expected, while results at some locations where simulation outputs suggested CO 2 should be present were ambiguous. Acquisition noise impacted interpretation of data at several locations. Many lessons learned were generated by the study to inform and improve results on a follow-up study. The ultimate aim of the project was to evaluate whether deployment of a SASSA technology can provide a useful and cost-effective monitoring solution for future CO 2 injection projects. The answer appears to be affirmative, with the expectation that lessons learned applied to future iterations, together with technology advances, will likely result in significant improvements.« less

Properties of seismic absorption induced reflections

NASA Astrophysics Data System (ADS)

Zhao, Haixia; Gao, Jinghuai; Peng, Jigen

2018-05-01

Seismic reflections at an interface are often regarded as the variation of the acoustic impedance (product of seismic velocity and density) in a medium. In fact, they can also be generated due to the difference in absorption of the seismic energy. In this paper, we investigate the properties of such reflections. Based on the diffusive-viscous wave equation and elastic diffusive-viscous wave equation, we investigate the dependency of the reflection coefficients on frequency, and their variations with incident angles. Numerical results at a boundary due to absorption contrasts are compared with those resulted from acoustic impedance variation. It is found that, the reflection coefficients resulted from absorption depend significantly on the frequency especially at lower frequencies, but vary very slowly at small incident angles. At the higher frequencies, the reflection coefficients of diffusive-viscous wave and elastic diffusive-viscous wave are close to those of acoustic and elastic cases, respectively. On the other hand, the reflections caused by acoustic impedance variation are independent of frequency but vary distinctly with incident angles before the critical angle. We also investigate the difference between the seismograms generated in the two different media. The numerical results show that the amplitudes of these reflected waves are attenuated and their phases are shifted. However, the reflections obtained by acoustic impedance contrast, show no significant amplitude attenuation and phase shift.

Wide-angle Marine Seismic Refraction Imaging of Vertical Faults: Pre-Stack Turning Wave Migrations of Synthetic Data and Implications for Survey Design

NASA Astrophysics Data System (ADS)

Miller, N. C.; Lizarralde, D.; McGuire, J.; Hole, J. A.

2006-12-01

We consider methodologies, including survey design and processing algorithms, which are best suited to imaging vertical reflectors in oceanic crust using marine seismic techniques. The ability to image the reflectivity structure of transform faults as a function of depth, for example, may provide new insights into what controls seismicity along these plate boundaries. Turning-wave migration has been used with success to image vertical faults on land. With synthetic datasets we find that this approach has unique difficulties in the deep ocean. The fault-reflected crustal refraction phase (Pg-r) typically used in pre-stack migrations is difficult to isolate in marine seismic data. An "imagable" Pg-r is only observed in a time window between the first arrivals and arrivals from the sediments and the thick, slow water layer at offsets beyond ~25 km. Ocean- bottom seismometers (OBSs), as opposed to a long surface streamer, must be used to acquire data suitable for crustal-scale vertical imaging. The critical distance for Moho reflections (PmP) in oceanic crust is also ~25 km, thus Pg-r and PmP-r are observed with very little separation, and the fault-reflected mantle refraction (Pn-r) arrives prior to Pg-r as the observation window opens with increased OBS-to-fault distance. This situation presents difficulties for "first-arrival" based Kirchoff migration approaches and suggests that wave- equation approaches, which in theory can image all three phases simultaneously, may be more suitable for vertical imaging in oceanic crust. We will present a comparison of these approaches as applied to a synthetic dataset generated from realistic, stochastic velocity models. We will assess their suitability, the migration artifacts unique to the deep ocean, and the ideal instrument layout for such an experiment.

Geophysical and geochemical constraints on the geodynamic origin of the Vrancea Seismogenic Zone Romania

NASA Astrophysics Data System (ADS)

Fillerup, Melvin A.

The Vrancea Seismogenic Zone (VSZ) of Romania is a steeply NW-dipping volume (30 x 70 x 200 km) of intermediate-depth seismicity in the upper mantle beneath the bend zone of the Eastern Carpathians. The majority of tectonic models lean heavily on subduction processes to explain the Vrancea mantle seismicity and the presence of a Miocene age calc-alkaline volcanic arc in the East Carpathian hinterland. However, recent deep seismic reflection data collected over the Eastern Carpathian bend zone image an orogen lacking (1) a crustal root and (2) dipping crustal-scale fabrics routinely imaged in modern and ancient subduction zones. The DRACULA I and DACIA-PLAN deep seismic reflection profiles show that the East Carpathian orogen is supported by crust only 30-33 km thick while the Focsani basin (foreland) and Transylvanian basin (hinterland) crust is 42 km and 46 km thick respectively. Here the VSZ is interpreted as the former Eastern Carpathian orogenic root which was removed as a result of continental lithospheric delamination and is seismically foundering beneath the East Carpathian bend zone. Because large volumes of calc-alkaline volcanism are typically associated with subduction settings existing geochemical analyses from the Calimani, Gurghiu, and Harghita Mountains (CGH) have been reinterpreted in light of the seismic data which does not advocate the subduction of oceanic lithosphere. CGH rocks exhibit a compositional range from basalt to rhyolite, many with high-Mg# (Mg/Mg+Fe > 0.60), high-Sr (>1000 ppm), and elevated delta-O18 values (6-8.7 /) typical of arc lavas, and are consistent with mixing of mantle-derived melts with a crustal component. The 143Nd/144Nd (0.5123-0.5129) and 87Sr/86Sr (0.7040-0.7103) ratios similarly suggest mixing of mantle and crustal end members to obtain the observed isotopic compositions. A new geochemical model is presented whereby delamination initiates a geodynamic process like subduction but with the distinct absence of subducted oceanic lithosphere to produce the CGH lavas. The origin of the VSZ presented here suggests that the delamination of continental lithosphere is a process capable of producing mantle earthquakes and calc-alkaline volcanism without subduction tectonics.

TkPl_SU: An Open-source Perl Script Builder for Seismic Unix

NASA Astrophysics Data System (ADS)

Lorenzo, J. M.

2017-12-01

TkPl_SU (beta) is a graphical user interface (GUI) to select parameters for Seismic Unix (SU) modules. Seismic Unix (Stockwell, 1999) is a widely distributed free software package for processing seismic reflection and signal processing. Perl/Tk is a mature, well-documented and free object-oriented graphical user interface for Perl. In a classroom environment, shell scripting of SU modules engages students and helps focus on the theoretical limitations and strengths of signal processing. However, complex interactive processing stages, e.g., selection of optimal stacking velocities, killing bad data traces, or spectral analysis requires advanced flows beyond the scope of introductory classes. In a research setting, special functionality from other free seismic processing software such as SioSeis (UCSD-NSF) can be incorporated readily via an object-oriented style to programming. An object oriented approach is a first step toward efficient extensible programming of multi-step processes, and a simple GUI simplifies parameter selection and decision making. Currently, in TkPl_SU, Perl 5 packages wrap 19 of the most common SU modules that are used in teaching undergraduate and first-year graduate student classes (e.g., filtering, display, velocity analysis and stacking). Perl packages (classes) can advantageously add new functionality around each module and clarify parameter names for easier usage. For example, through the use of methods, packages can isolate the user from repetitive control structures, as well as replace the names of abbreviated parameters with self-describing names. Moose, an extension of the Perl 5 object system, greatly facilitates an object-oriented style. Perl wrappers are self-documenting via Perl programming document markup language.

Characterization of gas hydrate distribution using conventional 3D seismic data in the Pearl River Mouth Basin, South China Sea

USGS Publications Warehouse

Wang, Xiujuan; Qiang, Jin; Collett, Timothy S.; Shi, Hesheng; Yang, Shengxiong; Yan, Chengzhi; Li, Yuanping; Wang, Zhenzhen; Chen, Duanxin

2016-01-01

A new 3D seismic reflection data volume acquired in 2012 has allowed for the detailed mapping and characterization of gas hydrate distribution in the Pearl River Mouth Basin in the South China Sea. Previous studies of core and logging data showed that gas hydrate occurrence at high concentrations is controlled by the presence of relatively coarse-grained sediment and the upward migration of thermogenic gas from the deeper sediment section into the overlying gas hydrate stability zone (BGHSZ); however, the spatial distribution of the gas hydrate remains poorly defined. We used a constrained sparse spike inversion technique to generate acoustic-impedance images of the hydrate-bearing sedimentary section from the newly acquired 3D seismic data volume. High-amplitude reflections just above the bottom-simulating reflectors (BSRs) were interpreted to be associated with the accumulation of gas hydrate with elevated saturations. Enhanced seismic reflections below the BSRs were interpreted to indicate the presence of free gas. The base of the BGHSZ was established using the occurrence of BSRs. In areas absent of well-developed BSRs, the BGHSZ was calculated from a model using the inverted P-wave velocity and subsurface temperature data. Seismic attributes were also extracted along the BGHSZ that indicate variations reservoir properties and inferred hydrocarbon accumulations at each site. Gas hydrate saturations estimated from the inversion of acoustic impedance of conventional 3D seismic data, along with well-log-derived rock-physics models were also used to estimate gas hydrate saturations. Our analysis determined that the gas hydrate petroleum system varies significantly across the Pearl River Mouth Basin and that variability in sedimentary properties as a product of depositional processes and the upward migration of gas from deeper thermogenic sources control the distribution of gas hydrates in this basin.

Crustal thickness across the Trans-European Suture Zone from ambient noise autocorrelations

NASA Astrophysics Data System (ADS)

Becker, G.; Knapmeyer-Endrun, B.

2018-02-01

We derive autocorrelations from ambient seismic noise to image the reflectivity of the subsurface and to extract the Moho depth beneath the stations for two different data sets in Central Europe. The autocorrelations are calculated by smoothing the spectrum of the data in order to suppress high amplitude, narrow-band signals of industrial origin, applying a phase autocorrelation algorithm and time-frequency domain phase-weighted stacking. The stacked autocorrelation results are filtered and analysed predominantly in the frequency range of 1-2 Hz. Moho depth is automatically picked inside uncertainty windows obtained from prior information. The processing scheme we developed is applied to data from permanent seismic stations located in different geological provinces across Europe, with varying Moho depths between 25 and 50 km, and to the mainly short period temporary PASSEQ stations along seismic profile POLONAISE P4. The autocorrelation results are spatially and temporarily stable, but show a clear correlation with the existence of cultural noise. On average, a minimum of six months of data is needed to obtain stable results. The obtained Moho depth results are in good agreement with the subsurface model provided by seismic profiling, receiver function estimates and the European Moho depth map. In addition to extracting the Moho depth, it is possible to identify an intracrustal layer along the profile, again closely matching the seismic model. For more than half of the broad-band stations, another change in reflectivity within the mantle is observed and can be correlated with the lithosphere-asthenosphere boundary to the west and a mid-lithospheric discontinuity beneath the East European Craton. With the application of the developed autocorrelation processing scheme to different stations with varying crustal thicknesses, it is shown that Moho depth can be extracted independent of subsurface structure, when station coverage is low, when no strong seismic sources are present, and when only limited amounts of data are available.

Montana: Filling A Gap In The GeoSwath

NASA Astrophysics Data System (ADS)

Jensen, B.; Keller, G. R.

2010-12-01

The proposed Geoswath transect crosses southern Montana, and the swath of MT stations deployed as part of EarthScope cover all but a small portion of eastern Montana. USArray broadband stations of course cover the entire region. However, modern controlled-source seismic data are very sparse in this large state, and most of it dates from the 1960’s. In this study, we have taken an integrated approach to analyzing lithospheric structure by compiling and analyzing all the public domain geophysical results and data we could locate and combining them with industry seismic reflection data that were released for our study. This information was employed to interpret a suite of filtered regional maps gravity and magnetic data and to construct integrated gravity models of long profiles that reflect crustal structure and deeper features within the upper mantle of the region. Our analysis included previous seismic refraction/reflection results, EarthScope Automated Array receiver functions, new 2D seismic reflection data, seismic tomography, potential field data, and previous geological studies in order to investigate structural and compositional variations within the crust and upper mantle. Our targets included Precambrian structure and tectonics, Sevier and Laramide features, and Late Cenozoic extension. Our main conclusions are: 1) Receiver function and seismic refraction/reflection crustal thickness estimates show a W-E crustal thickening with thicknesses greater than 50 km in the central and eastern Montana; 2) Seismic reflection data reveal Laramide basement-involved structures as far east as central Montana. These structures also show that the western edge of the North American craton was affected by late Mesozoic to Cenozoic deformation and has thus been decratonized; 3) Potential field filtering methods revealed regional trends and tectonic province outlines. The tilt derivative of the reduced-to-pole magnetic data enhances crystalline basement patterns that reflect tectonic province boundary locations. The upward continuation of the complete Bouguer anomaly grid revealed a gravity high in the northeast portion of the region, which is interpreted to be associated with density variations in the upper mantle. This interpretation is consistent with seismic tomography that reveals a “wedge-like” zone fast material beneath the craton in this region.

Archive of digital boomer seismic reflection data collected during USGS cruises 94GFP01, 95GFP01, 96GFP01, 97GFP01, and 98GFP02 in Lakes Pontchartrain, Borgne, and Maurepas, Louisiana, 1994-1998

USGS Publications Warehouse

Calderon, Karynna; Dadisman, Shawn V.; Kindinger, Jack G.; Williams, S. Jeffress; Flocks, James G.; Penland, Shea; Wiese, Dana S.

2003-01-01

The U.S. Geological Survey, in cooperation with the University of New Orleans, the Lake Pontchartrain Basin Foundation, the National Oceanic and Atmospheric Administration, the Coalition to Restore Coastal Louisiana, the U.S. Army Corps of Engineers, the Environmental Protection Agency, and the University of Georgia, conducted five geophysical surveys of Lakes Pontchartrain, Borgne, and Maurepas in Louisiana from 1994 to 1998. This report serves as an archive of unprocessed digital boomer seismic reflection data, trackline maps, navigation files, observers' logbooks, GIS information, and formal FGDC metadata. In addition, a filtered and gained digital GIF image of each seismic profile is provided. Refer to the Acronyms page for expansion of acronyms and abbreviations used in this report. The archived trace data are in standard Society of Exploration Geophysicists (SEG) SEG-Y format (Barry and others, 1975) and may be downloaded and processed with commercial or public domain software such as Seismic Unix (SU). Examples of SU processing scripts and in-house (USGS) software for viewing SEG-Y headers (Zihlman, 1992) are also provided. Processed profile images, trackline maps, navigation files, and formal metadata may be viewed with a web browser, and scanned handwritten logbooks may be viewed with Adobe Reader. To access the information contained on these discs, open the file 'index.htm' located at the top level of the discs using a web browser. This report also contains hyperlinks to USGS collaborators and other agencies. These links are only accessible if access to the Internet is available while viewing these documents.

Classical seismic sequence stratigraphic interpretation of intraslope basin fill: Deepwater Nigeria

DOE Office of Scientific and Technical Information (OSTI.GOV)

Duncan, E.A.

Detailed interpretation of seismic facies patterns performed within the workstation environment provides an observation based methodology for constructing depositional models of turbidite and other reservoir bearing systems expected in deepwater Nigeria. The increased fidelity of the workstation allows greater detail and accuracy to be imposed onto depositional model construction by vastly improving the discrimination of depositional from structural seismic reflection geometries. In deepwater Nigeria interslope basins, depositional cyclicity is clearly indicated by vertical seismic facies successions in the same way as can be recognized in bed thickness trends from outcrop or well log data. The recognition of the seismic faciesmore » successions appears to break the stratigraphy into at least fourth and fifth order scale sequences. Highly {open_quotes}zoomed{close_quotes} instantaneous phase displays enhance the reflection character so that near outcrop scale (resolution less than 50 mters) interpretations of depositional facies can be made. Common seismic facies and geologic interpretation include: (1) low angle erosional surfaces as channel scour or mass wasting detachment; (2) low relief mounds, often in compensation cycle overlapping stacks reflecting compacted channelbelt fill; (3) unidirectional, low angle clinoform sets suggesting laterial accretion within a channel belt or possible contourite mounds; (4) abrupt, shingled blocks illustrating tilted fault blocks of small scale intraformation slumping; and (5) high reflection amplitude and continuous, parallel reflections of pelagic and hemipelagic condensed sections. There are other subtle seismic facies resolvable given the incraesed fidelity of the workstation interpretation. Mapping and translation of these geometries into more robust stratigraphic predictions should have positive impact on exploration and development success.« less

The Summerville Formation: Evidence for a sub-horizontal stratigraphic sequence below the post-rift unconformity in the Middleton Place Summerville Seismic Zone

NASA Astrophysics Data System (ADS)

Getz, Joseph Edward

The Middleton Place Summerville Seismic Zone (MPSSZ) near Summerville, South Carolina was the site of renewed extensive investigation, beginning in the 1970's, for the source of the 1886 Charleston earthquake. Reactivation of faults associated with a putative fault-bounded Triassic rift basin through analysis of seismic reflection, seismic refraction, and well data has since become the favored interpretation for the source of MPSSZ seismicity. Critical to this interpretation is the association of continental redbed sedimentary rocks with Triassic basins identified throughout the North American Atlantic margin. Reanalysis of 18 seismic reflection profiles and 25 seismic refraction profiles within the MPSSZ suggests that the red beds found here are a thin, sub-horizontal, regionally extensive, generally unbroken subsurface stratigraphic sequence distinct from the sedimentary architecture observed in analog Triassic rift systems. In addition, this sequence appears to unconformably overly a structural depression (the Jedberg basin) previously interpreted as a Triassic rift basin in the vicinity of the MPSSZ. In addition to the geometries observed on seismic reflection profiles, seismic refraction velocities ranging from 4.2 to 6.1 km/s can be correlated with (1) Jurassic basalt flows, (2) the newly proposed Summerville Formation, and (3) the Basement (B) sequences respectively. The current study maps the Summerville red bed section and its bounding reflectors. In addition to mapping the regional extent of the newly proposed Summerville Formation, refraction velocities and changes in reflection character, the lateral extent of the basalt flows can be changed to a more localized flow rather than a regionally extensive flow of which was previously thought. Reanalysis of data in the MPSSZ suggests that the area may not be part of the Triassic South Georgia Rift system due to the sub-horizontal geometry of the red bed reflections, the apparent lack of faulting, and their regional extent.

Use of a Land Streamer System to Image the Potomac Formation in Northern Delaware

NASA Astrophysics Data System (ADS)

Velez, C. C.; McLaughlin, P. P.; McGeary, S.; Sargent, S. L.

2008-12-01

A land streamer system, an alternative to conventional seismic acquisition equipment for collecting large amounts of seismic reflection data in urbanized and semi-urbanized areas, was used to collect a network of high-resolution seismic reflection data in northern Delaware. The principal objective of this work is to image the distribution and geometry of sand bodies in the Cretaceous (Aptian to Cenomanian) non-marine deposits of the Potomac Formation. The Potomac Formation includes the most important confined aquifers in the Coastal Plain of northern Delaware. Previous studies indicate these deposits onlap Paleozoic basement at depths from 115 m to 400 m in the study area and are truncated by an unconformity. Previous descriptions of sedimentary facies from nearby cores and geophysical logs indicate that the Potomac Formation is a predominantly fine-grained alluvial unit with laterally discontinuous fluvial sand bodies, resulting in a "labyrinth style heterogeneity" for aquifer facies. The 20-km seismic dataset collected for this study indicates that land-streamer seismic methods can be used in this area to image the subsurface geology as shallow as 18 m and as deep as the basement at 315 m. The theoretical quarter wavelength of the seismic dataset suggests a resolution of 2 to 4 m, which is sufficient to resolve aquifer sands in the Potomac Formation ranging from 10 to 20 m thick. Final processed seismic sections will be integrated with geophysical logs and core data to provide a robust 2-D dataset that will allow assessment of current concepts for facies and correlations in the Potomac Formation, thus benefiting understanding of critical ground-water resources.

Near-surface structure of the Carpathian Foredeep marginal zone in the Roztocze Hills area

NASA Astrophysics Data System (ADS)

Majdański, M.; Grzyb, J.; Owoc, B.; Krogulec, T.; Wysocka, A.

2018-03-01

Shallow seismic survey was made along 1280 m profile in the marginal zone of the Carpathian Foredeep. Measurements performed with standalone wireless stations and especially designed accelerated weight drop system resulted in high fold (up to 60), long offset seismic data. The acquisition has been designed to gather both high-resolution reflection and wide-angle refraction data at long offsets. Seismic processing has been realised separately in two paths with focus on the shallow and deep structures. Data processing for the shallow part combines the travel time tomography and the wide angle reflection imaging. This difficult analysis shows that a careful manual front mute combined with correct statics leads to detailed recognition of structures between 30 and 200 m. For those depths, we recognised several SW dipping tectonic displacements and a main fault zone that probably is the main fault limiting the Roztocze Hills area, and at the same time constitutes the border of the Carpathian Forebulge. The deep interpretation clearly shows a NE dipping evaporate layer at a depth of about 500-700 m. We also show limitations of our survey that leads to unclear recognition of the first 30 m, concluding with the need of joint interpretation with other geophysical methods.

ENAM: A community seismic experiment targeting rifting processes and post-rift evolution of the Mid Atlantic US margin

NASA Astrophysics Data System (ADS)

Van Avendonk, H. J.; Magnani, M. B.; Shillington, D. J.; Gaherty, J. B.; Hornbach, M. J.; Dugan, B.; Long, M. D.; Lizarralde, D.; Becel, A.; Benoit, M. H.; Harder, S. H.; Wagner, L. S.; Christeson, G. L.

2014-12-01

The continental margins of the eastern United States formed in the Early Jurassic after the breakup of supercontinent Pangea. The relationship between the timing of this rift episode and the occurrence of offshore magmatism, which is expressed in the East Coast Magnetic Anomaly, is still unknown. The possible influence of magmatism and existing lithospheric structure on the rifting processes along margin of the eastern U.S. was one of the motivations to conduct a large-scale community seismic experiment in the Eastern North America (ENAM) GeoPRISMS focus site. In addition, there is also a clear need for better high-resolution seismic data with shallow penetration on this margin to better understand the geological setting of submarine landslides. The ENAM community seismic experiment is a project in which a team of scientists will gather both active-source and earthquake seismic data in the vicinity of Cape Hatteras on a 500 km wide section of the margin offshore North Carolina and Virginia. The timing of data acquisition in 2014 and 2015 facilitates leveraging of other geophysical data acquisition programs such as Earthscope's Transportable Array and the USGS marine seismic investigation of the continental shelf. In April of 2014, 30 broadband ocean-bottom seismometers were deployed on the shelf, slope and abyssal plain of the study site. These instruments will record earthquakes for one year, which will help future seismic imaging of the deeper lithosphere beneath the margin. In September and October of 2014, regional marine seismic reflection and refraction data will be gathered with the seismic vessel R/V Marcus Langseth, and airgun shots will also be recorded on land to provide data coverage across the shoreline. Last, in the summer of 2015, a land explosion seismic refraction study will provide constraints on the crustal structure in the adjacent coastal plain of North Carolina and Virginia. All seismic data will be distributed to the community through IRIS/DMC and the LDEO/UTIG Seismic data center. Two workshops are planned for 2015, where new users get an opportunity to engage in basic processing and analysis of the new data set.

High Resolution Near Surface 3D Seismic Experiments: A Carbonate Platform vs. a Siliciclastic Sequence

NASA Astrophysics Data System (ADS)

Filippidou, N.; Drijkoningen, G.; Braaksma, H.; Verwer, K.; Kenter, J.

2005-05-01

Interest in high-resolution 3D seismic experiments for imaging shallow targets has increased over the past years. Many case studies presented, show that producing clear seismic images with this non-evasive method, is still a challenge. We use two test-sites where nearby outcrops are present so that an accurate geological model can be built and the seismic result validated. The first so-called natural field laboratory is located in Boulonnais (N. France). It is an upper Jurassic siliciclastic sequence; age equivalent of the source rock of N. Sea. The second one is located in Cap Blanc,to the southwest of the Mallorca island(Spain); depicting an excellent example of Miocene prograding reef platform (Llucmajor Platform); it is a textbook analog for carbonate reservoirs. In both cases, the multidisciplinary experiment included the use of multicomponent and quasi- or 3D seismic recordings. The target depth does not exceed 120m. Vertical and shear portable vibrators were used as source. In the center of the setups, boreholes were drilled and Vertical Seismic Profiles were shot, along with core and borehole measurements both in situ and in the laboratory. These two geologically different sites, with different seismic stratigraphy have provided us with exceptionally high resolution seismic images. In general seismic data was processed more or less following standard procedures, a few innovative techniques on the Mallorca data, as rotation of horizontal components, 3D F-K filter and addition of parallel profiles, have improved the seismic image. In this paper we discuss the basic differences as seen on the seismic sections. The Boulonnais data present highly continuous reflection patterns of extremenly high resolution. This facilitated a high resolution stratigraphic description. Results from the VSP showed substantial wave energy attenuation. However, the high-fold (330 traces ) Mallorca seismic experiment returned a rather discontinuous pattern of possible reflectors, opposing to the predicted seismic stratigraphy/geology of the area. The Llumajor Platform has been buried only a few meters at most, therefore primary and secondary porocity remains intact, creating a fractal like environment of scatterers and diffractors. We have interpreted two possible reflections, the top of the reef and the water table; the former is nicely coupled with the VSP. The seismic wave attenuation observed is believed to be predominantly due to the scattering effects.

Upper and lower plate controls on the great 2011 Tohoku-oki earthquake

PubMed Central

2018-01-01

The great 2011 Tohoku-oki earthquake [moment magnitude (Mw) 9.0)] is the best-documented megathrust earthquake in the world, but its causal mechanism is still in controversy because of the poor state of knowledge on the nature of the megathrust zone. We constrain the structure of the Tohoku forearc using seismic tomography, residual topography, and gravity data, which reveal a close relationship between structural heterogeneities in and around the megathrust zone and rupture processes of the 2011 Tohoku-oki earthquake. Its mainshock nucleated in an area with high seismic velocity, low seismic attenuation, and strong seismic coupling, probably indicating a large asperity (or a cluster of asperities) in the megathrust zone. Strong coseismic high-frequency radiations also occurred in high-velocity patches, whereas large afterslips took plate in low-velocity areas, differences that may reflect changes in fault friction and lithological variations. These structural heterogeneities in and around the Tohoku megathrust originate from both the overriding and subducting plates, which controlled the nucleation and rupture processes of the 2011 Tohoku-oki earthquake.

Seismic Reflection Methods

EPA Pesticide Factsheets

Seismic methods are the most commonly conducted geophysical surveys for engineering investigations. Seismic refraction provides engineers and geologists with the most basic of geologic data via simple procedures with common equipment.

Seismic and Petrological Constraints on Deep Crustal Evolution in North America: Where and What are 7.x Layers?

NASA Astrophysics Data System (ADS)

Mahan, K. H.; Schulte-Pelkum, V.; Shen, W.; Ritzwoller, M. H.

2012-12-01

Continental crust worldwide has been found to have areas with a lowermost layer characterized by unusually high seismic P velocities of over 7 km/s, often called 7.x layers. Such layers are commonly ascribed to underplating - in some cases by underthrusting, but in most cases by magmatic processes. In North America, high-velocity lower crust underlies upper crust of Archean, Proterozoic, and younger ages. Its presence reflects the tectonic and magmatic processes associated with continental rifting, collision, subduction, and other evolutionary (e.g. thermal) trends, and its occurrence also provides clues on the nature of the underlying mantle. Detection of a lower crustal high-velocity layer stems mostly from seismic refraction and wide-angle reflection experiments, and information on its geographical extent is very spotty. Similarly sparse are age determinations and knowledge of the tectonic processes responsible for construction of these layers. Despite glimpses of 7.x layers on many profiles across the continental U.S. and Canada, there is no systematic geographical and age information on this fundamental process of crustal growth, and many of the existing observations contradict current hypotheses on underplating. We compare compositional and physical property data of lower crustal and uppermost mantle xenoliths from Montana, Wyoming, and other localities with maps of lower crustal and uppermost mantle seismic velocities obtained from joint inversions of receiver functions with surface waves, and to mapped distinct high-velocity lower crustal layers in receiver functions in areas covered by the EarthScope Transportable Array. Xenolith observations from Montana indicate that portions of metasomatized uppermost mantle exist in that area that may be difficult to distinguish from mafic lower crust based on seismic velocities alone, raising the interesting question of whether a 7.x layer may be below rather than above the seismic Moho in some cases. The persistence of high-velocity, presumably strong lower crust under the Laramide-affected Wyoming craton and the Colorado Plateau suggest that crustal strength may influence surface deformation. The Rocky Mountain Front and Rio Grande rift largely separate fast lower crust to the East from slower lower crust to the West, cutting across NE-SW trends inherited from continental assembly and suggesting that the velocity distribution may be dominated by thermal effects; however, recent volcanics do not correlate well geographically with lower crustal velocity.

The nature of crustal boundaries: combined interpretation of wide-angle and normal-incidence seismic data

NASA Astrophysics Data System (ADS)

Long, Roger E.; Matthews, Patricia A.; Graham, Daniel P.

1994-04-01

After a few seconds two-way traveltime, normal-incidence seismic reflection sections are composed mainly of assemblages of short reflections. Very rarely are seen continuous reflections that might correspond to the Moho or a mid-crustal discontinuity. The inferred continuity of these boundaries has traditionally come from refraction seismology. There is now a body of high quality, coincident wide-angle and normal-incidence seismic data that have been recorded with 50-100 m shot spacing and with high frequency sources (e.g. MOBIL, BABEL). The complexity and characteristics of the wide-angle arrivals seen on these data suggest that they do not originate from continuous boundaries. It is suggested that these arrivals are reflections from the same assemblage of short length reflectors that are responsible for normal-incidence reflections. Seismic velocities below the middle crust may (1) change corresponding to normal-incidence reflectivity, or (2) generally increase with depth with localised sills or lens structures of different velocity accounting for the observed reflections. Wide-angle arrivals that have traditionally been identified as reflections from crustal boundaries (e.g. the mid-crust and Moho) and which were considered indicative of a sharp velocity discontinuity from continuous boundaries, may instead result from a concentration of lamellae.

New data of the Gakkel Ridge seismicity

NASA Astrophysics Data System (ADS)

Antonovskaya, Galina; Basakina, Irina; Kremenetskaya, Elena

2016-04-01

250 earthquakes were recorded in the Gakkel Ridge during the period 2012-2014 by Arkhangelsk seismic network. The magnitude Ml of these earthquakes is 1.5 - 5.7, 70% of them have Ml up to 3.0. Seismic events are arranged along to a narrow center line of the Mid-Arctic Ridge, most of the earthquakes are confined to the southern board of the Ridge. Presumably it's connected with the reflection of spreading processes. The high seismic activity zones, which we associate with the volcano-tectonic processes, have been identified. Have been recorded 13 events per day in the Western Volcanic Zone. The largest number of events (75%) is confined to the Sparsely Magmatic Zone. About 30% of all recorded earthquakes with magnitudes above 2.9 have a T-phase. We divided the Gakkel Ridge's earthquakes into two groups by using spectral-time analysis. The first group: maximum energy of the earthquake is observed from 1.5 to 10 Hz, values of magnitudes Ml 2.50-5.29. Earthquakes are distributed along the Gakkel Ridge. The second group: maximum energy of the earthquake is observed from 1.5 to 20 Hz, clearly expressed a high-frequency component, values of magnitudes Ml 2.3-3.4. Earthquakes 2 groups focused only in the Sparsely Magmatic Zone. The new seismic data shows an unique information about geodynamic processes of the Gakkel Ridge.

Geophysical Analysis of Major Geothermal Anomalies in Romania

NASA Astrophysics Data System (ADS)

Panea, Ionelia; Mocanu, Victor

2017-11-01

The Romanian segment of the Eastern Pannonian Basin and the Moesian Platform are known for their geothermal and hydrocarbon-bearing structures. We used seismic, gravity, and geothermal data to analyze the geothermal behavior in the Oradea and Timisoara areas, from the Romanian segment of Eastern Pannonian Basin, and the Craiova-Bals-Optasi area, from the Moesian Platform. We processed 22 seismic reflection data sets recorded in the Oradea and Timisoara areas to obtain P-wave velocity distributions and time seismic sections. The P-wave velocity distributions correlate well with the structural trends observed along the seismic lines. We observed a good correlation between the high areas of crystalline basement seen on the time seismic sections and the high heat flow and gravity-anomaly values. For the Craiova-Bals-Optasi area, we computed a three-dimensional (3D) temperature model using calculated and measured temperature and geothermal gradient values in wells with an irregular distribution on the territory. The high temperatures from the Craiova-Bals-Optasi area correlate very well with the uplifted basement blocks seen on the time seismic sections and high gravity-anomaly values.

Northeastward growth of the Tibetan Plateau along the Tibet-Ordos transition zone-revealed from Liupanshan deep seismic reflection profile

NASA Astrophysics Data System (ADS)

Gao, R.; Wang, H.; Guo, X.; Li, W.; Li, H.; Hou, H.; Xiong, X.; Xu, X.; Liang, H.; Li, Q.

2015-12-01

Most previous studies of the Tibetan Plateau have focused on the processes of crustal thickening and subsequent lateral extrusion to account for the outward growth of the plateau. However, lithospheric structure across the tectonic boundaries of the Tibetan Plateau has not yet been fully imaged and, therefore, how geological structures evolved in association with the lateral expansion of the northeastern margin in particular remains unclear. Here, together with interpretation of regional geological and geophysical data, we employ a recently acquired 165 km-long deep seismic reflection image that crosses the Liupan shan (Fig. 1) northeastern flank of the Tibetan Plateau to show that crustal shortening, structural integrity, and topographic relief are strongly correlated. The resulting stratigraphic "architecture" suggests that crustal shortening is a primary driver for plateau uplift and expansion of northeastern Tibet and decoupled crustal deformation owing to differential structural integrity is accommodated during the subsequent northeastward growth of the plateau. Figure 1.Showing the seismic reflection line location and the topographic relief of the northeastern Tibetan Plateau and the western Ordos basin (KF: Kunlun Fault; LP Shan: Liupan Shan; HF: Haiyuan Fault; YTSF: Yangtongshan Fault; NSS-LSF: Niushou Shan-Luoshan Fault)XG Shan: Xiaoguan Shan; YJD: Yanjiadian Diorite; GS: Guanshan Shan; CCP: Caochuanpu; LS Complex: Longshan Complex)

Mapping nuclear craters on Enewetak Atoll, Marshall Islands

USGS Publications Warehouse

Hampson, John C., Jr.

1986-01-01

In 1984, the U.S. Geological Survey conducted a detailed geologic analysis of two nuclear test craters at Enewetak Atoll, Marshall Islands, on behalf of the Defense Nuclear Agency. A multidisciplinary task force mapped the morphology, surface character, and subsurface structure of two craters, OAK and KOA. The field mapping techniques include echo sounding, sidescan sonar imaging, single-channel and multichannel seismic reflection profiling, a seismic refraction survey, and scuba and submersible operations. All operations had to be navigated precisely and correlatable with subsequent drilling and sampling operations. Mapping with a high degree of precision at scales as large as 1:1500 required corrections that often are not considered in marine mapping. Corrections were applied to the bathymetric data for location of the echo- sounding transducer relative to the navigation transponder on the ship and for transducer depth, speed of sound, and tidal variations. Sidescan sonar, single-channel seismic reflection, and scuba and submersible data were correlated in depth and map position with the bathymetric data to provide a precise, internally consistent data set. The multichannel and refraction surveys were conducted independently but compared well with bathymetry. Examples drawn from processing the bathymetric, sidescan sonar, and single- channel reflection data help illustrate problems and procedures in precision mapping.

Integrated geologic and geophysical studies of North American continental intraplate seismicity

USGS Publications Warehouse

Van Lanen, X.; Mooney, W.D.

2007-01-01

The origin of earthquakes within stable continental regions has been the subject of debate over the past thirty years. Here, we examine the correlation of North American stable continental region earthquakes using five geologic and geophysical data sets: (1) a newly compiled age-province map; (2) Bouguer gravity data; (3) aeromagnetic anomalies; (4) the tectonic stress field; and (5) crustal structure as revealed by deep seismic-reflection profiles. We find that: (1) Archean-age (3.8-2.5 Ga) North American crust is essentially aseismic, whereas post-Archean (less than 2.5 Ga) crust shows no clear correlation of crustal age and earthquake frequency or moment release; (2) seismicity is correlated with continental paleorifts; and (3) seismicity is correlated with the NE-SW structural grain of the crust of eastern North America, which in turn reflects the opening and closing of the proto- and modern Atlantic Ocean. This structural grain can be discerned as clear NE-SW lineaments in the Bouguer gravity and aeromagnetic anomaly maps. Stable continental region seismicity either: (1) follows the NE-SW lineaments; (2) is aligned at right angles to these lineaments; or (3) forms clusters at what have been termed stress concentrators (e.g., igneous intrusions and intersecting faults). Seismicity levels are very low to the west of the Grenville Front (i.e., in the Archean Superior craton). The correlation of seismicity with NE-SW-oriented lineaments implies that some stable continental region seismicity is related to the accretion and rifting processes that have formed the North American continental crust during the past 2 b.y. We further evaluate this hypothesis by correlating stable continental region seismicity with recently obtained deep seismic-reflection images of the Appalachian and Grenville crust of southern Canada. These images show numerous faults that penetrate deep (40 km) into the crust. An analysis of hypocentral depths for stable continental region earthquakes shows that the frequency and moment magnitude of events are nearly uniform for the entire 0-35 km depths over which crustal earthquakes extend. This is in contradiction with the hypothesis that larger events have deeper focal depths. We conclude that the deep structure of the crust, in particular the existence of deeply penetrating faults, is the controlling parameter, rather than lateral variations in temperature, rheology, or high pore pressure. The distribution of stable continental region earthquakes in eastern North America is consistent with the existence of deeply penetrating crustal faults that have been reactivated in the present stress field. We infer that future earthquakes may occur anywhere along the geophysical lineations that we have identified. This implies that seismic hazard is more widespread in central and eastern North America than indicated by the limited known historical distribution of seismicity. ?? 2007 The Geological Society of America.

Extracting physical parameters from marine seismic data: New methods in seismic oceanography and velocity inversion

NASA Astrophysics Data System (ADS)

Fortin, Will F. J.

The utility and meaning of a geophysical dataset is dependent on good interpretation informed by high-quality data, processing, and attribute examination via technical methodologies. Active source marine seismic reflection data contains a great deal of information in the location, phase, and amplitude of both pre- and post-stack seismic reflections. Using pre- and post-stack data, this work has extracted useful information from marine reflection seismic data in novel ways in both the oceanic water column and the sub-seafloor geology. In chapter 1 we develop a new method for estimating oceanic turbulence from a seismic image. This method is tested on synthetic seismic data to show the method's ability to accurately recover both distribution and levels of turbulent diffusivity. Then we apply the method to real data offshore Costa Rica where we observe lee waves. Our results find elevated diffusivities near the seafloor as well as above the lee waves five times greater than surrounding waters and 50 times greater than open ocean diffusivities. Chapter 2 investigates subsurface geology in the Cascadia Subduction Zone and outlines a workflow for using pre-stack waveform inversion to produce highly detailed velocity models and seismic images. Using a newly developed inversion code, we achieve better imaging results as compared to the product of a standard, user-intensive method for building a velocity model. Our results image the subduction interface ~30 km farther landward than previous work and better images faults and sedimentary structures above the oceanic plate as well as in the accretionary prism. The resultant velocity model is highly detailed, inverted every 6.25 m with ~20 m vertical resolution, and will be used to examine the role of fluids in the subduction system. These results help us to better understand the natural hazards risks associated with the Cascadia Subduction Zone. Chapter 3 returns to seismic oceanography and examines the dynamics of nonlinear internal wave pulses in the South China Sea. Coupling observations from the seismic images with turbulent patterns, we find no evidence for hydraulic jumps in the Luzon passage. Our data suggests geometric resonance may be the underlying physics behind large amplitude nonlinear internal wave pulses seen in the region. We find increased levels of turbulent diffusivity in deep water below 1000 m, associated with internal tide pulses, and near the steep slopes of both the Heng-Chun and Lan-Yu ridges.

Imaging an Active Volcano Edifice at Tenerife Island, Spain

NASA Astrophysics Data System (ADS)

Ibáñez, Jesús M.; Rietbrock, Andreas; García-Yeguas, Araceli

2008-08-01

An active seismic experiment to study the internal structure of Teide volcano is being carried out on Tenerife, a volcanic island in Spain's Canary Islands archipelago. The main objective of the Tomography at Teide Volcano Spain (TOM-TEIDEVS) experiment, begun in January 2007, is to obtain a three-dimensional (3-D) structural image of Teide volcano using seismic tomography and seismic reflection/refraction imaging techniques. At present, knowledge of the deeper structure of Teide and Tenerife is very limited, with proposed structural models based mainly on sparse geophysical and geological data. The multinational experiment-involving institutes from Spain, the United Kingdom, Italy, Ireland, and Mexico-will generate a unique high-resolution structural image of the active volcano edifice and will further our understanding of volcanic processes.

Three-dimensional seismic reflection images of axial melt lens and seismic layer 2A between 9°42'N and 9°57'N on the East Pacific Rise

NASA Astrophysics Data System (ADS)

Carton, H. D.; Carbotte, S. M.; Mutter, J. C.; Canales, J.; Nedimovic, M. R.; Aghaei, O.; Marjanovic, M.; Newman, K. R.

2010-12-01

We present results from 3D time-domain processing of the dual-source, four-streamer seismic dataset acquired in 2008 by R/V Langseth at the 9°50’N Integrated Study Site (ISS) on the East Pacific Rise. The survey was designed with a main goal to determine the fine-scale geometry of the magmatic system across three fourth-order ridge axis discontinuities (at 9°45.2’N, 9°48.7’N, and 9°51.5’N), and to study relationships with the hydrothermal system and eruptive/intrusive processes, in particular related to the 2005-06 eruption. Seismic processing included flexible binning to regularize the fold coverage, CMP stacking within 6.25m x 37.5m bins using velocity functions derived from constant-velocity stack analyses, post-stack interpolation to 6.25m x 18.75m bin size, and 3D post-stack time migration, resulting in a fully migrated area of 18km across-axis by 27km along-axis. The axial melt lens is ~500-600m wide at 9°50’N beneath the northern vent cluster, and up to 1km wide beneath the southern vent cluster. The fourth-order segment boundaries, as defined from seafloor morphology and structure of the axial summit trough (AST), coincide with geometrically complex regions of the magmatic system, with cross-axis views showing two separate magma bodies distant by up to a few hundreds of meters. Discontinuities in the axial magma lens thus appear like mini-overlap basins encircled by north and south lens segments, which may trend at a slightly oblique angle to the average ridge axis direction. A deeper magma body, likely also part of the axial system, is imaged near 9°51’N at ~125m from the western edge of the axial melt lens, while near 9°47.5’N a bright near-axis magma body is imaged at ~1360m from the eastern edge of the axial melt lens, at a shorter travel time below seafloor. Seismic layer 2A is imaged both as a basal reflection-refraction event, spatially continuous but variable in brightness, and through shallow layering (reflections at ~30ms i.e. 70-120m interval), observed in particular in along-axis direction, delimiting the area of elevated topography of the ISS bull’s eye. Regionally, layer 2A shows a classical off-axis thickening pattern and is thinnest beneath the AST, which is distinctly imaged in the seafloor reflection. Relationships between the variations in layer 2A through the seismic volume and magma lens geometry and seafloor morphology will be analyzed.

Full Waveform Inversion of Reflection Seismic Data for Ocean Temperature Profiles

DTIC Science & Technology

2008-01-01

ographic processes and properties, such as internal-wave spectra [Holbrook and Fer, 2005; Krahmann et al, 2006] and temperature contrasts [ Paramo and...contribute little to the reflectance in the Norwegian Sea data set used here [ Paramo and Holbrook, 2005], so we assume for this study that all...bathyther- mograph) profiles presented by Paramo and Holbrook [2005], displayed here in the intercept time-slowness (Tau-p) domain, rather than the

Variations in pockmark composition at the Vestnesa Ridge: Insights from marine controlled source electromagnetic and seismic data

NASA Astrophysics Data System (ADS)

Goswami, Bedanta K.; Weitemeyer, Karen A.; Bünz, Stefan; Minshull, Timothy A.; Westbrook, Graham K.; Ker, Stephan; Sinha, Martin C.

2017-03-01

The Vestnesa Ridge marks the northern boundary of a known submarine gas hydrate province in the west Svalbard margin. Several seafloor pockmarks at the eastern segment of the ridge are sites of active methane venting. Until recently, seismic reflection data were the main tool for imaging beneath the ridge. Coincident controlled source electromagnetic (CSEM), high-resolution two-dimensional (2-D) airgun, sweep frequency SYSIF, and three-dimensional (3-D) p-cable seismic reflection data were acquired at the south-eastern part of the ridge between 2011 and 2013. The CSEM and seismic data contain profiles across and along the ridge, passing several active and inactive pockmarks. Joint interpretation of resistivity models obtained from CSEM and seismic reflection data provides new information regarding the fluid composition beneath the pockmarks. There is considerable variation in transverse resistance and seismic reflection characteristics of the gas hydrate stability zone (GHSZ) between the ridge flanks and chimneys beneath pockmarks. Layered seismic reflectors on the flanks are associated with around 300 Ωm2 transverse resistance, whereas the seismic reflectors within the chimneys exhibit amplitude blanking and chaotic patterns. The transverse resistance of the GHSZ within the chimneys vary between 400 and 1200 Ωm2. Variance attributes obtained from the 3-D p-cable data also highlight faults and chimneys, which coincide with the resistivity anomalies. Based on the joint data interpretation, widespread gas hydrate presence is likely at the ridge, with both hydrates and free gas contained within the faults and chimneys. However, at the active chimneys the effect of gas likely dominates the resistive anomalies.

Subsurface imaging in a sector of Cerro Prieto transform fault near to pull-apart basin, Mexicali Valley, Baja California, Mexico, based on crooked lines 2D seismic reflection.

NASA Astrophysics Data System (ADS)

Mares-Agüero, M. A.; González-Escobar, M.; Arregui, S.

2016-12-01

In the transition zone between San Andres continental transformation system and the coupled transform faults system and rifting of Gulf of California is located the Cerro Prieto pull-apart basin delimitated by Imperial fault (northeast) and Cerro Prieto fault (CPF) (southwest), this last, is the limit west of Cerro Prieto geothermic field (CPGF). Crooked lines 2D seismic reflection, covering a portion near the intersection of CPF and CPGF are processed and interpreted. The seismic data were obtained in the early 80's by Petróleos Mexicanos (PEMEX). By decades, technical and investigation works in Cerro Prieto geothermic field and its vicinity had mapped faults at several depths but do not stablish a clear limit where this faults and CPF interact due the complex hydrothermal effects imaging the subsurface. The profiles showing the presence of a zone of uplift effect due to CPF. Considering the proximity of the profiles to CPF, it is surprising almost total absence of faults. A strong reflector around 2 km of depth, it is present in all profiles. This seismic reflector is considered a layer of shale, result of the correlation with a well located in the same region.

The crustal structure in the transition zone between the western and eastern Barents Sea

NASA Astrophysics Data System (ADS)

Shulgin, Alexey; Mjelde, Rolf; Faleide, Jan Inge; Høy, Tore; Flueh, Ernst; Thybo, Hans

2018-07-01

We present a crustal-scale seismic profile in the Barents Sea based on new data. Wide-angle seismic data were recorded along a 600 km long profile at 38 ocean bottom seismometer and 52 onshore station locations. The modelling uses the joint refraction/reflection tomography approach where co-located multichannel seismic reflection data constrain the sedimentary structure. Further, forward gravity modelling is based on the seismic model. We also calculate net regional erosion based on the calculated shallow velocity structure. Our model reveals a complex crustal structure of the Baltic Shield to Barents shelf transition zone, as well as strong structural variability on the shelf itself. We document large volumes of pre-Carboniferous sedimentary strata in the transition zone which reach a total thickness of 10 km. A high-velocity crustal domain found below the Varanger Peninsula likely represents an independent crustal block. Large lower crustal bodies with very high velocity and density below the Varanger Peninsula and the Fedynsky High are interpreted as underplated material that may have fed mafic dykes in the Devonian. We speculate that these lower crustal bodies are linked to the Devonian rifting processes in the East European Craton, or belonging to the integral part of the Timanides, as observed onshore in the Pechora Basin.

Weighted stacking of seismic AVO data using hybrid AB semblance and local similarity

NASA Astrophysics Data System (ADS)

Deng, Pan; Chen, Yangkang; Zhang, Yu; Zhou, Hua-Wei

2016-04-01

The common-midpoint (CMP) stacking technique plays an important role in enhancing the signal-to-noise ratio (SNR) in seismic data processing and imaging. Weighted stacking is often used to improve the performance of conventional equal-weight stacking in further attenuating random noise and handling the amplitude variations in real seismic data. In this study, we propose to use a hybrid framework of combining AB semblance and a local-similarity-weighted stacking scheme. The objective is to achieve an optimal stacking of the CMP gathers with class II amplitude-variation-with-offset (AVO) polarity-reversal anomaly. The selection of high-quality near-offset reference trace is another innovation of this work because of its better preservation of useful energy. Applications to synthetic and field seismic data demonstrate a great improvement using our method to capture the true locations of weak reflections, distinguish thin-bed tuning artifacts, and effectively attenuate random noise.

Seismic Expression of Fault Related Folding in Southeastern Turkey

NASA Astrophysics Data System (ADS)

Beauchamp, W.; McDonald, D.

2009-12-01

Weldon Beauchamp, and David McDonald,TransAtlantic Petroleum Corp. 5910 N. Central Expressway, Suite 1755, Dallas, TX 75206 weldon@tapcor.com, 214-395-7125 The Zagros fold belt extends northwest from Iran and Iraq into southeastern Turkey. Large scale fault related folds control the topography of this region and the path of the Tigris river. Large surface anticlines in the Zagros Mountains provide traps for giant oil and gas fields in Iran and Iraq. Similar scale folds extend into southeast Turkey. These southward verging fault related folds are believed to detach in the Paleozoic. Borehole data, surface geological maps, satellite data and digital topographic models were used to create models to constrain structure at depth. Structural modeling of these folds was used to design, acquire and process seismic reflection data in the region. The seismic reflection data confirmed the presence of asymmetrical, south verging complex fault related folding. Faults related to these folds detach in the Lower Ordovician to Cambrian age shales. These folds are believed to form doubly plunging structures that fold Tertiary through Paleozoic age rocks forming multiple levels of possible hydrocarbon entrapment.

High resolution seismic stratigraphy and Mass Transport Deposits of the proximal continental margin, offshore Quarteira, South Portugal: Preliminary Results.

NASA Astrophysics Data System (ADS)

Duarte, Débora; Santos, Joana; Terrinha, Pedro; Brito, Pedro; Noiva, João; Ribeiro, Carlos; Roque, Cristina

2017-04-01

More than 300 nautical miles of multichannel seismic reflection data were acquired in the scope of the ASTARTE project (Assessment Strategy and Risk Reduction for Tsunamis in Europe), off Quarteira, Algarve, South Portugal. The main goal of this very high resolution multichannel seismic survey was to obtain high-resolution images of the sedimentary record to try to discern the existence of high energy events, possibly tsunami backwash deposits associated with large magnitude earthquakes generated at the Africa-Eurasia plate boundary This seismic dataset was processed at the Instituto Português do Mar e da Atmosfera (IPMA), with the SeisSpace PROMAX Seismic Processing software. A tailor-made processing flow was applied, focusing in the removal of the seafloor multiple and in the enhancement of the superficial layers. A sparker source, using with 300 J of energy and a fire rate of 0,5 s was used onboard Xunauta, an 18 m long vessel. The preliminary seismostratigraphic interpretation of the Algarve ASTARTE seismic dataset allowed the identification of a complex sequence seismic units of progradational and agradational bodies as well as Mass Transported Deposits (MTD). The MTD package of sediments has a very complex internal structure, 20m of thickness, is apparently spatially controlled by an escarpment probably associated to past sea level low stands. The MTD covers across an area, approximately parallel to an ancient coastline, with >30 km (length) x 5 km (across). Acknowledgements: This work was developed as part of the project ASTARTE (603839 FP7) supported by the grant agreement No 603839 of the European Union's Seventh. The Instituto Portugues do Mar e da Atmosfera acknowledges support by Landmark Graphics (SeisWorks) via the Landmark University Grant Program.

Archive of Digital Boomer Seismic Reflection Data Collected During USGS Field Activity 02LCA02 in Lakes Ada, Crystal, Jennie, Mary, Rice, and Sylvan, Central Florida, July 2002

USGS Publications Warehouse

Harrison, Arnell S.; Dadisman, Shawn V.; Davis, Jeffrey B.; Wiese, Dana S.

2008-01-01

In July of 2002, the U.S. Geological Survey and St. Johns River Water Management District (SJRWMD) conducted geophysical surveys in Lakes Ada, Crystal, Jennie, Mary, Rice, and Sylvan, central Florida, as part of the USGS Lakes and Coastal Aquifers (LCA) study. This report serves as an archive of unprocessed digital boomer seismic reflection data, trackline maps, navigation files, Geographic Information System (GIS) files, and formal Federal Geographic Data Committee (FGDC) metadata. Filtered and gained (a relative increase in signal amplitude) digital images of the seismic profiles are also provided. Refer to the Acronyms page for expansions of acronyms and abbreviations used in this report. The archived trace data are in standard Society of Exploration Geophysicists (SEG) SEG-Y format (Barry and others, 1975) and may be downloaded and processed with commercial or public domain software such as Seismic Unix (SU). Example SU processing scripts and USGS software for viewing the SEG-Y files (Zihlman, 1992) are also provided. The USGS Florida Integrated Science Center (FISC) - St. Petersburg assigns a unique identifier to each cruise or field activity. For example, 02LCA02 tells us the data were collected in 2002 for the Lakes and Coastal Aquifers (LCA) study and the data were collected during the second field activity for that study in that calendar year. Refer to http://walrus.wr.usgs.gov/infobank/programs/html/definition/activity.html for a detailed description of the method used to assign the field activity ID. The boomer plate is an acoustic energy source that consists of capacitors charged to a high voltage and discharged through a transducer in the water. The transducer is towed on a sled floating on the water surface and when discharged emits a short acoustic pulse, or shot, which propagates through the water, sediment column, or rock beneath. The acoustic energy is reflected at density boundaries (such as the seafloor, sediment, or rock layers beneath the seafloor), detected by the receiver, and recorded by a PC-based seismic acquisition system. This process is repeated at timed intervals (for example, 0.5 s) and recorded for specific intervals of time (for example, 100 ms). In this way, a two-dimensional (2-D) vertical profile of the shallow geologic structure beneath the ship track is produced. Figure 1 displays the acquisition geometry. Refer to table 1 for a summary of acquisition parameters. Table 2 lists trackline statistics. The unprocessed seismic data are stored in SEG-Y format (Barry and others, 1975). For a detailed description of the data format, refer to the SEG-Y Format page. See the How To Download SEG-Y Data page for download instructions. The printable profiles provided here are GIF images that were filtered and gained using Seismic Unix software. Refer to the Software page for details about the processing and examples of the processing scripts. The processed SEG-Y data were exported to Chesapeake Technology, Inc. (CTI) SonarWeb software to produce an interactive Web page of the profile, which allows the user to obtain a geographic location and depth from the profile for a curser position. This information is displayed in the status bar of the browser.

Crustal reflectivity in the Skagerrak area

NASA Astrophysics Data System (ADS)

Larsson, F. R.; Husebye, E. S.

1991-04-01

Reflectors within the crystalline crust are often observed in deep seismic reflection profiling surveys. The lower crust in extensional areas is generally credited with an abundance of reflectors. The deep seismic reflection data (16 s TWT) from the M.V. Mobil Search cruise in Skagerrak show a reflective lower crust and a relatively transparent upper crust in most of the area. Reflectivity seems to be less inside the Oslo Rift, and also beneath the sediment-covered areas. Reflectivity maxima are found near the Moho and at depths of 10-20 km. The latter is taken to coincide with the transition between the brittle upper and ductile lower crust. The distribution of crustal reflectors in Skagerrak and their possible relationships with seismic velocities, earthquake depth distribution and major tectonic elements such as the Fennoscandian Border Zone, the Oslo Rift system and the shield environment are discussed. Hypotheses on the formation of the crustal reflectors are also briefly reviewed.

Geothermal induced seismicity: What links source mechanics and event magnitudes to faulting regime and injection rates?

NASA Astrophysics Data System (ADS)

Martinez-Garzon, Patricia; Kwiatek, Grzegorz; Bohnhoff, Marco; Dresen, Georg

2017-04-01

Improving estimates of seismic hazard associated to reservoir stimulation requires advanced understanding of the physical processes governing induced seismicity, which can be better achieved by carefully processing large datasets. To this end, we investigate source-type processes (shear/tensile/compaction) and rupture geometries with respect to the local stress field using seismicity from The Geysers (TG) and Salton Sea geothermal reservoirs, California. Analysis of 869 well-constrained full moment tensors (MW 0.8-3.5) at TG reveals significant non-double-couple (NDC) components (>25%) for 65% of the events and remarkably diversity in the faulting mechanisms. Volumetric deformation is clearly governed by injection rates with larger NDC components observed near injection wells and during high injection periods. The overall volumetric deformation from the moment tensors increases with time, possibly reflecting a reservoir pore pressure increase after several years of fluid injection with no significant production nearby. The obtained source mechanisms and fault orientations are magnitude-dependent and vary significantly between faulting regimes. Normal faulting events (MW < 2) reveal substantial NDC components indicating dilatancy, and they occur on varying fault orientations. In contrast, strike-slip events dominantly reveal a double-couple source, larger magnitudes (MW > 2) and mostly occur on optimally oriented faults with respect to the local stress field. NDC components indicating closure of cracks and pore spaces in the source region are found for reverse faulting events with MW > 2.5. Our findings from TG are generally consistent with preliminary source-type results from a reduced subset of well-recorded seismicity at the Salton Sea geothermal reservoir. Combined results imply that source processes and magnitudes of geothermal-induced seismicity are strongly affected by and systematically related to the hydraulic operations and the local stress state.

Sidescan-sonar imagery, multibeam bathymetry, and surficial geologic interpretations of the sea floor in Rhode Island Sound, off Sakonnet Point, Rhode Island

USGS Publications Warehouse

McMullen, Katherine Y.; Poppe, Lawrence J.; Twomey, Erin R.; Danforth, William W.; Haupt, Todd A.; Crocker, James M.

2007-01-01

The U.S. Geological Survey (USGS) is working with the National Oceanic and Atmospheric Administration (NOAA) to interpret the surficial geology in estuaries and sounds along the northeastern coast of the United States. This report interprets the area covered by NOAA Survey H11320, about 72 km² of sea floor in eastern Rhode Island Sound (RIS), located about 8 km south of Sakonnet Point, Rhode Island (fig. 1). Previous work in RIS includes studies of both sea-floor processes and subsurface geologic framework. McMaster (1960) mapped surficial sediment samples in Narragansett Bay and RIS and McMaster and others (1968) conducted a seismic-reflection survey in Block Island Sound and RIS. O'Hara and Oldale (1980) collected seismic-reflection profiles, sidescan-sonar data, and vibracores in eastern RIS (fig. 2). They interpreted the geologic history, assessed sand and gravel resources, and evaluated the mining impact of these resources. McMaster's (1960) interpretation of the surficial sediment within this study area consisted of sand with several isolated areas of gravel. Several other sediment samples were previously obtained within the study area: three National Oceanographic Data Center (NODC) dredge samples from 1942 consisted of sand and one National Ocean Service (NOS) sample from 1939 was rocky (fig. 2; Poppe and others, 2003). The purpose of this report is to define the sea-floor morphology and sedimentary environments and interpret processes occurring on the sea floor using sidescan-sonar imagery, multibeam bathymetry, and historic seismic-reflection profiles.

Seismic reflection data imaging and interpretation from Braniewo2014 experiment using additional wide-angle refraction and reflection and well-logs data

NASA Astrophysics Data System (ADS)

Trzeciak, Maciej; Majdański, Mariusz; Białas, Sebastian; Gaczyński, Edward; Maksym, Andrzej

2015-04-01

Braniewo2014 reflection and refraction experiment was realized in cooperation between Polish Oil and Gas Company (PGNiG) and the Institute of Geophysics (IGF), Polish Academy of Sciences, near the locality of Braniewo in northern Poland. PGNiG realized a 20-km-long reflection profile, using vibroseis and dynamite shooting; the aim of the reflection survey was to characterise Silurian shale gas reservoir. IGF deployed 59 seismic stations along this profile and registered additional full-spread wide-angle refraction and reflection data, with offsets up to 12 km; maximum offsets from the seismic reflection survey was 3 km. To improve the velocity information two velocity logs from near deep boreholes were used. The main goal of the joint reflection-refraction interpretation was to find relations between velocity field from reflection velocity analysis and refraction tomography, and to build a velocity model which would be consistent for both, reflection and refraction, datasets. In this paper we present imaging results and velocity models from Braniewo2014 experiment and the methodology we used.

Interpretation of reflection seismic data acquired for Knight Hawk Coal, LLC.

DOT National Transportation Integrated Search

2011-10-01

The Missouri University of Science and Technology geophysical crew acquired approximately 3000 lineal feet of reflection seismic : data along five separate traverses (1-5) at the PEUG South mine site. The objective was to determine if any of the trav...

Seismic stratigraphic architecture of the Disko Bay trough-mouth fan system, West Greenland

NASA Astrophysics Data System (ADS)

Hofmann, Julia C.; Knutz, Paul C.

2015-04-01

Spatial and temporal changes of the Greenland Ice Sheet on the continental shelf bordering Baffin Bay remain poorly constrained. Then as now, fast-flowing ice streams and outlet glaciers have played a key role for the mass balance and stability of polar ice sheets. Despite their significance for Greenland Ice Sheet dynamics and evolution, our understanding of their long-term behaviour is limited. The central West Greenland margin is characterized by a broad continental shelf where a series of troughs extend from fjords to the shelf margin, acting as focal points for trough-mouth fan (TMF) accummulations. The sea-ward bulging morphology and abrupt shelf-break of these major depositional systems is generated by prograding depocentres that formed during glacial maxima when ice streams reached the shelf edge, delivering large amounts of subglacial sediment onto the continental slope (Ó Cofaigh et al., 2013). The aim of this study is to unravel the seismic stratigraphic architecture and depositional processes of the Disko Bay TMF, aerially the largest single sedimentary system in West Greenland, using 2D and 3D seismic reflection data, seabed bathymetry and stratigraphic information from exploration well Hellefisk-1. The south-west Disko Bay is intersected by a deep, narrow trough, Egedesminde Dyb, which extends towards the southwest and links to the shallower and broader cross-shelf Disko Trough (maximum water depths of > 1000 m and a trough length of c. 370 km). Another trough-like depression (trough length of c. 120 km) in the northern part of the TMF, indicating a previous position of the ice stream, can be distinguished on the seabed topographic map and the seismic images. The Disko Bay TMF itself extends from the shelf edge down to the abyssal plain (abyssal floor depths of 2000 m) of the southern Baffin Bay. Based on seismic stratigraphic configurations relating to reflection terminations, erosive patterns and seismic facies (Mitchum et al., 1977), the TMF succession has been divided into five seismic units, each representing different stages in the progradational accumulation of the TMF system. This poster and ongoing study will discuss how the ice-stream flow switching is linked to changes in depocentres of sedimentary sequences and further investigate the major controls, e.g. ice-sheet dynamics, ocean-climate changes, tectonic forcing and subglacial geology, that determined the evolution of the Disko Bay TMF. Essencial bibliography Mitchum, R.M. Jr., Vail, P.R., Sangree, J.B., 1977. Seismic stratigraphy and global changes of sea level, Part 6: Stratigraphic interpretation of seismic reflection patterns in depositional sequences. AAPG Memoir 26, 117-133. Ó Cofaigh, C., Andrews, J.T., Jennings, A.E., Dowdeswell, J.A., Hogan, K.A., Kilfeather, A.A., Sheldon, C., 2013. Glacimarine lithofacies, provenance and depositional processes on a West Greenland trough-mouth fan. Journal of Quaternary Science, 28(1), 13-26.

Anatomy of the Chesapeake Bay impact structure revealed by seismic imaging, Delmarva Peninsula, Virginia, USA

USGS Publications Warehouse

Catchings, R.D.; Powars, D.S.; Gohn, G.S.; Horton, J. Wright; Goldman, M.R.; Hole, J.A.

2008-01-01

A 30-km-long, radial seismic reflection and refraction survey completed across the northern part of the late Eocene Chesapeake Bay impact structure (CBIS) on the Delmarva Peninsula, Virginia, USA, confirms that the CBIS is a complex central-peak crater. We used a tomographic P wave velocity model and low-fold reflection images, constrained by data from two deep boreholes located on the profile, to interpret the structure and composition of the upper 5 km of crust. The seismic images exhibit well-defined structural features, including (with increasing radial distance) a collapsed central uplift, a breccia-filled moat, and a collapsed transient-crater margin (which collectively constitute a ???40-km-wide collapsed transient crater), and a shallowly deformed annular trough. These seismic images are the first to resolve the deep structure of the crater (>1 km) and the boundaries between the central uplift, moat, and annular trough. Several distinct seismic signatures distinguish breccia units from each other and from more coherent crystalline rocks below the central uplift, moat, and annular trough. Within the moat, breccia extends to a minimum depth of 1.5 km or a maximum of 3.5 km, depending upon the interpretation of the deepest layered materials. The images show ???350 to 500 m of postimpact sediments above the impactites. The imaged structure of the CBIS indicates a complex sequence of event during the cratering process that will provide new constraints for numerical modeling. Copyright 2008 by the American Geophysical Union.

Arc-arc Collision Structure in the Southernmost Part of the Kuril Trench Region -Results from Integrated Analyses of the 1998-2000 Hokkaido Transect Seismic Data-

NASA Astrophysics Data System (ADS)

Iwasaki, Takaya; Tsumura, Noriko; Ito, Tanio; Sato, Hiroshi; Kurashimo, Eiji; Hirata, Naoshi; Arita, Kazunori; Noda, Katsuya; Fujiwara, Akira; Abe, Susumu; Kikkuchi, Shunsuke; Suzuki, Kazuko

2015-04-01

The Hokkaido Island, located in the southernmost part of the Kuril trench region, has been under a unique tectonic environment of arc-arc collision. Due to the oblique subduction of the Pacific (PAC) plate, the Kuril forearc sliver started to collide against Northeast (NE) Japan arc from the east at the time of middle Miocene to form complicated structures in the Hidaka collision zone (HCZ), as characterized by the westward obduction of the crustal rocks of the Kuril arc (the Hidaka metamorphic belt (HMB)) along the Hidaka main thrust (HMT) and a thick foreland fold-and-thrust belt. In and around the HCZ, a series of seismic reflection/refraction experiments were undertaken from 1994 to 2000, which provided important structural features including crustal delamination in the southern HCZ and a thick fold-and-thrust belt with velocity reversals (low velocity layers) in the northern HCZ. Reprocessing/reinterpretation for these data sets, which started in 2012, is aimed to construct a more detailed collision model through new processing and interpretation techniques. A multi-disciplinary project of the 1998-2000 Hokkaido Transect, crossing the northern part of the HCZ in EW direction, collected high-quality seismic data on a 227-km seismic refraction/wide-angle reflection profile and three seismic reflection lines. Our reanalyses revealed interesting collision structure ongoing in the northern part of the HCZ. The westward obduction of the Kuril arc crust was clearly imaged along the HMT. This obduction occurs at a depth of 27-30 km, much deeper than in the southern HCZ (23-25 km). The CRS/MDRS processing to the reflection data firstly succeeded in imaging clear reflection events at a 30-45 km depth below the obducted Kuril arc crust. These events show an eastward dip, probably corresponding to the lower crust/Moho within the NE Japan arc descending down to the east under the collision zone. Gently eastward dipping structures above these events (in a depth range of 5-10 km) are interpreted to be fragments of Cretaceous subduction/arc complexes or deformation interfaces branched from the HMT. The refraction/wide-angle reflection analysis revealed a series of eastward dipping interfaces at depths of 15-30 km east of the HMT, some of which show a very large Vp contrast exceeding 0.5-1.0 km/s. The subducted NE Japan arc meets the Kuril arc 20-40 km east of the HMT at a depth of 20-30 km. The above mentioned high Vp contrasts may result from the mixture of the upper crustal (low Vp) materials of the NE Japan arc and lower crustal (high Vp) materials of the Kuril arc. Seismic reflection image in the southern HCZ reprocessed by almost the same techniques confirms a clear crustal delamination, where the upper 23-km crust is thrust up along the HMT while the lower part of the crust descends down to the subducted PAC plate. At the moment, the results in the northern HCZ do not provide positive evidence on shallow crustal delamination as found in the case of the southern HCZ, suggesting regional difference in collision style along the HMT.

Enhancing analog seismic data resolution using the A/D converter: Examples of Sicilia Channel and Marmara Sea data set

NASA Astrophysics Data System (ADS)

Alp, H.

2015-12-01

We present here two data set composed of about 20 multichannel seismic data profiles, for a total of 1102 km of data acquired in the Sicilia Channel in Italy and Marmara Sea in Turkey. The data set of Multichannel seismic reflection profiles and well information acquired for commercial purpose by oil companies in the 1970's and 1980's. All profiles in Sicilia Channel, which are available on .pdf files were downloaded from VIDEPI website. Other profiles in Marmara Sea were taken from Turkish Petroleum Corporation. The first step was to convert the graphic files SEG-Y format files, using SeisTrans® software. Due to the great inhomogeneity of the various seismic lines, which have been recorded from different companies with different acquisition parameters, it has been necessary a great job of homogenization and noise reduction through the use of adequate band-pass filters. Then, for each reconstructed seismic line, SEG-Y header editing was necessary in order to assign the CDP (common-depth-points) and the SP (shot points) to the corresponding geographic coordinates. The SEG-Y files so created were uploaded and archived into a project using the Kingdom Suite® seismic package. To perform the calibration of seismic data with the stratigraphic wells, the classic problem is to identify on seismic profiles the reflections corresponding to the lithological variations identified in the wells. This is because the vertical scale of the seismic data is expressed in time, while that of the wells is expressed in meters. The main unknown is then the sound velocity within the different lithologies. In order to better correlate real data reflections with the corresponding stratigraphic discontinuities, synthetic seismogram have been created from the reflectivity series obtained through acoustic impedance calculations. They represent an example of forward modeling to match as closely as possible the real seismic data.

Velocity Model for CO2 Sequestration in the Southeastern United States Atlantic Continental Margin

NASA Astrophysics Data System (ADS)

Ollmann, J.; Knapp, C. C.; Almutairi, K.; Almayahi, D.; Knapp, J. H.

2017-12-01

The sequestration of carbon dioxide (CO2) is emerging as a major player in offsetting anthropogenic greenhouse gas emissions. With 40% of the United States' anthropogenic CO2 emissions originating in the southeast, characterizing potential CO2 sequestration sites is vital to reducing the United States' emissions. The goal of this research project, funded by the Department of Energy (DOE), is to estimate the CO2 storage potential for the Southeastern United States Atlantic Continental Margin. Previous studies find storage potential in the Atlantic continental margin. Up to 16 Gt and 175 Gt of storage potential are estimated for the Upper Cretaceous and Lower Cretaceous formations, respectively. Considering 2.12 Mt of CO2 are emitted per year by the United States, substantial storage potential is present in the Southeastern United States Atlantic Continental Margin. In order to produce a time-depth relationship, a velocity model must be constructed. This velocity model is created using previously collected seismic reflection, refraction, and well data in the study area. Seismic reflection horizons were extrapolated using well log data from the COST GE-1 well. An interpolated seismic section was created using these seismic horizons. A velocity model will be made using P-wave velocities from seismic reflection data. Once the time-depth conversion is complete, the depths of stratigraphic units in the seismic refraction data will be compared to the newly assigned depths of the seismic horizons. With a lack of well control in the study area, the addition of stratigraphic unit depths from 171 seismic refraction recording stations provides adequate data to tie to the depths of picked seismic horizons. Using this velocity model, the seismic reflection data can be presented in depth in order to estimate the thickness and storage potential of CO2 reservoirs in the Southeastern United States Atlantic Continental Margin.

Shear-wave seismic reflection imaging and impedance inversion for a near-surface point-bar

NASA Astrophysics Data System (ADS)

Benton, N. W.; Morrison, M.; Lorenzo, J. M.; Odom, B.; Clift, P. D.; Olson, E.; Gostic, A.

2017-12-01

Imaging and inversion of SH-waves are useful to detect, map, and quantitatively characterize near-surface point-bar strata. We conduct a horizontally-polarized (SH) reflection survey across and along a near-surface (9 - 40 m) downstream point-bar. We invert for shear-impedance profiles and correlate our interpretation to electrical conductivity (EC) logs in adjacent wells to study the internal architecture and lithology of point-bars. We acquire two common-midpoint (CMP) SH-wave seismic reflection lines at False River (Point Coupee Parish, Louisiana). A 104 m long seismic line (L1) is oriented orthogonal (NW - SE) to point-bar strike. A second line (L2) is 48 m long and set parallel to point-bar strike (NE - SW). Two EC wells lie 33 m apart. Both wells are parallel with respect to the L1 survey and offset from it by 15 m. EC log measurements range from 1 - 25 m depth. Interference of Love-waves prevents seismic imaging at depths less than 9 m. The L1 and L2 data sets are inverted for shear-impedance using a model-based band-limited impedance (BLIMP) algorithm that incorporates a low-frequency velocity model. This model is also used for the depthing processing. The L1 cross-section shows coherent dipping reflection events ( 4 - 7º) from 0.15 - 0.35 s (10 - 40 m). The corresponding shear-impedance profile also reveals coherent and dipping impedance contrasts that grow in magnitude with increasing depth. The L2 cross-section shows comparatively less dip ( 1º) as well as sharper and shallower continuity of reflection events (0.1 - 0.28 s TWT or 9 - 25 m). Depth-converted (TVD) seismic amplitudes and impedance values correlate to near-surface point-bar geology via superposition of log data. The first well (W5) shows distinct EC local maxima (+50 - 70 mS/m) at 14.5 and 15.5 m depth that correlate well with the seismic amplitudes and impedance values from both L1 and L2 data sets. The second well (W7) shows comparatively lower local maxima (+40 - 60 mS/m) but at greater depths (15.5 and 16.5 m). W5 correlates better with the seismic cross-section and impedance profile from L2 at 10, 12.5, 14.5, 15.5, and 19 m depth. EC maxima align with distinct shear-impedance values for L1 and L2 profiles. Our results provide a new and useful perspective of remotely analyzing the architecture and lithological properties of near-surface point-bars.

Inversion of multicomponent seismic data and rock-physics intepretation for evaluating lithology, fracture and fluid distribution in heterogeneous anisotropic reservoirs

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ilya Tsvankin; Kenneth L. Larner

2004-11-17

Within the framework of this collaborative project with the Lawrence Livermore National Laboratory (LLNL) and Stanford University, the Colorado School of Mines (CSM) group developed and implemented a new efficient approach to the inversion and processing of multicomponent, multiazimuth seismic data in anisotropic media. To avoid serious difficulties in the processing of mode-converted (PS) waves, we devised a methodology for transforming recorded PP- and PS-wavefields into the corresponding SS-wave reflection data that can be processed by velocity-analysis algorithms designed for pure (unconverted) modes. It should be emphasized that this procedure does not require knowledge of the velocity model and canmore » be applied to data from arbitrarily anisotropic, heterogeneous media. The azimuthally varying reflection moveouts of the PP-waves and constructed SS-waves are then combined in anisotropic stacking-velocity tomography to estimate the velocity field in the depth domain. As illustrated by the case studies discussed in the report, migration of the multicomponent data with the obtained anisotropic velocity model yields a crisp image of the reservoir that is vastly superior to that produced by conventional methods. The scope of this research essentially amounts to building the foundation of 3D multicomponent, anisotropic seismology. We have also worked with the LLNL and Stanford groups on relating the anisotropic parameters obtained from seismic data to stress, lithology, and fluid distribution using a generalized theoretical treatment of fractured, poroelastic rocks.« less

Encasement and subsidence of salt minibasins: observations from the SE Precaspian Basin and numerical modeling.

NASA Astrophysics Data System (ADS)

Fernandez, Naiara; Duffy, Oliver B.; Hudec, Michael R.; Jackson, Christopher A.-L.; Dooley, Tim P.; Jackson, Martin P. A.; Burg, George

2017-04-01

The SE Precaspian Basin is characterized by an assemblage of Upper Permian to Triassic minibasins. A recently acquired borehole-constrained 3D reflection dataset reveals the existence of abundant intrasalt reflection packages lying in between the Permo-Triassic minibasins. We propose that most of the mapped intrasalt reflection packages in the study area are minibasins originally deposited on top of salt that were later incorporated into salt by encasement processes. This makes the SE Precaspian Basin a new example of a salt province populated by encased minibasins, which until now had been mainly described from the Gulf of Mexico. Identifying salt-encased sediment packages in the study area has been crucial, not only because they provide a new exploration target, but also because they can play a key role on improving seismic imaging of adjacent or deeper stratigraphic sections. Another remarkable feature observed in the seismic dataset is the widespread occurrence of distinct seismic sequences in the Permo-Triassic minibasins. Bowl- and wedge-shaped seismic sequences define discrete periods of vertical and asymmetric minibasin subsidence. In the absence of shortening, the bowl-to-wedge transition is typically associated with the timing of basal welding and subsequent rotation of the minibasins. Timing of minibasin welding has important implications when addressing the likelihood of suprasalt reservoir charging. We performed a set of 2D numerical simulations aimed at investigating what drives the tilting of minibasins and how it relates to welding. A key observation from the numerical models is that the bowl-to-wedge transition can predate the time of basal welding.

The Investigation of Active Tectonism Offshore Cide-Sinop, Southern Black Sea by Seismic Reflection and Bathymetric Data

NASA Astrophysics Data System (ADS)

Alp, Y. I.; Ocakoglu, N.; Kılıc, F.; Ozel, A. O.

2017-12-01

The active tectonism offshore Cide-Sinop at the Southern Black Sea shelf area was first time investigated by multi-beam bathymetric and multi-channel seismic reflection data under the Research Project of The Scientific and Technological Research Council of Turkey (TUBİTAK-ÇAYDAG-114Y057). The multi-channel seismic reflection data of about 700 km length were acquired in 1991 by Turkish Petroleum Company (TP). Multibeam bathymetric data were collected between 2002-2008 by the Turkish Navy, Department of Navigation, Hydrography and Oceanography (TN-DNHO). Conventional data processing steps were applied as follows: in-line geometry definition, shot-receiver static correction, editing, shot muting, gain correction, CDP sorting, velocity analysis, NMO correction, muting, stacking, predictive deconvolution, band-pass filtering, finite-difference time migration, and automatic gain correction. Offshore area is represented by a quite smooth and large shelf plain with an approx. 25 km wide and the water depth of about -100 m. The shelf gently deepens and it is limited by the shelf break with average of -120 m contour. The seafloor morphology is charasterised by an erosional surface. Structurally, E-W trending strike-slip faults with generally compression components and reverse/thrust faults have been regionally mapped for the first time. Most of these faults deform all seismic units and reach the seafloor delimiting the morphological highs and submarine plains. Thus, these faults are intepreted as active faults. These results support the idea that the area is under the active compressional tectonic regime

Mapping the megathrust beneath the northern Gulf of Alaska using wide-angle seismic reflection/refraction profiles

DOE Office of Scientific and Technical Information (OSTI.GOV)

Brocher, T.M.; Fuis, G.S.; Fisher, M.A.

1993-04-01

In the northern Gulf of Alaska and Prince William Sound, wide-angle seismic reflection/refraction profiling, earthquake studies, and laboratory measurements of physical properties are used to determine the geometry of the Prince William and Yakutat terranes, and the subducting Pacific plate. In this complex region, the Yakutat terrane is underthrust beneath the Prince William terrane, and both terranes are interpreted to be underlain by the Pacific plate. Wide-angle seismic reflection/refraction profiles recorded along 5 seismic lines are used to unravel this terrane geometry. Modeled velocities in the upper crust of the Prince William terrane (to 18-km depth) agree closely with laboratorymore » velocity measurements of Orca Group phyllites and quartzofeldspathic graywackes (the chief components of the Prince William terrane) to hydrostatic pressures as high as 600 MPa (6 KBAR). An interpretation consistent with these data extends the Prince William terrane to at least 18-km depth. A landward dipping reflection at depths of 16--24 km is interpreted as the base of the Prince William terrane. This reflector corresponds to the top of the Wadati-Benioff zone seismicity and is interpreted as the megathrust. Beneath this reflector is a 6.9-km/s refractor, that is strongly reflective and magnetic, and is interpreted to be gabbro in Eocene age oceanic crust of the underthrust Yakutat terrane. Both wide-angle seismic and magnetic anomaly data indicate that the Yakutat terrane has been underthrust beneath the Prince William terrane for at least a few hundred kilometers. Wide-angle seismic data are consistent with a 9 to 10[degree] landward dip of the subducting Pacific plate, distinctly different from the inferred average 3 to 4[degree] dip of the overlying 6.9-km/s refractor and Wadati-Benioff seismic zone. The preferred interpretation of the geophysical data is that one composite plate, composed of the Pacific and Yakutat plates, is subducting beneath southern Alaska.« less

Two-dimensional magnetotelluric inversion using reflection seismic data as constraints and application in the COSC project

NASA Astrophysics Data System (ADS)

Yan, Ping; Kalscheuer, Thomas; Hedin, Peter; Garcia Juanatey, Maria A.

2017-04-01

We present a novel 2-D magnetotelluric (MT) inversion scheme, in which the local weights of the regularizing smoothness constraints are based on the envelope attribute of a reflection seismic image. The weights resemble those of a previously published seismic modification of the minimum gradient support method. We measure the directional gradients of the seismic envelope to modify the horizontal and vertical smoothness constraints separately. Successful application of the inversion to MT field data of the Collisional Orogeny in the Scandinavian Caledonides (COSC) project using the envelope attribute of the COSC reflection seismic profile helped to reduce the uncertainty of the interpretation of the main décollement by demonstrating that the associated alum shales may be much thinner than suggested by a previous inversion model. Thus, the new model supports the proposed location of a future borehole COSC-2 which is hoped to penetrate the main décollement and the underlying Precambrian basement.

High-resolution seismic reflection survey near SPR surface collapse feature at Weeks Island, Louisiana

DOE Office of Scientific and Technical Information (OSTI.GOV)

Miller, R.D.; Xia, J.; Harding, R.S. Jr.

1994-12-31

Shallow high resolution 2-D and 3-D seismic reflection techniques are assisting in the subsurface delineation of a surface collapse feature (sinkhole) at Weeks Island, Louisiana. Seismic reflection surveys were conducted in March 1994. Data from walkaway noise tests were used to assist selection of field recording parameters. The top of the salt dome is about 180 ft below ground surface at the sinkhole. The water table is an estimated 90 ft below the ground surface. A single coherent reflection was consistently recorded across the entire area of the survey, although stacking velocity and spectral content of the event varied. Onmore » the basis of observed travel times and stacking velocities, the coherent reflection event appears to originate above the top of the salt, possibly at or near the water table. Identification of this reflector will be made form borehole investigations currently planned for the sinkhole site. A depression or time sag in this reflection event is clearly evident in both the 2-D and 3-D seismic data in the immediate vicinity of the sinkhole. The time sag appears to be related to the subsurface structure of the reflector and not to near surface topography or velocity effects. Elsewhere in the survey area, observed changes in reflection travel times and wavelet character appear to be related to subsurface geologic structure. These seismic observations may assist in predicting where future sinkholes will develop after they have been tied to borehole data collected at the site.« less

Seismic-reflection data on the eastern U.S. continental shelf acquired by M. V. L'OLONNOIS as part of the Atlantic Margin Coring Project (AMCOR) of the U.S. Geological Survey, July-September 1976

USGS Publications Warehouse

Robb, James M.

1980-01-01

In 1976 the U.S. Geological Survey undertook a program to sample the eastern United States Shelf for stratigraphic information by drilling a set of core holes. Results of this Atlantic Margin Coring Program (AMCOR) have been reported by Hathaway and others. Sites were chosen from seismic-reflection data and were reviewed by a safety panel to minimize the risk of penetrating any hydrocarbon accumulation which might lead to environmental contamination.The M-V-L'OLONNOIS, the service ship for the drilling operation, was fitted with seismic-reflection profiling equipment (listed below), to run seismic-reflection profiles before drilling began on each hole. This provided additional assurance that no closed structures would be penetrated and allowed minor adjustment with the site selection. A total of 491 km of high-resolution seismic profiles was collected on 22 sites.Equipment used (specifics for each site noted on records): Bolt Air Guns 1-40 cubic inch chambers EPC Recorder Teledyne Minisparker (last two sites) Navigation used two Internav 101 Loran-C receivers.

Waveform modeling of the seismic response of a mid-ocean ridge axial melt sill

NASA Astrophysics Data System (ADS)

Xu, Min; Stephen, R. A.; Canales, J. Pablo

2017-12-01

Seismic reflections from axial magma lens (AML) are commonly observed along many mid-ocean ridges, and are thought to arise from the negative impedance contrast between a solid, high-speed lid and the underlying low-speed, molten or partially molten (mush) sill. The polarity of the AML reflection ( P AML P) at vertical incidence and the amplitude vs offset (AVO) behavior of the AML reflections (e.g., P AML P and S-converted P AML S waves) are often used as a diagnostic tool for the nature of the low-speed sill. Time-domain finite difference calculations for two-dimensional laterally homogeneous models show some scenarios make the interpretation of melt content from partial-offset stacks of P- and S-waves difficult. Laterally heterogeneous model calculations indicate diffractions from the edges of the finite-width AML reducing the amplitude of the AML reflections. Rough seafloor and/or a rough AML surface can also greatly reduce the amplitude of peg-leg multiples because of scattering and destructive interference. Mid-crustal seismic reflection events are observed in the three-dimensional multi-channel seismic dataset acquired over the RIDGE-2000 Integrated Study Site at East Pacific Rise (EPR, cruise MGL0812). Modeling indicates that the mid-crustal seismic reflection reflections are unlikely to arise from peg-leg multiples of the AML reflections, P-to- S converted phases, or scattering due to rough topography, but could probably arise from deeper multiple magma sills. Our results support the identification of Marjanović et al. (Nat Geosci 7(11):825-829, 2014) that a multi-level complex of melt lenses is present beneath the axis of the EPR.

Imaging Basin Structure with Teleseismic Virtual Source Reflection Profiles

NASA Astrophysics Data System (ADS)

Yang, Z.; Sheehan, A. F.; Yeck, W. L.; Miller, K. C.; Worthington, L. L.; Erslev, E.; Harder, S. H.; Anderson, M. L.; Siddoway, C. S.

2011-12-01

We demonstrate a case of using teleseisms recorded on single channel high frequency geophones to image upper crustal structure across the Bighorn Arch in north-central Wyoming. The dataset was obtained through the EarthScope FlexArray Bighorn Arch Seismic Experiment (BASE). In addition to traditional active and passive source seismic data acquisition, BASE included a 12 day continuous (passive source) deployment of 850 geophones with 'Texan' dataloggers. The geophones were deployed in three E-W lines in north-central Wyoming extending from the Powder River Basin across the Bighorn Mountains and across the Bighorn Basin, and two N-S lines on east and west flanks of the Bighorn Mountains. The station interval is roughly 1.5-2 km, good for imaging coherent shallow structures. The approach used in this study uses the surface reflection as virtual seismic source and reverberated teleseismic P-wave phase (PpPdp) (teleseismic P-wave reflected at receiver side free surface and then reflected off crustal seismic interface) to construct seismic profiles. These profiles are equivalent to conventional active source seismic reflection profiles except that high-frequency (up to 2.4 Hz) transmitted wave fields from distant earthquakes are used as sources. On the constructed seismic profiles, the coherent PpPdp phases beneath Powder River and Bighorn Basins are distinct after the source wavelet is removed from the seismograms by deconvolution. Under the Bighorn Arch, no clear coherent signals are observed. We combine phases PpPdp and Ps to constrain the averaged Vp/Vs: 2.05-2.15 for the Powder River Basin and 1.9-2.0 for the Bighorn Basin. These high Vp/Vs ratios suggest that the layers within which P-wave reverberates are sedimentary. Assuming Vp as 4 km/s under the Powder River Basin, the estimated thickness of sedimentary layer above reflection below the profile is 3-4.5 km, consistent with the depth of the top of the Tensleep Fm. Therefore we interpret the coherent PpPdp phases about 1-3 s after direct P-wave arrival as the reflections off the interface between the Paleozoic carbonates/sandstones and Mesozoic shales.

OCT structure, COB location and magmatic type of the S Angolan & SE Brazilian margins from integrated quantitative analysis of deep seismic reflection and gravity anomaly data

NASA Astrophysics Data System (ADS)

Cowie, Leanne; Kusznir, Nick; Horn, Brian

2014-05-01

Integrated quantitative analysis using deep seismic reflection data and gravity inversion have been applied to the S Angolan and SE Brazilian margins to determine OCT structure, COB location and magmatic type. Knowledge of these margin parameters are of critical importance for understanding rifted continental margin formation processes and in evaluating petroleum systems in deep-water frontier oil and gas exploration. The OCT structure, COB location and magmatic type of the S Angolan and SE Brazilian rifted continental margins are much debated; exhumed and serpentinised mantle have been reported at these margins. Gravity anomaly inversion, incorporating a lithosphere thermal gravity anomaly correction, has been used to determine Moho depth, crustal basement thickness and continental lithosphere thinning. Residual Depth Anomaly (RDA) analysis has been used to investigate OCT bathymetric anomalies with respect to expected oceanic bathymetries and subsidence analysis has been used to determine the distribution of continental lithosphere thinning. These techniques have been validated for profiles Lusigal 12 and ISE-01 on the Iberian margin. In addition a joint inversion technique using deep seismic reflection and gravity anomaly data has been applied to the ION-GXT BS1-575 SE Brazil and ION-GXT CS1-2400 S Angola deep seismic reflection lines. The joint inversion method solves for coincident seismic and gravity Moho in the time domain and calculates the lateral variations in crustal basement densities and velocities along the seismic profiles. Gravity inversion, RDA and subsidence analysis along the ION-GXT BS1-575 profile, which crosses the Sao Paulo Plateau and Florianopolis Ridge of the SE Brazilian margin, predict the COB to be located SE of the Florianopolis Ridge. Integrated quantitative analysis shows no evidence for exhumed mantle on this margin profile. The joint inversion technique predicts oceanic crustal thicknesses of between 7 and 8 km thickness with normal oceanic basement seismic velocities and densities. Beneath the Sao Paulo Plateau and Florianopolis Ridge, joint inversion predicts crustal basement thicknesses between 10-15km with high values of basement density and seismic velocities under the Sao Paulo Plateau which are interpreted as indicating a significant magmatic component within the crustal basement. The Sao Paulo Plateau and Florianopolis Ridge are separated by a thin region of crustal basement beneath the salt interpreted as a regional transtensional structure. Sediment corrected RDAs and gravity derived "synthetic" RDAs are of a similar magnitude on oceanic crust, implying negligible mantle dynamic topography. Gravity inversion, RDA and subsidence analysis along the S Angolan ION-GXT CS1-2400 profile suggests that exhumed mantle, corresponding to a magma poor margin, is absent..The thickness of earliest oceanic crust, derived from gravity and deep seismic reflection data, is approximately 7km consistent with the global average oceanic crustal thicknesses. The joint inversion predicts a small difference between oceanic and continental crustal basement density and seismic velocity, with the change in basement density and velocity corresponding to the COB independently determined from RDA and subsidence analysis. The difference between the sediment corrected RDA and that predicted from gravity inversion crustal thickness variation implies that this margin is experiencing approximately 500m of anomalous uplift attributed to mantle dynamic uplift.

A study of the Herald-Phillipstown fault in the Wabash Valley using drillhole and 3-D seismic reflection data

NASA Astrophysics Data System (ADS)

Kroenke, Samantha E.

In June 2009, a 2.2 square mile 3-D high resolution seismic reflection survey was shot in southeastern Illinois in the Phillipstown Consolidated oilfield. A well was drilled in the 3-D survey area to tie the seismic to the geological data with a synthetic seismogram from the sonic log. The objectives of the 3-D seismic survey were three-fold: (1) To image and interpret faulting of the Herald-Phillipstown Fault using drillhole-based geological and seismic cross-sections and structural contour maps created from the drillhole data and seismic reflection data, (2) To test the effectiveness of imaging the faults by selected seismic attributes, and (3) To compare spectral decomposition amplitude maps with an isochron map and an isopach map of a selected geologic interval (VTG interval). Drillhole and seismic reflection data show that various formation offsets increase near the main Herald-Phillipstown fault, and that the fault and its large offset subsidiary faults penetrate the Precambrian crystalline basement. A broad, northeast-trending 10,000 feet wide graben is consistently observed in the drillhole data. Both shallow and deep formations in the geological cross-sections reveal small horst and graben features within the broad graben created possibly in response to fault reactivations. The HPF faults have been interpreted as originally Precambrian age high-angle, normal faults reactivated with various amounts and types of offset. Evidence for strike-slip movement is also clear on several faults. Changes in the seismic attribute values in the selected interval and along various time slices throughout the whole dataset correlate with the Herald-Phillipstown faults. Overall, seismic attributes could provide a means of mapping large offset faults in areas with limited or absent drillhole data. Results of the spectral decomposition suggest that if the interval velocity is known for a particular formation or interval, high-resolution 3-D seismic reflection surveys could utilize these amplitudes as an alternative seismic interpretation method for estimating formation thicknesses. A VTG isopach map was compared with an isochron map and a spectral decomposition amplitude map. The results reveal that the isochron map strongly correlates with the isopach map as well as the spectral decomposition map. It was also found that thicker areas in the isopach correlated with higher amplitude values in the spectral decomposition amplitude map. Offsets along the faults appear sharper in these amplitudes and isochron maps than in the isopach map, possibly as a result of increased spatial sampling.

Improvements of Travel-time Tomography Models from Joint Inversion of Multi-channel and Wide-angle Seismic Data

NASA Astrophysics Data System (ADS)

Begović, Slaven; Ranero, César; Sallarès, Valentí; Meléndez, Adrià; Grevemeyer, Ingo

2016-04-01

Commonly multichannel seismic reflection (MCS) and wide-angle seismic (WAS) data are modeled and interpreted with different approaches. Conventional travel-time tomography models using solely WAS data lack the resolution to define the model properties and, particularly, the geometry of geologic boundaries (reflectors) with the required accuracy, specially in the shallow complex upper geological layers. We plan to mitigate this issue by combining these two different data sets, specifically taking advantage of the high redundancy of multichannel seismic (MCS) data, integrated with wide-angle seismic (WAS) data into a common inversion scheme to obtain higher-resolution velocity models (Vp), decrease Vp uncertainty and improve the geometry of reflectors. To do so, we have adapted the tomo2d and tomo3d joint refraction and reflection travel time tomography codes (Korenaga et al, 2000; Meléndez et al, 2015) to deal with streamer data and MCS acquisition geometries. The scheme results in a joint travel-time tomographic inversion based on integrated travel-time information from refracted and reflected phases from WAS data and reflected identified in the MCS common depth point (CDP) or shot gathers. To illustrate the advantages of a common inversion approach we have compared the modeling results for synthetic data sets using two different travel-time inversion strategies: We have produced seismic velocity models and reflector geometries following typical refraction and reflection travel-time tomographic strategy modeling just WAS data with a typical acquisition geometry (one OBS each 10 km). Second, we performed joint inversion of two types of seismic data sets, integrating two coincident data sets consisting of MCS data collected with a 8 km-long streamer and the WAS data into a common inversion scheme. Our synthetic results of the joint inversion indicate a 5-10 times smaller ray travel-time misfit in the deeper parts of the model, compared to models obtained using just wide-angle seismic data. As expected, there is an important improvement in the definition of the reflector geometry, which in turn, allows to improve the accuracy of the velocity retrieval just above and below the reflector. To test the joint inversion approach with real data, we combined wide-angle (WAS) seismic and coincident multichannel seismic reflection (MCS) data acquired in the northern Chile subduction zone into a common inversion scheme to obtain a higher-resolution information of upper plate and inter-plate boundary.

2D Seismic Reflection Data across Central Illinois

DOE Office of Scientific and Technical Information (OSTI.GOV)

Smith, Valerie; Leetaru, Hannes

In a continuing collaboration with the Midwest Geologic Sequestration Consortium (MGSC) on the Evaluation of the Carbon Sequestration Potential of the Cambro-Ordovician Strata of the Illinois and Michigan Basins project, Schlumberger Carbon Services and WesternGeco acquired two-dimensional (2D) seismic data in the Illinois Basin. This work included the design, acquisition and processing of approximately 125 miles of (2D) seismic reflection surveys running west to east in the central Illinois Basin. Schlumberger Carbon Services and WesternGeco oversaw the management of the field operations (including a pre-shoot planning, mobilization, acquisition and de-mobilization of the field personnel and equipment), procurement of the necessarymore » permits to conduct the survey, post-shoot closure, processing of the raw data, and provided expert consultation as needed in the interpretation of the delivered product. Three 2D seismic lines were acquired across central Illinois during November and December 2010 and January 2011. Traversing the Illinois Basin, this 2D seismic survey was designed to image the stratigraphy of the Cambro-Ordovician sections and also to discern the basement topography. Prior to this survey, there were no regionally extensive 2D seismic data spanning this section of the Illinois Basin. Between the NW side of Morgan County and northwestern border of Douglas County, these seismic lines ran through very rural portions of the state. Starting in Morgan County, Line 101 was the longest at 93 miles in length and ended NE of Decatur, Illinois. Line 501 ran W-E from the Illinois Basin – Decatur Project (IBDP) site to northwestern Douglas County and was 25 miles in length. Line 601 was the shortest and ran N-S past the IBDP site and connected lines 101 and 501. All three lines are correlated to well logs at the IBDP site. Originally processed in 2011, the 2D seismic profiles exhibited a degradation of signal quality below ~400 millisecond (ms) which made interpretation of the Mt. Simon and Knox sections difficult. The data quality also gradually decreased moving westward across the state. To meet evolving project objectives, in 2012 the seismic data was re-processed using different techniques to enhance the signal quality thereby rendering a more coherent seismic profile for interpreters. It is believed that the seismic degradation could be caused by shallow natural gas deposits and Quaternary sediments (which include abandoned river and stream channels, former ponds, and swamps with peat deposits) that may have complicated or changed the seismic wavelet. Where previously limited by seismic coverage, the seismic profiles have provided valuable subsurface information across central Illinois. Some of the interpretations based on this survey included, but are not limited to: - Stratigraphy generally gently dips to the east from Morgan to Douglas County. - The Knox Supergroup roughly maintains its thickness. There is little evidence for faulting in the Knox. However, at least one resolvable fault penetrates the entire Knox section. - The Eau Claire Formation, the primary seal for the Mt. Simon Sandstone, appears to be continuous across the entire seismic profile. - The Mt. Simon Sandstone thins towards the western edge of the basin. As a result, the highly porous lowermost Mt. Simon section is absent in the western part of the state. - Overall basement dip is from west to east. - Basement topography shows evidence of basement highs with on-lapping patterns by Mt. Simon sediments. - There is evidence of faults within the lower Mt. Simon Sandstone and basement rock that are contemporaneous with Mt. Simon Sandstone deposition. These faults are not active and do not penetrate the Eau Claire Shale. It is believed that these faults are associated with a possible failed rifting event 750 to 560 million years ago during the breakup of the supercontinent Rodinia.« less

Seismic reflection imaging, accounting for primary and multiple reflections

NASA Astrophysics Data System (ADS)

Wapenaar, Kees; van der Neut, Joost; Thorbecke, Jan; Broggini, Filippo; Slob, Evert; Snieder, Roel

2015-04-01

Imaging of seismic reflection data is usually based on the assumption that the seismic response consists of primary reflections only. Multiple reflections, i.e. waves that have reflected more than once, are treated as primaries and are imaged at wrong positions. There are two classes of multiple reflections, which we will call surface-related multiples and internal multiples. Surface-related multiples are those multiples that contain at least one reflection at the earth's surface, whereas internal multiples consist of waves that have reflected only at subsurface interfaces. Surface-related multiples are the strongest, but also relatively easy to deal with because the reflecting boundary (the earth's surface) is known. Internal multiples constitute a much more difficult problem for seismic imaging, because the positions and properties of the reflecting interfaces are not known. We are developing reflection imaging methodology which deals with internal multiples. Starting with the Marchenko equation for 1D inverse scattering problems, we derived 3D Marchenko-type equations, which relate reflection data at the surface to Green's functions between virtual sources anywhere in the subsurface and receivers at the surface. Based on these equations, we derived an iterative scheme by which these Green's functions can be retrieved from the reflection data at the surface. This iterative scheme requires an estimate of the direct wave of the Green's functions in a background medium. Note that this is precisely the same information that is also required by standard reflection imaging schemes. However, unlike in standard imaging, our iterative Marchenko scheme retrieves the multiple reflections of the Green's functions from the reflection data at the surface. For this, no knowledge of the positions and properties of the reflecting interfaces is required. Once the full Green's functions are retrieved, reflection imaging can be carried out by which the primaries and multiples are mapped to their correct positions, with correct reflection amplitudes. In the presentation we will illustrate this new methodology with numerical examples and discuss its potential and limitations.

High-resolution seismic reflection surveying with a land streamer

NASA Astrophysics Data System (ADS)

Cengiz Tapırdamaz, Mustafa; Cankurtaranlar, Ali; Ergintav, Semih; Kurt, Levent

2013-04-01

In this study, newly designed seismic reflection data acquisition array (land streamer) is utilized to image the shallow subsurface. Our acquisition system consist of 24 geophones screwed on iron plates with 2 m spacing, moving on the surface of the earth which are connected with fire hose. Completely original, 4.5 Kg weight iron plates provides satisfactory coupling. This land-streamer system enables rapid and cost effective acquisition of seismic reflection data due to its operational facilities. First test studies were performed using various seismic sources such as a mini-vibro truck, buffalo-gun and hammer. The final fieldwork was performed on a landslide area which was studied before. Data acquisition was carried out on the line that was previously measured by the seismic survey using 5 m geophone and shot spacing. This line was chosen in order to re-image known reflection patterns obtained from the previous field study. Taking penetration depth into consideration, a six-cartridge buffalo-gun was selected as a seismic source to achieve high vertical resolution. Each shot-point drilled 50 cm for gunshots to obtain high resolution source signature. In order to avoid surface waves, the offset distance between the source and the first channel was chosen to be 50 m and the shot spacing was 2 m. These acquisition parameters provided 12 folds at each CDP points. Spatial sampling interval was 1 m at the surface. The processing steps included standard stages such as gain recovery, editing, frequency filtering, CDP sorting, NMO correction, static correction and stacking. Furthermore, surface consistent residual static corrections were applied recursively to improve image quality. 2D F-K filter application was performed to suppress air and surface waves at relatively deep part of the seismic section. Results show that, this newly designed, high-resolution land seismic data acquisition equipment (land-streamer) can be successfully used to image subsurface. Likewise, results are and compatible with the results obtained from the previous study. This tool is extremely practical and very effective in imaging the shallow subsurface. Next step, an integrated GPS receiver will be added to recorder to obtain shot and receiver station position information during data acquisition. Also, some mechanical parts will be placed to further improve the stability and durability of the land streamer. In addition, nonlinear geophone layout will be added after completion of test. We are planning to use this land streamer not only in landslide areas but also in archaeological sites, engineering applications such as detection of buried pipelines and faults. This equipment will make it possible to perform these studies both in urban and territory areas.

Combination of different seismic methods and geotechnical sounding for a rapid characterization of the near-surface ground

NASA Astrophysics Data System (ADS)

Dietrich, P.; Kretschmer, F.; Vienken, T.; Popp, S.

2009-04-01

For economical and feasible seismic exploration of the near-surface ground, an approach has been developed for the joint application of reflection and refraction seismics as well as multi-channel analysis of surface waves (MASW). The measuring concept was tested within the research project COMEXTECH, dealing with the exploration of construction ground. Besides the overall characterization of the subsurface by refraction and reflection seismics, the MASW can be used for the derivation of relevant soil parameters such as soil stiffness. The centre of the measuring concept represents a land streamer, pulled by a vehicle equipped with the seismic source. The 24-channel land streamer may be tipped with different geophones, according to the focus of investigation. We used three fully equipped land streamers with 72 channels at all at the test site Nauen close to Berlin, Germany. The first 24 positions of the land streamer nearby the seismic source were filled with 4.5 Hz geophones. The next two land streamers were tipped with 14 Hz geophones, respectively. The idea behind this arrangement is that the positions close to the shot point, which are not utilisable for reflection seismics, can be used for the interpretation of surface waves. The signal was given with an accelerated weight drop mounted on a cross-country vehicle. Shots were arranged every meter, and four shots per shot point were executed for an increased signal/noise ratio. Three registration units (GeodeTM by Geometrics) were connected in series for signal recording. At the site, a profile of 164 m length was investigated in bidirectional manner in combination with geotechnical exploration technique. The purpose of bidirectional recording is to check the reliability and sensitivity of the seismic array and to increase the resolution of the image of the subsurface. By using the same shot points forth and back, a multiple overlap rate for certain common depth points (CDP) can be achieved, which is thought to result in an increased data quality. Geotechnical investigations comprise the use of Cone Penetrating Tests (CPT) for characterization of properties of the subsurface. Thereby the lithology may be derived by means of the friction ratio, which represents the ratio of the in-situ determined parameters of sleeve friction and cone resistance during CPT soundings. First results of data processing are available for the interpolated shear wave velocities (Vs) of the analysis of the Rayleigh-type surface waves on a multichannel record (MASW) by using the program SURFSEIS. The velocities are more or less laterally layered with zones of lower velocities (<180 m/s) in the upper subsurface and in about 5 m depth at the southern part of the profile. The strong increase of shear-wave velocities in 10 m depth and below (>250 m/s) is supposed to correspondent to a glacial moraine underlying the sandy sediments. The characterization of the near-surface ground by MASW corresponds well with the results of the nearby CPT soundings. By comparing the MASW results of the forward and backward recording of the profile, however, it turns out that the methodical approach of bidirectional seismic measurements still needs some tests. The produced 2-D Vs profiles show some marginal differences in the Vs-distribution in detail. Processing of seismic refraction and reflection data are in progress yet. In summery, the land streamer has the real advantage of fast data recording with a variable geophone array for different applications. The slight loss in quality of seismic data does not limit the use of the land streamer even on arable land. If carefully performed, geophones fitted on the land streamer still record data in an adequate quality for a feasible characterization of the subsurface, as shown in our study. Especially along long profiles the employment of a land streamer outplays stuck geophones by the fast progress in data recording due to the pulled array of geophones in a fixed geometry.

Monitoring CO 2 Storage at Cranfield, Mississippi with Time-Lapse Offset VSP – Using Integration and Modeling to Reduce Uncertainty

DOE PAGES

Daley, Thomas M.; Hendrickson, Joel; Queen, John H.

2014-12-31

A time-lapse Offset Vertical Seismic Profile (OVSP) data set was acquired as part of a subsurface monitoring program for geologic sequestration of CO 2. The storage site at Cranfield, near Natchez, Mississippi, is part of a detailed area study (DAS) site for geologic carbon sequestration operated by the U.S. Dept. of Energy’s Southeast Regional Carbon Sequestration Partnership (SECARB). The DAS site includes three boreholes, an injection well and two monitoring wells. The project team selected the DAS site to examine CO 2 sequestration multiphase fluid flow and pressure at the interwell scale in a brine reservoir. The time-lapse (TL) OVSPmore » was part of an integrated monitoring program that included well logs, crosswell seismic, electrical resistance tomography and 4D surface seismic. The goals of the OVSP were to detect the CO 2 induced change in seismic response, give information about the spatial distribution of CO 2 near the injection well and to help tie the high-resolution borehole monitoring to the 4D surface data. The VSP data were acquired in well CFU 31-F1, which is the ~3200 m deep CO 2 injection well at the DAS site. A preinjection survey was recorded in late 2009 with injection beginning in December 2009, and a post injection survey was conducted in Nov 2010 following injection of about 250 kT of CO 2. The sensor array for both surveys was a 50-level, 3-component, Sercel MaxiWave system with 15 m (49 ft) spacing between levels. The source for both surveys was an accelerated weight drop, with different source trucks used for the two surveys. Consistent time-lapse processing was applied to both data sets. Time-lapse processing generated difference corridor stacks to investigate CO 2 induced reflection amplitude changes from each source point. Corridor stacks were used for amplitude analysis to maximize the signal-to-noise ratio (S/N) for each shot point. Spatial variation in reflectivity (used to ‘map’ the plume) was similar in magnitude to the corridor stacks but, due to relatively lower S/N, the results were less consistent and more sensitive to processing and therefore are not presented. We examined the overall time-lapse repeatability of the OVSP data using three methods, the NRMS and Predictability (Pred) measures of Kragh and Christie (2002) and the signal-to-distortion ratio (SDR) method of Cantillo (2011). Because time-lapse noise was comparable to the observed change, multiple methods were used to analyze data reliability. The reflections from the top and base reservoir were identified on the corridor stacks by correlation with a synthetic response generated from the well logs. A consistent change in the corridor stack amplitudes from pre- to post-CO 2 injection was found for both the top and base reservoir reflections on all ten shot locations analyzed. In addition to the well-log synthetic response, a finite-difference elastic wave propagation model was built based on rock/fluid properties obtained from well logs, with CO 2 induced changes guided by time-lapse crosswell seismic tomography (Ajo-Franklin, et al., 2013) acquired at the DAS site. Time-lapse seismic tomography indicated that two reservoir zones were affected by the flood. The modeling established that interpretation of the VSP trough and peak event amplitudes as reflectivity from the top and bottom of reservoir is appropriate even with possible tuning effects. Importantly, this top/base change gives confidence in an interpretation that these changes arise from within the reservoir, not from bounding lithology. The modeled time-lapse change and the observed field data change from 10 shotpoints are in agreement for both magnitude and polarity of amplitude change for top and base of reservoir. Therefore, we conclude the stored CO 2 has been successfully detected and, furthermore, the observed seismic reflection change can be applied to Cranfield’s 4D surface seismic for spatially delineating the CO 2/brine interface.« less

High-Resolution Seismic Reflection Imaging of the Reelfoot Fault, New Madrid, Missouri

NASA Astrophysics Data System (ADS)

Rosandich, B.; Harris, J. B.; Woolery, E. W.

2017-12-01

Earthquakes in the Lower Mississippi Valley are mainly concentrated in the New Madrid Seismic Zone and are associated with reactivated faults of the Reelfoot Rift. Determining the relationship between the seismogenic faults (in crystalline basement rocks) and deformation at the Earth's surface and in the shallow subsurface has remained an active research topic for decades. An integrated seismic data set, including compressional (P-) wave and shear (S-) wave seismic reflection profiles, was collected in New Madrid, Missouri, across the "New Madrid" segment of the Reelfoot Fault, whose most significant rupture produced the M 7.5, February 7, 1812, New Madrid earthquake. The seismic reflection profiles (215 m long) were centered on the updip projection of the fault, which is associated with a surface drainage feature (Des Cyprie Slough) located at the base of a prominent east-facing escarpment. The seismic reflection profiles were collected using 48-channel (P-wave) and 24-channel (S-wave) towable landsteamer acquisition equipment. Seismic energy was generated by five vertical impacts of a 1.8-kg sledgehammer on a small aluminum plate for the P-wave data and five horizontal impacts of the sledgehammer on a 10-kg steel I-beam for the S-wave data. Interpretation of the profiles shows a west-dipping reverse fault (Reelfoot Fault) that propagates upward from Paleozoic sedimentary rocks (>500 m deep) to near-surface Quaternary sediments (<10 m deep). The hanging wall of the fault is anticlinally folded, a structural setting almost identical to that imaged on the Kentucky Bend and Reelfoot Lake segments (of the Reelfoot Fault) to the south.

Evaluation of seismic reflection data in the Davis and Lavender Canyons study area, Paradox Basin, Utah. [Faults, folds, joints, and collapse structures

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kitcho, C.A.; Wong, I.G.; Turcotte, F.T.

1986-08-01

Seismic reflection data purchased from petroleum industry brokers and acquired through group speculative surveys were interpreted for information on the regional subsurface geologic structure and stratigraphy within and surrounding the Davis and Lavender Canyons study area in the Paradox Basin of southeastern Utah. Structures of interest were faults, folds, joints, and collapse structures related to salt dissolution. The seismic reflection data were used to interpret stratigraphy by identifying continuous and discontinuous reflectors on the seismic profiles. Thickening and thinning of strata and possible areas of salt flowage or dissolution could be identified from the seismic data. Identifiable reflectors included themore » tops of the Precambrian and Mississippian, a distinctive interbed close to the middle of the Pennsylvanian Paradox salt formation (probably the interval between Salt Cycles 10 and 13), and near the top of the Paradox salt. Of the 56 faults identified from the seismic reflection interpretation, 33 trend northwest, west-northwest, or west, and most affect only the deeper part of the stratigraphic section. These faults are part of the deep structural system found throughout the Paradox Basin, including the fold and fault belt in the northeast part of the basin. The faults bound basement Precambrian blocks that experienced minor activity during Mississippian and early Pennsylvanian deposition, and showed major displacement during early Paradox salt deposition as the Paradox Basin subsided. Based on the seismic data, most of these faults appear to have an upward terminus between the top of the Mississippian and the salt interbed reflector.« less

Using Near Surface P and S Wave Velocities and Seismic Reflection Images to Detect the Westerly Extension of the Active Meishan Fault in Southwestern Taiwan

NASA Astrophysics Data System (ADS)

Putriani, E.; Huang, W. H.; Shih, R. C.

2017-12-01

The Southwestern Taiwan has higher potential seismic risks among the island. In 1906 the Meishan earthquake of magnitude 7.1 caused very severe damages. The associated Meishan fault was believed extended from Meishan westerly to Hsingang area for 23 km long; however, only the eastern part of the fault could be traces on the surface. The western part of the Meishan fault was simply proposed from the observed lineation of sand blow from the middle of the fault, the Minhsiung area westerly to the Hsingang area. The purpose of this paper is hope to prove the extension of this fault by using near surface P wave and S wave velocities and the seismic reflection images acquired across the suspicious fault location. Totally, we have conducted 20 seismic velocity survey lines, which were deployed in six areas with and without liquefaction observed, and 2 seismic reflection lines. The P and S wave velocities variations were used to analyze depth of the water table, the elastic modulus, soil porosity and the safety factor for soil liquefaction assessment. Preliminary result of the seismic velocity distribution was effective within 17 m deep from surface and showed no particular difference at the sites of liquefaction observed or no liquefaction. The results could indicate that the sand blow observed in 1906 were not site dependent, but more likely related to activity of the Meishan fault. In order to detect the detailed fault trace, the seismic reflection images will be combined for interpreting the buried Meishan fault in the final result.

Semiautomatic and Automatic Cooperative Inversion of Seismic and Magnetotelluric Data

NASA Astrophysics Data System (ADS)

Le, Cuong V. A.; Harris, Brett D.; Pethick, Andrew M.; Takam Takougang, Eric M.; Howe, Brendan

2016-09-01

Natural source electromagnetic methods have the potential to recover rock property distributions from the surface to great depths. Unfortunately, results in complex 3D geo-electrical settings can be disappointing, especially where significant near-surface conductivity variations exist. In such settings, unconstrained inversion of magnetotelluric data is inexorably non-unique. We believe that: (1) correctly introduced information from seismic reflection can substantially improve MT inversion, (2) a cooperative inversion approach can be automated, and (3) massively parallel computing can make such a process viable. Nine inversion strategies including baseline unconstrained inversion and new automated/semiautomated cooperative inversion approaches are applied to industry-scale co-located 3D seismic and magnetotelluric data sets. These data sets were acquired in one of the Carlin gold deposit districts in north-central Nevada, USA. In our approach, seismic information feeds directly into the creation of sets of prior conductivity model and covariance coefficient distributions. We demonstrate how statistical analysis of the distribution of selected seismic attributes can be used to automatically extract subvolumes that form the framework for prior model 3D conductivity distribution. Our cooperative inversion strategies result in detailed subsurface conductivity distributions that are consistent with seismic, electrical logs and geochemical analysis of cores. Such 3D conductivity distributions would be expected to provide clues to 3D velocity structures that could feed back into full seismic inversion for an iterative practical and truly cooperative inversion process. We anticipate that, with the aid of parallel computing, cooperative inversion of seismic and magnetotelluric data can be fully automated, and we hold confidence that significant and practical advances in this direction have been accomplished.

Magma intrusion and accumulation in the southern Altiplano: Structural observations from the PLUTONS project

NASA Astrophysics Data System (ADS)

West, M. E.; Christensen, D. H.; Pritchard, M. E.; Del Potro, R.; Gottsmann, J.; Unsworth, M.; Minaya, E.; Sunagua, M.; McNutt, S. R.; Yu, Q.; Farrell, A. K.

2012-12-01

The PLUTONS project is attempting to capture the process of magma intrusion and pluton formation, in situ, through multi-disciplinary study of known magmatic inflation centers. With support from the NSF Continental Dynamics program, and a sister project in the UK funded by NERC, two such centers are receiving focused study. Uturuncu volcano in the Altiplano of southern Bolivia is being investigated with combined seismics, magnetotellurics, geodesy, microgravity, geomorphology, petrology, geochemistry, historical studies and modeling. 350 km to the south, comparable investigations are targeting the Lastarria-Cordon del Azufre complex. Field studies are ongoing into 2013. In this presentation we highlight results from Uturuncu that bear on the crustal magmatic process. Seismic tomography, gravity and magnetotellurics indicate a complex structure in the upper 20 km with some evidence for partial melt. Seismic receiver functions indicate a layer of very low velocities across the region at 15-25 km depth that is almost certainly melt-rich. High conductivities corroborate the interpretation of a partial melt component to this layer. In addition to the throughgoing melt layer, seismic velocities and attenuation indicate shallow features above the melt body extending upward toward the surface. It is not clear whether these features are associated with recent uplift or are remnants from a previous period of activity. Uturuncu is seismically active with hundreds of locatable earthquakes each year. Seismic lineations and swarm behavior suggest that the seismicity reflects regional stress patterns. While there is little evidence that these earthquakes are the direct result of magmatic intrusion, the resulting high heat flow may be hastening existing strains.

Location, Reprocessing, and Analysis of Two Dimensional Seismic Reflection Data on the Jicarilla Apache Indian Reservation, New Mexico, Final Report, September 1, 1997-February 1, 2000

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ridgley, Jennie; Taylor, David J.; Huffman, Jr., A. Curtis

2000-06-08

Multichannel surface seismic reflection data recording is a standard industry tool used to examine various aspects of geology, especially the stratigraphic characteristics and structural style of sedimentary formations in the subsurface. With the help of the Jicarilla Apache Tribe and the Bureau of Indian Affairs we were able to locate over 800 kilometers (500 miles) of multichannel seismic reflection data located on the Jicarilla Apache Indian reservation. Most of the data was received in hardcopy form, but there were data sets where either the demultiplexed digital field data or the processed data accompanied the hardcopy sections. The seismic data wasmore » acquired from the mid 1960's to the early 1990's. The most extensive seismic coverage is in the southern part of the reservation, although there are two good surveys located on the northeastern and northwestern parts of the reservation. Most of the data show that subsurface formations are generally flat-lying in the southern and western portion of the reservation. There is, however, a significant amount of structure imaged on seismic data located over the San Juan Basin margin along the east-central and northern part of the reservation. Several west to east trending lines in these areas show a highly faulted monoclinal structure from the deep basin in the west up onto the basin margin to the east. Hydrocarbon exploration in flat lying formations is mostly stratigraphic in nature. Where there is structure in the subsurface and indications are that rocks have been folded, faulted, and fractured, exploration has concentrated on structural traps and porosity/permeability "sweet spots" caused by fracturing. Therefore, an understanding of the tectonics influencing the entire section is critical in understanding mechanisms for generating faults and fractures in the Cretaceous. It is apparent that much of the hydrocarbon production on the reservation is from fracture porosity in either source or reservoir sequences. Therefore it is important to understand the mechanism that controls the location and intensity of the fractures. A possible mechanism may be deep seated basement faulting that has been active through time. Examining the basement fault patterns in this part of the basin and their relation to fracture production may provide a model for new plays on the Jicarilla Indian Reservation. There are still parts of the reservation where the subsurface has not been imaged geophysically with either conventional two-dimensional or three-dimensional reflection seismic techniques. These methods, especially 3-D seismic, would provide the best data for mapping deep basement faulting. The authors would recommend that 3-D seismic be acquired along the Basin margin located along the eastern edge of the reservation and the results be used to construct detailed fault maps which may help to locate areas with the potential to contain highly fractured zones in the subsurface.« less

Near-surface mapping using SH-wave and P-wave seismic land-streamer data acquisition in Illinois, U.S

USGS Publications Warehouse

Pugin, Andre J.M.; Larson, T.H.; Sargent, S.L.; McBride, J.H.; Bexfield, C.E.

2004-01-01

SH-wave and P-wave high-resolution seismic reflection combined with land-streamer technology provide 3D regional maps of geologic formations that can be associated with aquifers and aquitards. Examples for three study areas are considered to demonstrate this. In these areas, reflection profiling detected near-surface faulting and mapped a buried glacial valley and its aquifers in two settings. The resulting seismic data can be used directly to constrain hydrogeologic modeling of shallow aquifers.

Deep Europe today: Geophysical synthesis of the upper mantle structure and lithospheric processes over 3.5 Ga

USGS Publications Warehouse

Artemieva, I.M.; Thybo, H.; Kaban, M.K.; ,

2006-01-01

We present a summary of geophysical models of the subcrustal lithosphere of Europe. This includes the results from seismic (reflection and refraction profiles, P- and S-wave tomography, mantle anisotropy), gravity, thermal, electromagnetic, elastic and petrological studies of the lithospheric mantle. We discuss major tectonic processes as reflected in the lithospheric structure of Europe, from Precambrian terrane accretion and subduction to Phanerozoic rifting, volcanism, subduction and continent-continent collision. The differences in the lithospheric structure of Precambrian and Phanerozoic Europe, as illustrated by a comparative analysis of different geophysical data, are shown to have both a compositional and a thermal origin. We propose an integrated model of physical properties of the European subcrustal lithosphere, with emphasis on the depth intervals around 150 and 250 km. At these depths, seismic velocity models, constrained by body-and surface-wave continent-scale tomography, are compared with mantle temperatures and mantle gravity anomalies. This comparison provides a framework for discussion of the physical or chemical origin of the major lithospheric anomalies and their relation to large-scale tectonic processes, which have formed the present lithosphere of Europe. ?? The Geological Society of London 2006.

Tectonic Inversion Along the Algerian and Ligurian Margins: On the Insight Provided By Latest Seismic Processing Techniques Applied to Recent and Vintage 2D Offshore Multichannel Seismic Data

NASA Astrophysics Data System (ADS)

Schenini, L.; Beslier, M. O.; Sage, F.; Badji, R.; Galibert, P. Y.; Lepretre, A.; Dessa, J. X.; Aidi, C.; Watremez, L.

2014-12-01

Recent studies on the Algerian and the North-Ligurian margins in the Western Mediterranean have evidenced inversion-related superficial structures, such as folds and asymmetric sedimentary perched basins whose geometry hints at deep compressive structures dipping towards the continent. Deep seismic imaging of these margins is difficult due to steep slope and superficial multiples, and, in the Mediterranean context, to the highly diffractive Messinian evaporitic series in the basin. During the Algerian-French SPIRAL survey (2009, R/V Atalante), 2D marine multi-channel seismic (MCS) reflection data were collected along the Algerian Margin using a 4.5 km, 360 channel digital streamer and a 3040 cu. in. air-gun array. An advanced processing workflow has been laid out using Geocluster CGG software, which includes noise attenuation, 2D SRME multiple attenuation, surface consistent deconvolution, Kirchhoff pre-stack time migration. This processing produces satisfactory seismic images of the whole sedimentary cover, and of southward dipping reflectors in the acoustic basement along the central part of the margin offshore Great Kabylia, that are interpreted as inversion-related blind thrusts as part of flat-ramp systems. We applied this successful processing workflow to old 2D marine MCS data acquired on the North-Ligurian Margin (Malis survey, 1995, R/V Le Nadir), using a 2.5 km, 96 channel streamer and a 1140 cu. in. air-gun array. Particular attention was paid to multiple attenuation in adapting our workflow. The resulting reprocessed seismic images, interpreted with a coincident velocity model obtained by wide-angle data tomography, provide (1) enhanced imaging of the sedimentary cover down to the top of the acoustic basement, including the base of the Messinian evaporites and the sub-salt Miocene series, which appear to be tectonized as far as in the mid-basin, and (2) new evidence of deep crustal structures in the margin which the initial processing had failed to reveal.

National Archive of Marine Seismic Surveys (NAMSS): A USGS-Boem Partnership to Provide Free and Easy Access to Previously Proprietary Seismic Reflection Data on the U.S. Outer Continental Shelf

NASA Astrophysics Data System (ADS)

Triezenberg, P. J.; Hart, P. E.; Childs, J. R.

2014-12-01

The National Archive of Marine Seismic Surveys (NAMSS) was established by the USGS in 2004 in an effort to rescue marine seismic reflection profile data acquired largely by the oil exploration industry throughout the US outer continental shelf (OCS). It features a Web interface for easy on-line geographic search and download. The commercial value of these data had decreased significantly because of drilling moratoria and newer acquisition technology, and large quantities were at risk of disposal. But, the data still had tremendous value for scientific research and education purposes, and an effort was undertaken to ensure that the data were preserved and publicly available. More recently, the USGS and Bureau of Ocean Energy Management (BOEM) have developed a partnership to make similarly available a much larger quantity of 2D and 3D seismic data acquired by the U.S. government for assessment of resources in the OCS. Under Federal regulation, BOEM is required to publicly release all processed geophysical data, including seismic profiles, acquired under an exploration permit, purchased and retained by BOEM, no sooner than 25 years after issuance of the permit. Data acquired prior to 1989 are now eligible for release. Currently these data are distributed on CD or DVD, but data discovery can be tedious. Inclusion of these data within NAMSS vastly increases the amount of seismic data available for research purposes. A new NAMSS geographical interface provides easy and intuitive access to the data library. The interface utilizes OpenLayers, Mapnik, and the Django web framework. In addition, metadata capabilities have been greatly increased using a PostgresSQL/PostGIS database incorporating a community-developed ISO-compliant XML template. The NAMSS database currently contains 452 2D seismic surveys comprising 1,645,956 line km and nine 3D seismic surveys covering 9,385 square km. The 2D data holdings consist of stack, migrated and depth sections, most in SEG-Y format.

Digital interactive image analysis by array processing

NASA Technical Reports Server (NTRS)

Sabels, B. E.; Jennings, J. D.

1973-01-01

An attempt is made to draw a parallel between the existing geophysical data processing service industries and the emerging earth resources data support requirements. The relationship of seismic data analysis to ERTS data analysis is natural because in either case data is digitally recorded in the same format, resulting from remotely sensed energy which has been reflected, attenuated, shifted and degraded on its path from the source to the receiver. In the seismic case the energy is acoustic, ranging in frequencies from 10 to 75 cps, for which the lithosphere appears semi-transparent. In earth survey remote sensing through the atmosphere, visible and infrared frequency bands are being used. Yet the hardware and software required to process the magnetically recorded data from the two realms of inquiry are identical and similar, respectively. The resulting data products are similar.

Inhomogeneous Crustal Structure of the Rifting in the Okinawa Trough, a Backarc Basin West of Kyushu, Japan, Deduced from Seismic Reflection and Refraction Data

NASA Astrophysics Data System (ADS)

Nishizawa, A.; Kaneda, K.; Oikawa, M.; Horiuchi, D.; Fujioka, Y.; Okada, C.

2017-12-01

Several depressions found under the thick sediments in the East China Sea shelf have been considered as failed rift basins. Their formation age becomes progressively younger from NW to SE and the youngest rift basin is the Okinawa Trough, an active backarc basin of the Ryukyu (Nansei-Shoto) arc-trench system, to the southwest of Kyusyu, Japan. Its rifting is in progress and related hydrothermal activity is present in the trough. The knowledge of the crustal structure of the trough is fundamental to understand the current active tectonics and predict the future of the trough. We, Japan Coast Guard, have conducted extensive seismic reflection and refraction surveys in the Ryukyu region since 2008 and compiled the seismic structures of the Okinawa Trough. We will show the crustal structures along seven along-trough and ten across-trough seismic survey lines. The P-wave velocity models beneath the Okinawa Trough generally show a thinned continental/island arc crust consisting of upper, middle, and lower crusts. Moho depths below the trough were estimated mainly from Moho reflection (PmP) travel times. The crustal thickness of the trough is thinner than those of the East China Sea shelf and of the Ryukyu Islands. The depth of the Moho below the trough decreases from over 30 km in the north to about 13 km in the south, indicating a difference in degree of the rifting process. The position of the shallowest Moho along the across-trough lines in the northern trough does not necessarily correspond to the center of the trough defined as the deepest water depth, but it corresponds to the transition area between the East China Sea shelf and the Okinawa Trough. An M7.1 earthquake occurred at the transition area on Nov. 14, 2015 (JST) and many aftershocks were observed along the transition. This seismic activity demonstrated that the area is under rifting tectonics in the present.

Velocity changes at Volcán de Colima: Seismic and Experimental observations

NASA Astrophysics Data System (ADS)

Lamb, Oliver; Lavallée, Yan; De Angelis, Silvio; Varley, Nick; Reyes-Dávila, Gabriel; Arámbula-Mendoza, Raúl; Hornby, Adrian; Wall, Richard; Kendrick, Jackie

2016-04-01

Immediately prior to dome-building eruptions, volcano-seismic swarms are a direct consequence of strain localisation in the ascending magma. A deformation mechanism map of magma subjected to strain localisation will help develop accurate numerical models, which, coupled to an understanding of the mechanics driving monitored geophysical signals prior to lava eruption, will enhance forecasts. Here we present how seismic data from Volcán de Colima, Mexico, is combined with experimental work to give insights into fracturing in and around magma. Volcán de Colima is a dome-forming volcano that has been almost-continuously erupting since November 1998. We use coda-wave interferometry to quantify small changes in seismic velocity structure between pairs of similar earthquakes, employing waveforms from clusters of repeating earthquakes. The changes in all pairs of events were then used together to create a continuous function of velocity change at all stations within 7 km of the volcano from October to December 1998. We complement our seismic data with acoustic emission data from tensional experiments using samples collected at Volcán de Colima. Decreases in velocity and frequency reflect changes in the sample properties prior to failure. By comparing experimental and seismic observations, we may place constraints on the conditions of the natural seismogenic processes. Using a combination of field and experimental data promises a greater understanding of the processes affecting the rise of magma during an eruption. This will help with the challenge of forecasting and hazard mitigation during dome-forming eruptions worldwide.

Archive of Boomer Seismic Reflection Data Collected During USGS Cruises 01SCC01 and 01SCC02, Timbalier Bay and Offshore East Timbalier Island, Louisiana, June-August, 2001

USGS Publications Warehouse

Calderon, Karynna; Dadisman, Shawn V.; Flocks, James G.; Kindinger, Jack G.; Wiese, Dana S.

2003-01-01

In June, July, and August of 2001, the U.S. Geological Survey (USGS), in cooperation with the University of New Orleans (UNO), the U.S. Army Corps of Engineers, and the Louisiana Department of Natural Resources, conducted a shallow geophysical and sediment core survey of Timbalier Bay and the Gulf of Mexico offshore East Timbalier Island, Louisiana. This report serves as an archive of unprocessed digital seismic reflection data, trackline navigation files, trackline navigation maps, observers' logbooks, Geographic Information Systems (GIS) information, and formal Federal Geographic Data Committee (FGDC) metadata. In addition, a filtered and gained digital Graphics Interchange Format (GIF) image of each seismic profile is provided. Please see Kulp and others (2002), Flocks and others (2003), and Kulp and others (in prep.) for further information about the sediment cores collected and the geophysical results. For convenience, a list of acronyms and abbreviations frequently used in this report is also included. This Digital Versatile Disc (DVD) document is readable on any computing platform that has standard DVD driver software installed. Documentation on this DVD was produced using Hyper Text Markup Language (HTML) utilized by the World Wide Web (WWW) and allows the user to access the information using a web browser (i.e. Netscape, Internet Explorer). To access the information contained on this disc, open the file 'index.htm' located at the top level of the disc using a web browser. This report also contains WWW links to USGS collaborators and other agencies. These links are only accessible if access to the Internet is available while viewing this DVD. The archived boomer seismic reflection data are in standard Society of Exploration Geophysicists (SEG) SEG-Y format (Barry et al., 1975) and may be downloaded for processing with public domain software such as Seismic Unix (SU), currently located at http://www.cwp.mines.edu/cwpcodes/index.html. Examples of SU processing scripts are provided in the BOOM.tar file located in the SU subfolder of the SOFTWARE folder located at the top level of this disc. In-house (USGS) DOS and Microsoft Windows compatible software for viewing SEG-Y headers - DUMPSEGY.EXE (Zihlman, 1992) - is provided in the USGS subfolder of the SOFTWARE folder. Processed profile images, trackline navigation maps, logbooks, and formal metadata may be viewed with a web browser.

Archive of Chirp Seismic Reflection Data Collected During USGS Cruises 01SCC01 and 01SCC02, Timbalier Bay and Offshore East Timbalier Island, Louisiana, June 30 - July 9 and August 1 - 12, 2001

USGS Publications Warehouse

Calderon, Karynna; Dadisman, Shawn V.; Flocks, James G.; Wiese, Dana S.; Kindinger, Jack G.

2003-01-01

In June, July, and August of 2001, the U.S. Geological Survey (USGS), in cooperation with the University of New Orleans, the U.S. Army Corps of Engineers, and the Louisiana Department of Natural Resources, conducted a shallow geophysical and sediment core survey of Timbalier Bay and the Gulf of Mexico offshore East Timbalier Island, Louisiana. This report serves as an archive of unprocessed digital seismic reflection data, trackline navigation files, trackline navigation maps, observers' logbooks, Geographic Information Systems (GIS) information, and formal Federal Geographic Data Committee (FGDC) metadata. In addition, a gained digital Graphics Interchange Format (GIF) image of each seismic profile is provided. Please see Kulp and others (2002), Flocks and others (2003), and Kulp and others (in prep.) for further information about the sediment cores collected and the geophysical results. For convenience, a list of acronyms and abbreviations frequently used in this report is also included. This Digital Versatile Disc (DVD) document is readable on any computing platform that has standard DVD driver software installed. Documentation on this DVD was produced using Hyper Text Markup Language (HTML) utilized by the World Wide Web (WWW) and allows the user to access the information using a web browser (i.e. Netscape, Internet Explorer). To access the information contained on these discs, open the file 'index.htm' located at the top level of each disc using a web browser. This report also contains WWW links to USGS collaborators and other agencies. These links are only accessible if access to the internet is available while viewing these DVDs. The archived chirp seismic reflection data are in standard Society of Exploration Geophysicists (SEG) SEG-Y format (Barry et al., 1975) and may be downloaded for processing with public domain software such as Seismic Unix (SU), currently located at http://www.cwp.mines.edu/cwpcodes/index.html. Examples of SU processing scripts are provided in the CHIRP.tar file located in the SU subfolder of the SOFTWARE folder located at the top level of each disc. In-house (USGS) DOS and Microsoft Windows compatible software for viewing SEG-Y headers - DUMPSEGY.EXE (Zihlman, 1992) - is provided in the USGS subfolder of the SOFTWARE folder. Processed profile images, trackline navigation maps, logbooks, and formal metadata may be viewed with a web browser.

Spatial relationships between crustal structures and mantle seismicity in the Vrancea Seismogenic Zone of Romania: Implications for geodynamic evolution

NASA Astrophysics Data System (ADS)

Enciu, Dana-Mihaela

Integration of active and passive-source seismic data is employed to study the relationships between crustal structures and seismicity in the SE Carpathian foreland of Romania, and the connection with the Vrancea Seismogenic Zone. Relocated crustal epicenters and focal mechanisms are correlated with industry seismic profiles Comanesti, Ramnicu Sarat, Braila and Buzau, the reprocessed DACIA PLAN profile and the DRACULA (Deep Reflection Acquisition Constraining Unusual Lithospheric Activity) II and III profiles in order to understand the link between neo-tectonic foreland deformation and Vrancea mantle seismicity. Projection of crustal foreland hypocenters onto deep seismic profiles identified active crustal faults suggesting a mechanical coupling between sedimentary, crustal and upper mantle structures on the Trotus, Sinaia and newly observed Ialomita Faults. Seismic reflection imaging revealed the absence of west dipping reflectors in the crust and an east dipping to horizontal Moho in the proximity of the Vrancea area. These findings argue against both 'subduction-in-place' and 'slab break-off' as viable mechanisms for generating Vrancea mantle seismicity.

Documenting channel features associated with gas hydrates in the Krishna-Godavari Basin, offshore India

USGS Publications Warehouse

Riedel, M.; Collett, T.S.; Shankar, Ude

2011-01-01

During the India National Gas Hydrate Program (NGHP) Expedition 01 in 2006 significant sand and gas hydrate were recovered at Site NGHP-01-15 within the Krishna-Godavari Basin, East Coast off India. At the drill site NGHP-01-15, a 5-8m thick interval was found that is characterized by higher sand content than anywhere else at the site and within the KG Basin. Gas hydrate concentrations were determined to be 20-40% of the pore volume using wire-line electrical resistivity data as well as core-derived pore-fluid freshening trends. The gas hydrate-bearing interval was linked to a prominent seismic reflection observed in the 3D seismic data. This reflection event, mapped for about 1km2 south of the drill site, is bound by a fault at its northern limit that may act as migration conduit for free gas to enter the gas hydrate stability zone (GHSZ) and subsequently charge the sand-rich layer. On 3D and additional regional 2D seismic data a prominent channel system was imaged mainly by using the seismic instantaneous amplitude attribute. The channel can be clearly identified by changes in the seismic character of the channel fill (sand-rich) and pronounced levees (less sand content than in the fill, but higher than in surrounding mud-dominated sediments). The entire channel sequence (channel fill and levees) has been subsequently covered and back-filled with a more mud-prone sediment sequence. Where the levees intersect the base of the GHSZ, their reflection strengths are significantly increased to 5- to 6-times the surrounding reflection amplitudes. Using the 3D seismic data these high-amplitude reflection edges where linked to the gas hydrate-bearing layer at Site NGHP-01-15. Further south along the channel the same reflection elements representing the levees do not show similarly large reflection amplitudes. However, the channel system is still characterized by several high-amplitude reflection events (a few hundred meters wide and up to ~1km in extent) interpreted as gas hydrate-bearing sand intervals along the length of the channel. ?? 2010.

SEISMIC-REFLECTION STUDIES OF SINKHOLES AND LIMESTONE DISSOLUTION FEATURES ON THE NORTHEASTERN FLORIDA SHELF.

USGS Publications Warehouse

Popenoe, Peter; Kohout, F.A.; Manheim, F.T.; ,

1984-01-01

High-resolution seismic-reflection profiles show that the shelf off northern Florida is underlain by solution deformed limestone of Oligocene, Eocene, Paleocene and late Cretaceous age. Dissolution and collapse features are widely scattered. They are expressed in three general forms: as sinkholes that presently breach the sea floor, such as Red Snapper Sink and the Crescent Beach submarine spring; as sinkholes that have breached the seafloor in the past but are now filled with shelf sands; and as dissolution collapse structures that originate deep within the section and have caused buckling and folding of overlying Eocene, Oligocene, and to a lesser extent, Neogene strata. Although deformation caused by solution and collapse can be shown to be a continuous process, the major episode of karstification occurred in the late Oligocene and early Miocene when the shelf was exposed to subaerial conditions.

Archive of chirp seismic reflection data collected during USGS cruises 00SCC02 and 00SCC04, Barataria Basin, Louisiana, May 12-31 and June 17-July 2, 2000

USGS Publications Warehouse

Calderon, Karynna; Dadisman, S.V.; Kindinger, J.L.; Flocks, J.G.; Wiese, D.S.; Kulp, Mark; Penland, Shea; Britsch, L.D.; Brooks, G.R.

2003-01-01

This archive consists of two-dimensional marine seismic reflection profile data collected in the Barataria Basin of southern Louisiana. These data were acquired in May, June, and July of 2000 aboard the R/V G.K. Gilbert. Included here are data in a variety of formats including binary, American Standard Code for Information Interchange (ASCII), Hyper-Text Markup Language (HTML), shapefiles, and Graphics Interchange Format (GIF) and Joint Photographic Experts Group (JPEG) images. Binary data are in Society of Exploration Geophysicists (SEG) SEG-Y format and may be downloaded for further processing or display. Reference maps and GIF images of the profiles may be viewed with a web browser. The Geographic Information Systems (GIS) information provided here is compatible with Environmental Systems Research Institute (ESRI) GIS software.

Verification/development of seismic design specifications for downstate zone.

DOT National Transportation Integrated Search

2014-07-01

The New York City Department of Transportation (NYCDOT) Seismic Design Guidelines Report was : updated in September 2008 by Weidlinger Associates to reflect current state-of-the-art knowledge. The : NYCDOT seismic design guidelines are for use in the...

Steep-dip seismic imaging of the shallow San Andreas Fault near Parkfield

USGS Publications Warehouse

Hole, J.A.; Catchings, R.D.; St. Clair, K.C.; Rymer, M.J.; Okaya, D.A.; Carney, B.J.

2001-01-01

Seismic reflection and refraction images illuminate the San Andreas Fault to a depth of 1 kilometer. The prestack depth-migrated reflection image contains near-vertical reflections aligned with the active fault trace. The fault is vertical in the upper 0.5 kilometer, then dips about 70° to the southwest to at least 1 kilometer subsurface. This dip reconciles the difference between the computed locations of earthquakes and the surface fault trace. The seismic velocity cross section shows strong lateral variations. Relatively low velocity (10 to 30%), high electrical conductivity, and low density indicate a 1-kilometer-wide vertical wedge of porous sediment or fractured rock immediately southwest of the active fault trace.

Scale independence of décollement thrusting

USGS Publications Warehouse

McBride, John H.; Pugin, Andre J.M.; Hatcher, Robert D.

2007-01-01

Orogen-scale décollements (detachment surfaces) are an enduring subject of investigation by geoscientists. Uncertainties remain as to how crustal convergence processes maintain the stresses necessary for development of low-angle fault surfaces above which huge slabs of rock are transported horizontally for tens to hundreds of kilometers. Seismic reflection profiles from the southern Appalachian crystalline core and several foreland fold-and-thrust belts provide useful comparisons with high-resolution shallow-penetration seismic reflection profiles acquired over the frontal zone of the Michigan lobe of the Wisconsinan ice sheet northwest of Chicago, Illinois. These profiles provide images of subhorizontal and overlapping dipping reflections that reveal a ramp-and-flat thrust system developed in poorly consolidated glacial till. The system is rooted in a master décollement at the top of bedrock. These 2–3 km long images contain analogs of images observed in seismic reflection profiles from orogenic belts, except that the scale of observation in the profiles in glacial materials is two orders of magnitude less. Whereas the décollement beneath the ice lobe thrust belt lies ∼70 m below thrusted anticlines having wavelengths of tens of meters driven by an advancing ice sheet, seismic images from overthrust terranes are related to lithospheric convergence that produces décollements traceable for thousands of kilometers at depths ranging from a few to over 10 km. Dual vergence or reversals in vergence (retrocharriage) that developed over abrupt changes in depth to the décollement can be observed at all scales. The strikingly similar images, despite the contrast in scale and driving mechanism, suggest a scale- and driving mechanism–independent behavior for décollement thrust systems. All these systems initially had the mechanical properties needed to produce very similar geometries with a compressional driving mechanism directed subparallel to Earth's surface. Subduction-related accretionary complexes also produce thrust systems with similar geometries in semi- to unconsolidated materials.

Fault Imaging with High-Resolution Seismic Reflection for Earthquake Hazard and Geothermal Resource Assessment in Reno, Nevada

DOE Office of Scientific and Technical Information (OSTI.GOV)

Frary, Roxanna

2012-05-05

The Truckee Meadows basin is situated adjacent to the Sierra Nevada microplate, on the western boundary of the Walker Lane. Being in the transition zone between a range-front normal fault on the west and northwest-striking right-lateral strike slip faults to the east, there is no absence of faulting in this basin. The Reno- Sparks metropolitan area is located in this basin, and with a signi cant population living here, it is important to know where these faults are. High-resolution seismic reflection surveys are used for the imaging of these faults along the Truckee River, across which only one fault wasmore » previously mapped, and in southern Reno near and along Manzanita Lane, where a swarm of short faults has been mapped. The reflection profiles constrain the geometries of these faults, and suggest additional faults not seen before. Used in conjunction with depth to bedrock calculations and gravity measurements, the seismic reflection surveys provide de nitive locations of faults, as well as their orientations. O sets on these faults indicate how active they are, and this in turn has implications for seismic hazard in the area. In addition to seismic hazard, the faults imaged here tell us something about the conduits for geothermal fluid resources in Reno.« less

Micro-seismicity in the Gulf of Cadiz: Is there a link between micro-seismicity, high magnitude earthquakes and active faults?

NASA Astrophysics Data System (ADS)

Silva, Sónia; Terrinha, Pedro; Matias, Luis; Duarte, João C.; Roque, Cristina; Ranero, César R.; Geissler, Wolfram H.; Zitellini, Nevio

2017-10-01

The Gulf of Cadiz seismicity is characterized by persistent low to intermediate magnitude earthquakes, occasionally punctuated by high magnitude events such as the M 8.7 1755 Great Lisbon earthquake and the M = 7.9 event of February 28th, 1969. Micro-seismicity was recorded during 11 months by a temporary network of 25 ocean bottom seismometers (OBSs) in an area of high seismic activity, encompassing the potential source areas of the mentioned large magnitude earthquakes. We combined micro-seismicity analysis with processing and interpretation of deep crustal seismic reflection profiles and available refraction data to investigate the possible tectonic control of the seismicity in the Gulf of Cadiz area. Three controlling mechanisms are explored: i) active tectonic structures, ii) transitions between different lithospheric domains and inherited Mesozoic structures, and iii) fault weakening mechanisms. Our results show that micro-seismicity is mostly located in the upper mantle and is associated with tectonic inversion of extensional rift structures and to the transition between different lithospheric/rheological domains. Even though the crustal structure is well imaged in the seismic profiles and in the bathymetry, crustal faults show low to negligible seismic activity. A possible explanation for this is that the crustal thrusts are thin-skinned structures rooting in relatively shallow sub-horizontal décollements associated with (aseismic) serpentinization levels at the top of the lithospheric mantle. Therefore, co-seismic slip along crustal thrusts may only occur during large magnitude events, while for most of the inter-seismic cycle these thrusts remain locked, or slip aseismically. We further speculate that high magnitude earthquake's ruptures may only nucleate in the lithospheric mantle and then propagate into the crust across the serpentinized layers.

Automated Processing Workflow for Ambient Seismic Recordings

NASA Astrophysics Data System (ADS)

Girard, A. J.; Shragge, J.

2017-12-01

Structural imaging using body-wave energy present in ambient seismic data remains a challenging task, largely because these wave modes are commonly much weaker than surface wave energy. In a number of situations body-wave energy has been extracted successfully; however, (nearly) all successful body-wave extraction and imaging approaches have focused on cross-correlation processing. While this is useful for interferometric purposes, it can also lead to the inclusion of unwanted noise events that dominate the resulting stack, leaving body-wave energy overpowered by the coherent noise. Conversely, wave-equation imaging can be applied directly on non-correlated ambient data that has been preprocessed to mitigate unwanted energy (i.e., surface waves, burst-like and electromechanical noise) to enhance body-wave arrivals. Following this approach, though, requires a significant preprocessing effort on often Terabytes of ambient seismic data, which is expensive and requires automation to be a feasible approach. In this work we outline an automated processing workflow designed to optimize body wave energy from an ambient seismic data set acquired on a large-N array at a mine site near Lalor Lake, Manitoba, Canada. We show that processing ambient seismic data in the recording domain, rather than the cross-correlation domain, allows us to mitigate energy that is inappropriate for body-wave imaging. We first develop a method for window selection that automatically identifies and removes data contaminated by coherent high-energy bursts. We then apply time- and frequency-domain debursting techniques to mitigate the effects of remaining strong amplitude and/or monochromatic energy without severely degrading the overall waveforms. After each processing step we implement a QC check to investigate improvements in the convergence rates - and the emergence of reflection events - in the cross-correlation plus stack waveforms over hour-long windows. Overall, the QC analyses suggest that automated preprocessing of ambient seismic recordings in the recording domain successfully mitigates unwanted coherent noise events in both the time and frequency domain. Accordingly, we assert that this method is beneficial for direct wave-equation imaging with ambient seismic recordings.

Geophysical data reveal the crustal structure of the Alaska Range orogen within the aftershock zone of the Mw 7.9 Denali fault earthquake

USGS Publications Warehouse

Fisher, M.A.; Ratchkovski, N.A.; Nokleberg, W.J.; Pellerin, L.; Glen, J.M.G.

2004-01-01

Geophysical information, including deep-crustal seismic reflection, magnetotelluric (MT), gravity, and magnetic data, cross the aftershock zone of the 3 November 2002 Mw 7.9 Denali fault earthquake. These data and aftershock seismicity, jointly interpreted, reveal the crustal structure of the right-lateral-slip Denali fault and the eastern Alaska Range orogen, as well as the relationship between this structure and seismicity. North of the Denali fault, strong seismic reflections from within the Alaska Range orogen show features that dip as steeply as 25?? north and extend downward to depths between 20 and 25 km. These reflections reveal crustal structures, probably ductile shear zones, that most likely formed during the Late Cretaceous, but these structures appear to be inactive, having produced little seismicity during the past 20 years. Furthermore, seismic reflections mainly dip north, whereas alignments in aftershock hypocenters dip south. The Denali fault is nonreflective, but modeling of MT, gravity, and magnetic data suggests that the Denali fault dips steeply to vertically. However, in an alternative structural model, the Denali fault is defined by one of the reflection bands that dips to the north and flattens into the middle crust of the Alaska Range orogen. Modeling of MT data indicates a rock body, having low electrical resistivity (>10 ??-m), that lies mainly at depths greater than 10 km, directly beneath aftershocks of the Denali fault earthquake. The maximum depth of aftershocks along the Denali fault is 10 km. This shallow depth may arise from a higher-than-normal geothermal gradient. Alternatively, the low electrical resistivity of deep rocks along the Denali fault may be associated with fluids that have weakened the lower crust and helped determine the depth extent of the after-shock zone.

Anatomy of ridge discontinuities, transform fault and overlapping spreading centre, at the slow spreading sedimented Andaman Sea Spreading Centre

NASA Astrophysics Data System (ADS)

Jourdain, A.; Singh, S. C.; Klinger, Y.

2013-12-01

Transform faults are the major discontinuities and define the main segment boundaries along spreading centres but their anatomy is poorly understood because of their complex seafloor morphology, even though they are observed at all types of spreading centres. Here, we present high-resolution seismic reflection images across the sedimented Andaman Sea Transform Fault where the sediments record the faulting and allow studying the evolution of the transform fault both in space and time. Furthermore, sediments allow the imaging of the faults down to the Moho depth that provides insight on the interplay between tectonic and magmatic processes. On the other hand, overlapping spreading centres (OSC) are small-scale discontinuities, possibly transient, and are observed only along fast or intermediate spreading centres. Exceptionally, an overlapping spreading centre is present at the slow spreading Andaman Sea Spreading Centre, which, we suggest, is due to the presence of thick sediments that hamper the efficient hydrothermal circulation allowing magma to stay much longer in the crust at different depths, and up to close to the segment ends, leading to the development of an overlapping spreading. The seismic reflection images across the OSC indicate the presence of large magma bodies in the crust. Seismic images also provide images of active faults allowing to study the link between faulting and magmatism. Interestingly, an earthquake swarm occurred at propagating limb of the OSC in 2006, after the great 2004 Andaman-Sumatra earthquake of Mw=9.3, highlighting the migration of the OSC westward. In this paper, we will show seismic reflection images and interpret these images in the light of bathymetry and earthquake data, and provide the anatomy of the ridge discontinuities along the slow spreading sedimented Andaman Sea Spreading Centre.

Advantages of wet work for near-surface seismic reflection

USGS Publications Warehouse

Miller, R.D.; Markiewicz, R.D.; Rademacker, T.R.; Hopkins, R.; Rawcliffe, R.J.; Paquin, J.

2007-01-01

Benefits of shallow water settings (0.1 to 0.5 m) are pronounced on shallow, high-resolution seismic reflection images and, for examples discussed here, range from an order of magnitude increased signal-to-noise ratio to resolution potential elevated by more than 8 times. Overall data quality of high-resolution seismic reflection data at three sites notorious for poor near-surface reflection returns was improved by coupling the source and/or receivers to a well sorted and fully saturated surface. Half-period trace-to-trace static offsets evident in reflections from receivers planted into a creek bank were eliminated by moving the geophones to the base of a shallow creek at the toe of the bank. Reflections from a dipping bedrock were recorded with a dominant frequency approaching 1 KHz from hydrophones in 0.5 m of water at the toe of a dam using a hammer impact source. A tamper impacted by a dead blow hammer in a shallow (10-20 cm) deep creek produced reflections with a dominant frequency over 400 Hz at depths as shallow as 6 ms. ?? 2007 Society of Exploration Geophysicists.

A Program for Calculating and Plotting Synthetic Common-Source Seismic-Reflection Traces for Multilayered Earth Models.

ERIC Educational Resources Information Center

Ramananantoandro, Ramanantsoa

1988-01-01

Presented is a description of a BASIC program to be used on an IBM microcomputer for calculating and plotting synthetic seismic-reflection traces for multilayered earth models. Discusses finding raypaths for given source-receiver offsets using the "shooting method" and calculating the corresponding travel times. (Author/CW)

Seismic imaging and velocity structure around the JFAST drill site in the Japan Trench: low Vp, high Vp/ Vs in the transparent frontal prism

NASA Astrophysics Data System (ADS)

Nakamura, Yasuyuki; Kodaira, Shuichi; Cook, Becky J.; Jeppson, Tamara; Kasaya, Takafumi; Yamamoto, Yojiro; Hashimoto, Yoshitaka; Yamaguchi, Mika; Obana, Koichiro; Fujie, Gou

2014-12-01

Seismic image and velocity models were obtained from a newly conducted seismic survey around the Integrated Ocean Drilling Program (IODP) Japan Trench Fast Drilling Project (JFAST) drill site in the Japan Trench. Pre-stack depth migration (PSDM) analysis was applied to the multichannel seismic reflection data to produce an accurate depth seismic profile together with a P wave velocity model along a line that crosses the JFAST site location. The seismic profile images the subduction zone at a regional scale. The frontal prism where the drill site is located corresponds to a typically seismically transparent (or chaotic) zone with several landward-dipping semi-continuous reflections. The boundary between the Cretaceous backstop and the frontal prism is marked by a prominent landward-dipping reflection. The P wave velocity model derived from the PSDM analysis shows low velocity in the frontal prism and velocity reversal across the backstop interface. The PSDM velocity model around the drill site is similar to the P wave velocity model calculated from the ocean bottom seismograph (OBS) data and agrees with the P wave velocities measured from the core experiments. The average Vp/ Vs in the hanging wall sediments around the drill site, as derived from OBS data, is significantly larger than that obtained from core sample measurements.

Deep Structures of The Angola Margin

NASA Astrophysics Data System (ADS)

Moulin, M.; Contrucci, I.; Olivet, J.-L.; Aslanian, D.; Géli, L.; Sibuet, J.-C.

1 Ifremer Centre de Brest, DRO/Géosciences Marines, B.P. 70, 29280 Plouzané cedex (France) mmoulin@ifremer.fr/Fax : 33 2 98 22 45 49 2 Université de Bretagne Occidentale, Institut Universitaire Europeen de la Mer, Place Nicolas Copernic, 29280 Plouzane (France) 3 Total Fina Elf, DGEP/GSR/PN -GEOLOGIE, 2,place de la Coupole-La Defense 6, 92078 Paris la Defense Cedex Deep reflection and refraction seismic data were collected in April 2000 on the West African margin, offshore Angola, within the framework of the Zaiango Joint Project, conducted by Ifremer and Total Fina Elf Production. Vertical multichannel reflection seismic data generated by a « single-bubble » air gun array array (Avedik et al., 1993) were recorded on a 4.5 km long, digital streamer, while refraction and wide angle reflection seismic data were acquired on OBSs (Ocean Bottom Seismometers). Despite the complexity of the margin (5 s TWT of sediment, salt tectonics), the combination of seismic reflection and refraction methods results in an image and a velocity model of the ground structures below the Aptian salt layer. Three large seismic units appear in the reflection seismic section from the deep part on the margin under the base of salt. The upper seismic unit is layered with reflectors parallel to the base of the salt ; it represents unstructured sediments, filling a basin. The middle unit is seismically transparent. The lower unit is characterized by highly energetic reflectors. According to the OBS refraction data, these two units correspond to the continental crust and the base of the high energetic unit corresponds to the Moho. The margin appears to be divided in 3 domains, from east to west : i) a domain with an unthinned, 30 km thick, continental crust ; ii) a domain located between the hinge line and the foot of the continental slope, where the crust thins sharply, from 30 km to less than 7 km, this domain is underlain by an anormal layer with velocities comprising between 7,2 and 7,4 km/s. The maximum thickness of this layer is located where the crust shows the strongest thinning at the foot of the continental slope ; and iii) a transitional domain, 160 km wide, with an average crustal thickness of 6 km. Moreover, no tilted blocks nor detachment faults are observed on the reflection seismic sections. The consequences of these observations on the models of crustal thinning classically used in the litterature are examined. Avedik, F., V. Renard, J-P. Allenou, B. Morvan, "Single bubble" air gun for deep exploration, Geophysics, 58, 366-382, 1993.

4-D High-Resolution Seismic Reflection Monitoring of Miscible CO2 Injected into a Carbonate Reservoir

DOE Office of Scientific and Technical Information (OSTI.GOV)

Richard D. Miller; Abdelmoneam E. Raef; Alan P. Byrnes

2005-09-01

The objective of this research project is to acquire, process, and interpret multiple high-resolution 3-D compressional wave and 2-D, 2-C shear wave seismic data to observe changes in fluid characteristics in an oil field before, during, and after the miscible carbon dioxide (CO{sub 2}) flood that began around December 1, 2003, as part of the DOE-sponsored Class Revisit Project (DOE DE-AC26-00BC15124). Unique and key to this imaging activity is the high-resolution nature of the seismic data, minimal deployment design, and the temporal sampling throughout the flood. The 900-m-deep test reservoir is located in central Kansas oomoldic limestones of the Lansing-Kansasmore » City Group, deposited on a shallow marine shelf in Pennsylvanian time. After 18 months of seismic monitoring, one baseline and six monitor surveys clearly imaged changes that appear consistent with movement of CO{sub 2} as modeled with fluid simulators.« less

Monitoring the Earthquake source process in North America

USGS Publications Warehouse

Herrmann, Robert B.; Benz, H.; Ammon, C.J.

2011-01-01

With the implementation of the USGS National Earthquake Information Center Prompt Assessment of Global Earthquakes for Response system (PAGER), rapid determination of earthquake moment magnitude is essential, especially for earthquakes that are felt within the contiguous United States. We report an implementation of moment tensor processing for application to broad, seismically active areas of North America. This effort focuses on the selection of regional crustal velocity models, codification of data quality tests, and the development of procedures for rapid computation of the seismic moment tensor. We systematically apply these techniques to earthquakes with reported magnitude greater than 3.5 in continental North America that are not associated with a tectonic plate boundary. Using the 0.02-0.10 Hz passband, we can usually determine, with few exceptions, moment tensor solutions for earthquakes with M w as small as 3.7. The threshold is significantly influenced by the density of stations, the location of the earthquake relative to the seismic stations and, of course, the signal-to-noise ratio. With the existing permanent broadband stations in North America operated for rapid earthquake response, the seismic moment tensor of most earthquakes that are M w 4 or larger can be routinely computed. As expected the nonuniform spatial pattern of these solutions reflects the seismicity pattern. However, the orientation of the direction of maximum compressive stress and the predominant style of faulting is spatially coherent across large regions of the continent.

Catalog of offshore seismicity in Cascadia: Insights into the regional distribution of microseismicity and its relation to subduction processes

NASA Astrophysics Data System (ADS)

Stone, I.; Vidale, J. E.; Han, S.; Roland, E. C.

2017-12-01

We present a catalog of offshore seismicity generated from Cascadia Initiative OBS data. The catalog, which records 271 earthquakes along the coasts of Washington, Oregon, Northern California, and Vancouver Island, spans all 4 years of the OBS deployment and shows distinct along-strike variations in seismicity. Within the subduction zone, seismicity increases significantly from north to south, following trends in decreasing sediment thickness and increasing internal deformation of the incoming plate. Seismicity is sparse off the coasts of Vancouver Island and Washington (49-46°N), but abruptly increases south of the Washington/Oregon border. Off Northern and Central Oregon, widespread earthquakes are observed near the interface between 46 and 45°N, as well as at the previously identified clusters of seismicity off Newport, Oregon. South of Cape Blanco ( 43°N), seismicity is abundant and distributed across a large depth range. We locate an additional 440 events seaward of the deformation front, which show that rates of seismicity are higher in the Juan de Fuca plate south of 46°N, consistent with internal deformation trends observed during recent active source seismic reflection/refraction studies. Our observations imply that the smoothness and degree of hydration of the incoming plate, which are linked to the amount of underthrust sediment and amount of intraplate deformation, are major contributing factors to the distribution of microseismicity in the Cascadia Subduction Zone

Various Approaches to Forward and Inverse Wide-Angle Seismic Modelling Tested on Data from DOBRE-4 Experiment

NASA Astrophysics Data System (ADS)

Janik, Tomasz; Środa, Piotr; Czuba, Wojciech; Lysynchuk, Dmytro

2016-12-01

The interpretation of seismic refraction and wide angle reflection data usually involves the creation of a velocity model based on an inverse or forward modelling of the travel times of crustal and mantle phases using the ray theory approach. The modelling codes differ in terms of model parameterization, data used for modelling, regularization of the result, etc. It is helpful to know the capabilities, advantages and limitations of the code used compared to others. This work compares some popular 2D seismic modelling codes using the dataset collected along the seismic wide-angle profile DOBRE-4, where quite peculiar/uncommon reflected phases were observed in the wavefield. The 505 km long profile was realized in southern Ukraine in 2009, using 13 shot points and 230 recording stations. Double PMP phases with a different reduced time (7.5-11 s) and a different apparent velocity, intersecting each other, are observed in the seismic wavefield. This is the most striking feature of the data. They are interpreted as reflections from strongly dipping Moho segments with an opposite dip. Two steps were used for the modelling. In the previous work by Starostenko et al. (2013), the trial-and-error forward model based on refracted and reflected phases (SEIS83 code) was published. The interesting feature is the high-amplitude (8-17 km) variability of the Moho depth in the form of downward and upward bends. This model is compared with results from other seismic inversion methods: the first arrivals tomography package FAST based on first arrivals; the JIVE3D code, which can also use later refracted arrivals and reflections; and the forward and inversion code RAYINVR using both refracted and reflected phases. Modelling with all the codes tested showed substantial variability of the Moho depth along the DOBRE-4 profile. However, SEIS83 and RAYINVR packages seem to give the most coincident results.

Seismic evidence for an extensive gas-bearing layer at shallow depth, offshore from Prudhoe Bay, Alaska

USGS Publications Warehouse

Boucher, G.; Reimnitz, E.; Kempema, E.

1981-01-01

High-resolution seismic reflection data, recorded offshore from Prudhoe Bay, Alaska, were processed digitally to determine the reflectivity structure of the uppermost layers of the seafloor. A prominent reflector, found at 27 m below the mud line (water depths 7-9 m), has a negative reflection coefficient greater than 0.5. The large acoustic impedance contrast, coupled with a report of gas encountered at a corresponding depth in a nearby drillhole, shows that the reflector is the upper boundary of a zone containing gas. The gas exists in sandy gravel capped by stiff, silty clay. Analysis of unprocessed conventional high-resolution records from the region indicates that the gas-bearing layer may extend over an area of at least 50 km2 at a depth of 20-35 m below the mud line. Similar-appearing reflectors (Reimnitz, 1972), previously unexplained, occur in patches over wide regions of the shelf where offshore oil development is beginning at a rapid pace. This suggests the exercise of caution with respect to possible hazards from shallow gas pockets.

Early to middle Jurassic salt in Baltimore Canyon trough

USGS Publications Warehouse

McKinney, B. Ann; Lee, Myung W.; Agena, Warren F.; Poag, C. Wylie

2005-01-01

A pervasive, moderately deep (5-6 s two-way traveltime), high-amplitude reflection is traced on multichannel seismic sections over an approximately 7500 km² area of Baltimore Canyon Trough. The layer associated with the reflection is about 25 km wide, about 60 m thick in the center, and thins monotonically laterally, though asymmetrically, at the edges. Geophysical characteristics are compatible with an interpretation of this negative-polarity reflector as a salt lens deposited on the top of a synrift evaporite sequence. However, alternative interpretations of the layer as gas-saturated sediments, an overpressured shale, or a weathered igneous intrusion are also worthy of consideration.Geophysical analyses were made on three wavelet- and true-amplitude processed multichannel seismic dip lines. The lens-shaped layer demarked by the reflection has a velocity of 4.4 km/s; the lens lies within strata having velocities of 5.3 to 5.7 km/s. A trough marking the onset of the lens has an amplitude that is 10 to 20 db greater than reflections from the encasing layers and an apparent reflection coefficient of -0.24. Using amplitude versus offset analysis methods, we determined that observed reflection coefficients, though variable, decrease consistently with respect to increasing offset. Linear inversion yields a low density, about 2.2 g/cc. Integration of one of the true-amplitude-processed lines and one-dimensional modeling of the layer provide data on the impedance contrast and interference patterns that further reinforce the salt lens interpretation.The thin, horizontal salt lens was probably deposited or precipitated during the Jurassic in a shallow, narrow (peripheral) rift basin, as rifting progressed down the North Atlantic margin. Unlike thicker deposits in other areas that deformed and flowed, often into diapir structures, this thin lens has remained relatively undisturbed since deposition.

Shallow seismic reflection profiles and geological structure in the Benton Hills, southeast Missouri

USGS Publications Warehouse

Palmer, J.R.; Hoffman, D.; Stephenson, W.J.; Odum, J.K.; Williams, R.A.

1997-01-01

During late May and early June of 1993, we conducted two shallow, high-resolution seismic reflection surveys (Mini-Sosie method) across the southern escarpment of the Benton Hills segment of Crowleys Ridge. The reflection profiles imaged numerous post-late Cretaceous faults and folds. We believe these faults may represent a significant earthquake source zone. The stratigraphy of the Benton Hills consists of a thin, less than about 130 m, sequence of mostly unconsolidated Cretaceous, Tertiary and Quaternary sediments which unconformably overlie a much thicker section of Paleozoic carbonate rocks. The survey did not resolve reflectors within the upper 75-100 ms of two-way travel time (about 60-100 m), which would include all of the Tertiary and Quaternary and most of the Cretaceous. However, the Paleozoic-Cretaceous unconformity (Pz) produced an excellent reflection, and, locally a shallower reflector within the Cretaceous (K) was resolved. No coherent reflections below about 200 ms of two-way travel time were identified. Numerous faults and folds, which clearly offset the Paleozoic-Cretaceous unconformity reflector, were imaged on both seismic reflection profiles. Many structures imaged by the reflection data are coincident with the surface mapped locations of faults within the Cretaceous and Tertiary succession. Two locations show important structures that are clearly complex fault zones. The English Hill fault zone, striking N30??-35??E, is present along Line 1 and is important because earlier workers indicated it has Pleistocene Loess faulted against Eocene sands. The Commerce fault zone striking N50??E, overlies a major regional basement geophysical lineament, and is present on both seismic lines at the southern margin of the escarpment. The fault zones imaged by these surveys are 30 km from the area of intense microseismicity in the New Madrid seismic zone (NMSZ). If these are northeast and north-northeast oriented fault zones like those at Thebes Gap they are favorably oriented in the modern stress field to be reactivated as right-lateral strike slip faults. Currently, earthquake hazards assessments are most dependent upon historical seismicity, and there are little geological data available to evaluate the earthquake potential of fault zones outside of the NMSZ. We anticipate that future studies will provide evidence that seismicity has migrated between fault zones well beyond the middle Mississippi Valley. The potential earthquake hazards represented by faults outside the NMSZ may be significant.

The use of Graphic User Interface for development of a user-friendly CRS-Stack software

NASA Astrophysics Data System (ADS)

Sule, Rachmat; Prayudhatama, Dythia; Perkasa, Muhammad D.; Hendriyana, Andri; Fatkhan; Sardjito; Adriansyah

2017-04-01

The development of a user-friendly Common Reflection Surface (CRS) Stack software that has been built by implementing Graphical User Interface (GUI) is described in this paper. The original CRS-Stack software developed by WIT Consortium is compiled in the unix/linux environment, which is not a user-friendly software, so that a user must write the commands and parameters manually in a script file. Due to this limitation, the CRS-Stack become a non popular method, although applying this method is actually a promising way in order to obtain better seismic sections, which have better reflector continuity and S/N ratio. After obtaining successful results that have been tested by using several seismic data belong to oil companies in Indonesia, it comes to an idea to develop a user-friendly software in our own laboratory. Graphical User Interface (GUI) is a type of user interface that allows people to interact with computer programs in a better way. Rather than typing commands and module parameters, GUI allows the users to use computer programs in much simple and easy. Thus, GUI can transform the text-based interface into graphical icons and visual indicators. The use of complicated seismic unix shell script can be avoided. The Java Swing GUI library is used to develop this CRS-Stack GUI. Every shell script that represents each seismic process is invoked from Java environment. Besides developing interactive GUI to perform CRS-Stack processing, this CRS-Stack GUI is design to help geophysicists to manage a project with complex seismic processing procedures. The CRS-Stack GUI software is composed by input directory, operators, and output directory, which are defined as a seismic data processing workflow. The CRS-Stack processing workflow involves four steps; i.e. automatic CMP stack, initial CRS-Stack, optimized CRS-Stack, and CRS-Stack Supergather. Those operations are visualized in an informative flowchart with self explanatory system to guide the user inputting the parameter values for each operation. The knowledge of CRS-Stack processing procedure is still preserved in the software, which is easy and efficient to be learned. The software will still be developed in the future. Any new innovative seismic processing workflow will also be added into this GUI software.

The CoRoT target HD 49933: a possible seismic signature of heavy elements ionization in the deep convective zone

NASA Astrophysics Data System (ADS)

Brito, Ana; Lopes, Ilídio

2017-04-01

We use a seismic diagnostic, based on the derivative of the phase shift of the acoustic waves reflected by the surface, to probe the outer layers of the star HD 49933. This diagnostic is particularly sensitive to partial ionization processes occurring above the base of the convective zone. The regions of partial ionization of light elements, hydrogen and helium, have well-known seismological signatures. In this work, we detect a different seismic signature in the acoustic frequencies, which we showed to correspond to the location where the partial ionization of heavy elements occurs. The location of the corresponding acoustic glitch lies between the region of the second ionization of helium and the base of the convective zone, approximately 5 per cent below the surface of the stars.

Greenland to gather more exploration data

DOE Office of Scientific and Technical Information (OSTI.GOV)

Not Available

1991-01-28

Danish authorities are taking steps to make more exploration data available on Greenland in advance of a possible West Greenland shelf licensing round in 1993. Seismic data acquisition and other studies continue toward more fully evaluating Greenland's oil and gas potential. Geological Survey of Greenland (GGU), Copenhagen, Denmark, is processing 2,041 line miles of reflection seismic data shot on the West Greenland shelf in August and September of 1990. Sixty-fold stacks and migrations will be obtained. Total field magnetic data were also recorded during the survey, known as project Syd Vest Seis. Early work is under way to kick offmore » the multicompany Kanumas seismic acquisition project, proposed in 1986, during 1991. Meanwhile, the Mineral Resources Administration for Greenland (MRA), Copenhagen, the Danish and Greenland governments aim to sweeten Greenland's exploration regulations prior to making areas available.« less

Multichannel seismic-reflection profiling on the R/V Maurice Ewing during the Los Angeles Region Seismic Experiment (LARSE), California

USGS Publications Warehouse

Brocher, Thomas M.; Clayton, Robert W.; Klitgord, Kim D.; Bohannon, Robert G.; Sliter, Ray; McRaney, John K.; Gardner, James V.; Keene, J.B.

1995-01-01

This report describes the acquisition of deep-crustal multichannel seismic-reflection data in the Inner California Borderland aboard the R/V Maurice Ewing, conducted in October 1994 as part of the Los Angeles Regional Seismic Experiment (LARSE). LARSE is a cooperative study of the crustal structure of southern California involving earth scientists from the U.S. Geological Survey, Caltech, the University of Southern California, the University of California Los Angeles, and the Southern California Earthquake Center (SCEC). During LARSE, the R/V Ewing's 20- element air gun array, totaling 137.7 liters (8470 cu. in.), was used as the primary seismic source for wide-angle recording along three main onshore-offshore lines centered on the Los Angeles basin and the epicenters of the 1933 Long Beach and 1994 Northridge earthquakes. The LARSE onshore-offshore lines were each 200-250 km long, with the offshore portions being between 90 and 150 km long. The nearly 24,000 air gun signals generated by the Ewing were recorded by an array of 170 PASSCAL REFTEK recorders deployed at 2 km intervals along all three of the onshore lines and 9 ocean bottom seismometers (OBSs) deployed along two of the lines. Separate passes over the OBS-deployment lines were performed with a long air gun repetition rate (60 and 90 seconds) to minimize acoustic-wave interference from previous shots in the OBS data. The Ewing's 4.2-km, 160-channel, digital streamer was also used to record approximately 1250 km of 40-fold multichannel seismic-reflection data. To enhance the fold of the wide-angle data recorded onshore, mitigating against cultural and wind noise in the Los Angeles basin, the entire ship track was repeated at least once resulting in fewer than about 660 km of unique trackline coverage in the Inner Borderland. Portions of the seismic-reflection lines were repeated up to 6 times. A variety of other geophysical data were also continuously recorded, including 3.5 kHz bathymetry, multi-beam swath Hydrosweep bathymetry, magnetics, and gravity data. In this report, we describe the equipment and procedures used to acquire multichannel seismic-reflection and other geophysical data aboard the Ewing, provide a detailed cruise narrative, discuss the reduction of the data, and present near-trace constant offset seismic sections of the acquired profiles.

Fluid Induced Earthquakes: From KTB Experiments to Natural Seismicity Swarms.

NASA Astrophysics Data System (ADS)

Shapiro, S. A.

2006-12-01

Experiments with borehole fluid injections are typical for exploration and development of hydrocarbon or geothermal reservoirs (e.g., fluid-injection experiments at Soultz, France and at Fenton-Hill, USA). Microseismicity occurring during such operations has a large potential for understanding physics of the seismogenic process as well as for obtaining detailed information about reservoirs at locations as far as several kilometers from boreholes. The phenomenon of microseismicity triggering by borehole fluid injections is related to the process of the Frenkel-Biot slow wave propagation. In the low-frequency range (hours or days of fluid injection duration) this process reduces to the pore pressure diffusion. Fluid induced seismicity typically shows several diffusion indicating features, which are directly related to the rate of spatial grow, to the geometry of clouds of micro earthquake hypocentres and to their spatial density. Several fluid injection experiments were conducted at the German Continental Deep Drilling Site (KTB) in 1994, 2000 and 2003-2005. Microseismicity occurred at different depth intervals. We analyze this microseismicity in terms of its diffusion-related features. Its relation to the 3-D distribution of the seismic reflectivity has important rock physical and tectonic implications. Starting from such diffusion-typical signatures of man-made earthquakes, we seek analogous patterns for the earthquakes in Vogtland/Bohemia at the German/Czech border region in central Europe. There is strong geophysical evidence that there seismic events are correlated to fluid-related processes in the crust. We test the hypothesis that ascending magmatic fluids trigger earthquakes by the mechanism of pore pressure diffusion. This triggering process is mainly controlled by two physical fields, the hydraulic diffusivity and the seismic criticality (i.e., critical pore pressure value leading to failure; stable locations are characterized by higher critical pressures), both heterogeneously distributed in rocks. The results of the analysis of the most significant and best studied (year 2000) earthquake swarm support this concept. Using a numerical model, where spatially correlated diffusivity and criticalit y patches (where patches with higher diffusivity are assumed to be less stable) are considered, we successfully simulate a general seismicity pattern of the swarms, including the spatio-temporal clustering of events and the migration of seismic activity. Therefore, in some cases spontaneously triggered natural seismicity, like earthquake swarms, also shows diffusion-typical signatures mentioned above. However, it seems that there are also some principle differences. They are emphasized in this presentation.

2D magnetotelluric inversion using reflection seismic images as constraints and application in the COSC project

NASA Astrophysics Data System (ADS)

Kalscheuer, Thomas; Yan, Ping; Hedin, Peter; Garcia Juanatey, Maria d. l. A.

2017-04-01

We introduce a new constrained 2D magnetotelluric (MT) inversion scheme, in which the local weights of the regularization operator with smoothness constraints are based directly on the envelope attribute of a reflection seismic image. The weights resemble those of a previously published seismic modification of the minimum gradient support method introducing a global stabilization parameter. We measure the directional gradients of the seismic envelope to modify the horizontal and vertical smoothness constraints separately. An appropriate choice of the new stabilization parameter is based on a simple trial-and-error procedure. Our proposed constrained inversion scheme was easily implemented in an existing Gauss-Newton inversion package. From a theoretical perspective, we compare our new constrained inversion to similar constrained inversion methods, which are based on image theory and seismic attributes. Successful application of the proposed inversion scheme to the MT field data of the Collisional Orogeny in the Scandinavian Caledonides (COSC) project using constraints from the envelope attribute of the COSC reflection seismic profile (CSP) helped to reduce the uncertainty of the interpretation of the main décollement. Thus, the new model gave support to the proposed location of a future borehole COSC-2 which is supposed to penetrate the main décollement and the underlying Precambrian basement.

High-Resolution Seismic-Reflection and Marine Magnetic Data Along the Hosgri Fault Zone, Central California

USGS Publications Warehouse

Sliter, Ray W.; Triezenberg, Peter J.; Hart, Patrick E.; Watt, Janet T.; Johnson, Samuel Y.; Scheirer, Daniel S.

2009-01-01

The U.S. Geological Survey (USGS) collected high-resolution shallow seismic-reflection and marine magnetic data in June 2008 in the offshore areas between the towns of Cayucos and Pismo Beach, Calif., from the nearshore (~6-m depth) to just west of the Hosgri Fault Zone (~200-m depth). These data are in support of the California State Waters Mapping Program and the Cooperative Research and Development Agreement (CRADA) between the Pacific Gas & Electric Co. and the U.S. Geological Survey. Seismic-reflection and marine magnetic data were acquired aboard the R/V Parke Snavely, using a SIG 2Mille minisparker seismic source and a Geometrics G882 cesium-vapor marine magnetometer. More than 550 km of seismic and marine magnetic data was collected simultaneously along shore-perpendicular transects spaced 800 m apart, with an additional 220 km of marine magnetometer data collected across the Hosgri Fault Zone, resulting in spacing locally as smallas 400 m. This report includes maps of the seismic-survey sections, linked to Google Earth software, and digital data files showing images of each transect in SEG-Y, JPEG, and TIFF formats, as well as preliminary gridded marine-magnetic-anomaly and residual-magnetic-anomaly (shallow magnetic source) maps.

Seismic wave propagation in anisotropic ice - Part 2: Effects of crystal anisotropy in geophysical data

NASA Astrophysics Data System (ADS)

Diez, A.; Eisen, O.; Hofstede, C.; Lambrecht, A.; Mayer, C.; Miller, H.; Steinhage, D.; Binder, T.; Weikusat, I.

2015-02-01

We investigate the propagation of seismic waves in anisotropic ice. Two effects are important: (i) sudden changes in crystal orientation fabric (COF) lead to englacial reflections; (ii) the anisotropic fabric induces an angle dependency on the seismic velocities and, thus, recorded travel times. Velocities calculated from the polycrystal elasticity tensor derived for the anisotropic fabric from measured COF eigenvalues of the EDML ice core, Antarctica, show good agreement with the velocity trend determined from vertical seismic profiling. The agreement of the absolute velocity values, however, depends on the choice of the monocrystal elasticity tensor used for the calculation of the polycrystal properties. We make use of abrupt changes in COF as a common reflection mechanism for seismic and radar data below the firn-ice transition to determine COF-induced reflections in either data set by joint comparison with ice-core data. Our results highlight the possibility to complement regional radar surveys with local, surface-based seismic experiments to separate isochrones in radar data from other mechanisms. This is important for the reconnaissance of future ice-core drill sites, where accurate isochrone (i.e. non-COF) layer integrity allows for synchronization with other cores, as well as studies of ice dynamics considering non-homogeneous ice viscosity from preferred crystal orientations.

Estimation of the displacements among distant events based on parallel tracking of events in seismic traces under uncertainty

NASA Astrophysics Data System (ADS)

Huamán Bustamante, Samuel G.; Cavalcanti Pacheco, Marco A.; Lazo Lazo, Juan G.

2018-07-01

The method we propose in this paper seeks to estimate interface displacements among strata related with reflection seismic events, in comparison to the interfaces at other reference points. To do so, we search for reflection events in the reference point of a second seismic trace taken from the same 3D survey and close to a well. However, the nature of the seismic data introduces uncertainty in the results. Therefore, we perform an uncertainty analysis using the standard deviation results from several experiments with cross-correlation of signals. To estimate the displacements of events in depth between two seismic traces, we create a synthetic seismic trace with an empirical wavelet and the sonic log of the well, close to the second seismic trace. Then, we relate the events of the seismic traces to the depth of the sonic log. Finally, we test the method with data from the Namorado Field in Brazil. The results show that the accuracy of the event estimated depth depends on the results of parallel cross-correlation, primarily those from the procedures used in the integration of seismic data with data from the well. The proposed approach can correctly identify several similar events in two seismic traces without requiring all seismic traces between two distant points of interest to correlate strata in the subsurface.

Post-injection feasibility study with the reflectivity method for the Ketzin pilot site, Germany (CO2 storage in a saline aquifer)

NASA Astrophysics Data System (ADS)

Ivanova, Alexandra; Kempka, Thomas; Huang, Fei; Diersch [Gil], Magdalena; Lüth, Stefan

2016-04-01

3D time-lapse seismic surveys (4D seismic) have proven to be a suitable technique for monitoring of injected CO2, because when CO2 replaces brine as a free gas it considerably affects elastic properties of porous media. Forward modeling of a 4D seismic response to the CO2-fluid substitution in a storage reservoir is an inevitable step in such studies. At the Ketzin pilot site (CO2 storage) 67 kilotons of CO2 were injected into a saline aquifer between 2008 and 2013. In order to track migration of CO2 at Ketzin, 3D time-lapse seismic data were acquired by means of a baseline pre-injection survey in 2005 and 3 monitor surveys: in 2009, 2012 and in 2015 (the 1st post-injection survey). Results of the 4D seismic forward modeling with the reflectivity method suggest that effects of the injected CO2 on the 4D seismic data at Ketzin are significant regarding both seismic amplitudes and time delays. These results prove the corresponding observations in the real 4D seismic data at the Ketzin pilot site. But reservoir heterogeneity and seismic resolution, as well as random and coherent seismic noise are negative factors to be considered in this interpretation. Results of the 4D seismic forward modeling with the reflectivity method support the conclusion that even small amounts of injected CO2 can be monitored in such post-injected saline aquifer as the CO2 storage reservoir at the Ketzin pilot site both qualitatively and quantitatively with considerable uncertainties (Lüth et al., 2015). Reference: Lueth, S., Ivanova, A., Kempka, T. (2015): Conformity assessment of monitoring and simulation of CO2 storage: A case study from the Ketzin pilot site. - International Journal of Greenhouse Gas Control, 42, p. 329-339.

Deep Seismic Reflection Images of the Sumatra Seismic and Aseismic Gaps

NASA Astrophysics Data System (ADS)

Singh, S. C.; Hananto, N. D.; Chauhan, A.; Carton, H. D.; Midenet, S.; Djajadihardja, Y.

2009-12-01

The Sumatra subduction zone is seismically most active region on the Earth, and has been the site of three great earthquakes only in the last four years. The first of the series, the 2004 Boxing Day earthquake, broke 1300 km of the plate boundary and produced the devastating tsunami around the Indian Ocean. The second great earthquake occurred three months later in March 2005, about 150 km SE of the 2004 event. The Earth waited for three years, and then broke again in September 2007 at 1300 km SE of the 2004 event producing a twin earthquake of magnitudes of 8.5 and 7.9 at an interval of 12 hours, leaving a seismic gap of about 600 km between the second and third earthquake, the Sumatra Seismic Gap. Seismological and geodetic studies suggest that this gap is fully locked and may break any time. In order to study the seismic and tsunami risk in this locked region, a deep seismic reflection survey (Tsunami Investigation Deep Evaluation Seismic -TIDES) was carried out in May 2009 using the CGGVeritas vessel Geowave Champion towing a 15 long streamer, the longest ever used during a seismic survey, to image the nature of the subducting plate and associated features, including the seismogenic zone, from seafloor down to 50 km depth. A total of 1700 km of deep seismic reflection data were acquired. Three dip lines traverse the Sumatra subduction zone; one going through the Sumatra Seismic Gap, one crossing the region that broke during the 2007 great earthquake, and one going through the aseismic zone. These three dip profiles should provide insight about the locking mechanism and help us to understand why an earthquake occurs in one zone and not in aseismic zone. A strike-line was shot in the forearc basin connecting the locked zone with broken zone profiles, which should provide insight about barriers that might have stopped propagation of 2007 earthquake rupture further northward.

High-resolution shear-wave seismic reflection as a tool to image near-surface subrosion structures - a case study in Bad Frankenhausen, Germany

NASA Astrophysics Data System (ADS)

Wadas, Sonja H.; Polom, Ulrich; Krawczyk, Charlotte M.

2016-10-01

Subrosion is the subsurface leaching of soluble rocks that results in the formation of depression and collapse structures. This global phenomenon is a geohazard in urban areas. To study near-surface subrosion structures, four shear-wave seismic reflection profiles, with a total length of ca. 332 m, were carried out around the famous leaning church tower of Bad Frankenhausen in northern Thuringia, Germany, which shows an inclination of 4.93° from the vertical. Most of the geological underground of Thuringia is characterized by soluble Permian deposits, and the Kyffhäuser Southern Margin Fault is assumed to be a main pathway for water to leach the evaporite. The seismic profiles were acquired with the horizontal micro-vibrator ELVIS, developed at Leibniz Institute for Applied Geophysics (LIAG), and a 72 m long landstreamer equipped with 72 horizontal geophones. The high-resolution seismic sections show subrosion-induced structures to a depth of ca. 100 m and reveal five features associated with the leaching of Permian deposits: (1) lateral and vertical varying reflection patterns caused by strongly heterogeneous strata, (2) discontinuous reflectors, small offsets, and faults, which show the underground is heavily fractured, (3) formation of depression structures in the near-surface, (4) diffractions in the unmigrated seismic sections that indicate increased scattering of the seismic waves, and (5) varying seismic velocities and low-velocity zones that are presumably caused by fractures and upward-migrating cavities. A previously undiscovered southward-dipping listric normal fault was also found, to the north of the church. It probably serves as a pathway for water to leach the Permian formations below the church and causes the tilting of the church tower. This case study shows the potential of horizontal shear-wave seismic reflection to image near-surface subrosion structures in an urban environment with a horizontal resolution of less than 1 m in the uppermost 10-15 m.

Baseline seismic survey for the 2nd offshore methane hydrate production test in the Eastern Nankai Trough

NASA Astrophysics Data System (ADS)

Teranishi, Y.; Inamori, T.; Kobayashi, T.; Fujii, T.; Saeki, T.; Takahashi, H.; Kobayashi, F.

2017-12-01

JOGMEC carries out seismic monitoring surveys before and after the 2nd offshore methane hydrate (MH) production test in the Eastern Nankai Trough and evaluates MH dissociation behavior from the time-lapse seismic response. In 2016, JOGMEC deployed Ocean Bottom Cable (OBC) system provided by OCC in the Daini Atsumi Knoll with water depths of 900-1100 m. The main challenge of the seismic survey was to optimize the cable layout for ensuring an effective time-lapse seismic detectability while overcoming the following two issues: 1. OBC receiver lines were limited to only two lines. It was predicted that the imaging of shallow reflectors would suffer from lack of continuity and resolution due to this limitation of receiver lines. 2. The seafloor and shallow sedimentary layers including monitoring target are dipping to the Northwest direction. It was predicted that the refection points would laterally shift to up-dip direction (Southeast direction). In order to understand the impact of the issues above, the seismic survey was designed with elastic wave field simulation. The reflection seismic survey for baseline data was conducted in August 2016. A total of 70 receiver stations distributed along one cable were deployed successfully and a total of 9952 shots were fired. After the baseline seismic survey, the hydrophone and geophone vertical component datasets were processed as outlined below: designaturing, denoising, surface consistent deconvolution and surface consistent amplitude correction. High-frequency imaging with Reverse Time Migration (RTM) was introduced to these data sets. Improvements in imaging from the RTM are remarkable compared to the Kirchhoff migration and the existing Pre-stack time migration with 3D marine surface seismic data obtained and processed in 2002, especially in the following parts. The MH concentrated zone which has complex structures. Below the Bottom Simulating Reflector (BSR) which is present as a impedance-contrast boundary

A one year long continuous record of seismic activity and surface motion at the tongue of Rhonegletscher (Valais, Switzerland)

NASA Astrophysics Data System (ADS)

Dalban Canassy, Pierre; Röösli, Claudia; Walter, Fabian; Gabbi, Jeannette

2014-05-01

A critical gap in our current understanding of glaciers is how high sub-glacial water pressure controls the coupling of the glacier to its bed. Processes at the base of a glacier are inherently difficult to investigate due to their remoteness. Investigation of the sub-glacial environment with passive seismic methods is an innovative, rapidly growing interdisciplinary and promising endeavor. In combination with observations of surface motion and basal water pressure, this method is ideally suited to localize and quantify frictional and fracture processes which occur during periods of rapidly changing sub-glacial water pressure with consequent stress redistribution at the contact interface between ice and bed. Here we present the results of the first one-year-long glacier seismic monitoring performed on an Alpine glacier to our knowledge. Together with records of surface motion and hydrological measurements, we examine whether seasonal changes can be captured by seismic recording. Experiments were carried out from June 2012 to July 2013 on Rhonegletscher (Valais, Switzerland), by means of 3 three-components seismometers settled close to the tongue in 2 meters boreholes. An additional array of eleven sensors installed at the ice surface was also maintained during September 2012, in order to achieve more accurate icequakes locations. A high seismic emission is observed on Rhonegletscher, with icequakes located close to the surface or in the vicinity of the bedrock. The temporal distribution of seismic activity is shown to nicely reflect the seasonal evolution of the glacier hydrology, with a dramatic seismic release in early spring. During summer, released seismic activity is generally driven by diurnal ice/snow melting cycle. In winter, snow-cover conditions are associated with a reduced seismic release, with nevertheless some unexpected activity possibly related to snow-pack metamorphism. Based on icequake locations derived from data recorded in September, we discuss seasonal changes of the icequakes hypocenters distribution and possible source mechanisms are proposed.

Shallow subsurface structure of the Wasatch fault, Provo segment, Utah, from integrated compressional and shear-wave seismic reflection profiles with implications for fault structure and development

USGS Publications Warehouse

McBride, J.H.; Stephenson, W.J.; Williams, R.A.; Odum, J.K.; Worley, D.M.; South, J.V.; Brinkerhoff, A.R.; Keach, R.W.; Okojie-Ayoro, A. O.

2010-01-01

Integrated vibroseis compressional and experimental hammer-source, shear-wave, seismic reflection profiles across the Provo segment of the Wasatch fault zone in Utah reveal near-surface and shallow bedrock structures caused by geologically recent deformation. Combining information from the seismic surveys, geologic mapping, terrain analysis, and previous seismic first-arrival modeling provides a well-constrained cross section of the upper ~500 m of the subsurface. Faults are mapped from the surface, through shallow, poorly consolidated deltaic sediments, and cutting through a rigid bedrock surface. The new seismic data are used to test hypotheses on changing fault orientation with depth, the number of subsidiary faults within the fault zone and the width of the fault zone, and the utility of integrating separate elastic methods to provide information on a complex structural zone. Although previous surface mapping has indicated only a few faults, the seismic section shows a wider and more complex deformation zone with both synthetic and antithetic normal faults. Our study demonstrates the usefulness of a combined shallow and deeper penetrating geophysical survey, integrated with detailed geologic mapping to constrain subsurface fault structure. Due to the complexity of the fault zone, accurate seismic velocity information is essential and was obtained from a first-break tomography model. The new constraints on fault geometry can be used to refine estimates of vertical versus lateral tectonic movements and to improve seismic hazard assessment along the Wasatch fault through an urban area. We suggest that earthquake-hazard assessments made without seismic reflection imaging may be biased by the previous mapping of too few faults. ?? 2010 Geological Society of America.

The nature of crustal reflectivity at the southwest Iberian margin

NASA Astrophysics Data System (ADS)

Buffett, G. G.; Torne, M.; Carbonell, R.; Melchiorre, M.; Vergés, J.; Fernàndez, M.

2017-11-01

Reprocessing of multi-channel seismic reflection data acquired over the northern margin of the Gulf of Cádiz (SW Iberian margin) places new constraints on the upper crustal structure of the Guadalquivir-Portimão Bank. The data presented have been processed with optimized stacking and interval velocity models, a better approach to multiple attenuation, preserved amplitude information to derive the nature of seismic reflectivity, and accurate time-to-depth conversion after migration. The reprocessed data reveal a bright upper crustal reflector just underneath the Paleozoic basement that spatially coincides with the local positive free-air gravity high called the Gulf of Cádiz Gravity High. To investigate the nature of this reflector and to decipher whether it could be associated with pieces of mantle material emplaced at upper crustal levels, we calculated its reflection coefficient and compared it to a buried high-density ultramafic body (serpentinized peridotite) at the Gorringe Bank. Its reflection coefficient ratio with respect to the sea floor differs by only 4.6% with that calculated for the high-density ultramafic body of the Gorringe Bank, while it differs by 35.8% compared to a drilled Miocene limestone unconformity. This means that the Gulf of Cádiz reflector has a velocity and/or density contrast similar to the peridotite at the Gorringe Bank. However, considering the depth at which it is found (between 2.0 and 4.0 km) and the available geological information, it seems unlikely that the estimated shortening from the Oligocene to present is sufficient to emplace pieces of mantle material at these shallow levels. Therefore, and despite the similarity in its reflection coefficient with the peridotites of the Gorringe Bank, our preferred interpretation is that the upper crustal Gulf of Cádiz reflector represents the seismic response of high-density intracrustal magmatic intrusions that may partially contribute to the Gulf of Cádiz Gravity High.

Reflection seismic imaging in the volcanic area of the geothermal field Wayang Windu, Indonesia

NASA Astrophysics Data System (ADS)

Polom, Ulrich; Wiyono, Wiyono; Pramono, Bambang; Krawczyk, CharLotte M.

2014-05-01

Reflection seismic exploration in volcanic areas is still a scientific challenge and requires major efforts to develop imaging workflows capable of an economic utilization, e.g., for geothermal exploration. The SESaR (Seismic Exploration and Safety Risk study for decentral geothermal plants in Indonesia) project therefore tackles still not well resolved issues concerning wave propagation or energy absorption in areas covered by pyroclastic sediments using both active P-wave and S-wave seismics. Site-specific exploration procedures were tested in different tectonic and lithological regimes to compare imaging conditions. Based on the results of a small-scale, active seismic pre-site survey in the area of the Wayang Windu geothermal field in November 2012, an additional medium-scale active seismic experiment using P-waves was carried out in August 2013. The latter experiment was designed to investigate local changes of seismic subsurface response, to expand the knowledge about capabilities of the vibroseis method for seismic surveying in regions covered by pyroclastic material, and to achieve higher depth penetration. Thus, for the first time in the Wayang Windu geothermal area, a powerful, hydraulically driven seismic mini-vibrator device of 27 kN peak force (LIAG's mini-vibrator MHV2.7) was used as seismic source instead of the weaker hammer blow applied in former field surveys. Aiming at acquiring parameter test and production data southeast of the Wayang Windu geothermal power plant, a 48-channel GEODE recording instrument of the Badan Geologi was used in a high-resolution configuration, with receiver group intervals of 5 m and source intervals of 10 m. Thereby, the LIAG field crew, Star Energy, GFZ Potsdam, and ITB Bandung acquired a nearly 600 m long profile. In general, we observe the successful applicability of the vibroseis method for such a difficult seismic acquisition environment. Taking into account the local conditions at Wayang Windu, the method is superior to the common seismic explosive source techniques, both with respect to production rate as well as resolution and data quality. Source signal frequencies of 20-80 Hz are most efficient for the attempted depth penetration, even though influenced by the dry subsurface conditions during the experiment. Depth penetration ranges between 0.5-1 km. Based on these new experimental data, processing workflows can be tested the first time for adapted imaging strategies. This will not only allow to focus on larger exploration depths covering the geothermal reservoir at the Wayang Windu power plant site itself, but also opens the possibility to transfer the lessons learned to other sites.

Estimating Strain Accumulation in the New Madrid and Wabash Valley Seismic Zones

NASA Astrophysics Data System (ADS)

Craig, T. J.; Calais, E.

2014-12-01

The mechanical behaviour -- and hence earthquake potential -- of faults in continental interiors is a question of critical importance for the resultant seismic hazard, but no consensus has yet been reached on this controversial topic. The debate has focused on the central and eastern United States, in particular the New Madrid Seismic Zone, struck by three magnitude 7 or greater earthquakes in 1811--1812, and to a lesser extent the Wabash Valley Seismic Zone just to the north. A key aspect of this issue is the rate at which strain is currently accruing on those faults in the plate interior, a quantity that remains debated. Understanding if the present-day strain rates indicate sufficient motion to account for the historical and paleoseismological earthquakes by steady-state fault behaviour, or if strain accumulation is time-dependent in this area, is critical for investigating the causative process driving this seismicity in the plate interior, and how regional strain reflects the interplay between stresses arising from different geological processes. Here we address this issue with an analysis of up to 14 years of continuous GPS data from a network of 200 sites in the central United States centred on the New Madrid and Wabash Valley seismic zones. We find that high-quality sites in these regions show motions that are consistently within the 95% confidence limit of zero deformation relative to a rigid background. These results place an upper bound on regional strain accrual of 0.2 mm/yr and 0.5 mm/yr in the New Madrid and Wabash Valley Seismic Zones, respectively. These results, together with increasing evidence for temporal clustering and spatial migration of earthquake sequences in continental interiors, indicate that either tectonic loading rates or fault properties vary with time in the NMSZ and possibly plate-wide.

Calibration of Seismic Sources during a Test Cruise with the new RV SONNE

NASA Astrophysics Data System (ADS)

Engels, M.; Schnabel, M.; Damm, V.

2015-12-01

During autumn 2014, several test cruises of the brand new German research vessel SONNE were carried out before the first official scientific cruise started in December. In September 2014, BGR conducted a seismic test cruise in the British North Sea. RV SONNE is a multipurpose research vessel and was also designed for the mobile BGR 3D seismic equipment, which was tested successfully during the cruise. We spend two days for calibration of the following seismic sources of BGR: G-gun array (50 l @ 150 bar) G-gun array (50 l @ 207 bar) single GI-gun (3.4 l @ 150 bar) For this experiment two hydrophones (TC4042 from Reson Teledyne) sampling up to 48 kHz were fixed below a drifting buoy at 20 m and 60 m water depth - the sea bottom was at 80 m depth. The vessel with the seismic sources sailed several up to 7 km long profiles around the buoy in order to cover many different azimuths and distances. We aimed to measure sound pressure level (SPL) and sound exposure level (SEL) under the conditions of the shallow North Sea. Total reflections and refracted waves dominate the recorded wave field, enhance the noise level and partly screen the direct wave in contrast to 'true' deep water calibration based solely on the direct wave. Presented are SPL and RMS power results in time domain, the decay with distance along profiles, and the somehow complicated 2D sound radiation pattern modulated by topography. The shading effect of the vessel's hull is significant. In frequency domain we consider 1/3 octave levels and estimate the amount of energy in frequency ranges not used for reflection seismic processing. Results are presented in comparison of the three different sources listed above. We compare the measured SPL decay with distance during this experiment with deep water modeling of seismic sources (Gundalf software) and with published results from calibrations with other marine seismic sources under different conditions: E.g. Breitzke et al. (2008, 2010) with RV Polarstern, Tolstoy et al. (2004) with RV Ewing and Tolstoy et al. (2009) with RV Langseth, and Crone et al. (2014) with RV Langseth.

Reflection imaging of the Moon's interior using deep-moonquake seismic interferometry

NASA Astrophysics Data System (ADS)

Nishitsuji, Yohei; Rowe, C. A.; Wapenaar, Kees; Draganov, Deyan

2016-04-01

The internal structure of the Moon has been investigated over many years using a variety of seismic methods, such as travel time analysis, receiver functions, and tomography. Here we propose to apply body-wave seismic interferometry to deep moonquakes in order to retrieve zero-offset reflection responses (and thus images) beneath the Apollo stations on the nearside of the Moon from virtual sources colocated with the stations. This method is called deep-moonquake seismic interferometry (DMSI). Our results show a laterally coherent acoustic boundary around 50 km depth beneath all four Apollo stations. We interpret this boundary as the lunar seismic Moho. This depth agrees with Japan Aerospace Exploration Agency's (JAXA) SELenological and Engineering Explorer (SELENE) result and previous travel time analysis at the Apollo 12/14 sites. The deeper part of the image we obtain from DMSI shows laterally incoherent structures. Such lateral inhomogeneity we interpret as representing a zone characterized by strong scattering and constant apparent seismic velocity at our resolution scale (0.2-2.0 Hz).

Seismic reflection evidence for a northeast-dipping Hayward fault near Fremont, California: Implications for seismic hazard

USGS Publications Warehouse

Williams, R.A.; Simpson, R.W.; Jachens, R.C.; Stephenson, W.J.; Odum, J.K.; Ponce, D.A.

2005-01-01

A 1.6-km-long seismic reflection profile across the creeping trace of the southern Hayward fault near Fremont, California, images the fault to a depth of 650 m. Reflector truncations define a fault dip of about 70 degrees east in the 100 to 650 m depth range that projects upward to the creeping surface trace, and is inconsistent with a nearly vertical fault in this vicinity as previously believed. This fault projects to the Mission seismicity trend located at 4-10 km depth about 2 km east of the surface trace and suggests that the southern end of the fault is as seismically active as the part north of San Leandro. The seismic hazard implication is that the Hayward fault may have a more direct connection at depth with the Calaveras fault, affecting estimates of potential event magnitudes that could occur on the combined fault surfaces, thus affecting hazard assessments for the south San Francisco Bay region.

High-Resolution P'P' Precursor Imaging of Nazca-South America Plate Boundary Zones and Inferences for Transition Zone Temperature and Composition

NASA Astrophysics Data System (ADS)

Gu, Y. J.; Schultz, R.

2013-12-01

Knowledge of upper mantle transition zone stratification and composition is highly dependent on our ability to efficiently extract and properly interpret small seismic arrivals. A promising high-frequency seismic phase group particularly suitable for a global analysis is P'P' precursors, which are capable of resolving mantle structures at vertical and lateral resolution of approximately 5 and 200 km, respectively, owing to their shallow incidence angle and small, quasi-symmetric Fresnel zones. This study presents a simultaneous analysis of SS and P'P' precursors based on deconvolution, Radon transform and depth migration. Our multi-resolution survey of the mantle near Nazca-South America subduction zone reveals both olivine and garnet related transitions at depth below 400 km. We attribute a depressed 660 to thermal variations, whereas compositional variations atop the upper-mantle transition zone are needed to explain the diminished or highly complex reflected/scattered signals from the 410 km discontinuity. We also observe prominent P'P' reflections within the transition zone, especially near the plate boundary zone where anomalously high reflection amplitudes result from a sharp (~10 km thick) mineral phase change resonant with the dominant frequency of the P'P' precursors. Near the base of the upper mantle, the migration of SS precursors shows no evidence of split reflections near the 660-km discontinuity, but potential majorite-ilmenite (590-640 km) and ilmenite-perovskite transitions (740-750 km) are identified based on similarly processed high-frequency P'P' precursors. At nominal mantle temperatures these two phase changes may be seismically indistinguishable, but colder mantle conditions from the descending Nazca plate, the presence of water and variable Fe contents may cause sufficient separation for a reliable analysis. In addition, our preliminary results provide compelling evidence for multiple shallow lower-mantle reflections (at ~800 km) along the elongated plate boundary zones of South America. Slab stagnation at the base of the transition zone could play a key role, though a proper interpretation of this finding would likely entail compositional (rather than strictly thermal) variations in the vicinity of the descending oceanic crust and lithosphere. Overall, the resolution and sensitivity differences between low/intermediate- S and high-frequency P wave reflections are key considerations toward reconciling seismic and mineralogical models of transition zone structure, both at the study location and worldwide.

Shallow Reflection Method for Water-Filled Void Detection and Characterization

NASA Astrophysics Data System (ADS)

Zahari, M. N. H.; Madun, A.; Dahlan, S. H.; Joret, A.; Hazreek, Z. A. M.; Mohammad, A. H.; Izzaty, R. A.

2018-04-01

Shallow investigation is crucial in enhancing the characteristics of subsurface void commonly encountered in civil engineering, and one such technique commonly used is seismic-reflection technique. An assessment of the effectiveness of such an approach is critical to determine whether the quality of the works meets the prescribed requirements. Conventional quality testing suffers limitations including: limited coverage (both area and depth) and problems with resolution quality. Traditionally quality assurance measurements use laboratory and in-situ invasive and destructive tests. However geophysical approaches, which are typically non-invasive and non-destructive, offer a method by which improvement of detection can be measured in a cost-effective way. Of this seismic reflection have proved useful to assess void characteristic, this paper evaluates the application of shallow seismic-reflection method in characterizing the water-filled void properties at 0.34 m depth, specifically for detection and characterization of void measurement using 2-dimensional tomography.

Detecting voids in a 0.6 m coal seam, 7 m deep, using seismic reflection

USGS Publications Warehouse

Miller, R.D.; Steeples, D.W.

1991-01-01

Surface collapse over abandoned subsurface coal mines is a problem in many parts of the world. High-resolution P-wave reflection seismology was successfully used to evaluate the risk of an active sinkhole to a main north-south railroad line in an undermined area of southeastern Kansas, USA. Water-filled cavities responsible for sinkholes in this area are in a 0.6 m thick coal seam, 7 m deep. Dominant reflection frequencies in excess of 200 Hz enabled reflections from the coal seam to be discerned from the direct wave, refractions, air wave, and ground roll on unprocessed field files. Repetitive void sequences within competent coal on three seismic profiles are consistent with the "room and pillar" mining technique practiced in this area near the turn of the century. The seismic survey showed that the apparent active sinkhole was not the result of reactivated subsidence but probably erosion. ?? 1991.

High precision gas hydrate imaging of small-scale and high-resolution marine sparker multichannel seismic data

NASA Astrophysics Data System (ADS)

Luo, D.; Cai, F.

2017-12-01

Small-scale and high-resolution marine sparker multi-channel seismic surveys using large energy sparkers are characterized by a high dominant frequency of the seismic source, wide bandwidth, and a high resolution. The technology with a high-resolution and high-detection precision was designed to improve the imaging quality of shallow sedimentary. In the study, a 20KJ sparker and 24-channel streamer cable with a 6.25m group interval were used as a seismic source and receiver system, respectively. Key factors for seismic imaging of gas hydrate are enhancement of S/N ratio, amplitude compensation and detailed velocity analysis. However, the data in this study has some characteristics below: 1. Small maximum offsets are adverse to velocity analysis and multiple attenuation. 2. Lack of low frequency information, that is, information less than 100Hz are invisible. 3. Low S/N ratio since less coverage times (only 12 times). These characteristics make it difficult to reach the targets of seismic imaging. In the study, the target processing methods are used to improve the seismic imaging quality of gas hydrate. First, some technologies of noise suppression are combined used in pre-stack seismic data to suppression of seismic noise and improve the S/N ratio. These technologies including a spectrum sharing noise elimination method, median filtering and exogenous interference suppression method. Second, the combined method of three technologies including SRME, τ-p deconvolution and high precision Radon transformation is used to remove multiples. Third, accurate velocity field are used in amplitude energy compensation to highlight the Bottom Simulating Reflector (short for BSR, the indicator of gas hydrates) and gas migration pathways (such as gas chimneys, hot spots et al.). Fourth, fine velocity analysis technology are used to improve accuracy of velocity analysis. Fifth, pre-stack deconvolution processing technology is used to compensate for low frequency energy and suppress of ghost, thus formation reflection characteristics are highlighted. The result shows that the small-scale and high resolution marine sparker multi-channel seismic surveys are very effective in improving the resolution and quality of gas hydrate imaging than the conventional seismic acquisition technology.

Advanced seismic imaging of overdeepened alpine valleys

NASA Astrophysics Data System (ADS)

Burschil, Thomas; Buness, Hermann; Tanner, David; Gabriel, Gerald; Krawczyk, Charlotte M.

2017-04-01

Major European alpine valleys and basins are densely populated areas with infrastructure of international importance. To protect the environment by, e.g., geohazard assessment or groundwater estimation, understanding of the geological structure of these valleys is essential. The shape and deposits of a valley can clarify its genesis and allows a prediction of behaviour in future glaciations. The term "overdeepened" refers to valleys and basins, in which pressurized melt-water under the glacier erodes the valley below the fluvial level. Most overdeepened valleys or basins were thus refilled during the ice melt or remain in the form of lakes. The ICDP-project Drilling Overdeepened Alpine Valleys (DOVE) intends to correlate the sedimentary succession from boreholes between valleys in the entire alpine range. Hereby, seismic exploration is essential to predict the most promising well path and drilling site. In a first step, this DFG-funded project investigates the benefit of multi-component techniques for seismic imaging. At two test sites, the Tannwald Basin and the Lienz Basin, the Leibniz Institute for Applied Geophysics acquired P-wave reflection profiles to gain structural and facies information. Built on the P-wave information, several S-wave reflection profiles were acquired in the pure SH-wave domain as well as 6-C reflection profiles using a horizontal S-wave source in inline and crossline excitation and 3-C receivers. Five P-wave sections reveal the structure of the Tannwald Basin, which is a distal branch basin of the Rhine Glacier. Strong reflections mark the base of the basin, which has a maximum depth of 240 metres. Internal structures and facies vary strongly and spatially, but allow a seismic facies characterization. We distinguish lacustrine, glacio-fluvial, and deltaic deposits, which make up the fill of the Tannwald Basin. Elements of the SH-wave and 6-C seismic imaging correlate with major structures in the P-wave image, but vary in detail. Based on the interpretation, two possible drilling sites are suggested for DOVE that will also prove the seismic interpretation and explain differences in P- and S-wave imaging. First results for the intermountain Lienz Basin are available from four parallel P-wave sections which show the asymmetric basin shape. The sedimentary base is well imaged down to ca. 0.6 km depth, and internal reflectors point to a diverse fill. Here, S-wave imaging produces less distinct sections and requires more sophisticated processing. In summary, P-wave imaging is suitable to map overdeepened structures in the Alps while S-wave imaging can contribute additional information.

Seismic images of a Grenvillian terrane boundary

USGS Publications Warehouse

Milkereit, B.; Forsyth, D. A.; Green, A.G.; Davidson, A.; Hanmer, S.; Hutchinson, Deborah R.; Hinze, W. J.; Mereu, R.F.

1992-01-01

A series of gently dipping reflection zones extending to mid-crustal depths is recorded by seismic data from Lakes Ontario and Erie. These prominent reflection zones define a broad complex of southeast-dipping ductile thrust faults in the interior of the Grenville orogen. One major reflection zone provides the first image of a proposed Grenvillian suture—the listric boundary zone between allochthonous terranes of the Central Gneiss and Central Metasedimentary belts. Curvilinear bands of reflections that may represent "ramp folds" and "ramp anticlines" that originally formed in a deep crustal-scale duplex abut several faults. Vertical stacking of some curvilinear features suggests coeval or later out-of-sequence faulting of imbricated and folded thrust sheets. Grenvillian structure reflections are overlain by a thin, wedge-shaped package of shallow-dipping reflections that probably originates from sediments deposited in a local half graben developed during a period of post-Grenville extension. This is the first seismic evidence for such extension in this region, which could have occurred during terminal collapse of the Grenville orogen, or could have marked the beginning of pre-Appalachian continental rifting.

Evolution of basin and range structure in the Ruby Mountains and vicinity, Nevada

NASA Technical Reports Server (NTRS)

Blackwell, D. D.; Reese, N. M.; Kelley, S. A.

1985-01-01

Results from various age dating techniques, seismic reflection profiling hydrocarbon maturation studies, and structural analysis were used to evaluate the Cenozoic deformation in the Ruby Mountains and adjoining ranges (pinyon Range and Cortez Range) in Elko and Eureka Counties, Nevada. Age dating techniques used include potassium-argon ages of biotites from granites published by Kistler et al. (1981) and fission track ages from apatite and zircon. Fission track ages from apatite reflect a closing temperature of 100 plus or minus 20 deg C. Zircon fission track ages reflect a closing temperature of 175 plus or minus 25 deg C and potassium-argon ages from brotite reflect a closing temperature of 250 plus or minus 30 deg C. Thus these results allow a reasonably precise tracking of the evolution of the ranges during the Cenozoic. Seismic reflection data are available from Huntington Valley. Access to seismic reflection data directly to the west of the Harrison Pass Pluton in the central Ruby Mountains was obtained. In addition results are available from several deep exploration holes in Huntington Valley.

Seismic-reflection studies, offshore Santa Maria Province, California

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bird, K.J.; Childs, J.R.; Taylor, D.J.

1991-02-01

Well data and seismic-reflection records are being analyzed to provide a subsurface geologic framework for the US Geological Survey's Santa Maria Province project. This project, jointly sponsored by the Evolution of Sedimentary Basins and Onshore Oil and Gas Investigations Programs, in a basin-evolution and petroleum geology study focusing on the geologically complex and tectonically active south-central California margin. The area embraces several basins and basin fragments including the onshore Santa Maria, offshore Santa Maria, Pismo, Huasna, Sur, Santa Lucia, and western Santa Barbara-Ventura. These basins have many similarities, including generally synchronous formation at about the end of the Oligocene, developmentmore » on a complex assemblage of Mesozoic tectonostratigraphic terranes, and basin fill consisting of Neogene clastic marine and nonmarine deposits, minor volcanic rocks, and organic-rich biogenous deposits of the Monterey Formation. Despite these similarities, basin origins are controversial and paleogeographies uncertain. In 1990, the US Geological Survey collected approximately 130 line-mi of multichannel seismic reflection data in seven profiles off-shore California from Morro Bay south to the western Santa Barbara Channel. These are the first US Geological Survey seismic data collected in this area since the early 1980s exploratory drilling began in the offshore Santa Maria basin. Profiles were generally oriented perpendicular to structural grain and located to intersect as many well-sites and pre-existing seismic profiles as possible. Profile orientation and spacing were designed to provide the offshore extensions of onshore well-correlation profiles currently under construction. With synthetic seismograms the authors are integrating the stratigraphy of the wells with these seismic-reflection records.« less

Structure of the California Coast Ranges and San Andreas Fault at SAFOD from seismic waveform inversion and reflection imaging

USGS Publications Warehouse

Bleibinhaus, F.; Hole, J.A.; Ryberg, T.; Fuis, G.S.

2007-01-01

A seismic reflection and refraction survey across the San Andreas Fault (SAF) near Parkfield provides a detailed characterization of crustal structure across the location of the San Andreas Fault Observatory at Depth (SAFOD). Steep-dip prestack migration and frequency domain acoustic waveform tomography were applied to obtain highly resolved images of the upper 5 km of the crust for 15 km on either side of the SAF. The resulting velocity model constrains the top of the Salinian granite with great detail. Steep-dip reflection seismic images show several strong-amplitude vertical reflectors in the uppermost crust near SAFOD that define an ???2-km-wide zone comprising the main SAF and two or more local faults. Another prominent subvertical reflector at 2-4 km depth ???9 km to the northeast of the SAF marks the boundary between the Franciscan terrane and the Great Valley Sequence. A deep seismic section of low resolution shows several reflectors in the Salinian crust west of the SAF. Two horizontal reflectors around 10 km depth correlate with strains of seismicity observed along-strike of the SAF. They represent midcrustal shear zones partially decoupling the ductile lower crust from the brittle upper crust. The deepest reflections from ???25 km depth are interpreted as crust-mantle boundary. Copyright 2007 by the American Geophysical Union.

Imaging the Alpine Fault to depths of more than 2 km - Initial results from the 2011 WhataDUSIE seismic reflection profile, Whataroa Valley, New Zealand

NASA Astrophysics Data System (ADS)

Kovacs, A.; Gorman, A. R.; Buske, S.; Schmitt, D. R.; Eccles, J. D.; Toy, V. G.; Sutherland, R.; Townend, J.; Norris, R.; Pooley, B.; Cooper, J.; Bruce, C.; Smillie, M.; Bain, S.; Hellwig, O.; Hlousek, F.; Hellmich, J.; Riedel, M.; Schijns, H. M.

2011-12-01

The Alpine Fault is a major plate-bounding fault that is thought to fail in large earthquakes (Mw~7.9) every 200-400 years and to have last ruptured in AD 1717. It is the principal geological structure accommodating transpressional motion between the Australian and Pacific plates on the South Island, with a long-term horizontal motion over the last 1-2 million years of 21-27 mm/yr. Determining the Alpine Fault zone structure at depths of several kilometres beneath the Earth's surface is crucial for understanding not only what conditions govern earthquake rupture but also how ongoing faulting produces mountain ranges such as the Southern Alps. The valley of the Whataroa River, in the central sector of the Alpine Fault, provides rare access to the SE (hanging wall) side of the fault for the purpose of a seismic survey. During January and February 2011, a ~5-km-long seismic reflection line was collected that aimed to image the Alpine Fault at depth. The acquisition was undertaken with the use of 21 Geode seismographs and two Seistronix seismographs with a total capacity of 552 channels. Geophone spacing varied from 4 m in the north (close to the surface trace of the fault) to 8 m in the south (farther from the surface trace.) Sources were 400-g Pentex charges buried in 1.5-2.0 m deep holes of which ~100 were dug by an excavator and ~100 were dug by hand tools where heavy equipment could not access shot locations. Single shots had a nominal separation of 25 m at the north end of the line. At the south end of the line, shots were deployed in patterns of five with a nominal spacing of 125 m. Acquisition system requirements and surface morphology (meanders in the Whataroa River) required five separate acquisition systems. Timing of shots for these systems was accomplished with a radio-controlled firing system, GPS clocks linked to co-located Reftek seismographs, and overlapping traces between acquisition systems. Shot records have been merged and processed through to stacks using the GLOBE Claritas seismic processing package. Initial observations and interpretations of the data are presented. The hanging wall of the Alpine Fault beneath the Whataroa Valley contains at least two major units, a lower basement of Alpine Schist rocks overlain by a substantial layer of glacial sediments that are as much as 700 m thick in places. A sharp reflection marks the boundary between the two units. In places, the Alpine Fault is interpreted as a dipping reflection in the seismic data. The strength of the reflection varies, perhaps as a result of changes in the rocks of the footwall or changes in the geometry of the fault or fault zone.

A computer procedure to analyze seismic data to estimate outcome probabilities in oil exploration, with an initial application in the tabasco region of southeastern Mexico

NASA Astrophysics Data System (ADS)

Berlanga, Juan M.; Harbaugh, John W.

The Tabasco region contains a number of major oilfields, including some of the emerging "giant" oil fields which have received extensive publicity. Fields in the Tabasco region are associated with large geologic structures which are detected readily by seismic surveys. The structures seem to be associated with deepseated movement of salt, and they are complexly faulted. Some structures have as much as 1000 milliseconds relief of seismic lines. A study, interpreting the structure of the area, used initially only a fraction of the total seismic lines That part of Tabasco region that has been studied was surveyed with a close-spaced rectilinear network of seismic lines. A, interpreting the structure of the area, used initially only a fraction of the total seismic data available. The purpose was to compare "predictions" of reflection time based on widely spaced seismic lines, with "results" obtained along more closely spaced lines. This process of comparison simulates the sequence of events in which a reconnaissance network of seismic lines is used to guide a succession of progressively more closely spaced lines. A square gridwork was established with lines spaced at 10 km intervals, and using machine contour maps, compared the results with those obtained with seismic grids employing spacings of 5 and 2.5 km respectively. The comparisons of predictions based on widely spaced lines with observations along closely spaced lines provide information by which an error function can be established. The error at any point can be defined as the difference between the predicted value for that point, and the subsequently observed value at that point. Residuals obtained by fitting third-degree polynomial trend surfaces were used for comparison. The root mean square of the error measurement, (expressed in seconds or milliseconds reflection time) was found to increase more or less linearly with distance from the nearest seismic point. Oil-occurrence probabilities were established on the basis of frequency distributions of trend-surface residuals obtained by fitting and subtracting polynomial trend surfaces from the machine-contoured reflection time maps. We found that there is a strong preferential relationship between the occurrence of petroleum (i.e. its presence versus absence) and particular ranges of trend-surface residual values. An estimate of the probability of oil occurring at any particular geographic point can be calculated on the basis of the estimated trend-surface residual value. This estimate, however, must be tempered by the probable error in the estimate of the residual value provided by the error function. The result, we believe, is a simple but effective procedure for estimating exploration outcome probabilities where seismic data provide the principal form of information in advance of drilling. Implicit in this approach is the comparison between a maturely explored area, for which both seismic and production data are available, and which serves as a statistical "training area", with the "target" area which is undergoing exploration and for which probability forecasts are to be calculated.

Method for inverting reflection trace data from 3-D and 4-D seismic surveys and identifying subsurface fluid and pathways in and among hydrocarbon reservoirs based on impedance models

DOEpatents

He, W.; Anderson, R.N.

1998-08-25

A method is disclosed for inverting 3-D seismic reflection data obtained from seismic surveys to derive impedance models for a subsurface region, and for inversion of multiple 3-D seismic surveys (i.e., 4-D seismic surveys) of the same subsurface volume, separated in time to allow for dynamic fluid migration, such that small scale structure and regions of fluid and dynamic fluid flow within the subsurface volume being studied can be identified. The method allows for the mapping and quantification of available hydrocarbons within a reservoir and is thus useful for hydrocarbon prospecting and reservoir management. An iterative seismic inversion scheme constrained by actual well log data which uses a time/depth dependent seismic source function is employed to derive impedance models from 3-D and 4-D seismic datasets. The impedance values can be region grown to better isolate the low impedance hydrocarbon bearing regions. Impedance data derived from multiple 3-D seismic surveys of the same volume can be compared to identify regions of dynamic evolution and bypassed pay. Effective Oil Saturation or net oil thickness can also be derived from the impedance data and used for quantitative assessment of prospective drilling targets and reservoir management. 20 figs.

Method for inverting reflection trace data from 3-D and 4-D seismic surveys and identifying subsurface fluid and pathways in and among hydrocarbon reservoirs based on impedance models

DOEpatents

He, Wei; Anderson, Roger N.

1998-01-01

A method is disclosed for inverting 3-D seismic reflection data obtained from seismic surveys to derive impedance models for a subsurface region, and for inversion of multiple 3-D seismic surveys (i.e., 4-D seismic surveys) of the same subsurface volume, separated in time to allow for dynamic fluid migration, such that small scale structure and regions of fluid and dynamic fluid flow within the subsurface volume being studied can be identified. The method allows for the mapping and quantification of available hydrocarbons within a reservoir and is thus useful for hydrocarbon prospecting and reservoir management. An iterative seismic inversion scheme constrained by actual well log data which uses a time/depth dependent seismic source function is employed to derive impedance models from 3-D and 4-D seismic datasets. The impedance values can be region grown to better isolate the low impedance hydrocarbon bearing regions. Impedance data derived from multiple 3-D seismic surveys of the same volume can be compared to identify regions of dynamic evolution and bypassed pay. Effective Oil Saturation or net oil thickness can also be derived from the impedance data and used for quantitative assessment of prospective drilling targets and reservoir management.

Crustal structure and tectonics of the northern part of the Southern Granulite Terrane, India

USGS Publications Warehouse

Rao, V.V.; Sain, K.; Reddy, P.R.; Mooney, W.D.

2006-01-01

Deep seismic reflection studies investigating the exposed Archean lower continental crust of the Southern Granulite Terrane, India, yield important constraints on the nature and evolution of the deep crust, including the formation and exhumation of granulites. Seismic reflection images along the Kuppam-Bhavani profile reveal a band of reflections that dip southward from 10.5 to 15.0??s two-way-time (TWT), across a distance of 50??km. The bottom of these reflections beneath the Dharwar craton is interpreted as the Moho. Further south, another reflection band dipping northward is observed. These bands of reflectivity constitute a divergent reflection fabric that converges at the Moho boundary observed at the Mettur shear zone. Reflection fabrics that intersect at a steep angle are interpreted as a collisional signature due to the convergence of crustal blocks, which we infer resulted in crustal thickening and the formation of granulites. Anomalous gravity and magnetic signatures are also observed across the Mettur shear zone. The gravity model derived from the Bouguer gravity data corroborates seismic results. The tectonic regime and seismic reflection profiles are combined in a 3-D representation that illustrates our evidence for paleo-subduction at a collision zone. The structural dissimilarities and geophysical anomalies suggest that the Mettur shear zone is a suture between the Dharwar craton in the north and another crustal block in the south. This study contributes significantly to our understanding of the operation of Archean plate tectonics, here inferred to involve collision and subduction. Furthermore, it provides an important link between the Gondwanaland and global granulite evolution occurring throughout the late Archean. ?? 2006 Elsevier B.V. All rights reserved.

Seismic-reflection profiles of the New Madrid seismic zone-data along the Mississippi River near Caruthersville, Missouri

USGS Publications Warehouse

Crone, A.J.; Harding, S.T.; Russ, D.P.; Shedlock, K.M.

1986-01-01

Three major seismic-reflection programs have been conducted by the USGS in the New Madrid seismic zone. The first program consisted of 32 km of conventional Vibroseis profiling designed to investigate the subsurface structure associated with scarps and lineaments in northwestern Tennessee (Zoback, 1979). A second, more extensive Vibroseis program collected about 250 km of data from all parts of the New Madrid seismic zone in Missouri, Arkansas, and Tennessee (Hamilton and Zoback, 1979, 1982; Zoback and others, 1980). The profiles presented here are part of the third program that collected about 240 km of high-resolution seismic-reflection data from a boat along the Mississippi River between Osceola, Ark., and Wickliffe, Ky. (fig. 1). The data for profiles A, B, C, and D were collected between river miles 839-1/2 and 850-1/2 from near the Interstate-155 bridge to upstream of Caruthersville, Mo. (fig. 2). Profiles on this part of the river are important for three reasons: (1) they connect many of the land-based profiles on either side of the river, (2) they are near the northeast termination of a linear, 120km-long, northeast-southwest zone of seismicity that extends from northeast Arkansas to Caruthersville, Mo. (Stauder, 1982; fig. 1), and (3) they cross the southwesterly projection of the Cottonwood Grove fault (fig. 1), a fault having a substantial amount of vertical Cenozoic offset (Zoback and others, 1980).

Probabilistic seismic hazard zonation for the Cuban building code update

NASA Astrophysics Data System (ADS)

Garcia, J.; Llanes-Buron, C.

2013-05-01

A probabilistic seismic hazard assessment has been performed in response to a revision and update of the Cuban building code (NC-46-99) for earthquake-resistant building construction. The hazard assessment have been done according to the standard probabilistic approach (Cornell, 1968) and importing the procedures adopted by other nations dealing with the problem of revising and updating theirs national building codes. Problems of earthquake catalogue treatment, attenuation of peak and spectral ground acceleration, as well as seismic source definition have been rigorously analyzed and a logic-tree approach was used to represent the inevitable uncertainties encountered through the whole seismic hazard estimation process. The seismic zonation proposed here, is formed by a map where it is reflected the behaviour of the spectral acceleration values for short (0.2 seconds) and large (1.0 seconds) periods on rock conditions with a 1642 -year return period, which being considered as maximum credible earthquake (ASCE 07-05). In addition, other three design levels are proposed (severe earthquake: with a 808 -year return period, ordinary earthquake: with a 475 -year return period and minimum earthquake: with a 225 -year return period). The seismic zonation proposed here fulfils the international standards (IBC-ICC) as well as the world tendencies in this thematic.

Seismic Anisotropy from Surface Refraction Measurements

NASA Astrophysics Data System (ADS)

Vilhelm, J.; Hrdá, J.; Klíma, K.; Lokajícek, T.; Pros, Z.

2003-04-01

The contribution deals with the methods of determining P and S wave velocities in the shallow refraction seismics. The comparison of a P-wave anisotropy from samples and field surface measurement is performed. The laboratory measurement of the P-wave velocity is realized as omni directional ultrasound measurement on oriented spherical samples (diameter 5 cm) under a hydrostatic pressure up to 400 MPa. The field measurement is based on the processing of at least one pair of reversed time-distance curves of refracted waves. Different velocity calculation techniques are involved including tomographic approach from the surface. It is shown that field seismic measurement can reflect internal rock fabric (lineation, mineral anisotropy) as well as effects connected with the fracturing and weathering. The elastic constants derived from laboratory measurements exhibit transversal isotropy. For the estimation of anisotropy influence we perform ray-tracing by the software package ANRAY (Consortium Seismic Waves in Complex 3-D Structures). The use of P and S wave anisotropy measurement to determine hard rock hydro-geological collector (water resource) is presented. In a relatively homogeneous lutaceous sedimentary medium we identified a transversally isotropic layer which exhibits increased value of permeability (transmisivity). The seismic measurement is realized by three component geophones with both vertical and shear seismic sources. VLF and resistivity profiling accompany the filed survey.

New Geophysical Techniques for Offshore Exploration.

ERIC Educational Resources Information Center

Talwani, Manik

1983-01-01

New seismic techniques have been developed recently that borrow theory from academic institutions and technology from industry, allowing scientists to explore deeper into the earth with much greater precision than possible with older seismic methods. Several of these methods are discussed, including the seismic reflection common-depth-point…

Crustal insights from gravity and aeromagnetic analysis: Central North Slope, Alaska

USGS Publications Warehouse

Saltus, R.W.; Potter, C.J.; Phillips, J.D.

2006-01-01

Aeromagnetic and gravity data are processed and interpreted to reveal deep and shallow information about the crustal structure of the central North Slope, Alaska. Regional aeromagnetic anomalies primarily reflect deep crustal features. Regional gravity anomalies are more complex and require detailed analysis. We constrain our geophysical models with seismic data and interpretations along two transects including the Trans-Alaska Crustal Transect. Combined geophysical analysis reveals a remarkable heterogeneity of the pre-Mississippian basement. In the central North Slope, pre-Mississippian basement consists of two distinct geophysical domains. To the southwest, the basement is dense and highly magnetic; this basement is likely mafic and mechanically strong, possibly acting as a buttress to basement involvement in Brooks Range thrusting. To the northeast, the central North Slope basement consists of lower density, moderately magnetic rocks with several discrete regions (intrusions?) of more magnetic rocks. A conjugate set of geophysical trends, northwest-southeast and southwest-northeast, may be a factor in the crustal response to tectonic compression in this domain. High-resolution gravity and aeromagnetic data, where available, reflect details of shallow fault and fold structure. The maps and profile models in this report should provide useful guidelines and complementary information for regional structural studies, particularly in combination with detailed seismic reflection interpretations. Future challenges include collection of high-resolution gravity and aeromagnetic data for the entire North Slope as well as additional deep crustal information from seismic, drilling, and other complementary methods. Copyrights ?? 2006. The American Association of Petroleum Geologists. All rights reserved.

Local thickening of the Cascadia forearc crust and the origin of seismic reflectors in the uppermost mantle

USGS Publications Warehouse

Calvert, A.J.; Ramachandran, K.; Kao, H.; Fisher, M.A.

2006-01-01

Seismic reflection profiles from three different surveys of the Cascadia forearc are interpreted using P wave velocities and relocated hypocentres, which were both derived from the first arrival travel time inversion of wide-angle seismic data and local earthquakes. The subduction decollement, which is characterized beneath the continental shelf by a reflection of 0.5 s duration, can be traced landward into a large duplex structure in the lower forearc crust near southern Vancouver Island. Beneath Vancouver Island, the roof thrust of the duplex is revealed by a 5–12 km thick zone, identified previously as the E reflectors, and the floor thrust is defined by a short duration reflection from a − 1. We suggest that these relatively low velocities indicate the presence of either crustal rocks from the oceanic plate that have been underplated to the continent or crustal rocks from the forearc that have been transported downward by subduction erosion. The absence of seismicity from within the E reflectors implies that they are significantly weaker than the overlying crust, and the reflectors may be a zone of active ductile shear. In contrast, seismicity in parts of the D reflectors can be interpreted to mean that ductile shearing no longer occurs in the landward part of the duplex. Merging of the D and E reflectors at 42–46 km depth creates reflectivity in the uppermost mantle with a vertical thickness of at least 15 km. We suggest that pervasive reflectivity in the upper mantle elsewhere beneath Puget Sound and the Strait of Georgia arises from similar shear zones.

Misinterpretation of lateral acoustic variations on high-resolution seismic reflection profiles as fault offsets of Holocene bay mud beneath the southern part of San Francisco Bay, California

USGS Publications Warehouse

Marlow, M. S.; Hart, P.E.; Carlson, P.R.; Childs, J. R.; Mann, D. M.; Anima, R.J.; Kayen, R.E.

1996-01-01

We collected high-resolution seismic reflection profiles in the southern part of San Francisco Bay in 1992 and 1993 to investigate possible Holocene faulting along postulated transbay bedrock fault zones. The initial analog records show apparent offsets of reflection packages along sharp vertical boundaries. These records were originally interpreted as showing a complex series of faults along closely spaced, sharp vertical boundaries in the upper 10 m (0.013 s two-way travel time) of Holocene bay mud. A subsequent survey in 1994 was run with a different seismic reflection system, which utilized a higher power source. This second system generated records with deeper penetration (max. 20 m, 0.026 s two-way travel time) and demonstrated that the reflections originally interpreted as fault offsets by faulting were actually laterally continuous reflection horizons. The pitfall in the original interpretations was caused by lateral variations in the amplitude brightness of reflection events, coupled with a long (greater than 15 ms) source signature of the low-power system. These effects combined to show apparent offsets of reflection packages along sharp vertical boundaries. These boundaries, as shown by the second system, in fact occur where the reflection amplitude diminishes abruptly on laterally continuous reflection events. This striking lateral variation in reflection amplitude is attributable to the localized presence of biogenic(?) gas.

Sequence stratigraphy, seismic stratigraphy, and seismic structures of the lower intermediate confining unit and most of the Floridan aquifer system, Broward County, Florida

USGS Publications Warehouse

Cunningham, Kevin J.; Kluesner, Jared W.; Westcott, Richard L.; Robinson, Edward; Walker, Cameron; Khan, Shakira A.

2017-12-08

Deep well injection and disposal of treated wastewater into the highly transmissive saline Boulder Zone in the lower part of the Floridan aquifer system began in 1971. The zone of injection is a highly transmissive hydrogeologic unit, the Boulder Zone, in the lower part of the Floridan aquifer system. Since the 1990s, however, treated wastewater injection into the Boulder Zone in southeastern Florida has been detected at three treated wastewater injection utilities in the brackish upper part of the Floridan aquifer system designated for potential use as drinking water. At a time when usage of the Boulder Zone for treated wastewater disposal is increasing and the utilization of the upper part of the Floridan aquifer system for drinking water is intensifying, there is an urgency to understand the nature of cross-formational fluid flow and identify possible fluid pathways from the lower to upper zones of the Floridan aquifer system. To better understand the hydrogeologic controls on groundwater movement through the Floridan aquifer system in southeastern Florida, the U.S. Geological Survey and the Broward County Environmental Planning and Community Resilience Division conducted a 3.5-year cooperative study from July 2012 to December 2015. The study characterizes the sequence stratigraphy, seismic stratigraphy, and seismic structures of the lower part of the intermediate confining unit aquifer and most of the Floridan aquifer system.Data obtained to meet the study objective include 80 miles of high-resolution, two-dimensional (2D), seismic-reflection profiles acquired from canals in eastern Broward County. These profiles have been used to characterize the sequence stratigraphy, seismic stratigraphy, and seismic structures in a 425-square-mile study area. Horizon mapping of the seismic-reflection profiles and additional data collection from well logs and cores or cuttings from 44 wells were focused on construction of three-dimensional (3D) visualizations of eight sequence stratigraphic cycles that compose the Eocene to Miocene Oldsmar, Avon Park, and Arcadia Formations. The mapping of these seismic-reflection and well data has produced a refined Cenozoic sequence stratigraphic, seismic stratigraphic, and hydrogeologic framework of southeastern Florida. The upward transition from the Oldsmar Formation to the Avon Park Formation and the Arcadia Formation embodies the evolution from (1) a tropical to subtropical, shallow-marine, carbonate platform, represented by the Oldsmar and Avon Park Formations, to (2) a broad, temperate, mixed carbonate-siliciclastic shallow marine shelf, represented by the lower part of the Arcadia Formation, and to (3) a temperate, distally steepened carbonate ramp represented by the upper part of the Arcadia Formation.In the study area, the depositional sequences and seismic sequences have a direct correlation with hydrogeologic units. The approximate upper boundary of four principal permeable units of the Floridan aquifer system (Upper Floridan aquifer, Avon Park permeable zone, uppermost major permeable zone of the Lower Floridan aquifer, and Boulder Zone) have sequence stratigraphic and seismic-reflection signatures that were identified on cross sections, mapped, or both, and therefore the sequence stratigraphy and seismic stratigraphy were used to guide the development of a refined spatial representation of these hydrogeologic units. In all cases, the permeability of the four permeable units is related to stratiform megaporosity generated by ancient dissolution of carbonate rock associated with subaerial exposure and unconformities at the upper surfaces of carbonate depositional cycles of several hierarchical scales ranging from high-frequency cycles to depositional sequences. Additionally, interparticle porosity also contributes substantially to the stratiform permeability in much of the Upper Floridan aquifer. Information from seismic stratigraphy allowed 3D geomodeling of hydrogeologic units—an approach never before applied to this area. Notably, the 3D geomodeling provided 3D visualizations and geocellular models of the depositional sequences, hydrostratigraphy, and structural features. The geocellular data could be used to update the hydrogeologic structure inherent to groundwater flow simulations that are designed to address the sustainability of the water resources of the Floridan aquifer system.Two kinds of pathways that could enable upward cross-formational flow of injected treated wastewater from the Boulder Zone have been identified in the 80 miles of high-resolution seismic data collected for this study: a near-vertical reverse fault and karst collapse structures. The single reverse fault, inferred to be of tectonic origin, is in extreme northeastern Broward County and has an offset of about 19 feet at the level of the Arcadia Formation. Most of the 17 karst collapse structures identified manifest as columniform, vertically stacked sagging seismic reflections that span early Eocene to Miocene age rocks equivalent to much of the Floridan aquifer system and the lower part of the overlying intermediate confining unit. In some cases, the seismic-sag structures extend upward into strata of Pliocene age. The seismic-sag structures are interpreted to have a semicircular shape in plan view on the basis of comparison to (1) other seismic-sag structures in southeastern Florida mapped with two 2D seismic cross lines or 3D data, (2) comparison to these structures located in other carbonate provinces, and (3) plausible extensional ring faults detected with multi-attribute analysis. The seismic-sag structures in the study area have heights as great as 2,500 vertical feet, though importantly, one spans about 7,800 feet. Both multi-attribute analysis and visual detection of offset of seismic reflections within the seismic-sag structures indicate faults and fractures are associated with many of the structures. Multi-attribute analysis highlighting chimney fluid pathways also indicates that the seismic-sag structures have a high probability for potential vertical cross-formational fluid flow along the faulted and fractured structures. A collapse of the seismic-sag structures within a deep burial setting evokes an origin related to hypogenic karst processes by ascending flow of subsurface fluids. In addition, paleo-epigenic karst related to major regional subaerial unconformities within the Florida Platform generated collapse structures (paleo-sinkholes) that are much smaller in scale than the cross-formational seismic-sag structures.

Reflection Response of the Parnaíba Basin (NE Brazil) from Seismic Ambient Noise Autocorrelation Functions

NASA Astrophysics Data System (ADS)

Julià, Jordi; Schimmel, Martin; Cedraz, Victória

2017-04-01

Reflected-wave interferometry relies on the recording of transient seismic signals from random wavefields located beneath recording stations. Under vertical incidence, the recordings contain the full transmission response, which includes the direct wave as well as multiple reverberations from seismic discontinuities located between the wavefields and the receiver. It has been shown that, under those assumptions, the reflection response of the medium can be recovered from the autocorrelation function (ACF) of the transmission response at a given receiver, as if the wavefields had originated themselves at the free surface. This passive approach to seismic reflection profiling has the obvious advantage of being low-cost and non-invasive when compared to its active-source counterpart, and it has been successfully utilized in other sedimentary basins worldwide. In this paper we evaluate the ability of the autocorrelation of ambient seismic noise recorded in the Parnaíba basin - a large Paleozoic basin in NE Brazil - to recover the reflection response of the basin. The dataset was acquired by the Universidade Federal do Rio Grande do Norte during 2015 and 2016 under the Parnaíba Basin Analysis Project (PBAP), a multi-disciplinary and multi-institutional effort funded by BP Energy do Brasil aimed at improving our current understanding of the architecture of this cratonic basin. The dataset consists of about 1 year of continuous ground motion data from 10 short-period, 3-component stations located in the central portion of the basin. The stations were co-located with an existing (active-source) seismic reflection profile that was shot in 2012, making a linear array of about 100 km in aperture and about 10 km inter-station spacing. To develop the autocorrelation at a given station we considered the vertical component of ground motion only, which should result in the P-wave response. The vertical recordings were first split into 10 min-long windows, demeaned, de-trended, re-sampled, and band-pass filtered between 8 and 16 Hz before autocorrelation, and then stacked with phase-weighting to enhance coherency of the retrieved signal. The ACFs show coherent signal is recovered at lag times between 0.5 and 2 s, which we interpret as P- and S-wave energy reflected on top of an intra-sedimentary discontinuity. Our results are consistent, to first-order, with a previously developed active-source reflection response of the basin.

Pre-Holocene to Modern Evolution of the Lower Delaware Estuary: Constraints from High-Resolution Chirp Subbottom Profiles

NASA Astrophysics Data System (ADS)

Daw, Julianne

Throughout the Quaternary Period, the Delaware Estuary, which is located within the Mid-Atlantic region of the United States, has undergone substantial change as a result of sea-level fluctuations. To better understand the recent (late Pleistocene to Holocene) evolution of the region, chirp subbottom profiles were analyzed within Delaware Bay near the southern end of the Delaware River Navigation Channel including the adjacent shoals and sloughs, using RoxAnn bottom classification data and available vibracores to aid in interpreting sediment types and depositional environments within the study area. Using seismic processing software (SonarWiz6), chirp profiles were processed and reflection events were identified and their positions digitized. Major reflection events were analyzed using a seismic facies approach. The identified facies were each characterized as distinct units composed of reflections with unique elements, such as configuration, amplitude, and continuity. Five seismic facies were identified and their thicknesses determined. Depths to the major reflection events were correlated with sediment boundaries as observed in the available vibracores, allowing the seismic facies to be interpreted in terms of their associated sediment types and inferred environments of deposition. The distributions of surficial and subsurface seismic and sedimentological features were visualized using three-dimensional images. The interpretations of the identified facies are as follows: Facies I is a surficial unit of the modern Holocene estuarine deposits; Facies II is a beach-berm washover zone deposition; Facies III is a deposit of a lagoonal environment; Facies IV is a deposit of an open water environment; and Facies V is a marsh deposition. The chirp data, when integrated with available information from vibracores and RoxAnn bottom sediment classification, was also used to map the position of a former major river system (paleochannel). This paleochannel, trending generally northwest to southeast, can be correlated with the southern channel that was identified in previous work by Knebel and Circe (1988). In addition to the knowledge gained by studying the geological evolution of Delaware Bay, our data can be used by decision makers and stakeholders to inform future management of the Delaware Estuary in practical applications that range from planning for maintenance dredging of the navigation channel to determining locations and thicknesses of suitable sand resources for shoreline replenishment. The surficial layer that would be most affected by such applications is mostly composed of sand & muddy sand, but in the deeper portions and along the shoals, it is composed of mixed and coarse sediments and mud & sandy mud, respectively. Furthermore, the surficial unit is thickest (between 1.5 and 4 meters) in the central and eastern regions of the study area encompassing the deeper portions, and it is thinnest (up to 1 meter) along the western and northern regions that include the shoals.

Crustal high-velocity anomaly at the East European Craton margin in SE Poland (TESZ) modelled by 3-D seismic tomography of refracted and reflected arrivals

NASA Astrophysics Data System (ADS)

Środa, Piotr; Dec, Monika

2016-04-01

The area of Trans-European Suture Zone in SE Poland represents a contact of major tectonic units of different consolidation age - from the Precambrian East European Craton, through Palaeozoic West European Platform to Cenozoic Carpathian orogen. The region was built by several phases of crustal accretion, which resulted in a complex collage of tectonic blocks. In 2000, this region was studied by several seismic wide-angle profiles of CELEBRATION 2000 experiment, providing a dense coverage of seismic data in SE Poland and allowing for detailed investigations of the crustal structure and properties in this area. Beneath the marginal part of the EEC, the 2-D modelling of in-line data form several CELEBRATION profiles revealed a prominent high P-wave velocity anomaly in the upper crust, with Vp of 6.7-7.1 km/s, starting at 10-16 km depth (e.g., Środa et al., 2006). Anomalously high velocities are observed in the area located approximately beneath Lublin trough, to the NE of Teisseyre-Tornquist Zone. Based on 3-D tomography of first arrivals of in- and off-line CELEBRATION 2000 recordings (Malinowski et al., 2008), elevated velocities are also reported in the same area and seem to continue to the SW, off the craton margin. Gravimetric modelling also revealed anomalously high density in the same region at similar depths. High seismic velocities and densities are interpreted as indicative for a pronounced mafic intrusion, possibly related to extensional processes at the EEC margin. Previous 3-D models of the high-velocity intrusion were based on first arrivals (crustal refractions) only. In this study, also off-line reflections (not modelled up to now) are used, in order to enlarge the data set and to better constrain the geometry and properties of the velocity anomaly. A code for 3-D joint tomographic inversion of refracted and reflected arrivals, with model parametrization allowing for velocity discontinuities was used (Rawlinson, 2007). With this approach, besides the refractions from the anomalous zone, also the off-line reflections from the top of the intrusion were used for inversion. Presented results provide new information about the depth and horizontal extent of the high-velocity intrusion. The model is also compared with other seismic studies of similar velocity anomalies observed at continental margins.

Architecture and tectono-stratigraphic evolution of the intramontane Baza Basin (Bétics, SE-Spain): Constraints from seismic imaging

NASA Astrophysics Data System (ADS)

Haberland, Christian; Gibert, Luis; Jurado, María José; Stiller, Manfred; Baumann-Wilke, Maria; Scott, Gary; Mertz, Dieter F.

2017-07-01

The Baza basin is a large Neogene intramontane basin in the Bétic Cordillera of southern Spain that formed during the Tortonian (late Miocene). The Bétic Cordillera was produced by NW-SE oblique convergence between the Eurasian and African Plates. Three seismic reflection lines (each 18 km long; vibroseis method) were acquired across the Baza basin to reveal the architecture of the sedimentary infill and faulting during basin formation. We applied rather conventional CDP data processing followed by first arrival P-wave tomography to provide complementary structural information and establish velocity models for the post-stack migration. These images show a highly asymmetric structure for the Basin with sediments thickening westward, reaching a maximum observed thickness of > 2200 m near the governing Baza Fault zone (BFZ). Three major seismic units (including several subunits) on top of the acoustic basement could be identified. We use stratigraphic information from the uplifted block of the BFZ and other outcrops at the basin edges together with available information from neighboring Bétic basins to tentatively correlate the seismic units to the known stratigraphy in the area. Until new drilling or surface outcrop data is not available, this interpretation is preliminary. The seismic units could be associated to Tortonian marine deposits, and latest Miocene to Pleistocene continental fluvio-lacustrine sediments. Individual strands of the BFZ truncate the basin sediments. Strong fault reflections imaged in two lines are the product of the large impedance contrast between sedimentary fill and basement. In the central part of the Basin several basement faults document strong deformation related to the early stages of basin formation. Some of these faults can be traced up to the shallowest imaged depth levels indicating activity until recent times.

Reprocessing Seismic Data - Using Wits Seismic Exploration Data to Image the Karoo Basin

NASA Astrophysics Data System (ADS)

Webb, S. J.; Scheiber-Enslin, S. E.; Manzi, M. S.

2016-12-01

During the heyday of seismic exploration of the Witwatersrand Basin, Anglo American's Gold Division acquired several thousand kilometres of Vibroseis reflection seismic data. These data, acquired from 1983-1994, were collected with the goal of finding extensions to the Witwatersrand Basin. In a prescient move, over 500 line kilometres were collected at 16 s two way travel time (TWT), extending to depths of 50 -70 km and have provided critical insight into the formation of the Kaapvaal Craton. In addition to these deep seismic lines, Anglo American acquired an extensive network of heretofore unpublished seismic lines that were collected at 6 sec TWT extending well beyond the known limits of the Witwatersrand Basin. The South African government as part of the national geophysical program in the late 1980s acquired six research reflection seismic lines in varied geological settings accruing another 700 km of data. Many of these data are now hosted at the University of the Witwatersrand's newly established Seismic Research Centre and represent unprecedented coverage and research opportunities. With recent global interest in shale gas, attention focused on the Karoo Basin in South Africa. Early exploration seismic data acquired by Soekor in the 1970s has been lost; however, digitized paper records indicate clear reflection targets. Here we examine one of the AngloGold seismic lines that was acquired in the middle of the Karoo Basin just south of Trompsburg extending to the southeast towards Molteno. This 150 km long line crosses the edge of the Kaapvaal Craton and shows clear reflectors throughout the Karoo Basin. These include the well-defined base of the Karoo and a number of dolerite sills within it. Nearby gas escape structures have been identified on surface and it is likely that several disruptions along this line are related to these or to dykes associated with the sills.

A mean-based filter to remove power line harmonic noise from seismic reflection data

NASA Astrophysics Data System (ADS)

Karslı, Hakan; Dondurur, Derman

2018-06-01

Power line harmonic noise generated by power lines during the seismic data acquisition in land and marine seismic surveys generally appears as a single frequency with 50/60 Hz (or multiples of these frequencies) and contaminates seismic data leading to complicate the identification of fine details in the data. Commonly applied method during seismic data processing to remove the harmonic noise is classical notch filter (or very narrow band-stop filter), however, it also attenuates all recorded data around the notch frequencies and results in a complete loss of available information which corresponds to fine details in the seismic data. In this study, we introduce an application of the algorithm of iterative trimmed and truncated mean filter method (ITTM) to remove the harmonic noise from seismic data, and here, we name the method as local ITTM (LITTM) since we applied it to the seismic data locally in spectral domain. In this method, an optimal value is iteratively searched depending on a threshold value by trimming and truncating process for the spectral amplitude samples within the specified spectral window. Therefore, the LITTM filter converges to the median, but, there is no need to sort the data as in the case of conventional median filters. On the other hand, the LITTM filtering process doesn't require any reference signal or a precise estimate of the fundamental frequency of the harmonic noise, and only approximate frequency band of the noise within the amplitude spectra is considered. The only required parameter of the method is the width of this frequency band in the spectral domain. The LITTM filter is first applied to synthetic data and then we analyze a real marine dataset to compare the quality of the output after removing the power line noise by classical notch, median and proposed LITTM filters. We observe that the power line harmonic noise is completely filtered out by LITTM filter, and unlike the conventional notch filter, without any damage on the available frequencies around the notch frequency band. It also provides a more balanced amplitude spectrum since it does not produce amplitude notches in the spectrum.

URSEIS peeks under Urals for mountain-building clues

NASA Astrophysics Data System (ADS)

Carlowicz, Michael

Just three weeks out of the field, a team of geologists, geophysicists, and seismologists from four nations announced on December 11 that they have used seismic reflection techniques to see what appears to be the base of the lithosphere beneath Russia's Ural Mountains. Working on Project URSEIS Urals Reflection Seismic Experiment and Integrated Studies), the team of scientists from Spain, Germany, Russia, and the United States has produced a seismic profile of the southern Urals extending as far as 150-185 km beneath the Earth's skin. The group presented its preliminary findings at the AGU Fall Meeting in San Francisco.

Recurrent intraplate tectonism in the New Madrid seismic zone

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zoback, M.D.; Hamilton, R.M.; Crone, A.J.

1980-08-29

For the first time, New Madrid seismicity can be linked to specific structural features that have been reactivated through geologic time. Extensive seismic reflection profiling reveals major faults coincident with the main earthquake trends in the area and with structural deformation apparently caused by repeated episodes of igneous activity.

On the difficulties of detecting PP precursors

NASA Astrophysics Data System (ADS)

Lessing, Stephan; Thomas, Christine; Saki, Morvarid; Schmerr, Nicholas; Vanacore, Elizabeth

2015-06-01

The PP precursors are seismic waves that form from underside reflections of P waves off discontinuities in the upper mantle transition zone (MTZ). These seismic phases are used to map discontinuity topography, sharpness, and impedance contrasts; the resulting structural variations are then often interpreted as evidence for temperature and/or mineralogy variations within the mantle. The PP precursors as well as other seismic phases have been used to establish the global presence of seismic discontinuities at 410 and 660 km depth. Intriguingly, in more than 80 per cent of PP precursor observations the seismic wave amplitudes are significantly weaker than the amplitudes predicted by seismic reference models. Even more perplexing is the observation that 1-5 per cent of all earthquakes (which are 20-25 per cent of earthquakes with clear PP waveforms) do not show any evidence for the PP precursors from the discontinuities even in the presence of well-developed PP waveforms. Non-detections are found in six different data sets consisting of tens to hundreds of events. We use synthetic modelling to examine a suite of factors that could be responsible for the absence of the PP precursors. The take-off angles for PP and the precursors differ by only 1.2-1.5°; thus source-related complexity would affect PP and the precursors. A PP wave attenuated in the upper mantle would increase the relative amplitude of the PP precursors. Attenuation within the transition zone could reduce precursor amplitudes, but this would be a regional phenomenon restricted to particular source receiver geometries. We also find little evidence for deviations from the theoretical travel path of seismic rays expected for scattered arrivals. Factors that have a strong influence include the stacking procedures used in seismic array techniques in the presence of large, interfering phases, the presence of topography on the discontinuities on the order of tens of kilometres, and 3-D lateral heterogeneity in the velocity and density changes with depth across the transition zone. We also compare the observed precursors' amplitudes with seismic models from calculations of phase equilibria and find that a seismic velocity model derived from a pyrolite composition reproduces the data better than the currently available 1-D earth models. This largely owes to the pyrolite models producing a stronger minimum in the reflection coefficient across the epicentral distances where the reduction in amplitudes of the PP precursors is observed. To suppress the precursors entirely in a small subset of earthquakes, other effects, such as localized discontinuity topography and seismic signal processing effects are required in addition to the changed velocity model.

Processing and attenuation of noise in deep seismic-reflection data from the Gulf of Maine

USGS Publications Warehouse

Hutchinson, D.R.; Lee, M.W.

1989-01-01

The U.S. Geological Survey deep crustal studies reflection profile across the Gulf of Maine off southeastern New England was affected by three sources of noise: side-scattered noise, multiples, and 20-Hz whale sounds. The special processing most effective in minimizing this noise consisted of a combination of frequency-wavenumber (F-K) filtering, predictive deconvolution, and spectral whitening, each applied in the shot domain (prestack). Application of the F-K filter to remove side-scatter noise in the poststack domain resulted in a much poorer quality profile. The prestack noise suppression processing techniques resulted in a reflection profile with good signal-to-noise ratios and reliable strong reflections, especially at depths equivalent to the lower crust (24-34 km). Certain geologic features, such as a buried rift basin and a crustal fault are resolved much better within the upper crust after this processing. Finite difference migration of these data using realistic velocities produced excellent results. Migration was essential to distinguish between abundant dipping and subhorizontal reflections in the lower crust as well as to show an essentially transparent upper mantle. ?? 1989 Kluwer Academic Publishers.

High-resolution seismic-reflection images across the ICDP-USGS Eyreville deep drilling site, Chesapeake Bay impact structure

USGS Publications Warehouse

Powars, David S.; Catchings, Rufus D.; Goldman, Mark R.; Gohn, Gregory S.; Horton, J. Wright; Edwards, Lucy E.; Rymer, Michael J.; Gandhok, Gini

2009-01-01

The U.S. Geological Survey (USGS) acquired two 1.4-km-long, high-resolution (~5 m vertical resolution) seismic-reflection lines in 2006 that cross near the International Continental Scientific Drilling Program (ICDP)-USGS Eyreville deep drilling site located above the late Eocene Chesapeake Bay impact structure in Virginia, USA. Five-meter spacing of seismic sources and geophones produced high-resolution images of the subsurface adjacent to the 1766-m-depth Eyreville core holes. Analysis of these lines, in the context of the core hole stratigraphy, shows that moderate-amplitude, discontinuous, dipping reflections below ~527 m correlate with a variety of Chesapeake Bay impact structure sediment and rock breccias recovered in the cores. High-amplitude, continuous, subhorizontal reflections above ~527 m depth correlate with the uppermost part of the Chesapeake Bay impact structure crater-fill sediments and postimpact Eocene to Pleistocene sediments. Reflections with ~20-30 m of relief in the uppermost part of the crater-fill and lowermost part of the postimpact section suggest differential compaction of the crater-fill materials during early postimpact time. The top of the crater-fill section also shows ~20 m of relief that appears to represent an original synimpact surface. Truncation surfaces, locally dipping reflections, and depth variations in reflection amplitudes generally correlate with the lithostrati-graphic and sequence-stratigraphic units and contacts in the core. Seismic images show apparent postimpact paleochannels that include the first possible Miocene paleochannels in the Mid-Atlantic Coastal Plain. Broad downwarping in the postim-pact section unrelated to structures in the crater fill indicates postimpact sediment compaction.

Seismic reflection profile of the Blake Ridge near sites 994, 995, and 997: Chapter 4

USGS Publications Warehouse

Dillon, William P.; Hutchinson, Deborah R.; Drury, Rebecca M.

1996-01-01

Seismic reflection profiles near Sites 994, 995, and 997 were collected with seismic sources that provide maximum resolution with adequate power to image the zone of gas hydrate stability and the region direction beneath it. The overall structure of the sediment drift deposit that constitutes the Blake Ridge consists of southwestward-dipping strata. These strata are approximately conformal to the seafloor on the southwest side of the ridge and are truncated by erosion on the northeast side. A bottom-simulating reflection (BSR) marks the velocity contrast between gas hydrate-bearing sediment and regions containing free gas beneath the zone of gas hydrate stability. The BSR is strong and continuous near the ridge crest but becomes discontinuous on the flanks, where concentration of gas is reduced and dipping strata pass through the level of the base o fgas hydrate stability or the strata are disrupted by faults. Seismic reflection amplitudes appear to be reduced in the region of gas hydrate formation compared to normal amplitudes. A faulted zone ~0.5-0.6 s thick parallels reflections from strata. We infer that this may represent a formerly gas hydrate-bearing zone that was faulted because of a breakdown of hydrate near its phase limit (at the base of the zone). Strong reflections at the top of the faulted zone are caused by free-gas acccumulation at Site 994. Similar strong reflections probably are caused by free-gas accumulations where the top of the faulted zone rises above the BSR, although this would require local free gas within the hydrate-stable zone.

Investigation Of North Anatolian Fault In The Sea Of Marmara: Fault Geometry, The Cumulative Extension, Age Modeling In Çinarcik Basin Using Multi Channel Seismic Reflection Data

NASA Astrophysics Data System (ADS)

Atgın, Orhan; Çifçi, Günay; Soelien, Christopher; Seeber, Leonardo; Steckler, Michael; Shillington, Donna; Kurt, Hülya; Dondurur, Derman; Okay, Seda; Gürçay, Savaş; Sarıtaş, Hakan; Mert Küçük, H.; Barın, Burcu

2013-04-01

Marmara Sea is a limelight area for investigations due to its tectonic structure and remarkable seismic activity of North Anatolian Fault Zone (NAFZ). As NAFZ separates into 3 branches in the Marmara Sea, it has a complicated tectonic structure which gives rise to debates among researchers. Çınarcık Basin, which is close to Istanbul and very important for its tectonic activity is studied in this thesis. Two different multichannel seismic reflection data were used in this thesis. First data were acquired in 2008 in the frame of TAMAM (Turkish American Multichannel Project) and second data were in 2010 in the frame of TAMAM-2 (PirMarmara) onboard R/V K.Piri Reis. Also high resolution multibeam data were used which is provided by French Marine Institute IFREMER. In the scope of TAMAM project total 3000 km high resolution multi channel data were collected. 3000 km of multichannel seismic reflection profiles were collected in 2008 and 2010 using 72, 111, and 240 channels of streamer with a 6.25 m group interval. The generator-injector airgun was fired every 12.5 or 18.75 m and the resulting MCS data has 10-230 Hz frequency band. In this study, a detailed fault map of the basin is created and the fault on the southern slope of the basin which is interpreted by many researchers in many publications was investigated. And there is no evidence that such a fault exists on the southern part of the basin. With the multichannel seismic reflection data seismic stratigrafic interpretations of the basin deposits were done. The yearly cumulative north-south extension of the basin was calculated by making some calculations on the most active part of the faulting in the basin. In addition, the tilt angles of parallel tilted sediments were calculated and correlated with global sea level changes to calculate ages of the deposits in the basin. Keywords: NAFZ, multi channel seismic reflection, Çınarcık Basin

Accurate elevation and normal moveout corrections of seismic reflection data on rugged topography

USGS Publications Warehouse

Liu, J.; Xia, J.; Chen, C.; Zhang, G.

2005-01-01

The application of the seismic reflection method is often limited in areas of complex terrain. The problem is the incorrect correction of time shifts caused by topography. To apply normal moveout (NMO) correction to reflection data correctly, static corrections are necessary to be applied in advance for the compensation of the time distortions of topography and the time delays from near-surface weathered layers. For environment and engineering investigation, weathered layers are our targets, so that the static correction mainly serves the adjustment of time shifts due to an undulating surface. In practice, seismic reflected raypaths are assumed to be almost vertical through the near-surface layers because they have much lower velocities than layers below. This assumption is acceptable in most cases since it results in little residual error for small elevation changes and small offsets in reflection events. Although static algorithms based on choosing a floating datum related to common midpoint gathers or residual surface-consistent functions are available and effective, errors caused by the assumption of vertical raypaths often generate pseudo-indications of structures. This paper presents the comparison of applying corrections based on the vertical raypaths and bias (non-vertical) raypaths. It also provides an approach of combining elevation and NMO corrections. The advantages of the approach are demonstrated by synthetic and real-world examples of multi-coverage seismic reflection surveys on rough topography. ?? The Royal Society of New Zealand 2005.

Application of continuous seismic-reflection techniques to delineate paleochannels beneath the Neuse River at US Marine Corps Air Station, Cherry Point, North Carolina

USGS Publications Warehouse

Cardinell, Alex P.

1999-01-01

A continuous seismic-reflection profiling survey was conducted by the U.S. Geological Survey on the Neuse River near the Cherry Point Marine Corps Air Station during July 7-24, 1998. Approximately 52 miles of profiling data were collected during the survey from areas northwest of the Air Station to Flanner Beach and southeast to Cherry Point. Positioning of the seismic lines was done by using an integrated navigational system. Data from the survey were used to define and delineate paleochannel alignments under the Neuse River near the Air Station. These data also were correlated with existing surface and borehole geophysical data, including vertical seismic-profiling velocity data collected in 1995. Sediments believed to be Quaternary in age were identified at varying depths on the seismic sections as undifferentiated reflectors and lack the lateral continuity of underlying reflectors believed to represent older sediments of Tertiary age. The sediments of possible Quaternary age thicken to the southeast. Paleochannels of Quaternary age and varying depths were identified beneath the Neuse River estuary. These paleochannels range in width from 870 feet to about 6,900 feet. Two zones of buried paleochannels were identified in the continuous seismic-reflection profiling data. The eastern paleochannel zone includes two large superimposed channel features identified during this study and in re-interpreted 1995 land seismic-reflection data. The second paleochannel zone, located west of the first paleochannel zone, contains several small paleochannels near the central and south shore of the Neuse River estuary between Slocum Creek and Flanner Beach. This second zone of channel features may be continuous with those mapped by the U.S. Geological Survey in 1995 using land seismic-reflection data on the southern end of the Air Station. Most of the channels were mapped at the Quaternary-Tertiary sediment boundary. These channels appear to have been cut into the older sediments and deepen in a southerly or downgradient direction. If these paleochannels continue beneath the Marine Corps Air Station and are filled with permeable sediment, they may act as conduits for ground-water flow or movement of contaminants between the surficial and underlying freshwater aquifers where confining units are breached.

Time-lapse 3-D seismic imaging of shallow subsurface contaminant flow.

PubMed

McKenna, J; Sherlock, D; Evans, B

2001-12-01

This paper presents a physical modelling study outlining a technique whereby buoyant contaminant flow within water-saturated unconsolidated sand was remotely monitored utilizing the time-lapse 3-D (TL3-D) seismic response. The controlled temperature and pressure conditions, along with the high level of acquisition repeatability attainable using sandbox physical models, allow the TL3-D seismic response to pore fluid movement to be distinguished from all other effects. TL3-D seismic techniques are currently being developed to monitor hydrocarbon reserves within producing reservoirs in an endeavour to improve overall recovery. However, in many ways, sandbox models under atmospheric conditions more accurately simulate the shallow subsurface than petroleum reservoirs. For this reason, perhaps the greatest application for analogue sandbox modelling is to improve our understanding of shallow groundwater and environmental flow mechanisms. Two fluid flow simulations were conducted whereby air and kerosene were injected into separate water-saturated unconsolidated sand models. In both experiments, a base 3-D seismic volume was recorded and compared with six later monitor surveys recorded while the injection program was conducted. Normal incidence amplitude and P-wave velocity information were extracted from the TL3-D seismic data to provide visualization of contaminant migration. Reflection amplitudes displayed qualitative areal distribution of fluids when a suitable impedance contrast existed between pore fluids. TL3-D seismic reflection tomography can potentially monitor the change in areal distribution of fluid contaminants over time, indicating flow patterns. However, other research and this current work have not established a quantifiable relationship between either normal reflection amplitudes and attenuation and fluid saturation. Generally, different pore fluids will have unique seismic velocities due to differences in compressibility and density. The predictable relationships that exist between P-wave velocity and fluid saturation can allow a quantitative assessment of contaminant migration.

Seismic imaging of the Formosa Ridge cold seep site offshore of southwestern Taiwan

NASA Astrophysics Data System (ADS)

Hsu, Ho-Han; Liu, Char-Shine; Morita, Sumito; Tu, Shu-Lin; Lin, Saulwood; Machiyama, Hideaki; Azuma, Wataru; Ku, Chia-Yen; Chen, Song-Chuen

2017-12-01

Multi-scale reflection seismic data, from deep-penetration to high-resolution, have been analyzed and integrated with near-surface geophysical and geochemical data to investigate the structures and gas hydrate system of the Formosa Ridge offshore of southwestern Taiwan. In 2007, dense and large chemosynthetic communities were discovered on top of the Formosa Ridge at water depth of 1125 m by the ROV Hyper-Dolphin. A continuous and strong BSR has been observed on seismic profiles from 300 to 500 ms two-way-travel-time below the seafloor of this ridge. Sedimentary strata of the Formosa Ridge are generally flat lying which suggests that this ridge was formed by submarine erosion processes of down-slope canyon development. In addition, some sediment waves and mass wasting features are present on the ridge. Beneath the cold seep site, a vertical blanking zone, or seismic chimney, is clearly observed on seismic profiles, and it is interpreted to be a fluid conduit. A thick low velocity zone beneath BSR suggests the presence of a gas reservoir there. This "gas reservoir" is shallower than the surrounding canyon floors along the ridge; therefore as warm methane-rich fluids inside the ridge migrate upward, sulfate carried by cold sea water can flow into the fluid system from both flanks of the ridge. This process may drive a fluid circulation system and the active cold seep site which emits both hydrogen sulfide and methane to feed the chemosynthetic communities.

Seismic fragility assessment of low-rise stone masonry buildings

NASA Astrophysics Data System (ADS)

Abo-El-Ezz, Ahmad; Nollet, Marie-José; Nastev, Miroslav

2013-03-01

Many historic buildings in old urban centers in Eastern Canada are made of stone masonry reputed to be highly vulnerable to seismic loads. Seismic risk assessment of stone masonry buildings is therefore the first step in the risk mitigation process to provide adequate planning for retrofit and preservation of historical urban centers. This paper focuses on development of analytical displacement-based fragility curves reflecting the characteristics of existing stone masonry buildings in Eastern Canada. The old historic center of Quebec City has been selected as a typical study area. The standard fragility analysis combines the inelastic spectral displacement, a structure-dependent earthquake intensity measure, and the building damage state correlated to the induced building displacement. The proposed procedure consists of a three-step development process: (1) mechanics-based capacity model, (2) displacement-based damage model and (3) seismic demand model. The damage estimation for a uniform hazard scenario of 2% in 50 years probability of exceedance indicates that slight to moderate damage is the most probable damage experienced by these stone masonry buildings. Comparison is also made with fragility curves implicit in the seismic risk assessment tools Hazus and ELER. Hazus shows the highest probability of the occurrence of no to slight damage, whereas the highest probability of extensive and complete damage is predicted with ELER. This comparison shows the importance of the development of fragility curves specific to the generic construction characteristics in the study area and emphasizes the need for critical use of regional risk assessment tools and generated results.

Sublake geologic structure from high-resolution seismic-reflection data from four sinkhole lakes in the Lake Wales Ridge, Central Florida

USGS Publications Warehouse

Tihansky, A.B.; Arthur, J.D.; DeWitt, D.W.

1996-01-01

Seismic-reflection profiles from Lake Wales, Blue Lake, Lake Letta, and Lake Apthorp located along the Lake Wales Ridge in central Florida provide local detail within the regional hydrogeologic framework as described by litho- and hydrostratigraphic cross sections. Lakes located with the mantled karst region have long been considered to be sinkhole lakes, originating from subsidence activity. High-resolution seismic- reflection data confirm this origin for these four lakes. The geologic framework of the Lake Wales Ridge has proven to be a suitable geologic setting for continuous high-resolution seismic-reflection profiling in lakes; however, the nature of the lake-bottom sediments largely controls the quality of the seismic data. In lakes with significant organic-rich bottom deposits, interpretable record was limited to areas where organic deposits were minimal. In lakes with clean, sandy bottoms, the seismic-reflection methods were highly successful in obtaining data that can be correlated with sublake subsidence features. These techniques are useful in examining sublake geology and providing a better understanding of how confining units are affected by subsidence in a region where their continuity is of significant importance to local lake hydrology. Although local geologic control around each lake generally corresponds to the regional geologic framework, local deviations from regional geologic trends occur in sublake areas affected by subsidence activity. Each of the four lakes examined represents a unique set of geologic controls and provides some degree of structural evidence of subsidence activity. Sublake geologic structures identified include: (1) marginal lake sediments dipping into bathymetric lows, (2) lateral discontinuity of confining units including sags and breaches, (3) the disruption and reworking of overlying unconsolidated siliciclastic sediments as they subside into the underlying irregular limestone surface, and (4) sublake regions where confining units appear to remain intact and unaffected by nearby subsidence activity. Each lake likely is underlain by several piping features rather than one large subsidence feature.

Mapping a buried Quaternary valley and pre-Quaternary faults through seismic methods in Copenhagen, Denmark.

NASA Astrophysics Data System (ADS)

Martinez, Kerim; Alfredo Mendoza, Jose; Henrik, Olsen

2010-05-01

Limited knowledge of the subsurface geology motivates the use of geophysical techniques before large engineering projects are conducted. These applications are normally restricted to satisfy the project aims, like mapping the near surface sediments, unconsolidated rocks and/or geological structures that may affect the construction locally. However, the applications can also contribute to the general knowledge of the regional geology around the location of interest. This report highlights the mapping of a buried Quaternary valley and identification of regional faults by a reflection and refraction seismic survey performed in Copenhagen. A 13.9 Km seismic survey was carried out at Copenhagen city along six crooked lines in order to determine the velocity fields in the near subsurface segment of a planned metro line and reflection patterns in deeper levels. The aim of the survey was to collect information needed for designing the underground metro. In particular it was sought to map the interface between Quaternary sedimentary layers of clay, till and sand, and the underlying layers of Palaeogene limestone found between 7 and 40 m below the ground surface. The data acquisition was carried out using a 192 channels array, receiver groups with 5 m spacing and a Vibroseis as a source at 5 m spacing following a roll along technique to complete the survey spreads. The urban environment demanded extensive survey planning including traffic control, notifications to residents and a fluent coordination with municipal authorities in order to minimize disturbances and ensure data acquisition. The reflection data was processed under a conventional scheme and the refraction data was interpreted using a non-linear traveltime tomography algorithm. The reflection results indicate the presence of faults oriented NW-SE to NNW-SSE affecting the limestone sequences. The faults may be associated to the Sorgenfrei-Tornquist Zone at the transition between the Danish Basin and the Baltic Shield. The refraction interpretation allowed the mapping of the velocity distribution in the upper sediments and their interface with the underlying limestone sequences. In this work two sections along the northern part of the survey are presented and discussed. The cases show the ability of the seismic results to image the presence of a buried valley that has been previously reported but was geophysically mapped for the first time under these investigations. The results delineate the sediments-limestone interface as the depth to the limestone increases. These results are validated through borehole data from locations along the surveyed lines. Other minor lateral variations are also observed and compared to a geological model. The location of the buried valley corresponds to a fault zone observed in the reflection seismic investigation. Accordingly, the location of the valley may in part have been controlled by the faults. The overall results of the seismic investigations are currently being used as part of the design basis for the construction of the metro line and may be useful for future engineering projects in the area. In general, the investigation results demonstrated that in addition to meet specific project objectives near surface geophysics has the potential to provide insights to the general understanding of geological processes. The authors wish to acknowledge Metroselskabet I/S for permission in presenting the results, and the Cityringen Joint Venture partners COWI, Arup and Systra.

Seismic hydraulic fracture migration originated by successive deep magma pulses: The 2011-2013 seismic series associated to the volcanic activity of El Hierro Island

NASA Astrophysics Data System (ADS)

Díaz-Moreno, A.; Ibáñez, J. M.; De Angelis, S.; García-Yeguas, A.; Prudencio, J.; Morales, J.; Tuvè, T.; García, L.

2015-11-01

In this manuscript we present a new interpretation of the seismic series that accompanied eruptive activity off the coast of El Hierro, Canary Islands, during 2011-2013. We estimated temporal variations of the Gutenberg-Richter b value throughout the period of analysis, and performed high-precision relocations of the preeruptive and syneruptive seismicity using a realistic 3-D velocity model. Our results suggest that eruptive activity and the accompanying seismicity were caused by repeated injections of magma from the mantle into the lower crust. These magma pulses occurred within a small and well-defined volume resulting in the emplacement of fresh magma along the crust-mantle boundary underneath El Hierro. We analyzed the distribution of earthquake hypocenters in time and space in order to assess seismic diffusivity in the lower crust. Our results suggest that very high earthquake rates underneath El Hierro represent the response of a stable lower crust to stress perturbations with pulsatory character, linked to the injection of magma from the mantle. Magma input from depth caused large stress perturbations to propagate into the lower crust generating energetic seismic swarms. The absence of any preferential alignment in the spatial pattern of seismicity reinforces our hypothesis that stress perturbation and related seismicity, had diffusive character. We conclude that the temporal and spatial evolution of seismicity was neither tracking the path of magma migration nor it defines the boundaries of magma storage volumes such as a midcrustal sill. Our conceptual model considers pulsatory magma injection from the upper mantle and its propagation along the Moho. We suggest, within this framework, that the spatial and temporal distributions of earthquake hypocenters reflect hydraulic fracturing processes associated with stress propagation due to magma movement.

A Fusion Model of Seismic and Hydro-Acoustic Propagation for Treaty Monitoring

NASA Astrophysics Data System (ADS)

Arora, Nimar; Prior, Mark

2014-05-01

We present an extension to NET-VISA (Network Processing Vertically Integrated Seismic Analysis), which is a probabilistic generative model of the propagation of seismic waves and their detection on a global scale, to incorporate hydro-acoustic data from the IMS (International Monitoring System) network. The new model includes the coupling of seismic waves into the ocean's SOFAR channel, as well as the propagation of hydro-acoustic waves from underwater explosions. The generative model is described in terms of multiple possible hypotheses -- seismic-to-hydro-acoustic, under-water explosion, other noise sources such as whales singing or icebergs breaking up -- that could lead to signal detections. We decompose each hypothesis into conditional probability distributions that are carefully analyzed and calibrated. These distributions include ones for detection probabilities, blockage in the SOFAR channel (including diffraction, refraction, and reflection around obstacles), energy attenuation, and other features of the resulting waveforms. We present a study of the various features that are extracted from the hydro-acoustic waveforms, and their correlations with each other as well the source of the energy. Additionally, an inference algorithm is presented that concurrently infers the seismic and under-water events, and associates all arrivals (aka triggers), both from seismic and hydro-acoustic stations, to the appropriate event, and labels the path taken by the wave. Finally, our results demonstrate that this fusion of seismic and hydro-acoustic data leads to very good performance. A majority of the under-water events that IDC (International Data Center) analysts built in 2010 are correctly located, and the arrivals that correspond to seismic-to-hydroacoustic coupling, the T phases, are mostly correctly identified. There is no loss in the accuracy of seismic events, in fact, there is a slight overall improvement.

Wave equation datuming applied to marine OBS data and to land high resolution seismic profiling

NASA Astrophysics Data System (ADS)

Barison, Erika; Brancatelli, Giuseppe; Nicolich, Rinaldo; Accaino, Flavio; Giustiniani, Michela; Tinivella, Umberta

2011-03-01

One key step in seismic data processing flows is the computation of static corrections, which relocate shots and receivers at the same datum plane and remove near surface weathering effects. We applied a standard static correction and a wave equation datuming and compared the obtained results in two case studies: 1) a sparse ocean bottom seismometers dataset for deep crustal prospecting; 2) a high resolution land reflection dataset for hydrogeological investigation. In both cases, a detailed velocity field, obtained by tomographic inversion of the first breaks, was adopted to relocate shots and receivers to the datum plane. The results emphasize the importance of wave equation datuming to properly handle complex near surface conditions. In the first dataset, the deployed ocean bottom seismometers were relocated to the sea level (shot positions) and a standard processing sequence was subsequently applied to the output. In the second dataset, the application of wave equation datuming allowed us to remove the coherent noise, such as ground roll, and to improve the image quality with respect to the application of static correction. The comparison of the two approaches evidences that the main reflecting markers are better resolved when the wave equation datuming procedure is adopted.

High-resolution seismic-reflection profiles and sidescan-sonar records collected on Block Island Sound by U.S. Geological Survey, R/V ASTERIAS, cruise AST 81-2

USGS Publications Warehouse

Needell, S. W.; Lewis, R.S.

1982-01-01

Cruise AST 81-2 was conducted aboard the R/V ASTERIAS during September 10-18, 1981, in Block Island Sound by the U.S. Geological Survey. It was funded in part by the Connecticut Geological and Natural History Survey. The purpose of the study was to define and map the geology and shallow structure, to determine the geologic framework and late Tertiary to Holocene history, and to identify and map any potential geologic hazards of Block Island Sound.The survey was conducted using an EG&G Uniboom seismic system and an EDO Western sidescan-sonar system. Seismic signals were band-passed between 400 and 4,000 Hz and were recorded at a quarter-second sweep rate. Sidescan sonographs were collected at a 100-m scan range to each side of the ship track. In all, 702 km of seismic-reflection profiles and 402 km of sidescan-sonar records were collected. Navigation was by Loran-C, and the ship position was recorded at 5-minute intervals. Seismic-reflection profiling is continuous and good in quality. Sidescan-sonar records are varied in quality; coverage was intermittent and eventu­ally terminated owing to difficulties with the recorder.Original records can be seen and studied at the U.S. Geological Survey Data Library at Woods Hole, MA 02543. Microfilm copies of the seismic-reflection pro­files and the sidescan sonographs can be purchased only from the National Geo­physical and Solar-Terrestrial Data Center, NOAA/EDIS/NGSDC, Code D621, 325 Broad­way, Boulder, CO 80303 (telephone 303-497-6338).

Geometry and spatial variations of seismic reflection intensity of the upper surface of the Philippine Sea plate off the Boso Peninsula, Japan

NASA Astrophysics Data System (ADS)

Kono, Akihiro; Sato, Toshinori; Shinohara, Masanao; Mochizuki, Kimihiro; Yamada, Tomoaki; Uehira, Kenji; Shinbo, Takashi; Machida, Yuya; Hino, Ryota; Azuma, Ryousuke

2017-07-01

In the region off the Boso Peninsula, Japan, the Pacific plate is subducting westward beneath both the Honshu island arc and Philippine Sea plate, while the Philippine Sea plate is subducting northwestward beneath the Honshu island arc. These complex tectonic interactions have caused numerous seismic events occurred in the past. To better understand these seismic events, it is important to determine the geometry of the plate boundary, in particular the upper surface of the Philippine Sea plate. We conducted an active-source seismic refraction survey in July and August 2009 from which we obtained a 2-D P-wave velocity structure model along a 216-km profile. We used the velocity model and previously published data that indicate a P-wave velocity of 5.0 km/s for the upper surface of the subducting Philippine Sea plate to delineate its boundary with the overriding Honshu island arc. Our isodepth contours of the upper surface of the Philippine Sea plate show that its dip is shallow at depths of 10 to 15 km, far off the Boso Peninsula. This shallow dip may be a result of interference from the Pacific plate slab, which is subducting westward under the Philippine Sea plate. Within our survey data, we recognized numerous seismic reflections of variable intensity, some of which came from the upper surface of the Philippine Sea plate. An area of high seismic reflection intensity corresponds with the main slip area of the Boso slow slip events. Our modeling indicates that those reflections can be explained by an inhomogeneous layer close to the upper surface of the Philippine Sea plate.

Upper-crustal structure of the inner Continental Borderland near Long Beach, California

USGS Publications Warehouse

Baher, S.; Fuis, G.; Sliter, R.; Normark, W.R.

2005-01-01

A new P-wave velocity/structural model for the inner Continental Borderland (ICB) region was developed for the area near Long Beach, California. It combines controlled-source seismic reflection and refraction data collected during the 1994 Los Angeles Region Seismic Experiment (LARSE), multichannel seismic reflection data collected by the U.S. Geological Survey (1998-2000), and nearshore borehole stratigraphy. Based on lateral velocity contrasts and stratigraphic variation determined from borehole data, we are able to locate major faults such as the Cabrillo, Palos Verdes, THUMS-Huntington Beach, and Newport Inglewood fault zones, along with minor faults such as the slope fault, Avalon knoll, and several other yet unnamed faults. Catalog seismicity (1975-2002) plotted on our preferred velocity/structural model shows recent seismicity is located on 16 out of our 24 faults, providing evidence for continuing concern with respect to the existing seismic-hazard estimates. Forward modeling of P-wave arrival times on the LARSE line 1 resulted in a four-layer model that better resolves the stratigraphy and geologic structures of the ICB and also provides tighter constraints on the upper-crustal velocity structure than previous modeling of the LARSE data. There is a correlation between the structural horizons identified in the reflection data with the velocity interfaces determined from forward modeling of refraction data. The strongest correlation is between the base of velocity layer 1 of the refraction model and the base of the planar sediment beneath the shelf and slope determined by the reflection model. Layers 2 and 3 of the velocity model loosely correlate with the diffractive crust layer, locally interpreted as Catalina Schist.

A Cloud-Computing Service for Environmental Geophysics and Seismic Data Processing

NASA Astrophysics Data System (ADS)

Heilmann, B. Z.; Maggi, P.; Piras, A.; Satta, G.; Deidda, G. P.; Bonomi, E.

2012-04-01

Cloud computing is establishing worldwide as a new high performance computing paradigm that offers formidable possibilities to industry and science. The presented cloud-computing portal, part of the Grida3 project, provides an innovative approach to seismic data processing by combining open-source state-of-the-art processing software and cloud-computing technology, making possible the effective use of distributed computation and data management with administratively distant resources. We substituted the user-side demanding hardware and software requirements by remote access to high-performance grid-computing facilities. As a result, data processing can be done quasi in real-time being ubiquitously controlled via Internet by a user-friendly web-browser interface. Besides the obvious advantages over locally installed seismic-processing packages, the presented cloud-computing solution creates completely new possibilities for scientific education, collaboration, and presentation of reproducible results. The web-browser interface of our portal is based on the commercially supported grid portal EnginFrame, an open framework based on Java, XML, and Web Services. We selected the hosted applications with the objective to allow the construction of typical 2D time-domain seismic-imaging workflows as used for environmental studies and, originally, for hydrocarbon exploration. For data visualization and pre-processing, we chose the free software package Seismic Un*x. We ported tools for trace balancing, amplitude gaining, muting, frequency filtering, dip filtering, deconvolution and rendering, with a customized choice of options as services onto the cloud-computing portal. For structural imaging and velocity-model building, we developed a grid version of the Common-Reflection-Surface stack, a data-driven imaging method that requires no user interaction at run time such as manual picking in prestack volumes or velocity spectra. Due to its high level of automation, CRS stacking can benefit largely from the hardware parallelism provided by the cloud deployment. The resulting output, post-stack section, coherence, and NMO-velocity panels are used to generate a smooth migration-velocity model. Residual static corrections are calculated as a by-product of the stack and can be applied iteratively. As a final step, a time migrated subsurface image is obtained by a parallelized Kirchhoff time migration scheme. Processing can be done step-by-step or using a graphical workflow editor that can launch a series of pipelined tasks. The status of the submitted jobs is monitored by a dedicated service. All results are stored in project directories, where they can be downloaded of viewed directly in the browser. Currently, the portal has access to three research clusters having a total number of 70 nodes with 4 cores each. They are shared with four other cloud-computing applications bundled within the GRIDA3 project. To demonstrate the functionality of our "seismic cloud lab", we will present results obtained for three different types of data, all taken from hydrogeophysical studies: (1) a seismic reflection data set, made of compressional waves from explosive sources, recorded in Muravera, Sardinia; (2) a shear-wave data set from, Sardinia; (3) a multi-offset Ground-Penetrating-Radar data set from Larreule, France. The presented work was funded by the government of the Autonomous Region of Sardinia and by the Italian Ministry of Research and Education.

Advances through collaboration: sharing seismic reflection data via the Antarctic Seismic Data Library System for Cooperative Research (SDLS)

USGS Publications Warehouse

Wardell, N.; Childs, J. R.; Cooper, A. K.

2007-01-01

The Antarctic Seismic Data Library System for Cooperative Research (SDLS) has served for the past 16 years under the auspices of the Antarctic Treaty (ATCM Recommendation XVI-12) as a role model for collaboration and equitable sharing of Antarctic multichannel seismic reflection (MCS) data for geoscience studies. During this period, collaboration in MCS studies has advanced deciphering the seismic stratigraphy and structure of Antarctica’s continental margin more rapidly than previously. MCS data compilations provided the geologic framework for scientific drilling at several Antarctic locations and for high-resolution seismic and sampling studies to decipher Cenozoic depositional paleoenvironments. The SDLS successes come from cooperation of National Antarctic Programs and individual investigators in “on-time” submissions of their MCS data. Most do, but some do not. The SDLS community has an International Polar Year (IPY) goal of all overdue MCS data being sent to the SDLS by end of IPY. The community science objective is to compile all Antarctic MCS data to derive a unified seismic stratigraphy for the continental margin – a stratigraphy to be used with drilling data to derive Cenozoic circum-Antarctic paleobathymetry maps and local-to-regional scale paleoenvironmental histories.

Calibration method helps in seismic velocity interpretation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Guzman, C.E.; Davenport, H.A.; Wilhelm, R.

1997-11-03

Acoustic velocities derived from seismic reflection data, when properly calibrated to subsurface measurements, help interpreters make pure velocity predictions. A method of calibrating seismic to measured velocities has improved interpretation of subsurface features in the Gulf of Mexico. In this method, the interpreter in essence creates a kind of gauge. Properly calibrated, the gauge enables the interpreter to match predicted velocities to velocities measured at wells. Slow-velocity zones are of special interest because they sometimes appear near hydrocarbon accumulations. Changes in velocity vary in strength with location; the structural picture is hidden unless the variations are accounted for by mappingmore » in depth instead of time. Preliminary observations suggest that the presence of hydrocarbons alters the lithology in the neighborhood of the trap; this hydrocarbon effect may be reflected in the rock velocity. The effect indicates a direct use of seismic velocity in exploration. This article uses the terms seismic velocity and seismic stacking velocity interchangeably. It uses ground velocity, checkshot average velocity, and well velocity interchangeably. Interval velocities are derived from seismic stacking velocities or well average velocities; they refer to velocities of subsurface intervals or zones. Interval travel time (ITT) is the reciprocal of interval velocity in microseconds per foot.« less

Structural deformation and sedimentation in an active Caldera, Rabaul, Papua New Guinea

USGS Publications Warehouse

Greene, H. Gary; Tiffin, D.L.; McKee, C.O.

1986-01-01

Recent seismic and tectonic activity in Rabaul Caldera, Papua New Guinea, suggests that magma is accumulating at a shallow depth beneath this partially submerged structure and that a new volcano may be developing. Changes in onshore elevation since 1971 (as much as 2 m on south Matupit Island) indicate that rapid and large-scale uplifts have occurred on the seafloor near the center of the caldera. The frequency of seismic events within the caldera has also increased during this period. Earthquake locations define an elliptical ring surrounding the center of this uplift within the caldera. A marine geophysical survey in 1982 by the U.S. Geological Survey's R/V "S.P. Lee" in Rabaul Caldera shows the development of a bulge in the seafloor near the center of the caldera. High-resolution seismic reflection profiles show that this bulge consists of two domal uplifts bounded and separated by two major north-south-trending fault zones. Deformed sediments overlie these zones; a prominent slump flanks the area of the bulge. Five major acoustic units were identified in the seismic reflection profiles: an acoustic basement and four sedimentary units consisting of irregularly layered, cross-layered, contorted, and well-layered sequences. The acoustic basement is probably composed of crystalline volcanic rocks, and the layered acoustic units are probably sediments, primarily ash deposited in different environments. The cross-layered, irregularly layered, and contorted units appear to have been deposited in a dynamic environment subjected to strong currents, seismicity, and/or mass wasting, while the well-layered units were deposited in a low-energy environment. Locally, well-layered sequences interfinger with the other sedimentary units, indicating a transitional environment that alternated between high-energy and low-energy depositional processes. A submarine channel cuts most of the acoustic units and appears to be the conduit for sediment transport out of the caldera; it occupies an older buried channel north of the caldera that is presently being exhumed. In the south, active erosion of well-layered sediments is taking place. What are believed to be several young volcanic cones also disrupt the depositional layers. We conclude that the bulge in the seafloor and the associated fault zones are a result of emplacement of magma at a shallow depth. Contorted sediment and slumps adjacent to the bulge are probably the result of uplift and seismic activity. The pattern of seismicity appears to reflect increased magma pressure at depth beneath the caldera floor. This activity may eventually lead to an eruption. ?? 1986.

The character and amplitude of ‘discontinuous’ bottom-simulating reflections in marine seismic data

DOE PAGES

Hillman, Jess I. T.; Cook, Ann E.; Sawyer, Derek E.; ...

2016-11-22

Bottom-simulating reflections (BSRs) identified in seismic data are well documented; and are commonly interpreted to indicate the presence of gas hydrates along continental margins, as well as to estimate regional volumes of gas hydrate. A BSR is defined as a reflection that sub-parallels the seafloor but is opposite in polarity and cross-cuts dipping sedimentary strata. BSRs form as a result of a strong negative acoustic impedance contrast. BSRs, however, are a diverse seismic phenomena that manifest in strikingly contrasting ways in different geological settings, and in different seismic data types. We investigate the characteristics of BSRs, using conventional and highmore » resolution, 2D and 3D seismic data sets in three locations: the Terrebonne and Orca Basins in the Gulf of Mexico, and Blake Ridge on the US Atlantic Margin. The acquisition geometry and frequency content of the seismic data significantly impact the resultant character of BSRs, as observed with depth and amplitude maps of the BSRs. Furthermore, our amplitude maps reinforce the concept that the BSR represents a zone, over which the transition from hydrate to free gas occurs, as opposed to the conventional model of the BSR occurring at a single interface. Our results show that a BSR can be mapped in three dimensions but it is not spatially continuous, at least not at the basin scale. Rather, a BSR manifests itself as a discontinuous, or patchy, reflection and only at local scales is it continuous. We suggest the discontinuous nature of BSRs is the result of variable saturation and distribution of free gas and hydrate, acquisition geometry and frequency content of the recorded seismic data. Lastly, the commonly accepted definition of a BSR should be broadened with careful consideration of these factors, to represent the uppermost extent of enhanced amplitude at the shallowest occurrence of free gas trapped by overlying hydrate-bearing sediments.« less

The character and amplitude of 'discontinuous' bottom-simulating reflections in marine seismic data

NASA Astrophysics Data System (ADS)

Hillman, Jess I. T.; Cook, Ann E.; Sawyer, Derek E.; Küçük, H. Mert; Goldberg, David S.

2017-02-01

Bottom-simulating reflections (BSRs) identified in seismic data are well documented; and are commonly interpreted to indicate the presence of gas hydrates along continental margins, as well as to estimate regional volumes of gas hydrate. A BSR is defined as a reflection that sub-parallels the seafloor but is opposite in polarity and cross-cuts dipping sedimentary strata. BSRs form as a result of a strong negative acoustic impedance contrast. BSRs, however, are a diverse seismic phenomena that manifest in strikingly contrasting ways in different geological settings, and in different seismic data types. We investigate the characteristics of BSRs, using conventional and high resolution, 2D and 3D seismic data sets in three locations: the Terrebonne and Orca Basins in the Gulf of Mexico, and Blake Ridge on the US Atlantic Margin. The acquisition geometry and frequency content of the seismic data significantly impact the resultant character of BSRs, as observed with depth and amplitude maps of the BSRs. Furthermore, our amplitude maps reinforce the concept that the BSR represents a zone, over which the transition from hydrate to free gas occurs, as opposed to the conventional model of the BSR occurring at a single interface. Our results show that a BSR can be mapped in three dimensions but it is not spatially continuous, at least not at the basin scale. Rather, a BSR manifests itself as a discontinuous, or patchy, reflection and only at local scales is it continuous. We suggest the discontinuous nature of BSRs is the result of variable saturation and distribution of free gas and hydrate, acquisition geometry and frequency content of the recorded seismic data. The commonly accepted definition of a BSR should be broadened with careful consideration of these factors, to represent the uppermost extent of enhanced amplitude at the shallowest occurrence of free gas trapped by overlying hydrate-bearing sediments.

Crustal structure of the northern margin of the eastern Tien Shan, China, and its tectonic implications for the 1906 M~7.7 Manas earthquake

USGS Publications Warehouse

Wang, Chun-Yong; Yang, Zhu-En; Luo, Hai; Mooney, W.D.

2004-01-01

The Tien Shan orogenic belt is the most active intracontinental mountain belt in the world. We describe an 86-km-long N–S-trending deep seismic reflection profile (which passes through the southern Junggar basin) located on the northeastern Tien Shan piedmont. Two distinct anticlines beneath the northern margin of the Tien Shan are clearly imaged in the seismic section. In addition, we have imaged two detachment surfaces at depths of ∼7 and ∼16 km. The detachment surface at 16-km depth corresponds to the main detachment that converges with the steep angle reverse fault (the Junggar Southern Marginal Fault) on which the 1906 M~7.7 Manas earthquake occurred. A 12–14-km-thick sedimentary basin is imaged beneath the southern Junggar basin near Shihezi. The crust beneath the northern margin of the Tien Shan is 50–55-km thick, and decreases beneath the Junggar basin to 40–45-km thick. The crustal image of the deep seismic reflection profile is consistent with models derived from nearby seismic refraction data and Bouguer gravity anomalies in the same region. The faulting associated with the 1906 Manas earthquake also fits within the structural framework imaged by the seismic reflection profile. Present-day micro-seismicity shows a hypocentral depth-distribution between 5 and 35 km, with a peak at 20 km. We hypothesize that the 1906 Manas earthquake initiated at a depth of ∼20 km and propagated upwards, causing northward slip on the sub-horizontal detachments beneath the southern Junggar basin. Thus, in accord with regional geological mapping, the current shortening within the eastern Tien Shan is accommodated both by high-angle reverse faulting and detachment faulting that can be clearly imaged at depth in seismic reflection data.

The character and amplitude of ‘discontinuous’ bottom-simulating reflections in marine seismic data

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hillman, Jess I. T.; Cook, Ann E.; Sawyer, Derek E.

Bottom-simulating reflections (BSRs) identified in seismic data are well documented; and are commonly interpreted to indicate the presence of gas hydrates along continental margins, as well as to estimate regional volumes of gas hydrate. A BSR is defined as a reflection that sub-parallels the seafloor but is opposite in polarity and cross-cuts dipping sedimentary strata. BSRs form as a result of a strong negative acoustic impedance contrast. BSRs, however, are a diverse seismic phenomena that manifest in strikingly contrasting ways in different geological settings, and in different seismic data types. We investigate the characteristics of BSRs, using conventional and highmore » resolution, 2D and 3D seismic data sets in three locations: the Terrebonne and Orca Basins in the Gulf of Mexico, and Blake Ridge on the US Atlantic Margin. The acquisition geometry and frequency content of the seismic data significantly impact the resultant character of BSRs, as observed with depth and amplitude maps of the BSRs. Furthermore, our amplitude maps reinforce the concept that the BSR represents a zone, over which the transition from hydrate to free gas occurs, as opposed to the conventional model of the BSR occurring at a single interface. Our results show that a BSR can be mapped in three dimensions but it is not spatially continuous, at least not at the basin scale. Rather, a BSR manifests itself as a discontinuous, or patchy, reflection and only at local scales is it continuous. We suggest the discontinuous nature of BSRs is the result of variable saturation and distribution of free gas and hydrate, acquisition geometry and frequency content of the recorded seismic data. Lastly, the commonly accepted definition of a BSR should be broadened with careful consideration of these factors, to represent the uppermost extent of enhanced amplitude at the shallowest occurrence of free gas trapped by overlying hydrate-bearing sediments.« less

Revealing small-scale diffracting discontinuities by an optimization inversion algorithm

NASA Astrophysics Data System (ADS)

Yu, Caixia; Zhao, Jingtao; Wang, Yanfei

2017-02-01

Small-scale diffracting geologic discontinuities play a significant role in studying carbonate reservoirs. The seismic responses of them are coded in diffracted/scattered waves. However, compared with reflections, the energy of these valuable diffractions is generally one or even two orders of magnitude weaker. This means that the information of diffractions is strongly masked by reflections in the seismic images. Detecting the small-scale cavities and tiny faults from the deep carbonate reservoirs, mainly over 6 km, poses an even bigger challenge to seismic diffractions, as the signals of seismic surveyed data are weak and have a low signal-to-noise ratio (SNR). After analyzing the mechanism of the Kirchhoff migration method, the residual of prestack diffractions located in the neighborhood of the first Fresnel aperture is found to remain in the image space. Therefore, a strategy for extracting diffractions in the image space is proposed and a regularized L 2-norm model with a smooth constraint to the local slopes is suggested for predicting reflections. According to the focusing conditions of residual diffractions in the image space, two approaches are provided for extracting diffractions. Diffraction extraction can be directly accomplished by subtracting the predicted reflections from seismic imaging data if the residual diffractions are focused. Otherwise, a diffraction velocity analysis will be performed for refocusing residual diffractions. Two synthetic examples and one field application demonstrate the feasibility and efficiency of the two proposed methods in detecting the small-scale geologic scatterers, tiny faults and cavities.

Near-surface, marine seismic-reflection data defines potential hydrogeologic confinement bypass in a tertiary carbonate aquifer, southeastern Florida

USGS Publications Warehouse

Cunningham, Kevin J.; Walker, Cameron; Westcott, Richard L.

2012-01-01

Approximately 210 km of near-surface, high-frequency, marine seismic-reflection data were acquired on the southeastern part of the Florida Platform between 2007 and 2011. Many high-resolution, seismic-reflection profiles, interpretable to a depth of about 730 m, were collected on the shallow-marine shelf of southeastern Florida in water as shallow as 1 m. Landward of the present-day shelf-margin slope, these data image middle Eocene to Pleistocene strata and Paleocene to Pleistocene strata on the Miami Terrace. This high-resolution data set provides an opportunity to evaluate geologic structures that cut across confining units of the Paleocene to Oligocene-age carbonate rocks that form the Floridan aquifer system.Seismic profiles image two structural systems, tectonic faults and karst collapse structures, which breach confining beds in the Floridan aquifer system. Both structural systems may serve as pathways for vertical groundwater flow across relatively low-permeability carbonate strata that separate zones of regionally extensive high-permeability rocks in the Floridan aquifer system. The tectonic faults occur as normal and reverse faults, and collapse-related faults have normal throw. The most common fault occurrence delineated on the reflection profiles is associated with karst collapse structures. These high-frequency seismic data are providing high quality structural analogs to unprecedented depths on the southeastern Florida Platform. The analogs can be used for assessment of confinement of other carbonate aquifers and the sealing potential of deeper carbonate rocks associated with reservoirs around the world.

A seismic-reflection investigation of gas hydrates and sea-floor features of the upper continental slope of the Garden Banks and Green Canyon regions, northern Gulf of Mexico: report for cruise G1-99-GM (99002)

USGS Publications Warehouse

Cooper, Alan; Twichell, David; Hart, Patrick

1999-01-01

During April 1999, the U.S. Geological Survey (USGS) conducted a 13-day cruise in the Garden Banks and Green Canyon regions of the Gulf of Mexico. The R/V Gyre, owned by Texas A&M University, was chartered for the cruise. The general objectives were (1) to acquire very high resolution seismic-reflection data and side-scan sonar images of the upper and middle continental slope (200-1200-m water depths), (2) to study the acoustic character and features of the sea floor for evidence of sea-floor hazards, and (3) to look for evidence of subsurface gas hydrates and their effects. The Gulf of Mexico is well known for hydrocarbon resources, with emphasis now on frontier deep-water areas. For water depths greater than about 250 m, the pressure-termperature conditions are correct for the development of shallow-subsurface gas hydrate formation (Anderson et al., 1992). Gas hydrates are ice-like mixtures of gas and water (Kvenvolden, 1993). They are known to be present from extensive previous sampling in sea-floor cores and from mound-like features observed on the sea floor in many parts of the northern Gulf, including the Green Canyon and Garden Banks areas (e.g., Roberts, 1995). Seismic-reflection data are extensive in the Gulf of Mexico, but few very-high-resolution data like those needed for gas-hydrate studies exist in the public domain. The occurrence and mechanisms of gas hydrate formation and dissociation are important to understand, because of their perceived economic potential for methane gas, their potential controls on local and regional sea-floor stability, and their possible effects on earth climates due to massive release of methane greenhouse gas into the atmosphere. Three high-resolution seismic-reflection systems and one side-scan sonar system were used on the cruise to map the surface reflectance and features of the sea floor and the acoustic geometries and character of the shallow sub-surface. The cruise was designed to acquire regional and detailed local information. The regional survey covered an area about 3400 km2 in the Green Canyon and Garden Banks regions. Data recorded included 15 cu. in. water gun multichannel seismic-reflection and Huntec boomer information. Detailed surveys were planned in two parts of the study area, but due to a winch failure only one detailed survey was done in the Green Canyon area. The detailed survey included collection of 15 cu. in. water gun multichannel seismic-reflection, chirp seismic-reflection, and side-scan data.

Archive of Boomer seismic reflection data: collected during USGS Cruise 96CCT01, nearshore south central South Carolina coast, June 26 - July 1, 1996

USGS Publications Warehouse

Calderon, Karynna; Dadisman, Shawn V.; Kindinger, Jack G.; Flocks, James G.; Wiese, Dana S.

2003-01-01

This archive consists of marine seismic reflection profile data collected in four survey areas from southeast of Charleston Harbor to the mouth of the North Edisto River of South Carolina. These data were acquired June 26 - July 1, 1996, aboard the R/V G.K. Gilbert. Included here are data in a variety of formats including binary, American Standard Code for Information Interchange (ASCII), Hyper Text Markup Language (HTML), Portable Document Format (PDF), Rich Text Format (RTF), Graphics Interchange Format (GIF) and Joint Photographic Experts Group (JPEG) images, and shapefiles. Binary data are in Society of Exploration Geophysicists (SEG) SEG-Y format and may be downloaded for further processing or display. Reference maps and GIF images of the profiles may be viewed with a web browser. The Geographic Information Systems (GIS) map documents provided were created with Environmental Systems Research Institute (ESRI) GIS software ArcView 3.2 and 8.1.

Seismicity and active tectonics in the Alboran Sea, Western Mediterranean: Constraints from an offshore-onshore seismological network and swath bathymetry data

NASA Astrophysics Data System (ADS)

Grevemeyer, Ingo; Gràcia, Eulàlia; Villaseñor, Antonio; Leuchters, Wiebke; Watts, Anthony B.

2015-12-01

Seismicity and tectonic structure of the Alboran Sea were derived from a large amphibious seismological network deployed in the offshore basins and onshore in Spain and Morocco, an area where the convergence between the African and Eurasian plates causes distributed deformation. Crustal structure derived from local earthquake data suggests that the Alboran Sea is underlain by thinned continental crust with a mean thickness of about 20 km. During the 5 months of offshore network operation, a total of 229 local earthquakes were located within the Alboran Sea and neighboring areas. Earthquakes were generally crustal events, and in the offshore domain, most of them occurred at crustal levels of 2 to 15 km depth. Earthquakes in the Alboran Sea are poorly related to large-scale tectonic features and form a 20 to 40 km wide NNE-SSW trending belt of seismicity between Adra (Spain) and Al Hoceima (Morocco), supporting the case for a major left-lateral shear zone across the Alboran Sea. Such a shear zone is in accord with high-resolution bathymetric data and seismic reflection imaging, indicating a number of small active fault zones, some of which offset the seafloor, rather than supporting a well-defined discrete plate boundary fault. Moreover, a number of large faults known to be active as evidenced from bathymetry, seismic reflection, and paleoseismic data such as the Yusuf and Carboneras faults were seismically inactive. Earthquakes below the Western Alboran Basin occurred at 70 to 110 km depth and hence reflected intermediate depth seismicity related to subducted lithosphere.

Properties of induced seismicity at the geothermal reservoir Insheim, Germany

NASA Astrophysics Data System (ADS)

Olbert, Kai; Küperkoch, Ludger; Thomas, Meier

2017-04-01

Within the framework of the German MAGS2 Project the processing of induced events at the geothermal power plant Insheim, Germany, has been reassessed and evaluated. The power plant is located close to the western rim of the Upper Rhine Graben in a region with a strongly heterogeneous subsurface. Therefore, the location of seismic events particularly the depth estimation is challenging. The seismic network consisting of up to 50 stations has an aperture of approximately 15 km around the power plant. Consequently, the manual processing is time consuming. Using a waveform similarity detection algorithm, the existing dataset from 2012 to 2016 has been reprocessed to complete the catalog of induced seismic events. Based on the waveform similarity clusters of similar events have been detected. Automated P- and S-arrival time determination using an improved multi-component autoregressive prediction algorithm yields approximately 14.000 P- and S-arrivals for 758 events. Applying a dataset of manual picks as reference the automated picking algorithm has been optimized resulting in a standard deviation of the residuals between automated and manual picks of about 0.02s. The automated locations show uncertainties comparable to locations of the manual reference dataset. 90 % of the automated relocations fall within the error ellipsoid of the manual locations. The remaining locations are either badly resolved due to low numbers of picks or so well resolved that the automatic location is outside the error ellipsoid although located close to the manual location. The developed automated processing scheme proved to be a useful tool to supplement real-time monitoring. The event clusters are located at small patches of faults known from reflection seismic studies. The clusters are observed close to both the injection as well as the production wells.

Further Constraints and Uncertainties on the Deep Seismic Structure of the Moon

NASA Technical Reports Server (NTRS)

Lin, Pei-Ying Patty; Weber, Renee C.; Garnero, Ed J.; Schmerr, Nicholas C.

2011-01-01

The Apollo Passive Seismic Experiment (APSE) consisted of four 3-component seismometers deployed between 1969 and 1972, that continuously recorded lunar ground motion until late 1977. The APSE data provide a unique opportunity for investigating the interior of a planet other than Earth, generating the most direct constraints on the elastic structure, and hence the thermal and compositional evolution of the Moon. Owing to the lack of far side moonquakes, past seismic models of the lunar interior were unable to constrain the lowermost 500 km of the interior. Recently, array methodologies aimed at detecting deep lunar seismic reflections found evidence for a lunar core, providing an elastic model of the deepest lunar interior consistent with geodetic parameters. Here we study the uncertainties in these models associated with the double array stacking of deep moonquakes for imaging deep reflectors in the Moon. We investigate the dependency of the array stacking results on a suite of parameters, including amplitude normalization assumptions, polarization filters, assumed velocity structure, and seismic phases that interfere with our desired target phases. These efforts are facilitated by the generation of synthetic seismograms at high frequencies (approx. 1Hz), allowing us to directly study the trade-offs between different parameters. We also investigate expected amplitudes of deep reflections relative to direct P and S arrivals, including predictions from arbitrarily oriented focal mechanisms in our synthetics. Results from separate versus combined station stacking help to establish the robustness of stacks. Synthetics for every path geometry of data were processed identically to that done with data. Different experiments were aimed at examining various processing assumptions, such as adding random noise to synthetics and mixing 3 components to some degree. The principal stacked energy peaks put forth in recent work persist, but their amplitude (which maps into reflector impedance contrast) and timing (which maps into reflector depth) depend on factors that are not well constrained -- most notably, the velocity structure of the overlying lunar interior. Thus, while evidence for the lunar core remains strong, the depths of imaged reflectors have associated uncertainties that will require new seismic data and observations to constrain. These results strongly advocate further investigations on the Moon to better resolve the interior (e.g., Selene missions), for the Moon apparently has a rich history of construction and evolution that is inextricably tied to that of Earth.

Clay-clast aggregates: A new textural evidence for seismic fault sliding?

NASA Astrophysics Data System (ADS)

Boutareaud, Sébastien; Calugaru, Dan-Gabriel; Han, Raehee; Fabbri, Olivier; Mizoguchi, Kazuo; Tsutsumi, Akito; Shimamoto, Toshihiko

2008-03-01

To determine the processes responsible for slip-weakening in clayey gouge zones, rotary-shear experiments were conducted at seismic slip rates (equivalent to 0.9 and 1.3 m/s) at 0.6 MPa normal stress on a natural clayey gouge for saturated and non-saturated initial conditions. The mechanical behavior of the simulated faults shows a reproducible slip-weakening behavior, whatever initial moisture conditions. Examination of gouge obtained at the residual friction stage in saturated and non-saturated initial conditions allows the definition of two types of microstructures: a foliated type reflecting strain localization, and a non-foliated type composed of spherical aggregates. Friction experiments demonstrate that liquid-vapor transition of water within gouge due to frictional heating has a high capacity to explain the formation of spherical aggregates in the first meters of displacement. This result suggests that the occurrence of spherical aggregates in natural clayey fault gouges can constitute a new textural evidence for shallow depth pore water phase transition at seismic slip velocity and consequently for past seismic fault sliding.

Seismic measurements of the internal properties of fault zones

USGS Publications Warehouse

Mooney, W.D.; Ginzburg, A.

1986-01-01

The internal properties within and adjacent to fault zones are reviewed, principally on the basis of laboratory, borehole, and seismic refraction and reflection data. The deformation of rocks by faulting ranges from intragrain microcracking to severe alteration. Saturated microcracked and mildly fractured rocks do not exhibit a significant reduction in velocity, but, from borehole measurements, densely fractured rocks do show significantly reduced velocities, the amount of reduction generally proportional to the fracture density. Highly fractured rock and thick fault gouge along the creeping portion of the San Andreas fault are evidenced by a pronounced seismic low-velocity zone (LVZ), which is either very thin or absent along locked portions of the fault. Thus there is a correlation between fault slip behavior and seismic velocity structure within the fault zone; high pore pressure within the pronounced LVZ may be conductive to fault creep. Deep seismic reflection data indicate that crustal faults sometimes extend through the entire crust. Models of these data and geologic evidence are consistent with a composition of deep faults consisting of highly foliated, seismically anisotropic mylonites. ?? 1986 Birkha??user Verlag, Basel.

The Virtual Seismic Atlas Project: sharing the interpretation of seismic data

NASA Astrophysics Data System (ADS)

Butler, R.; Mortimer, E.; McCaffrey, B.; Stuart, G.; Sizer, M.; Clayton, S.

2007-12-01

Through the activities of academic research programs, national institutions and corporations, especially oil and gas companies, there is a substantial volume of seismic reflection data. Although the majority is proprietary and confidential, there are significant volumes of data that are potentially within the public domain and available for research. Yet the community is poorly connected to these data and consequently geological and other research using seismic reflection data is limited to very few groups of researchers. This is about to change. The Virtual Seismic Atlas (VSA) is generating an independent, free-to-use, community based internet resource that captures and shares the geological interpretation of seismic data globally. Images and associated documents are explicitly indexed using not only existing survey and geographical data but also on the geology they portray. By using "Guided Navigation" to search, discover and retrieve images, users are exposed to arrays of geological analogues that provide novel insights and opportunities for research and education. The VSA goes live, with evolving content and functionality, through 2008. There are opportunities for designed integration with other global data programs in the earth sciences.

Seismic responses and controlling factors of Miocene deepwater gravity-flow deposits in Block A, Lower Congo Basin

NASA Astrophysics Data System (ADS)

Wang, Linlin; Wang, Zhenqi; Yu, Shui; Ngia, Ngong Roger

2016-08-01

The Miocene deepwater gravity-flow sedimentary system in Block A of the southwestern part of the Lower Congo Basin was identified and interpreted using high-resolution 3-D seismic, drilling and logging data to reveal development characteristics and main controlling factors. Five types of deepwater gravity-flow sedimentary units have been identified in the Miocene section of Block A, including mass transport, deepwater channel, levee, abandoned channel and sedimentary lobe deposits. Each type of sedimentary unit has distinct external features, internal structures and lateral characteristics in seismic profiles. Mass transport deposits (MTDs) in particular correspond to chaotic low-amplitude reflections in contact with mutants on both sides. The cross section of deepwater channel deposits in the seismic profile is in U- or V-shape. The channel deposits change in ascending order from low-amplitude, poor-continuity, chaotic filling reflections at the bottom, to high-amplitude, moderate to poor continuity, chaotic or sub-parallel reflections in the middle section and to moderate-weak amplitude, good continuity, parallel or sub-parallel reflections in the upper section. The sedimentary lobes are laterally lobate, which corresponds to high-amplitude, good-continuity, moundy reflection signatures in the seismic profile. Due to sediment flux, faults, and inherited terrain, few mass transport deposits occur in the northeastern part of the study area. The front of MTDs is mainly composed of channel-levee complex deposits, while abandoned-channel and lobe-deposits are usually developed in high-curvature channel sections and the channel terminals, respectively. The distribution of deepwater channel, levee, abandoned channel and sedimentary lobe deposits is predominantly controlled by relative sea level fluctuations and to a lesser extent by tectonism and inherited terrain.

Stochastic Gabor reflectivity and acoustic impedance inversion

NASA Astrophysics Data System (ADS)

Hariri Naghadeh, Diako; Morley, Christopher Keith; Ferguson, Angus John

2018-02-01

To delineate subsurface lithology to estimate petrophysical properties of a reservoir, it is possible to use acoustic impedance (AI) which is the result of seismic inversion. To change amplitude to AI, removal of wavelet effects from the seismic signal in order to get a reflection series, and subsequently transforming those reflections to AI, is vital. To carry out seismic inversion correctly it is important to not assume that the seismic signal is stationary. However, all stationary deconvolution methods are designed following that assumption. To increase temporal resolution and interpretation ability, amplitude compensation and phase correction are inevitable. Those are pitfalls of stationary reflectivity inversion. Although stationary reflectivity inversion methods are trying to estimate reflectivity series, because of incorrect assumptions their estimations will not be correct, but may be useful. Trying to convert those reflection series to AI, also merging with the low frequency initial model, can help us. The aim of this study was to apply non-stationary deconvolution to eliminate time variant wavelet effects from the signal and to convert the estimated reflection series to the absolute AI by getting bias from well logs. To carry out this aim, stochastic Gabor inversion in the time domain was used. The Gabor transform derived the signal’s time-frequency analysis and estimated wavelet properties from different windows. Dealing with different time windows gave an ability to create a time-variant kernel matrix, which was used to remove matrix effects from seismic data. The result was a reflection series that does not follow the stationary assumption. The subsequent step was to convert those reflections to AI using well information. Synthetic and real data sets were used to show the ability of the introduced method. The results highlight that the time cost to get seismic inversion is negligible related to general Gabor inversion in the frequency domain. Also, obtaining bias could help the method to estimate reliable AI. To justify the effect of random noise on deterministic and stochastic inversion results, a stationary noisy trace with signal-to-noise ratio equal to 2 was used. The results highlight the inability of deterministic inversion in dealing with a noisy data set even using a high number of regularization parameters. Also, despite the low level of signal, stochastic Gabor inversion not only can estimate correctly the wavelet’s properties but also, because of bias from well logs, the inversion result is very close to the real AI. Comparing deterministic and introduced inversion results on a real data set shows that low resolution results, especially in the deeper parts of seismic sections using deterministic inversion, creates significant reliability problems for seismic prospects, but this pitfall is solved completely using stochastic Gabor inversion. The estimated AI using Gabor inversion in the time domain is much better and faster than general Gabor inversion in the frequency domain. This is due to the extra number of windows required to analyze the time-frequency information and also the amount of temporal increment between windows. In contrast, stochastic Gabor inversion can estimate trustable physical properties close to the real characteristics. Applying to a real data set could give an ability to detect the direction of volcanic intrusion and the ability of lithology distribution delineation along the fan. Comparing the inversion results highlights the efficiency of stochastic Gabor inversion to delineate lateral lithology changes because of the improved frequency content and zero phasing of the final inversion volume.

Retrieval of Body-Wave Reflections Using Ambient Noise Interferometry Using a Small-Scale Experiment

NASA Astrophysics Data System (ADS)

Dantas, Odmaksuel Anísio Bezerra; do Nascimento, Aderson Farias; Schimmel, Martin

2018-02-01

We report the retrieval of body-wave reflections from noise records using a small-scale experiment over a mature oil field. The reflections are obtained by cross-correlation and stacking of the data. We used the stacked correlograms to create virtual source-to-receiver common shot gathers and are able to obtain body-wave reflections. Surface waves that obliterate the body-waves in our noise correlations were attenuated following a standard procedure from active source seismics. Further different strategies were employed to cross-correlate and stack the data: classical geometrical normalized cross-correlation (CCGN), phase cross-correlation (PCC), linear stacking**** and phase weighted stacking (PWS). PCC and PWS are based on the instantaneous phase coherence of analytic signals. The four approaches are independent and reveal the reflections; nevertheless, the combination of PWS and CCGN provided the best results. Our analysis is based on 2145 cross-correlations of 600 s data segments. We also compare the resulted virtual shot gathers with an active 2D seismic line near the passive experiment. It is shown that our ambient noise analysis reproduces reflections which are present in the active seismic data.

Reconnaissance profiles with WLP in complex geological regions

NASA Astrophysics Data System (ADS)

Michon, Dominique

1993-04-01

3-D has now become an essential technique for subsurface imaging. Until recently, it was predominantly employed for reservoir description, but is now starting to be used for exploration. However, in crustal seismic, it would seem that such a tool is still far from being cost-effective. WLP, or Wide Line Profiling, developed by CGG in 1973, is an attractive alternative which we shall examine. First, we shall examine why 3-D is so difficult to apply, for both financial and technical reasons. Next, we shall study the principle of WLP, and emphasize the fundamental differences between WLP and 3-D. We shall then study the resulting data processing and parameters. Using a set of examples, we shall also examine the special characteristics of the method and the advantages that it can offer: (1) 3-D analysis of reflections on a 2-D section. (2) Avoiding interference between reflections. (3) Highlighting faults or folds. (4) For continuous horizons, positioning reflection points. (5) Possibility of mapping in depth, whether in migrated time or not, the swaths explored by the seismic line. (6) Improving the quality of the standard time section by noise reduction.

Seismic ground motion scenarios in Lower Tagus Valley Basin

NASA Astrophysics Data System (ADS)

Borges, José; Torres, Ricardo; Furtado, José; Silva, Hugo; Caldeira, Bento; Pinto, Carlos; Bezzeghoud, Mourad; Carvalho, João

2013-04-01

Throughout its history the Lower Tagus Valley (LTV) has been struck by several earthquakes which produced important material damage and loss of lives: The 1st of November 1755 Lisbon earthquake and the 1969 earthquake (Mw=7.3), located in the SW Iberia Margin and the 1344, 1531 and 1909 (M= 6 to 7) with epicenter located inside the LTV basin. Since this region is the most highly populated region in Portugal, it is expected that an earthquake of similar magnitude of those that have occurred in the past will cause an enormous destruction and casualties. This fact makes LTV a high priority area for earthquake research in Portugal. In order to overcome the problems related to the absence of geological outcrops, low slip-rates (<0,4 mm/year) and the processes of sedimentation and erosion, we use in this work seismic reflection profiles, potential field data, soundings, wells and geological cartography to obtain a map of the main seismogenic structures and to characterize their seismic potential [1]. Moreover, a 3D structural model has been developed for de LTV based on Seismic reflection, Seismic Noise and potential field data [2,3]. In order to improve assessment of the seismic hazard in the LTV basin, we simulate long-period (0-1 Hz) ground motion time histories for a suite of scenarios earthquakes (Mw =5.5 to 7) within the basin, using fault geometries and the 3D seismic velocity structure based on the previous mentioned works. References [1] Pinto, Carlos C. (2011). Identification of Seismogenic Structures in the Lower Tagus Basin. Master Thesis, Universidade de Évora, 128 pp. [2] Torres, R.J.G., (2012). Modelo de velocidade da Bacia do Vale do Tejo: uma abordagem baseada no estudo do ruído sísmico ambiental, Master Thesis, Universidade de Évora, 83pp. [3] Furtado, J.A (2010). Confirmação do modelo da estrutura 3D do Vale Inverior do Tejo a partir de dados de ruído sísmico ambiente, Master Thesis, Universidade de Évora, 136pp.

Evidence of Enhanced Subrosion in a Fault Zone and Characterization of Hazard Zones with Elastic Parameters derived from SH-wave reflection Seismics and VSP

NASA Astrophysics Data System (ADS)

Wadas, S. H.; Tanner, D. C.; Tschache, S.; Polom, U.; Krawczyk, C. M.

2017-12-01

Subrosion, the dissolution of soluble rocks, e.g., sulfate, salt, or carbonate, requires unsaturated water and fluid pathways that enable the water to flow through the subsurface and generate cavities. Over time, different structures can occur that depend on, e.g., rock solubility, flow rate, and overburden type. The two main structures are sinkholes and depressions. To analyze the link between faults, groundwater flow, and soluble rocks, and to determine parameters that are useful to characterize hazard zones, several shear-wave (SH) reflection seismic profiles were surveyed in Thuringia in Germany, where Permian sulfate rocks and salt subcrop close to the surface. From the analysis of the seismic sections we conclude that areas affected by tectonic deformation phases are prone to enhanced subrosion. The deformation of fault blocks leads to the generation of a damage zone with a dense fracture network. This increases the rock permeability and thus serves as a fluid pathway for, e.g., artesian-confined groundwater. The more complex the fault geometry and the more interaction between faults, the more fractures are generated, e.g., in a strike slip-fault zone. The faults also act as barriers for horizontal groundwater flow perpendicular to the fault surfaces and as conduits for groundwater flow along the fault strike. In addition, seismic velocity anomalies and attenuation of seismic waves are observed. Low velocities <200 m/s and high attenuation may indicate areas affected by subrosion. Other parameters that characterize the underground stability are the shear modulus and the Vp/Vs ratio. The data revealed zones of low shear modulus <100 MPa and high Vp/Vs ratio >2.5, which probably indicate unstable areas due to subrosion. Structural analysis of S-wave seismics is a valuable tool to detect near-surface faults in order to determine whether or not an area is prone to subrosion. The recognition of even small fault blocks can help to better understand the hydrodynamic groundwater conditions, which is another key factor to understand the subrosion process. The elastic parameters derived from seismic velocities can help to identify possible zones of instability.

Investigation of sinkhole areas in Germany using 2D shear wave reflection seismics and zero-offset VSP

NASA Astrophysics Data System (ADS)

Tschache, Saskia; Wadas, Sonja; Polom, Ulrich; Krawczyk, Charlotte M.

2017-04-01

Sinkholes pose a serious geohazard for humans and infrastructure in populated areas. The Junior Research Group Subrosion within the Leibniz Institute for Applied Geophysics and the joint project SIMULTAN work on the multi-scale investigation of subrosion processes in the subsurface, which cause natural sinkholes. In two case studies in sinkhole areas of Thuringia in Germany, we applied 2D shear wave reflection seismics using SH-waves with the aim to detect suitable parameters for the characterisation of critical zones. This method has the potential to image near-surface collapse and faulting structures in improved resolution compared to P-wave surveys resulting from the shorter wavelength of shear waves. Additionally, the shear wave velocity field derived by NMO velocity analysis is a basis to calculate further physical parameters, as e.g. the dynamic shear modulus. In both investigation areas, vertical seismic profiles (VSP) were acquired by generating P- and SH-waves (6 component VSP) directly next to a borehole equipped with a 3C downhole sensor. They provide shear and compressional wave velocity profiles, which are used to improve the 2D shear wave velocity field from surface seismics, to perform a depth calibration of the seismic image and to calculate the Vp/Vs ratio. The signals in the VSP data are analysed with respect to changes in polarisation and attenuation with depth and/or azimuth. The VSP data reveal low shear wave velocities of 200-300 m/s in rock layers known to be heavily affected by subrosion and confirm the low velocities calculated from the surface seismic data. A discrepancy of the shear wave velocities is observed in other intervals probably due to unsymmetrical travel paths in the surface seismics. In some VSP data dominant conversion of the direct SH-wave to P-wave is observed that is assumed to be caused by an increased presence of cavities. A potential fault distorting the vertical travel paths was detected by abnormal P-wave first arrivals in the VSP dataset of a borehole located near the city of Bad Frankenhausen. In addition, a strong attenuation of the source signals may indicate areas influenced by subrosion.

Refraction and reflection seismic investigations for geological energy-storage site characterization: Dalby (Tornquist Zone), southwest Sweden

NASA Astrophysics Data System (ADS)

Malehmir, Alireza; Bergman, Bo; Andersson, Benjamin; Sturk, Robert; Johansson, Mattis

2017-04-01

Three high-resolution, 5 m shot and receiver spacing using 141-172 receivers, refraction and reflection seismic profiles for the planning of a major underground energy-storage site near the town of Dalby-Lund within the Scania Tornquist suture zone in southwest of Sweden were acquired during August 2015. The site is situated ca. 1 km north of the RFZ (Romeleåsen fault and flexure zone) with a complex geologic and tectonic history. Near vertical dikes are observed from several quarries in the area crosscutting granitic-gneissic-amphibiotic rocks and form clear magnetic lineaments. These dikes likely have also acted as surfaces on which further faulting have occurred. Although a major high-speed and traffic road runs in the middle of the study area, the seismic data show excellent quality particularly for the data along two profiles (profiles 2 and 3) perpendicular to the road, and slightly noisy, due to high wind, for the data along a profile (profile 4) parallel to the road. A bobcat-mounted drop hammer (500 kg) was used to generate the seismic signal. To provide continuity from one side of the road to another, 51 wireless recorders connected to 10 Hz geophones and operating in an autonomous mode were used. GPS times of the source impacts were used to extract the data from the wireless recorders and then merged with the data from the cabled recorders (also 10 Hz geophones). Three shot records per source position were generated and vertically stacked to improve the signal-to-noise ratio. First arrivals are clear in most shot gathers allowing them to be used for traditional refraction seismic data analysis and also for more advanced traveltime tomography. The velocity models obtained through traveltime tomography clearly depict bedrock surface and its undulations and in many places show good correlation with the boreholes recently drilled in the area. At places where bedrock is intersected at greater depths than usual, for example 25 m at one place, depression-looking bedrock is clearly observed in the tomograms suggesting the possibility of weakness zones (likely highly fractured and/or weathered) in the bedrock. Signs of reflections in the raw shot gathers were encouraging and motivated to process the reflection component of the data for the purpose of subsurface imaging. Several northeast dipping, about 60-65 degree, reflections were imaged down to 400 m depth thanks to the close shot and receiver spacing strategy of the data acquisition. These reflections often show coherent character but at occasions are discontinuous and have different appearances. Reflections along profile 4 have for example different characters, shorter and more gently dipping, compared to those observed in profiles 2 and 3 suggesting that the main dip favors the orientation of profiles 2 and 3. The origins of the reflections are unclear ranging from amphibolite sheets to diabase dykes within the gneissic rocks, and each of this implies a different geological scenario (when compared with the geological data from a nearby quarry north of the study area) at where the site will be developed. Future studies should aim at understanding the cause of the reflections, constraining their locations at depth, and if they play any major role for the planning of the underground facilities. This study however illustrates the potential of the combined refraction and reflection imaging for these types of projects. For future developments of the site however a full 3D seismic survey can highly be useful. Acknowledgments: This work was supported by Skanska, and benefited collaborations among experts from Sweco, Lund University and Skanska. Trust project (http://www.trust-geoinfra.se) was fundamental to initiate this project.

Estimating tectonic history through basin simulation-enhanced seismic inversion: Geoinformatics for sedimentary basins

USGS Publications Warehouse

Tandon, K.; Tuncay, K.; Hubbard, K.; Comer, J.; Ortoleva, P.

2004-01-01

A data assimilation approach is demonstrated whereby seismic inversion is both automated and enhanced using a comprehensive numerical sedimentary basin simulator to study the physics and chemistry of sedimentary basin processes in response to geothermal gradient in much greater detail than previously attempted. The approach not only reduces costs by integrating the basin analysis and seismic inversion activities to understand the sedimentary basin evolution with respect to geodynamic parameters-but the technique also has the potential for serving as a geoinfomatics platform for understanding various physical and chemical processes operating at different scales within a sedimentary basin. Tectonic history has a first-order effect on the physical and chemical processes that govern the evolution of sedimentary basins. We demonstrate how such tectonic parameters may be estimated by minimizing the difference between observed seismic reflection data and synthetic ones constructed from the output of a reaction, transport, mechanical (RTM) basin model. We demonstrate the method by reconstructing the geothermal gradient. As thermal history strongly affects the rate of RTM processes operating in a sedimentary basin, variations in geothermal gradient history alter the present-day fluid pressure, effective stress, porosity, fracture statistics and hydrocarbon distribution. All these properties, in turn, affect the mechanical wave velocity and sediment density profiles for a sedimentary basin. The present-day state of the sedimentary basin is imaged by reflection seismology data to a high degree of resolution, but it does not give any indication of the processes that contributed to the evolution of the basin or causes for heterogeneities within the basin that are being imaged. Using texture and fluid properties predicted by our Basin RTM simulator, we generate synthetic seismograms. Linear correlation using power spectra as an error measure and an efficient quadratic optimization technique are found to be most effective in determining the optimal value of the tectonic parameters. Preliminary 1-D studies indicate that one can determine the geothermal gradient even in the presence of observation and numerical uncertainties. The algorithm succeeds even when the synthetic data has detailed information only in a limited depth interval and has a different dominant frequency in the synthetic and observed seismograms. The methodology presented here even works when the basin input data contains only 75 per cent of the stratigraphic layering information compared with the actual basin in a limited depth interval.

Mapping seismic azimuthal anisotropy of the Japan subduction zone

NASA Astrophysics Data System (ADS)

Zhao, D.; Liu, X.

2016-12-01

We present 3-D images of azimuthal anisotropy tomography of the crust and upper mantle of the Japan subduction zone, which are determined using a large number of high-quality P- and S-wave arrival-time data of local earthquakes and teleseismic events recorded by the dense seismic networks on the Japan Islands. A tomographic method for P-wave velocity azimuthal anisotropy is modified and extended to invert S-wave travel times for 3-D S-wave velocity azimuthal anisotropy. A joint inversion of the P and S wave data is conducted to constrain the 3-D azimuthal anisotropy of the Japan subduction zone. Main findings of this work are summarized as follows. (1) The high-velocity subducting Pacific and Philippine Sea (PHS) slabs exhibit trench-parallel fast-velocity directions (FVDs), which may reflect frozen-in lattice-preferred orientation of aligned anisotropic minerals formed at the mid-ocean ridge as well as shape-preferred orientation such as normal faults produced at the outer-rise area near the trench axis. (2) Significant trench-normal FVDs are revealed in the mantle wedge, which reflects corner flow in the mantle wedge due to the active subduction and dehydration of the oceanic plates. (3) Obvious toroidal FVDs and low-velocity anomalies exist in and around a window (hole) in the aseismic PHS slab beneath Southwest Japan, which may reflect a toroidal mantle flow pattern resulting from hot and wet mantle upwelling caused by the joint effects of deep dehydration of the Pacific slab and the convective circulation process in the mantle wedge above the Pacific slab. (4) Significant low-velocity anomalies with trench-normal FVDs exist in the mantle below the Pacific slab beneath Northeast Japan, which may reflect a subducting oceanic asthenosphere affected by hot mantle upwelling from the deeper mantle. ReferencesLiu, X., D. Zhao (2016) Seismic velocity azimuthal anisotropy of the Japan subduction zone: Constraints from P and S wave traveltimes. J. Geophys. Res. 121, doi:10.1002/2016JB013116. Zhao, D., S. Yu, X. Liu (2016) Seismic anisotropy tomography: New insight into subduction dynamics. Gondwana Res. 33, 24-43.

Multi-azimuth Anisotropic Velocity Measurements in Fractured Crystalline Rock From the International Continental Drilling Program Outokumpu Borehole, Finland

NASA Astrophysics Data System (ADS)

Schijns, H.; Duo, X.; Heinonen, S.; Schmitt, D. R.; Kukkonen, I. T.; Heikkinen, P.

2008-12-01

A high resolution seismic survey consisting of a multi-depth multi-azimuth VSP, a zero-offset VSP and a reflection/refraction survey was conducting in May, 2006, near the town of Outokumpu, Finland, using the International Continental Scientific Drilling Program 2.5 km deep fully cored scientific borehole. The survey was undertaken in order to create an anisotropic velocity model for future micro-seism studies as well as to provide a higher resolution reflection profile through the area than was previously available. The seismic survey high frequency seismic vibrator as a source, employing 8 s linear taper sweeps from 15-250 Hz at 20 m shot spacing. Receivers were 14 Hz single component geophones on the surface and a three component geophone downhole. The walk-away VSP included measurements over two azimuths with the receiver at depths of 1000, 1750 and 2500 m, while the zero-offset VSP used a 2 m depth increment. Surface geophones were located along the same seismic lines as employed in the walk-away VSP and were nominally 4 m apart. The survey area is located on the Fennoscandian shield, and the glacial history of the area required significant static corrections to account for the variable overburden overlying the mica-rich schist and pegmatitic granite composing the bedrock. These were calculated using travel-time inversion of the refraction data and were applied to the walk-away VSP and reflection profiles, significantly improving the quality of both. Anisotropic velocity analysis was performed using a plane-wave decomposition of the processed walk-away VSP. The maximum anisotropy was observed in the walk-away VSPs along the Southeastern azimuth, with the P-wave phase velocity ranging from 5330-5950 m/s between 50-1000 m in depth, and up to 6150 m/s between 1000-1750 m in depth. Shear wave splitting was observed in the Northeastern direction. Preliminary analysis of the zero-offset VSP has revealed shown good agreement with the relevant portions of the anisotropic velocity measurements and the reflection profile.

Seismic inversion for incoming sedimentary sequence in the Nankai Trough margin off Kumano Basin, southwest Japan

NASA Astrophysics Data System (ADS)

Naito, K.; Park, J.

2012-12-01

The Nankai Trough off southwest Japan is one of the best subduction-zone to study megathrust earthquake mechanism. Huge earthquakes have been repeated in the cycle of 100-150 years in the area, and in these days the next emergence of the earthquake becomes one of the most serious issue in Japan. Therefore, detailed descriptions of geological structure are urgently needed there. IODP (Integrated Ocean Drilling Program) have investigated this area in the NanTroSEIZE science plan. Seismic reflection, core sampling and borehole logging surveys have been executed during the NanTroSEIZE expeditions. Core-log-seismic data integration (CLSI) is useful for understanding the Nankai seismogenic zone. We use the seismic inversion method to do the CLSI. The seismic inversion (acoustic impedance inversion, A.I. inversion) is a method to estimate rock physical properties using seismic reflection and logging data. Acoustic impedance volume is inverted for seismic data with density and P-wave velocity of several boreholes with the technique. We use high-resolution 3D multi-channel seismic (MCS) reflection data obtained during KR06-02 cruise in 2006, and measured core sample properties by IODP Expeditions 322 and 333. P-wave velocities missing for some core sample are interpolated by the relationship between acoustic impedance and P-wave velocity. We used Hampson-Russell software for the seismic inversion. 3D porosity model is derived from the 3D acoustic impedance model to figure out rock physical properties of the incoming sedimentary sequence in the Nankai Trough off Kumano Basin. The result of our inversion analysis clearly shows heterogeneity of sediments; relatively high porosity sediments on the shallow layer of Kashinosaki Knoll, and distribution of many physical anomaly bands on volcanic and turbidite sediment layers around the 3D MCS survey area. In this talk, we will show 3D MCS, acoustic impedance, and porosity data for the incoming sedimentary sequence and discuss its possible implications for the Nankai seismogenic behavior.

High-resolution reflection seismic survey at a CCS site, Taiwan

NASA Astrophysics Data System (ADS)

Wang, Chien-Ying; Chung, Chen-Tung; Kuo, Hsuan-Yu; Wu, Ming-shyan; Kuo-Chen, Hao

2017-04-01

To control the effect of greenhouse gas on global warming, the reduction of carbon dioxide emission has become a significant international issue in recent years. The capture of carbon dioxide during its manufacturing and storing in adjacent areas are the most economical way. This research uses high-resolution seismic reflection survey to investigate the region around the world's largest coal-fired power plant at Taichung Port, Taiwan. We aim to detect proper geological structures and to evaluate the possible way to store carbon dioxide. This research uses reflection seismic survey with two mini-vibrators and 240 channels to investigate detailed underground structures. The total length of seismic lines is more than 20 kilometers. By aligning sequential seismic lines, we are able to correlate stratigraphic layers over a wide area. Two adjacent wells along the seismic line are used to identified possible formations. The TaiChung Power Plant (TCPP) at Taichung Port is our target which has more cross-tied seismic lines and a seismic line even extending into the sea water. We analyze these seismic profiles to establish the geological model for carbon dioxide storage and evaluate the possibility of storage systems. Furthermore, this research may prepare some baseline data for the future carbon dioxide injection monitoring. The result shows that the geological structures striking 8 degrees east of north and dipping 2.8 degrees to the east. This means that carbon dioxide will migrate toward the sea direction after injection. The structural layers are relatively flat without any sign of faults. Three carbon dioxide storage systems : Mushan Wuchihshan—Paling(bottom), Peiliao—Talu(middle) and Kueichulin—Chinshui(upper) system are identified. All has the proper reservoir with high porosity and capable caprocks more than 100 meters thick. The geological storage of carbon dioxide injected into TCPP site is a feasible, commercial and safe way to reduce the emission of carbon dioxide from TCPP.

Lower Crstal Reflectity bands and Magma Emplacement in Norweigian sea, NE Atlantic

NASA Astrophysics Data System (ADS)

Rai, A.; Breivik, A. J.; Mjelde, R.

2013-12-01

In this study we present the OBS data collected along seismic profiles in the norweigian sea. The traveltime modelling of the OBS data provides first-hand information about seismic structure of the subsurface. However, waveform modelling is used to further constrain the fine scale structure, velocity constrast and velocity gradients. By forward modelling and inversion of the seismic waveforms, we show that the multiple bands of reflectivity could be due to multiple episodes of magma emplacements that might have frozen in the form of sills. These mafic intrusions probably intruded into the ductile lower crust during the main rifting phase of Europe and Greenland.

Archive of Digital Boomer Seismic Reflection Data Collected During USGS Field Activity 08LCA01 in 10 Central Florida Lakes, March 2008

USGS Publications Warehouse

Harrison, Arnell S.; Dadisman, Shawn V.; Davis, Jeffrey B.; Flocks, James G.; Wiese, Dana S.

2009-01-01

In March of 2008, the U.S. Geological Survey and St. Johns River Water Management District (SJRWMD) conducted geophysical surveys in Lakes Avalon, Big, Colby, Helen, Johns, Prevatt, Searcy, Saunders, Three Island, and Trout, located in central Florida, as part of the USGS Lakes and Coastal Aquifers (LCA) study. This report serves as an archive of unprocessed digital boomer seismic reflection data, trackline maps, navigation files, Field Activity Collection System (FACS) logs, Geographic Information System (GIS) files, and formal Federal Geographic Data Committee (FGDC) metadata. Filtered and gained (a relative increase in signal amplitude) digital images of the seismic profiles are also provided. Refer to the Acronyms page for expansions of acronyms and abbreviations used in this report. The archived trace data are in standard Society of Exploration Geophysicists (SEG) SEG-Y format (Barry and others, 1975) and may be downloaded and processed with commercial or public domain software such as Seismic Unix (SU) (Cohen and Stockwell, 2005). Example SU processing scripts and USGS software for viewing the SEG-Y files (Zihlman, 1992) are also provided. The USGS Florida Integrated Science Center (FISC) - St. Petersburg assigns a unique identifier to each cruise or field activity. For example, 08LCA01 tells us the data were collected in 2008 for the Lakes and Coastal Aquifers (LCA) study and the data were collected during the first field activity for that study in that calendar year. Refer to http://walrus.wr.usgs.gov/infobank/programs/html/definition/activity.html for a detailed description of the method used to assign the field activity ID. The naming convention used for each seismic line is as follows: yye##a, where yy is the last two digits of the year in which the data were collected, e is a 1-letter abbreviation for the equipment type (for example, b for boomer), ## is a 2-digit number representing a specific track, and a is a letter representing the section of a line if recording was prematurely terminated or rerun for quality or acquisition problems. The boomer plate is an acoustic energy source that consists of capacitors charged to a high voltage and discharged through a transducer in the water. The transducer is towed on a sled floating on the water surface and when discharged emits a short acoustic pulse, or shot, which propagates through the water, sediment column, or rock beneath. The acoustic energy is reflected at density boundaries (such as the lake bottom, sediment, or rock layers beneath the lake bottom), detected by the receiver, and recorded by a PC-based seismic acquisition system. This process is repeated at timed intervals (for example, 0.5 s) and recorded for specific intervals of time (for example, 100 ms). In this way, a two-dimensional (2-D) vertical profile of the shallow geologic structure beneath the ship track is produced. Figure 1 displays the three boomer acquisition geometries used during this survey. The second method was used because windy weather conditions hindered steerage, and driving the boat in reverse actually helped maintain course and prevented the possibility of the streamer cables becoming entangled in the boat propellers. The third method was used to help attenuate propeller and generator noise. Refer to table 1 for a summary of acquisition parameters. Table 2 lists trackline statistics. The unprocessed seismic data are stored in SEG-Y format (Barry and others, 1975). For a detailed description of the data format, refer to the SEG-Y Format page. See the How To Download SEG-Y Data page for download instructions. The printable profiles provided here are GIF images that were filtered and gained using Seismic Unix software. Refer to the Software page for details about the processing and examples of the processing scripts. The processed SEG-Y data were exported to Chesapeake Technology, Inc. (CTI) SonarWeb software to produce a geospatially interactive Web page of the profile,

Imaging Shallow Aquitard Breaches with P waves: Results from a Walk-away test and a Reflection Survey at two Sites in Memphis, Tennessee, USA

NASA Astrophysics Data System (ADS)

Ge, J.; Magnani, M.; Waldron, B. A.

2006-12-01

We present the results of two seismic reflection experiments conducted in the Great Memphis area in April and July 2006. The two experiments consisted in a walk-away test and in the acquisition of a 1 km seismic reflection profile. The acquisition of the seismic data is part of a larger effort aimed at imaging the lateral continuity of the Upper Claiborne confining clay that separates the Memphis aquifer, the region's primary drinking water source, from the upper unconfined aquifer and protects the drinking aquifer from exposure to potential contamination. During the walk-away test, four P-wave sources, a 7.5 kg sledge hammer, a 20 kg weight drop, a 12-gauge Buffalo gun, and a Minivibe source were tested at two sites with the goal of selecting the best P-wave seismic source and acquisition parameters for shallow reflection surveys. Boreholes nearby both sites encountered the Upper Claiborne unit at a depth ranging from 10 m to 40 m. One site is located within a 100-meter length of road median that can be considered an urban environment. The second site is located at Shelby Farms within the City of Memphis yet reflects a rural setting with minimal noise and no subsurface infrastructure. Performing identical walk-away tests at both sites, the results indicate that the energy source selection is site dependent. At the urban site, the energy generated by the weight drop source is more coherent and can be interpreted with more confidence on the recorded data. However the Shelby Farms site the 12-gauge shotgun produced the strongest recorded energy, the highest dominant frequency and the broadest frequency band (6- 110 Hz). Strong attenuations are observed at both sites with a much higher attenuation in the urban road median site, where the near surface materials consisted of gravels, sands, clays, and pebbles. For both sites, surface waves and refractions dominate the seismic recordings. Filtering and gain of the data revealed the presence of shallow reflections related to the targeted clay layer. Based on the results of the walk-away test and on additional supporting data such as water table measurements, neotectonic structural mapping and borehole data, the location for a 1 km long, north-south trending seismic reflection profile was chosen at Shelby Farms extending south to the Wolf River. Based on the walk-away testing the 12-gauge Buffalo gun was selected as the energy source, used to detonate a single 200 g black powder shell in a 0.6 m deep water filled hole with a 1 m source interval and a 0.25 m geophone interval. Preliminary analysis of the data indicates dominating surface waves and refractions. Upon filtering, consistent reflections can be observed. Correlation of reflections at the start of the seismic line to nearby boreholes evidenced the signature of the Upper Claiborne confining clay at a depth of 18 m.

Diversified seabed substrate, sediment remobilisation and fluid migration features offshore NW Greenland - new insights from marine seismic data acquisition in the Northern Nares Strait during the RV Oden cruise 2015

NASA Astrophysics Data System (ADS)

Andresen, Katrine Juul; Heirman, Katrien; Kamla, Elina; Nielsen, Tove; Rønø Clausen, Ole; Jakobsson, Martin; Mix, Alan C.; Andersen, Søren T.; Nørmark, Egon; Piotrowski, Jan A.; Knutz, Paul; Larsen, Nicolaj K.; Hogan, Kelly

2016-04-01

We present some preliminary observations from acquired seismic data from the Northern Nares Strait, NW Greenland. The studied area covers the Hall Basin in front of the Petermann Glacier and extends southward into the Kennedy Channel. It represents an area intensely affected by glacial related processes as well as deep tectonics. The data were acquired during the RV Oden cruise in late summer 2015, and thus represent valuable input to the understanding of the geological development of this scarcely accessed area of the Arctic. The data were acquired in nearly ice-free conditions and consist of >700 km 2D seismic airgun data, supplemented by high-resolution subbottom profiler data and multibeam data. The different acoustic data acquired simultaneously enable us to correlate deeper geological observations (e.g. faults observed on airgun seismics) with shallow depositional architectures (observed on subbottom profiler) and finally correlate the relatively scattered 2D interpretation with the detailed 3D seafloor morphology obtained by the multibeam. The seismic data reveal several provinces of varying seabed substrate geometry. The provinces include A: confined mini-basins; B: larger sedimentary basins; C: larger structural highs and D: "rough-and-faulted" terrain. The data also reveal a number of seismic anomalies, which indicate fluid flow and sediment remobilisation. The mini-basins are 100-600 m wide, in contrast to the larger basins which typically extend over 6-12 km. The mini-basins are characterized by a flat, smooth and continuous seafloor reflection and have an infill dominated by parallel and sub-horizontal reflections onlapping the edges of the basins. The larger basins, where the internal reflection pattern appears more diverse and less parallel, have much greater relief at the seafloor. Vertical disturbance zones typically emerging above minor structures at the floor of the mini-basins are likely related to vertical fluid migration. The zones occasionally continue to the seafloor but more often terminate within the sediments. Scattered amplitude anomalies in conjunction with sag-like depressions are further potential indications of fluid migration within the mini-basins (palaeo-pockmarks?). Slumps and mounded features within the mini-basins and at the larger structural highs indicate syn-depositional sediment remobilisation. A BSR-like reflection, potentially representing the base of gas hydrates, is occasionally observed in the larger sedimentary basins (ca. 15-20 ms TWT b.s.fl.) and at the culmination of the larger structural highs (ca. 40-50 ms TWT b.s.fl.). Cone-shaped to elongated ridges 15-20 m high and 500 m across appear to be linked with deeper structures and might indicate remobilisation of the shallow subsurface sediments potentially linked to fluid escape. Alternatively, they might be of glacial origin. Our preliminary results indicate that the basins are filled with subglacial and glaciofluvial sediments and that small-scale fluid migration and sediment remobilisation represent important processes in generating the depositional architecture in the Northern Nares Strait region. Further analyses are expected to constrain the interpretation of the observed features in detail, especially regarding the origin of the fluids.

Reflection seismic characterization of the Grängesberg iron deposit and its mining-induced structures, central Sweden

NASA Astrophysics Data System (ADS)

Place, Joachim; Malehmir, Alireza; Högdahl, Karin; Juhlin, Christopher; Persson Nilsson, Katarina

2014-05-01

Reflection seismic investigation has been conducted on the Grängesberg apatite iron deposit where over 150 Mt of iron ore were produced until the mine closed in 1989. The mine infrastructure with shafts and tunnels extend down to ca. 650 m below the surface. Both natural and mine induced fracture and fault systems are today water-filled (some of them extending to the surface). The disputed ore genesis of the apatite-iron ores and its exploration potential due to large remaining quantities once again attracts both scientific and commercial interests. A good understanding of the geometry of mineral deposits and their hostrock structures at depth is essential for optimizing their exploration and exploitation. In addition, deep understanding of the fracture system is vital if mining activity is resumed as these may impact the terrain stability and seismicity, which may put at risk new populated and industrial areas. To address some of these challenging issues related to the past mining and also to obtain information about the depth continuation of the existing deposit, two E-W oriented reflection lines with a total length of 3.5 km were acquired in May 2013 by Uppsala University. A weight drop mounted on an hydraulic bobcat truck (traditionally used for concrete breaking in demolition sector) was used to generate seismic signal. In order to increase the signal-to-noise ratio, several impacts were generated at each shot point and stacked together. The seismic lines intersect at high angle the Grängesberg ore body and open pit, as well as several mining-induced faults. A combination of cabled and wireless receivers placed at every 10 m was used for the data recording. Use of wireless receivers was necessary as deploying cabled sensors was not possible due to city infrastructures, roads and houses. A careful analysis of the data suggested that several field-related issues such as (1) the crooked geometry of the lines (due to the available path and road network), (2) electric and vibration noise due to populated areas and roads, as well as a rock crusher working close to the line, (3) significant static variations (due to the variable nature of the terrain: forest, roads, open pit filled with 10s of meters of unconsolidated materials...), make this dataset similar to a city-kind dataset. Preprocessing of the data first required the cable- and wireless- recorded sub-datasets to be merged using GPS time stamps (nanoseconds accuracy) registered in the active data. Vertical shift and stack was then carried out to stack all data available at each shot point. Preliminary results from brute stacks exhibit evidences of reflections or diffractions. It is anticipated that further processing, involving especially appropriate static corrections and velocity analysis, would help interpreting such seismic events in relation to the ore body and its surrounding structures. Possible along-profile compartmentalization is also detected; further processing is however necessary before interpreting such features in terms of recent faulting. Acknowledgements: Formas, Grängesberg Iron AB, Spendrups and Geological Survey of Sweden

Bright Spots, Structure, and Magmatism in Southern Tibet from INDEPTH Seismic Reflection Profiling

PubMed

Brown; Zhao; Nelson; Hauck; Alsdorf; Ross; Cogan; Clark; Liu; Che

1996-12-06

INDEPTH seismic reflection profiling shows that the decollement beneath which Indian lithosphere underthrusts the Himalaya extends at least 225 kilometers north of the Himalayan deformation front to a depth of approximately 50 kilometers. Prominent reflections appear at depths of 15 to 18 kilometers near where the decollement reflector apparently terminates. These reflections extend north of the Zangbo suture to the Damxung graben of the Tibet Plateau. Some of these reflections have locally anomalous amplitudes (bright spots) and coincident negative polarities implying that they are produced by fluids in the crust. The presence of geothermal activity and high heat flow in the regions of these reflections and the tectonic setting suggest that the bright spots mark granitic magmas derived by partial melting of the tectonically thickened crust.

Mineral, Virginia earthquake illustrates seismicity of a passive-aggressive margin

NASA Astrophysics Data System (ADS)

Stein, S. A.; Pazzaglia, F. J.; Meltzer, A.; Berti, C.; Wolin, E.; Kafka, A. L.

2011-12-01

The August 2011 M5.8 Virginia earthquake illustrated again that "passive" continental margins, at which the continent and neighboring seafloor are part of the same plate, are often seismically active. This phenomenon occurs worldwide, with the east coast of North America a prime example. Examples from North to South include the 1933 M 7.3 Baffin Bay, 1929 M 7.2 Grand Banks of Newfoundland, 1755 M 6 Cape Ann, Massachusetts, and 1886 M 7 Charleston earthquakes. The mechanics of these earthquakes remains unclear. Their overall alignment along the margin suggests that they reflect reactivation of generally margin-parallel faults remaining from continental convergence and later rifting by the modern stress field. This view accords with the occurrence of the Virginia earthquake by reverse faulting on a margin-parallel NE-SW striking fault. However, it occurred on the northern edge of the central Virginia seismic zone, a seismic trend normal to the fault plane, margin, and associated structures, that has no clear geologic expression. Hence it is unclear why this and similar seismic zones have the geometry they do. Although it is tempting to correlate these zones with extensions of Atlantic fracture zones, this correlation has little explanatory power given the large number of such zones. It is similarly unclear whether these zones and the intervening seismic gaps reflect areas that are relatively more active over time, or are instead the present loci of activity that migrates. It is also possible that the presently-active zones reflect long-lived aftershocks of large prehistoric earthquakes. The forces driving the seismicity are also unclear. In general, seismic moment release decreases southward along the margin, consistent with the variation in vertical motion rates observed by GPS, suggesting that glacial-isostatic adjustment (GIA) provides some of the stresses involved. However, in the mid-Atlantic region - south of the area of significant GIA - deformed stratigraphic and geomorphic markers, localized high-relief topography, and rapid river incision show uplift of the Piedmont and Appalachians relative to the Coastal Plain for the past 10 Ma, suggesting that the seismicity reflects active and long-term deformation. These challenging questions are natural candidates for further study using new seismological and GPS data from the EarthScope program, together with geological and modeling studies. The dense deployment of seismometers in the wake of the Mineral VA earthquake and the arrival of EarthScope on the eastern seaboard in 2012 and 2013 can provide the required observations at multiple scales to better understand the mechanics of and forces driving east coast seismicity. Here we begin this study by comparing the aftershock sequence of the Mineral VA earthquake to previously recorded events in the Reading Lancaster Seismic Zone and the Central Virginia Seismic Zone.

Seismic reflection characteristics of naturally-induced subsidence affecting transportation

USGS Publications Warehouse

Miller, R.D.; Xia, J.; Steeples, D.W.

2009-01-01

High-resolution seismic reflections have been used effectively to investigate sinkholes formed from the dissolution of a bedded salt unit found throughout most of Central Kansas. Surface subsidence can have devastating effects on transportation structures. Roads, rails, bridges, and pipelines can even be dramatically affected by minor ground instability. Areas susceptible to surface subsidence can put public safety at risk. Subsurface expressions significantly larger than surface depressions are consistently observed on seismic images recorded over sinkholes in Kansas. Until subsidence reaches the ground surface, failure appears to be controlled by compressional forces evidenced by faults with reverse orientation. Once a surface depression forms or dissolution of the salt slows or stops, subsidence structures are consistent with a tensional stress environment with prevalent normal faults. Detecting areas of rapid subsidence potential, prior to surface failure, is the ultimate goal of any geotechnical survey where the ground surface is susceptible to settling. Seismic reflection images have helped correlate active subsidence to dormant paleofeatures, project horizontal growth of active sinkholes based on subsurface structures, and appraise the risk of catastrophic failure. ?? China University of Geosciences (Wuhan) and Springer-Verlag GmbH 2009.

High-resolution shallow reflection seismic image and surface evidence of the Upper Tiber Basin active faults (Northern Apennines, Italy)

USGS Publications Warehouse

Donne, D.D.; Plccardi, L.; Odum, J.K.; Stephenson, W.J.; Williams, R.A.

2007-01-01

Shallow seismic reflection prospecting has been carried out in order to investigate the faults that bound to the southwest and northeast the Quaternary Upper Tiber Basin (Northern Apennines, Italy). On the northeastern margin of the basin a ??? 1 km long reflection seismic profile images a fault segment and the associated up to 100 meters thick sediment wedge. Across the southwestern margin a 0.5 km-long seismic profile images a 50-55??-dipping extensional fault, that projects to the scarp at the base of the range-front, and against which a 100 m thick syn-tectonic sediment wedge has formed. The integration of surface and sub-surface data allows to estimate at least 190 meters of vertical displacement along the fault and a slip rate around 0.25 m/kyr. Southwestern fault might also be interpreted as the main splay structure of regional Alto Tiberina extensional fault. At last, the 1917 Monterchi earthquake (Imax=X, Boschi et alii, 2000) is correlable with an activation of the southwestern fault, and thus suggesting the seismogenic character of this latter.

Seismarmara experiment: results from reprocessing of selected multi-channel seismic reflection profiles

NASA Astrophysics Data System (ADS)

Cetin, S.; Voogd, B.; Carton, H.; Laigle, M.; Becel, A.; Saatcilar, R.; Singh, S.; Hirn, A.

2003-04-01

The North Anatolian Fault (NAF) has been responsible for the earthquakes of Izmit and Duzce in 1999. The occurrence of these earthquakes has drawn scientific attention into the Sea of Marmara since the NAF enters into the Sea of Marmara where the latest Izmit earthquake rupture stopped. The SEISMARMARA-2001 survey is a combined seismic reflection, refraction and earthquake experiment carried out in 2001 in the Marmara Region in Turkey by French-Turkish scientific cooperation. The objectives of this survey were to image the various branches of the NAF and related other fault systems. R/V Le Nadir was equipped with a 4.5 km long streamer with 360 channels and a large airgun source. During Leg 1, a grid of large regional lines encompassing the whole Marmara trough was shot. For part of them a strong 8100 cu.in. source for deepest penetration was used, with a 150 m shot interval giving a 15-fold coverage. Another part was shot for a higher resolution with a 2900 cu. in. array at a 50m or 38 m interval to give a 45 or 60-fold coverage. The latter acquisition parameters were used for Leg 2 that was devoted to a very dense grid of lines in the Cinarcik Basin Reprocessing of the multi-channel seismic data is currently being undertaken in several Institutions using different seismic processing softwares (GeoVecteur, ProMAX, Focus), to take advantage of the diverse acquisitions and cope with their limitations, for instance high fold-order for Leg 2 and strength of signal but loose spatial sampling for the bigger source. The main objectives of the reprocessing of the selected profiles are to do a detailed velocity analysis and stacking after deconvolution, filtering to remove or suppress deep sea bottom multiples and out of plane reflections, and time-migration and depth conversion and thus reveal both the shallow and deeper reflection image of the crust in the Sea of Marmara. We show that choosing an appropriate processing sequence for different sources and acquisition geometries makes it possible to obtain an enhanced image of different targets such as faults, basins with several seconds of sedimentary infill, lower crust and Moho structure. Along selected lines reflected events from the top of lower crust and the Moho boundary (7 to 12 seconds two-way time) have been identified and will contribute together with wide-angle data recorded at fixed receivers (OBS and land stations) to a joint structural and velocity model at crustal scale. Improved images shed light on the tectonic evolution of the Marmara Sea at crustal scale and contribute to its discussion in terms of structure and earthquake activity.

Seismic study of the Mesozoic carbonate basement around Mt. Somma Vesuvius, Italy

NASA Astrophysics Data System (ADS)

Bruno, Pier Paolo G.; Cippitelli, Giuseppe; Rapolla, Antonio

1998-09-01

Fifteen seismic reflection lines from AGIP surveys, in and around the Campanian Plain and Mt. Somma-Vesuvius (south Italy) have been interpreted. The attention has been focused to the horizon pertinent to the top of the Mesozoic carbonate sequence and the Quaternary faults dissecting it. As a matter of fact, both are very important elements for understanding the origin of the volcanic activity in the area, that often in the past, has been the topic of debates not supported by reliable data. In the study area, referring to the depth of the carbonate basement, comparison between the result achieved by the seismic prospecting and previous gravity studies has been made. It shows coherence in some areas but large discrepancy within others. Near the town of S. Anastasia, the gravity and seismic depth estimates differ as much as 1000 m or more. Furthermore, the seismic data show that the source of the greatest volcanic eruption in the area (the so-called `Campanian Ignimbrite') is probably not located in the Acerra depression, as suggested by other authors. A main NE-SW fault directed toward Vesuvius, considered as playing a primary role on volcanogenetic processes and previously recognised only offshore by marine seismic survey, has been now identified also inland using this new seismic information. The results presented here strengthen the hypothesis that Mt. Vesuvius is located at the crossing point of two regional Quaternary sets of fault heading NW-SE and NE-SW.

Archive of digital boomer seismic reflection data collected offshore east-central Florida during USGS cruise 00FGS01, July 14-22, 2000

USGS Publications Warehouse

Subino, Janice A.; Dadisman, Shawn V.; Wiese, Dana S.; Calderon, Karynna; Phelps, Daniel C.

2009-01-01

In July of 2000, the U.S. Geological Survey (USGS), in cooperation with the Florida Geological Survey (FGS), conducted a geophysical survey of the Atlantic Ocean offshore Florida's east coast from Brevard County to northern Martin County. This report serves as an archive of unprocessed digital boomer seismic reflection data, trackline maps, navigation files, Geographic Information System (GIS) information, digital and handwritten Field Activity Collection System (FACS) logs, and Federal Geographic Data Committee (FGDC) metadata. A filtered and gained (a relative increase in signal amplitude) digital image of each seismic profile is also provided. Refer to the Acronyms page for expansions of all acronyms and abbreviations used in this report. The archived trace data are in standard Society of Exploration Geophysicists (SEG) SEG-Y format (Barry and others, 1975) and may be downloaded and processed with commercial or public domain software such as Seismic Unix (SU) (Cohen and Stockwell, 2005). Example SU processing scripts and USGS Software for viewing the SEG-Y files (Zihlman, 1992) are also provided. The USGS St. Petersburg Coastal and Marine Science Center assigns a unique identifier to each cruise or field activity. For example, 00FGS01 tells us the data were collected in 2000 for cooperative work with the Florida Geological Survey (FGS) and the data were collected during the first field activity for that study in that calendar year. Refer to http://walrus.wr.usgs.gov/infobank/programs/html/definition/activity.html for a detailed description of the method used to assign the field activity ID. The boomer plate is an acoustic energy source that consists of capacitors charged to a high voltage and discharged through a transducer in the water. The transducer is towed on a sled floating on the water surface and when discharged, emits a short acoustic pulse, or shot, which propagates through the water, sediment column, or rock beneath. The acoustic energy is reflected at density boundaries (such as the seafloor, sediment, or rock layers beneath the seafloor), detected by the receiver, and recorded by a PC-based seismic acquisition system. This process is repeated at timed intervals (for example, 0.5 s) and recorded for specific intervals of time (for example, 100 ms). In this way, a two-dimensional (2D) vertical profile of the shallow geologic structure beneath the ship track is produced. Figure 1 displays the acquisition geometry. Refer to table 1 for a summary of acquisition parameters. The unprocessed seismic data are stored in SEG-Y format (Barry and others, 1975). For a detailed description of the data format, refer to the SEG-Y Format page. See the How To Download SEG-Y Data page for download instructions. The printable profiles provided are GIF images that were filtered and gained using Seismic Unix software. Refer to the Software page for details about the processing and examples of the processing scripts. The printable profiles can be viewed from the Profiles page or from links located on the trackline maps. To view the trackline maps and navigation files, and for more information about these items, see the Navigation page. Detailed information about the navigation system used can be found in table 1. Of a total record length of 200 ms, only the upper 100 ms of each profile are displayed because no useful information was observed deeper in the sections. A 10 ms deep water delay appears on lines b57-b63 and sl2-sl28. No digital data were collected for line sl6. However, line sl6r is a second attempt to collect digital data for this line. Digital data and 500-shot-interval location navigation are not available for the last 1,161 shots of line sl26 due to an equipment malfunction.

Seismic reflection study of Flathead Lake, Montana

USGS Publications Warehouse

Wold, Richard J.

1982-01-01

A seismic reflection survey of Flathead Lake, Montana, was carried out in 1970 to study the geologic structure underlying the lake. Approximately 200 km of track lines were surveyed resulting in about 140 km of useable data (Fig. 1). A one cu. in. air gun was used as the energy source. Navigation was by a series of theodolite sitings of the boat from pairs of shore-based control points. 

Interferometric imaging of crustal structure from wide-angle multicomponent OBS-airgun data

NASA Astrophysics Data System (ADS)

Shiraishi, K.; Fujie, G.; Sato, T.; Abe, S.; Asakawa, E.; Kodaira, S.

2015-12-01

In wide-angle seismic surveys with ocean bottom seismograph (OBS) and airgun, surface-related multiple reflections and upgoing P-to-S conversions are frequently observed. We applied two interferometric imaging methods to the multicomponent OBS data in order to highly utilize seismic signals for subsurface imaging.First, seismic interferometry (SI) is applied to vertical component in order to obtain reflection profile with multiple reflections. By correlating seismic traces on common receiver records, pseudo seismic data are generated with virtual sources and receivers located on all original shot positions. We adopt the deconvolution SI because source and receiver spectra can be canceled by spectral division. Consequently, gapless reflection images from just below the seafloor to the deeper are obtained.Second, receiver function (RF) imaging is applied to multicomponent OBS data in order to image P-to-S conversion boundary. Though RF is commonly applied to teleseismic data, our purpose is to extract upgoing PS converted waves from wide-angle OBS data. The RF traces are synthesized by deconvolution of radial and vertical components at same OBS location for each shot. Final section obtained by stacking RF traces shows the PS conversion boundaries beneath OBSs. Then, Vp/Vs ratio can be estimated by comparing one-way traveltime delay with two-way traveltime of P wave reflections.We applied these methods to field data sets; (a) 175 km survey in Nankai trough subduction zone using 71 OBSs with from 1 km to 10 km intervals and 878 shots with 200 m interval, and (b) 237 km survey in northwest pacific ocean with almost flat layers before subduction using 25 OBSs with 6km interval and 1188 shots with 200 m interval. In our study, SI imaging with multiple reflections is highly applicable to OBS data even in a complex geological setting, and PS conversion boundary is well imaged by RF imaging and Vp/Vs ratio distribution in sediment is estimated in case of simple structure.

Seismic reflection imaging with conventional and unconventional sources

NASA Astrophysics Data System (ADS)

Quiros Ugalde, Diego Alonso

This manuscript reports the results of research using both conventional and unconventional energy sources as well as conventional and unconventional analysis to image crustal structure using reflected seismic waves. The work presented here includes the use of explosions to investigate the Taiwanese lithosphere, the use of 'noise' from railroads to investigate the shallow subsurface of the Rio Grande rift, and the use of microearthquakes to image subsurface structure near an active fault zone within the Appalachian mountains. Chapter 1 uses recordings from the land refraction and wide-angle reflection component of the Taiwan Integrated Geodynamic Research (TAIGER) project. The most prominent reflection feature imaged by these surveys is an anomalously strong reflector found in northeastern Taiwan. The goal of this chapter is to analyze the TAIGER recordings and to place the reflector into a geologic framework that fits with the modern tectonic kinematics of the region. Chapter 2 uses railroad traffic as a source for reflection profiling within the Rio Grande rift. Here the railroad recordings are treated in an analogous way to Vibroseis recordings. These results suggest that railroad noise in general can be a valuable new tool in imaging and characterizing the shallow subsurface in environmental and geotechnical studies. In chapters 3 and 4, earthquakes serve as the seismic imaging source. In these studies the methodology of Vertical Seismic Profiling (VSP) is borrowed from the oil and gas industry to develop reflection images. In chapter 3, a single earthquake is used to probe a small area beneath Waterboro, Maine. In chapter 4, the same method is applied to multiple earthquakes to take advantage of the increased redundancy that results from multiple events illuminating the same structure. The latter study demonstrates how dense arrays can be a powerful new tool for delineating, and monitoring temporal changes of deep structure in areas characterized by significant seismic activity.

Terahertz reflection imaging using Kirchhoff migration.

PubMed

Dorney, T D; Johnson, J L; Van Rudd, J; Baraniuk, R G; Symes, W W; Mittleman, D M

2001-10-01

We describe a new imaging method that uses single-cycle pulses of terahertz (THz) radiation. This technique emulates data-collection and image-processing procedures developed for geophysical prospecting and is made possible by the availability of fiber-coupled THz receiver antennas. We use a simple migration procedure to solve the inverse problem; this permits us to reconstruct the location and shape of targets. These results demonstrate the feasibility of the THz system as a test-bed for the exploration of new seismic processing methods involving complex model systems.

Land 3D-seismic data: Preprocessing quality control utilizing survey design specifications, noise properties, normal moveout, first breaks, and offset

USGS Publications Warehouse

Raef, A.

2009-01-01

The recent proliferation of the 3D reflection seismic method into the near-surface area of geophysical applications, especially in response to the emergence of the need to comprehensively characterize and monitor near-surface carbon dioxide sequestration in shallow saline aquifers around the world, justifies the emphasis on cost-effective and robust quality control and assurance (QC/QA) workflow of 3D seismic data preprocessing that is suitable for near-surface applications. The main purpose of our seismic data preprocessing QC is to enable the use of appropriate header information, data that are free of noise-dominated traces, and/or flawed vertical stacking in subsequent processing steps. In this article, I provide an account of utilizing survey design specifications, noise properties, first breaks, and normal moveout for rapid and thorough graphical QC/QA diagnostics, which are easy to apply and efficient in the diagnosis of inconsistencies. A correlated vibroseis time-lapse 3D-seismic data set from a CO2-flood monitoring survey is used for demonstrating QC diagnostics. An important by-product of the QC workflow is establishing the number of layers for a refraction statics model in a data-driven graphical manner that capitalizes on the spatial coverage of the 3D seismic data. ?? China University of Geosciences (Wuhan) and Springer-Verlag GmbH 2009.

4-D High-Resolution Seismic Reflection Monitoring of Miscible CO2 Injected into a Carbonate Reservoir

DOE Office of Scientific and Technical Information (OSTI.GOV)

Richard D. Miller; Abdelmoneam E. Raef; Alan P. Byrnes

2007-06-30

The objective of this research project was to acquire, process, and interpret multiple high-resolution 3-D compressional wave and 2-D, 2-C shear wave seismic data in the hopes of observing changes in fluid characteristics in an oil field before, during, and after the miscible carbon dioxide (CO{sub 2}) flood that began around December 1, 2003, as part of the DOE-sponsored Class Revisit Project (DOE No.DE-AC26-00BC15124). Unique and key to this imaging activity is the high-resolution nature of the seismic data, minimal deployment design, and the temporal sampling throughout the flood. The 900-m-deep test reservoir is located in central Kansas oomoldic limestonesmore » of the Lansing-Kansas City Group, deposited on a shallow marine shelf in Pennsylvanian time. After 30 months of seismic monitoring, one baseline and eight monitor surveys clearly detected changes that appear consistent with movement of CO{sub 2} as modeled with fluid simulators and observed in production data. Attribute analysis was a very useful tool in enhancing changes in seismic character present, but difficult to interpret on time amplitude slices. Lessons learned from and tools/techniques developed during this project will allow high-resolution seismic imaging to be routinely applied to many CO{sub 2} injection programs in a large percentage of shallow carbonate oil fields in the midcontinent.« less

Redox-influenced seismic properties of upper-mantle olivine

NASA Astrophysics Data System (ADS)

Cline, C. J., II; Faul, U. H.; David, E. C.; Berry, A. J.; Jackson, I.

2018-03-01

Lateral variations of seismic wave speeds and attenuation (dissipation of strain energy) in the Earth’s upper mantle have the potential to map key characteristics such as temperature, major-element composition, melt fraction and water content. The inversion of these data into meaningful representations of physical properties requires a robust understanding of the micromechanical processes that affect the propagation of seismic waves. Structurally bound water (hydroxyl) is believed to affect seismic properties but this has yet to be experimentally quantified. Here we present a comprehensive low-frequency forced-oscillation assessment of the seismic properties of olivine as a function of water content within the under-saturated regime that is relevant to the Earth’s interior. Our results demonstrate that wave speeds and attenuation are in fact strikingly insensitive to water content. Rather, the redox conditions imposed by the choice of metal sleeving, and the associated defect chemistry, appear to have a substantial influence on the seismic properties. These findings suggest that elevated water contents are not responsible for low-velocity or high-attenuation structures in the upper mantle. Instead, the high attenuation observed in hydrous and oxidized regions of the upper mantle (such as above subduction zones) may reflect the prevailing oxygen fugacity. In addition, these data provide no support for the hypothesis whereby a sharp lithosphere–asthenosphere boundary is explained by enhanced grain boundary sliding in the presence of water.

Onshore-offshore seismic reflection profiling across the southern margin of the Sea of Japan: back-arc opening, shortening and active strike-slip deformation

NASA Astrophysics Data System (ADS)

Sato, Hiroshi; Ishiyama, Tatsuya; Kato, Naoko; Toda, Shigeru; Kawasaki, Shinji; Fujiwara, Akira; Tanaka, Yasuhisa; Abe, Susumu

2017-04-01

M7-class crustal earthquakes of overlying plate in subduction system have tendency to increase before megathrust earthquake events. Due to stress buildup by the upcoming Nankai Trough megathrust earthquake, SW Japan has being seismically active for last 20 years. In terms of the mitigation of earthquake and tsunami hazards, to construct seismogenic source fault models is first step for evaluating the strong ground motions and height of tsunamis. Since 2013, we performed intense seismic profiling in and around the southern part of the Sea of Japan. In 2016, a 180-km-long onshore -offshore seismic survey was carried out across the volcanic arc and back-arc basins (from Kurayoshi to the Yamato basin). Onshore section, CMP seismic reflection data were collected using four vibroseis trucks and fixed 1150 channel recorders. Offshore part we acquired the seismic reflection data using 1950 cu inch air-guns towing a 4-km-long streamer cable. We performed CMP reflection and refraction tomography analysis. Obtained seismic section portrays compressively deformed rifted continental crust and undeformed oceanic back-arc basin, reflecting the rheological features. These basic structures were formed during the opening of the Sea of Japan in early Miocene. The sub-horizontal Pliocene sediments unconformably cover the folded Miocene sediments. The opening and clock-wise rotation of SW Japan has been terminated at 15 Ma and contacted to the young Shikoku basin along the Nankai trough. Northward motion of Philippine Sea plate (PHS) and the high thermal regime in the Shikoku basin produced the strong resistance along the Nankai trough. The main shortening deformation observed in the seismic section has been formed this tectonic event. After the initiation of the subduction along the Nankai trough, the rate of shortening deformation was decreased and the folded strata were covered by sub-horizontal Pliocene sediments. The thrusting trending parallel to the arc has been continued from Pliocene to early Pleistocene along the limited fault system. The change in the direction of the motion of PHS at 1 Ma produced major change in stress regime from NS compression to EW compression in the back-arc. Following the change of stress regime, former reverse faults reactivated as strike-slip fault. Reuse of pre-existing faults are common, and crustal deformation concentrates relatively narrow zone in the back-arc failed rifts. Two-months after from our survey, Mw 6.2 Tottoriken-chubu earthquake occurred just beneath the onshore part of the seismic line. The source fault corresponds to the boundary of abrupt change in P-wave velocity, however there were no surface ruptures and distinctive geologic faults. The bottom of seismogenic layer corresponds to TWT 4.5 sec., which is almost the top horizon of reflective middle crust.

Vertical Cable Seismic Survey for SMS exploration

NASA Astrophysics Data System (ADS)

Asakawa, Eiichi; Murakami, Fumitoshi; Tsukahara, Hotoshi; Mizohata, Shigeharu

2014-05-01

The Vertical Cable Seismic (VCS) survey is one of the reflection seismic methods. It uses hydrophone arrays vertically moored from the seafloor to record acoustic waves generated by sea-surface, deep-towed or ocean bottom sources. Analyzing the reflections from the sub-seabed, we could look into the subsurface structure. Because the VCS is an efficient high-resolution 3D seismic survey method for a spatially-bounded area, we proposed it for the SMS survey tool development program that the Ministry of Education, Culture, Sports, Science and Technology (MEXT) started in 2009. We have been developing the VCS survey system, including not only data acquisition hardware but data processing and analysis technique. We carried out several VCS surveys combining with surface towed source, deep towed source and ocean bottom source. The water depths of these surveys are from 100m up to 2100 m. Through these experiments, our VCS data acquisition system has been also completed. But the data processing techniques are still on the way. One of the most critical issues is the positioning in the water. The uncertainty in the positions of the source and of the hydrophones in water degraded the quality of subsurface image. GPS navigation system is available on sea surface, but in case of deep-towed source or ocean bottom source, the accuracy of shot position with SSBL/USBL is not sufficient for the very high-resolution imaging. We have developed a new approach to determine the positions in water using the travel time data from the source to VCS hydrophones. In 2013, we have carried out the second VCS survey using the surface-towed high-voltage sparker and ocean bottom source in the Izena Cauldron, which is one of the most promising SMS areas around Japan. The positions of ocean bottom source estimated by this method are consistent with the VCS field records. The VCS data with the sparker have been processed with 3D PSTM. It gives the very high resolution 3D volume deeper than two hundred meters. Our VCS system has been demonstrated as a promising survey tool for the SMS exploration.

Trade-off of Elastic Structure and Q in Interpretations of Seismic Attenuation

NASA Astrophysics Data System (ADS)

Deng, Wubing; Morozov, Igor B.

2017-10-01

The quality factor Q is an important phenomenological parameter measured from seismic or laboratory seismic data and representing wave-energy dissipation rate. However, depending on the types of measurements and models or assumptions about the elastic structure, several types of Qs exist, such as intrinsic and scattering Qs, coda Q, and apparent Qs observed from wavefield fluctuations. We consider three general types of elastic structures that are commonly encountered in seismology: (1) shapes and dimensions of rock specimens in laboratory studies, (2) geometric spreading or scattering in body-, surface- and coda-wave studies, and (3) reflectivity on fine layering in reflection seismic studies. For each of these types, the measured Q strongly trades off with the (inherently limited) knowledge about the respective elastic structure. For the third of the above types, the trade-off is examined quantitatively in this paper. For a layered sequence of reflectors (e.g., an oil or gas reservoir or a hydrothermal zone), reflection amplitudes and phases vary with frequency, which is analogous to a reflection from a contrast in attenuation. We demonstrate a quantitative equivalence between phase-shifted reflections from anelastic zones and reflections from elastic layering. Reflections from the top of an elastic layer followed by weaker reflections from its bottom can appear as resulting from a low Q within or above this layer. This apparent Q can be frequency-independent or -dependent, according to the pattern of thin layering. Due to the layering, the interpreted Q can be positive or negative, and it can depend on source-receiver offsets. Therefore, estimating Q values from frequency-dependent or phase-shifted reflection amplitudes always requires additional geologic or rock-physics constraints, such as sparseness and/or randomness of reflectors, the absence of attenuation in certain layers, or specific physical mechanisms of attenuation. Similar conclusions about the necessity of extremely detailed models of the elastic structure apply to other types of Q measurements.

Seismic Oceanography in the Tyrrhenian Sea: Thermohaline Staircases, Eddies, and Internal Waves

NASA Astrophysics Data System (ADS)

Buffett, G. G.; Krahmann, G.; Klaeschen, D.; Schroeder, K.; Sallarès, V.; Papenberg, C.; Ranero, C. R.; Zitellini, N.

2017-11-01

We use seismic oceanography to document and analyze oceanic thermohaline fine structure across the Tyrrhenian Sea. Multichannel seismic (MCS) reflection data were acquired during the MEDiterranean OCcidental survey in April-May 2010. We deployed along-track expendable bathythermograph probes simultaneous with MCS acquisition. At nearby locations we gathered conductivity-temperature-depth data. An autonomous glider survey added in situ measurements of oceanic properties. The seismic reflectivity clearly delineates thermohaline fine structure in the upper 2,000 m of the water column, indicating the interfaces between Atlantic Water/Winter Intermediate Water, Levantine Intermediate Water, and Tyrrhenian Deep Water. We observe the Northern Tyrrhenian Anticyclone, a near-surface mesoscale eddy, plus laterally and vertically extensive thermohaline staircases. Using MCS, we are able to fully image the anticyclone to a depth of 800 m and to confirm the horizontal continuity of the thermohaline staircases of more than 200 km. The staircases show the clearest step-like gradients in the center of the basin while they become more diffuse toward the periphery and bottom, where impedance gradients become too small to be detected by MCS. We quantify the internal wave field and find it to be weak in the region of the eddy and in the center of the staircases, while it is stronger near the coastlines. Our results indicate this is because of the influence of the boundary currents, which disrupt the formation of staircases by preventing diffusive convection. In the interior of the basin, the staircases are clearer and the internal wave field weaker, suggesting that other mixing processes such as double diffusion prevail.

Influence of fluvial processes on the quaternary geologic framework of the continental shelf, North Carolina, USA

USGS Publications Warehouse

Boss, S.K.; Hoffman, C.W.; Cooper, B.

2002-01-01

Digital, single-channel, high-resolution seismic reflection profiles were acquired from the insular continental shelf of North Carolina, USA along a data grid extending from Oregon Inlet northward 48 km to Duck, North Carolina and from the nearshore zone seaward approximately 28 km (total surveyed area= 1334 km2). These data were processed and interpreted to delineate principal reflecting horizons and develop a three-dimensional seismic stratigraphic framework for the continental shelf that was compared to stratigraphic data from the shoreward back-barrier (estuarine) and barrier island system. Six principal reflecting horizons (designated R0 through R5) were present within the upper 60 m of the shelf stratigraphic succession. Three-dimensional mapping of reflector R1 demonstrated its origin from fluvial incision of the continental shelf during an episode (or episodes) of lowered sea-level. Fluvial processes during development of reflector R1 were responsible for extensive reworking and re-deposition of sediment throughout most of the northern half of the study area. Five seismic stratigraphic units (designated S1 through S5) were tentatively correlated with depositional sequences previously identified from the North Carolina back-barrier (estuarine) and barrier island system. These five stratigraphic units span the Quaternary Period (S1 = early Holocene; S2 = 51-78 ka; S3 = 330-530 ka; S4 = 1.1-1.8 Ma; S5 = earliest Pleistocene). Unit S1 is composed of fine-grained fluvial/estuarine sediment that back-filled incised streams during early Holocene sea-level rise. The four other stratigraphic units (S2-S5) display tabular depositional geometries, low total relief, and thicken toward the east-southeast as their basal reflectors dip gently between 0.41 m km-1 (0.02??) and 0.54 m km-1 (0.03??). Knowledge of the three-dimensional subsurface stratigraphic architecture of the continental shelf enhances understanding of the development of shelf depositional successions and provides a framework for development of better Quaternary sea-level data, especially offshore North Carolina where such data are sparse. ?? 2002 Elsevier Science B.V. All rights reserved.

Pre-stack depth Migration imaging of the Hellenic Subduction Zone

NASA Astrophysics Data System (ADS)

Hussni, S. G.; Becel, A.; Schenini, L.; Laigle, M.; Dessa, J. X.; Galve, A.; Vitard, C.

2017-12-01

In 365 AD, a major M>8-tsunamignic earthquake occurred along the southwestern segment of the Hellenic subduction zone. Although this is the largest seismic event ever reported in Europe, some fundamental questions remain regarding the deep geometry of the interplate megathrust, as well as other faults within the overriding plate potentially connected to it. The main objective here is to image those deep structures, whose depths range between 15 and 45 km, using leading edge seismic reflection equipment. To this end, a 210-km-long multichannel seismic profile was acquired with the 8 km-long streamer and the 6600 cu.in source of R/V Marcus Langseth. This was realized at the end of 2015, during the SISMED cruise. This survey was made possible through a collective effort gathering labs (Géoazur, LDEO, ISTEP, ENS-Paris, EOST, LDO, Dpt. Geosciences of Pau Univ). A preliminary processing sequence has first been applied using Geovation software of CGG, which yielded a post-stack time migration of collected data, as well as pre-stack time migration obtained with a model derived from velocity analyses. Using Paradigm software, a pre-stack depth migration was subsequently carried out. This step required some tuning in the pre-processing sequence in order to improve multiple removal, noise suppression and to better reveal the true geometry of reflectors in depth. This iteration of pre-processing included, the use of parabolic Radon transform, FK filtering and time variant band pass filtering. An initial velocity model was built using depth-converted RMS velocities obtained from SISMED data for the sedimentary layer, complemented at depth with a smooth version of the tomographic velocities derived from coincident wide-angle data acquired during the 2012-ULYSSE survey. Then, we performed a Kirchhoff Pre-stack depth migration with traveltimes calculated using the Eikonal equation. Velocity model were then tuned through residual velocity analyses to flatten reflections in common reflection point gathers. These new results improve the imaging of deep reflectors and even reveal some new features. We will present this work, a comparison with our previously obtained post-stack time migration, as well as some insights into the new geological structures revealed by the depth imaging.

Seismic images of the Brooks Range fold and thrust belt, Arctic Alaska, from an integrated seismic reflection/refraction experiment

USGS Publications Warehouse

Levander, A.; Fuis, G.S.; Wissinger, E.S.; Lutter, W.J.; Oldow, J.S.; Moore, Thomas E.

1994-01-01

We describe results of an integrated seismic reflection/refraction experiment across the Brooks Range and flanking geologic provinces in Arctic Alaska. The seismic acquisition was unusual in that reflection and refraction data were collected simultaneously with a 700 channel seismograph system deployed numerous times along a 315 km profile. Shot records show continuous Moho reflections from 0-180 km offset, as well as numerous upper- and mid-crustal wide-angle events. Single and low-fold near-vertical incidence common midpoint (CMP) reflection images show complex upper- and middle-crustal structure across the range from the unmetamorphosed Endicott Mountains allochthon (EMA) in the north, to the metamorphic belts in the south. Lower-crustal and Moho reflections are visible across the entire reflection profile. Travel-time inversion of PmP arrivals shows that the Moho, at 33 km depth beneath the North Slope foothills, deepens abruptly beneath the EMA to a maximum of 46 km, and then shallows southward to 35 km at the southern edge of the range. Two zones of upper- and middle-crustal reflections underlie the northern Brooks Range above ~ 12-15 km depth. The upper zone, interpreted as the base of the EMA, lies at a maximum depth of 6 km and extends over 50 km from the range front to the north central Brooks Range where the base of the EMA outcrops above the metasedimentary rocks exposed in the Doonerak window. We interpret the base of the lower zone, at ~ 12 km depth, to be from carbonate rocks above the master detachment upon which the Brooks Range formed. The seismic data suggest that the master detachment is connected to the faults in the EMA by several ramps. In the highly metamorphosed terranes south of the Doonerak window, the CMP section shows numerous south-dipping events which we interpret as a crustal scale duplex involving the Doonerak window rocks. The basal detachment reflections can be traced approximately 100 km, and dip southward from about 10-12 km near the range front, to 14-18 km beneath the Doonerak window, to 26-28 km beneath the metamorphic belts in the central Brooks Range. The section documents middle- and lower-crustal involvement in the formation of the Brooks Range. ?? 1994.

PICTURES (Pisagua/Iquique Crustal Tomography to Understand the Region of the Earthquake Source): seismic imaging of the source region of the April 1, 2014 Mw 8.2 earthquake offshore northern Chile

NASA Astrophysics Data System (ADS)

Trehu, A. M.

2017-12-01

The 2014 event partially filled a well-recognized seismic gap that had not experienced a large earthquake since a pair of devastating M9 events in 1868 and 1877. The rupture sequence was marked by an unusually long and distinct precursory period that was well recorded by onshore seismic and geodetic instruments of the Integrated Plate Boundary Observatory Chile (IPOC). The pattern of foreshock activity, which defined a "classic" Mogi donut, is correlated with a circular residual gravity high that surrounds the patch of greatest slip during the main shock. Aftershocks generally propagated to the south and stopped in a region of relatively low pre-earthquake coupling. The remaining nearly 300-km long seismic gap is correlated with a distinct forearc residual gravity high. The correlation between the pre-, syn- and post-earthquake deformation patterns and the residual gravity anomalies indicates that crustal structure affects the distribution of seismic and aseismic deformation in response to plate convergence. Because the non-uniqueness inherent in modeling gravity data does not allow for a detailed geologic interpretation of the correlation between structure and slip, we conducted an ambitious seismic experiment using the R/V Marcus Langseth to acquire 5000 km of multichannel seismic seismic data using an 8-12.5-km long streamer and a 6600 cubic inch tuned air-gun array. The 45000 shots were also recorded on 70 ocean-bottom and 50 land-based seismometers. Shipboard analysis of the data indicates that the Moho of the Nazca plate is well imaged west of the trench, that deformation is distributed throughout the outer 10 km of the accretionary wedge as the rough topography of the Nazca plate is subducted, and that a reflection tentatively interpreted to be the plate boundary can be imaged continuously from the trench to the coast on at least one transect across the margin. Post-cruise data analysis is underway to process the MCS data using various techniques to determine along-strike continuity of plate boundary reflectivity and to use OBS and onshore large-aperture data to obtain high-resolution models of the crustal velocity structure of the subducting and overriding plates. The PICTURES Science Team incudes investigators in the US, Chile, Germany, France and the UK.

Seismic imaging of small horizontal scale structures of the shallow thermocline on the western Brittany continental shelf (North-East Atlantic)

NASA Astrophysics Data System (ADS)

Piete, H.; Marié, L.; Marsset, B.; Gutscher, M.

2012-12-01

The recent development of the seismic oceanography technique has made possible the imaging of a variety of deep oceanographic structures (Holbrook et al., 2003); however, until now this method has remained ill suited for the study of shallow (<200m) thermohaline structures. This difficulty is partly due to the fact that both important seismic trace lengths and large offsets that characterize the acoustic receiver device (seismic streamer) cause significant signal attenuations through an induced antenna filter effect. Further difficulties are related to limitations of currently employed seismic sources, which do not conciliate 1- high power (essential to the imaging of weakly reflective structures in a noisy environment) and 2- spectral contents offering high vertical resolutions (relevant to the mapping of small vertical wavelength structures). In this study we defined and tested a new experimental seismic acquisition system capable of imaging the ~10 m thick seasonal thermocline on the western Brittany continental shelf. To accomplish this task, we pursued two complementary approaches: 1. Analysis of legacy seismic data (multi-channel seismic reflection profiles acquired on the East-Corsican margin, Bahamas Plateau and Gulf of Cadiz in various oceanographic environments) featuring reflectors at depths between 25 and 150 m, in order to identify and quantify the influence of acquisition parameters (seismic trace length, offsets, emission level and frequency content). 2. Incorporation of new oceanographic data acquired during the FROMVAR cruise (July 28th to August 10th 2010) on the western Brittany shelf in thermally stratified waters for use in the simulation of the seismic acquisition, in order to further define the optimal parameters for the system. Finally a 3D seismic system has emerged and was tested during the ASPEX scientific cruise led from June 17th to 19th 2012 across the western Brittany shelf. The device featured: i- four seismic streamers, each consisting of 6 traces at a spacing of 1.80 m; ii- a 1000 J SIG Sparker producing a 400 Hz signal with a 220 dB re 1μPa @1m level of emission, towed at a 8 m distance of the first seismic trace. This survey provided high lateral resolution images of the seasonal thermocline located at a 30 m depth with vertical displacements induced by internal waves. References Holbrook, W.S., Paramo, P., Pearse, S. and Schmitt, R.W., 2003. Thermohaline Fine Structure in an Oceanographic Front from Seismic Reflection Profiling. Science, 301(5634): 821.

Feasibility of the Scalable, Automated, Semipermanent Seismic Array (SASSA) to Monitor Possible Carbon Dioxide Migration

NASA Astrophysics Data System (ADS)

Livers, A. J.; Burnison, S. A.; Salako, O.; Barajas-Olalde, C.; Hamling, J. A.; Gorecki, C. D.

2016-12-01

The feasibility of monitoring potential carbon dioxide (CO2) migration in a reservoir using a sparse seismic array is being evaluated by the Energy & Environmental Research Center (EERC) at the Denbury Onshore LLC-operated Bell Creek oil field in Montana, which is undergoing commercial CO2 enhanced oil recovery (EOR). This new method may provide an economical means of continuously monitoring the CO2 plume edge and the CO2 reservoir boundaries and/or to interpret vertical or lateral out-of-reservoir CO2 migration. A 96-station scalable, automated, semipermanent seismic array (SASSA) was deployed in October 2015 to detect and track CO2 plume migration not by imaging, but by monitoring discrete source-receiver midpoints. Midpoints were strategically located within and around four injector-producer patterns covering approximately one square mile. Three-dimensional (3-D) geophysical ray tracing was used to determine surface receiver locations. Receivers used were FairfieldNodal Zland three-component, autonomous, battery-powered nodes. A GISCO ESS850 accelerated weight drop source located in a secure structure was remotely fired on a weekly basis for one calendar year, including a two-month period prior to initiation of CO2 injection to establish a baseline. Fifty shots were fired one day each week to facilitate increased signal-to-noise through novel receiver domain processing and vertical stacking. Receiver domain processing allowed for individualization of processing parameters to maximize signal enhancement and noise attenuation. Reflection events in the processed SASSA data correlate well to 3-D surface survey data collected in the field. Preliminary time-lapse data results for several individual SASSA receivers show a phase shift in the reflection events below the reservoir after injection, suggesting possible migration of the CO2 in the reservoir to the corresponding midpoint locations. This work is supported by the U.S. Department of Energy National Energy Technology Laboratory under Award No. FE0012665.

Reducing the uncertainty in the fidelity of seismic imaging results

NASA Astrophysics Data System (ADS)

Zhou, H. W.; Zou, Z.

2017-12-01

A key aspect in geoscientific inversion is quantifying the quality of the results. In seismic imaging, we must quantify the uncertainty of every imaging result based on field data, because data noise and methodology limitations may produce artifacts. Detection of artifacts is therefore an important aspect in uncertainty quantification in geoscientific inversion. Quantifying the uncertainty of seismic imaging solutions means assessing their fidelity, which defines the truthfulness of the imaged targets in terms of their resolution, position error and artifact. Key challenges to achieving the fidelity of seismic imaging include: (1) Difficulty to tell signal from artifact and noise; (2) Limitations in signal-to-noise ratio and seismic illumination; and (3) The multi-scale nature of the data space and model space. Most seismic imaging studies of the Earth's crust and mantle have employed inversion or modeling approaches. Though they are in opposite directions of mapping between the data space and model space, both inversion and modeling seek the best model to minimize the misfit in the data space, which unfortunately is not the output space. The fact that the selection and uncertainty of the output model are not judged in the output space has exacerbated the nonuniqueness problem for inversion and modeling. In contrast, the practice in exploration seismology has long established a two-fold approach of seismic imaging: Using velocity modeling building to establish the long-wavelength reference velocity models, and using seismic migration to map the short-wavelength reflectivity structures. Most interestingly, seismic migration maps the data into an output space called imaging space, where the output reflection images of the subsurface are formed based on an imaging condition. A good example is the reverse time migration, which seeks the reflectivity image as the best fit in the image space between the extrapolation of time-reversed waveform data and the prediction based on estimated velocity model and source parameters. I will illustrate the benefits of deciding the best output result in the output space for inversion, using examples from seismic imaging.

Unconsolidated sediments at the bottom of Lake Vostok from seismic data

USGS Publications Warehouse

Filina, I.; Lukin, V.; Masolov, V.; Blankenship, D.

2007-01-01

Seismic soundings of Lake Vostok have been performed by the Polar Marine Geological Research Expedition in collaboration with the Russian Antarctic Expedition since the early 1990s. The seismograms recorded show at least two relatively closely spaced reflections associated with the lake bottom. These were initially interpreted as boundaries of a layer of unconsolidated sediments at the bottom of the lake. A more recent interpretation suggests that the observed reflections are side echoes from the rough lake bottom, and that there are no unconsolidated sediments at the bottom of the lake. The major goal of this paper is to reveal the nature of those reflections by testing three hypotheses of their origin. The results show that some of the reflections, but not all of them, are consistent with the hypothesis of a non-flat lake bottom along the source-receiver line (2D case). The reflections were also evaluated as side echoes from an adjacent sloping interface, but these tests implied unreasonably steep slopes (at least 8 degrees) at the lake bottom. The hypothesis that is the most compatible with seismic data is the presence of a widespread layer of unconsolidated sediments at the bottom of Lake Vostok. The modeling suggests the presence of a two hundred meter thick sedimentary layer with a seismic velocity of 1700 -1900 m/sec in the southern and middle parts of the lake. The sedimentary layer thickens in the northern basin to ~350 m

Alternative Energy Sources in Seismic Methods

NASA Astrophysics Data System (ADS)

Tün, Muammer; Pekkan, Emrah; Mutlu, Sunay; Ecevitoğlu, Berkan

2015-04-01

When the suitability of a settlement area is investigated, soil-amplification, liquefaction and fault-related hazards should be defined, and the associated risks should be clarified. For this reason, soil engineering parameters and subsurface geological structure of a new settlement area should be investigated. Especially, faults covered with quaternary alluvium; thicknesses, shear-wave velocities and geometry of subsurface sediments could lead to a soil amplification during an earthquake. Likewise, changes in shear-wave velocities along the basin are also very important. Geophysical methods can be used to determine the local soil properties. In this study, use of alternative seismic energy sources when implementing seismic reflection, seismic refraction and MASW methods in the residential areas of Eskisehir/Turkey, were discussed. Our home developed seismic energy source, EAPSG (Electrically-Fired-PS-Gun), capable to shoot 2x24 magnum shotgun cartridges at once to generate P and S waves; and our home developed WD-500 (500 kg Weight Drop) seismic energy source, mounted on a truck, were developed under a scientific research project of Anadolu University. We were able to reach up to penetration depths of 1200 m for EAPSG, and 800 m for WD-500 in our seismic reflection surveys. WD-500 seismic energy source was also used to perform MASW surveys, using 24-channel, 10 m apart, 4.5 Hz vertical geophone configuration. We were able to reach 100 m of penetration depth in MASW surveys.

Seismic reflection results of the GYRE 1997 Cruise at the Bryant Canyon of the Louisiana Gulf Coast

USGS Publications Warehouse

Nealon, Jeffrey W.; Dillon, William P.; Twichell, David

2000-01-01

The TexasLouisiana continental slope is one of the few remaining frontiers for hydrocarbon exploration within the US Exclusive Economic Zone.  This area has a complex seafloor morphology and highly discontinuous shallow stratigraphy that are the result of deformation by the highly mobile Louann salt that underlies much of this margin shoreward of the Sigsbee Escarpment.Gas hydrates exist both on the sea floor and at depth throughout the gas hydrate stability zone which extends to several hundred meters beneath the sea floor at greater water depths.  Multibeam bathymetry, GLORIA sidescan sonar imagery, and site-specific studies have identified the presence of faults, mass-wasting deposits, variable sediment types, and gas hydrates exposed on the seafloor.  The expression of these features on the seafloor suggests a tectonically active area.  The distribution of these different processes and their relation to the subsurface stratigraphy and tectonic setting are not well understood, yet an understanding of these issues is essential as exploration extends into this deep-water area.To address the questions of surficial processes and their connection with deeper structures underlying this continental margin, a three-week cruise was conducted by the USGS in April, 1997 aboard the RV GYRE. The study area focussed on Bryant Canyon, a former submarine canyon, through which turbidity currents transported sands from a shelf-edge delta upslope of the study area to the Bryant Fan on the rise seaward of the base of the slope.  The cruise was divided into two parts.  The first part was devoted to collecting seismic-reflection profiles across parts of the canyon system to define the shallow stratigraphy and to determine the presence and distribution of gas hydrates in this area.  Approximately 555 km of single-channel seismic-reflection data were collected during this first part of the cruise.  A track map showing the locations of the profiles, low-resolution images of the profiles, and the SEG-Y format of these data are all presented on this CD-ROM.  During the second part of the cruise, 38 piston cores were collected to describe the shallow subsurface facies of the study area. The coring data will be availible in an open file report to be published by Hans Nelson.We acknowledge the U.S. Department of Energy, Office of Fossil Energy, which provided partial support for seismic data gathering and processing.

Seismic Reflection Imaging of Detachment Faulting at 13°N on the Mid-Atlantic Ridge

NASA Astrophysics Data System (ADS)

Falder, M.; Reston, T. J.; Peirce, C.; Simão, N.; MacLeod, C. J.; Searle, R. C.

2016-12-01

The observation of domal corrugated surfaces at slow spreading ridges less than two decades ago, has dramatically challenged our understanding of seafloor spreading. These `oceanic core complexes' are believed to be caused by large-scale detachment faults which accommodate plate separation during periods when melt supply is low or absent entirely. Despite increasing recognition of their importance, the mechanics of, and interactions between, detachment faults at OCCs is not well understood. In Jan-Feb 2016, seismic reflection and refraction data were acquired across the 13N OCCs. The twelve-airgun array seismic source was recorded by a 3000m-long streamer, with shots fired with the full array at either 20 s intervals, or with half the array in a "flip flop" fashion every 10 s. A shorter firing rate results in significantly less spatial aliasing and enhances the performance of the F-K domain filtering. Here we present preliminary seismic reflection images of the 13N region. The currently active 13° 20'N detachment fault is imaged continuing downwards from the smooth fault plane exposed at the seabed. Away from the fault, and between the two OCCs in the area, fewer subsurface structures are observed, which may either represent an actual lack of sharp acoustic contrasts or be as a result of the challenging imaging conditions. Acoustic energy scattered by rough bathymetry both within and out of plane of section is the main challenge of seismic reflection imaging in this area and various strategies are being investigated for its attenuation, including prediction based on high-resolution bathymetry acquired.

Evaluating geophysical lithology determination methods in the central offshore Nile Delta, Egypt

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nada, H.; Shrallow, J.

1994-12-31

Two post stack and one prestack geophysical techniques were used to extract lithology and fluid information from seismic data. The purpose of this work was to evaluate the effectiveness of such methods in helping to find more hydrocarbons and reduce exploration risk in Egypt`s Nile Delta. Amplitude Variations with Offset (AVO) was used as a direct hydrocarbon indicator. CDP gathers were sorted into common angle gathers. The angle traces from 0--10 degrees were stacked to form a near angle stack and those from 30--40 degrees were stacked to form a far angle stack. Comparison of the far and near anglemore » stacks indicate areas which have seismic responses that match gas bearing sand models in the Pliocene and Messinian. Seismic Sequence Attribute mapping was used to measure the reflectivity of a seismic sequence. The specific sequence attribute measured in this study was the Maximum Absolute Amplitude of the seismic reflections within a sequence. Post stack seismic inversion was used to convert zero phase final migrated data to pseudo acoustic impedance data to interpret lithology from seismic data. All three methods are useful in the Nile Delta for identifying sand prone areas, but only AVO can be used to detect fluid content.« less

Volcanism offshore of Vesuvius Volcano in Naples Bay

USGS Publications Warehouse

Milia, A.; Mirabile, L.; Torrente, M.M.; Dvorak, J.J.

1998-01-01

High-resolution seismic reflection data are used to identify structural features in Naples Bay near Vesuvius Volcano. Several buried seismic units with reflection-free interiors are probably volcanic deposits erupted during and since the formation of the breached crater of Monte Somma Volcano, which preceded the growth of Vesuvius. The presumed undersea volcanic deposits are limited in extent; thus, stratigraphie relationships cannot be established among them. Other features revealed by our data include (a) the warping of lowstand marine deposits by undersea cryptodomes located approximately 10 km from the summit of Vesuvius, (b) a succession of normal step faults that record seaward collapse of the volcano, and (c) a small undersea slump in the uppermost marine deposits of Naples Bay, which may be the result of nue??e ardentes that entered the sea during a major eruption of Vesuvius in 1631. Detection of these undersea features illustrates some capabilities of making detailed seismic reflection profiles across undersea volcanoes.

Retrieval of P wave Basin Response from Autocorrelation of Seismic Noise-Jakarta, Indonesia

NASA Astrophysics Data System (ADS)

Saygin, E.; Cummins, P. R.; Lumley, D. E.

2016-12-01

Indonesia's capital city, Jakarta, is home to a very large (over 10 million), vulnerable population and is proximate to known active faults, as well as to the subduction of Australian plate, which has a megathrust at abut 300 km distance, as well as intraslab seismicity extending to directly beneath the city. It is also located in a basin filled with a thick layer of unconsolidated and poorly consolidated sediment, which increases the seismic hazard the city is facing. Therefore, the information on the seismic velocity structure of the basin is crucial for increasing our knowledge of the seismic risk. We undertook a passive deployment of broadband seismographs throughout the city over a 3-month interval in 2013-2014, recording ambient seismic noise at over 90 sites for intervals of 1 month or more. Here we consider autocorrelations of the vertical component of the continuously recorded seismic wavefield across this dense network to image the shallow P wave velocity structure of Jakarta, Indonesia. Unlike the surface wave Green's functions used in ambient noise tomography, the vertical-component autocorrelograms are dominated by body wave energy that is potentially sensitive to sharp velocity contrasts, which makes them useful in seismic imaging. Results show autocorrelograms at different seismic stations with travel time variations that largely reflect changes in sediment thickness across the basin. We also confirm the validity our interpretation of the observed autocorrelation waveforms by conducting 2D finite difference full waveform numerical modeling for randomly distributed seismic sources to retrieve the reflection response through autocorrelation.

Seismic imaging for an ocean drilling site survey and its verification in the Izu rear arc

NASA Astrophysics Data System (ADS)

Yamashita, Mikiya; Takahashi, Narumi; Tamura, Yoshihiko; Miura, Seiichi; Kodaira, Shuichi

2018-01-01

To evaluate the crustal structure of a site proposed for International Ocean Discovery Program drilling, the Japan Agency for Marine-Earth Science and Technology carried out seismic surveys in the Izu rear arc between 2006 and 2008, using research vessels Kaiyo and Kairei. High-resolution dense grid surveys, consisting of three kinds of reflection surveys, generated clear seismic profiles, together with a seismic velocity image obtained from a seismic refraction survey. In this paper, we compare the seismic profiles with the geological column obtained from the drilling. Five volcaniclastic sedimentary units were identified in seismic reflection profiles above the 5 km/s and 6 km/s contours of P-wave velocity obtained from the velocity image from the seismic refraction survey. However, some of the unit boundaries interpreted from the seismic images were not recognised in the drilling core, highlighting the difficulties of geological target identification in volcanic regions from seismic images alone. The geological core derived from drilling consisted of seven lithological units (labelled I to VII). Units I to V were aged at 0-9 Ma, and units VI and VII, from 1320-1806.5 m below seafloor (mbsf) had ages from 9 to ~15 Ma. The strong heterogeneity of volcanic sediments beneath the drilling site U1437 was also identified from coherence, calculated using cross-spectral analysis between grid survey lines. Our results suggest that use of a dense grid configuration is important in site surveys for ocean drilling in volcanic rear-arc situations, in order to recognise heterogeneous crustal structure, such as sediments from different origins.

Multimode seismoelectric phenomena generated using explosive and vibroseis sources

NASA Astrophysics Data System (ADS)

Butler, Karl E.; Kulessa, Bernd; Pugin, André J.-M.

2018-05-01

A field trial of seismoelectric surveying was carried out at a site underlain by 20 m of water-saturated clayey Champlain Sea sediments, renowned for their amenability to high resolution imaging by seismic reflection surveys. Seismically induced electrokinetic effects were recorded using an array of 26 grounded dipole electric field antennas, and two different seismic sources including an eight-gauge shotgun, and a moderate power (10 000 lb Minivib) vibrator. Despite the high electrical conductivity of the sediments, shot records show evidence of possible interfacial seismoelectric conversions caused by the arrival of P-waves at the base of the clay/top of bedrock and at the top of a layer of elevated porosity and conductivity within the clay at 7 m depth. However, the data are more remarkable for the fact that P-wave, S-wave, and PS/SP converted wave reflections evident in the seismic records all give rise to electrical arrivals exhibiting very similar moveout patterns in the seismoelectric records. Superficially, these electrical responses could be misinterpreted as simple coseismic seismoelectric effects associated with the arrival of reflected seismic waves at each dipole antenna on surface. However, their broader bandwidth, superior coherency and earlier arrival times compared to their corresponding seismic arrivals indicate that the electrical effects are generated by the arrival of seismic reflections below each dipole at the shallow intraclay interface 7 m below surface. Such quasi-coseismic arrivals have recently been predicted by full-waveform seismoelectric modelling and characterized as evanescent electromagnetic (EM) waves. In retrospect, they were also observed in earlier seismoelectric field trials, but not measured as clearly nor recognized as a distinct seismoelectric mode intermediate between interfacial and coseismic effects. We propose that the observed quasi-coseismic effect can be understood physically as a fringing field emanating from the travelling charge separation associated with a P-wave (direct or mode-converted) crossing a subsurface interface at an oblique angle. Such effects may be nearly indistinguishable from coseismic effects if the interface depth is small compared to the seismic wavelength, but recognition of the phenomenon contributes to an improved understanding of the seismoelectric wavefield, and will lead to improved interpretations. From a practical standpoint, the results of this field trial suggest that using electric field receivers to supplement geophones on surface could yield significantly higher resolution seismic reflection images in those areas where suitable near-surface layers exist for the generation of quasi-coseismic effects. The results also reinforce the importance of using multichannel recording to allow interfacial seismoelectric conversions originating at depth to be distinguished from stronger coseismic and quasi-coseismic arrivals originating in the near-surface by measurement of their arrival time versus offset (moveout) and amplitude versus offset behaviours.

Seismic velocity structure and spatial distribution of reflection intensity off the Boso Peninsula, Central Japan, revealed by an ocean bottom seismographic experiment

NASA Astrophysics Data System (ADS)

Kono, Akihiro; Sato, Toshinori; Shinohara, Masanao; Mochizuki, Kimihiro; Yamada, Tomoaki; Uehira, Kenji; Shinbo, Takashi; Machida, Yuuya; Hino, Ryota; Azuma, Ryosuke

2016-04-01

Off the Boso Peninsula, central Japan, where the Sagami Trough is in the south and the Japan Trench is in the east, there is a triple junction where the Pacific plate (PAC), the Philippine Sea plate (PHS) and the Honshu island arc (HIA) meet each other. In this region, the PAC subducts beneath the PHS and the HIA, and the PHS subducts beneath the HIA. Due to the subduction of 2 oceanic plates, numerous seismic events took place in the past. In order to understand these events, it is important to image structure of these plates. Hence, many researchers attempted to reveal the substructure from natural earthquakes and seismic experiments. Because most of the seismometers are placed inland area and the regular seismicity off Boso is inactive, it is difficult to reveal the precise substructure off Boso area using only natural earthquakes. Although several marine seismic experiments using active sources were conducted, vast area remains unclear off Boso Peninsula. In order to improve the situation, a marine seismic experiment, using airgun as an active source, was conducted from 30th July to 4th of August, 2009. The survey line has 216 km length and 20 Ocean Bottom Seismometers (OBSs) were placed on it. We estimated 2-D P-wave velocity structure from the airgun data using the PMDM (Progressive Model Development Method; Sato and Kenett, 2000) and the FAST (First Arrival Seismic Tomography ; Zelt and Barton, 1998). Furthermore, we identified the probable reflection phases from the data and estimated the location of reflectors using Travel time mapping method (Fujie et al. 2006). We found some reflection phases from the data, and the reflectors are located near the region where P-wave velocity is 5.0 km/s. We interpret that the reflectors indicate the plate boundary between the PHS and the HIA. The variation of the intensity of reflection along the upper surface of PHS seems to be consistent with the result from previous reflection seismic experiment conducted by Kimura et al. (2009). Acknowledgement The marine seismic experiment was conducted by R/V Hakuhou-maru of Japan Agency for Marine-Earth Science and Technology, and the OBSs were retrieved by Shincho-maru of Shin-Nihon-Kaiji co. Ltd. (Present, Fukada salvage co. Ltd.). We would like to thank captains and the crew of Hakuho-maru and Shincho-maru. This study was supported by the Ministry of Education, Culture, Sports, Science and Technology (MEXT) of Japan, under its Observation and Research Program for Prediction of Earthquakes and Volcanic Eruptions, and from the Grants in Aid for Scientific Research (25287109).

Cenozoic pulsed compression of Da'an-Dedu Fault Zone in Songliao Basin (NE China) and its implications for earthquake potential: Evidence from seismic data

NASA Astrophysics Data System (ADS)

Yu, Zhongyuan; Zhang, Peizhen; Min, Wei; Wei, Qinghai; Zhao, Bin

2018-01-01

The Da'an-Dedu Fault Zone (DDFZ) is a major tectonic feature cutting through the Songliao Basin from south to north in NE China. Pulsed compression deformation of DDFZ during the Cenozoic implies a complex geodynamic process, and the latest stage of which occurred in the Quaternary directly influences the present seismicity of the interior basin. Although most of the evidence for Quaternary deformation about the Songliao Basin in the past decades was concentrated in marginal faults, all five earthquake swarms with magnitudes over 5.0 along the buried DDFZ with no surface expression during the past 30 years suggest it is a main seismogenic structure with seismic potential, which should deserve more attention of geologists. However, limited by the coverage of the Quaternary sedimentary and absence of strong historic and instrumental earthquakes records (M > 7), the geometric pattern, Quaternary activity and seismic potential of the DDFZ remain poorly understood. Thus, unlike previous geophysical studies focused on crust/mantle velocity structure across the fault and the aim of exploring possible mineral resources in the basin, in this study we have integrated a variety of the latest seismic data and drilling holes from petroleum explorations and shallow-depth seismic reflection profiles, to recognize the Cenozoic pulsed compression deformation of the DDFZ, and to discuss its implication for earthquake potential. The results show that at least four stages of compression deformation have occurred along the DDFZ in the Cenozoic: 65 Ma, 23 Ma, 5.3 Ma, and 1.8 Ma, respectively, although the geodynamic process behind which still in dispute. The results also imply that the tectonic style of the DDFZ fits well with the occurrence of modern seismic swarms. Moderate earthquake potential (M ≤ 7.0) is suggested along the DDFZ.

Effects of the symmetry axis orientation of a TI overburden on seismic images

NASA Astrophysics Data System (ADS)

Chang, Chih-Hsiung; Chang, Young-Fo; Tseng, Cheng-Wei

2017-07-01

In active tectonic regions, the primary formations are often tilted and subjected to the processes of folding and/or faulting. Dipping formations may be categorised as tilted transverse isotropy (TTI). While carrying out hydrocarbon exploration in areas of orogenic structures, mispositioning and defocusing effects in apparent reflections are often caused by the tilted transverse isotropy of the overburden. In this study, scaled physical modelling was carried out to demonstrate the behaviours of seismic wave propagation and imaging problems incurred by transverse isotropic (TI) overburdens that possess different orientations of the symmetry axis. To facilitate our objectives, zero-offset reflections were acquired from four stratum-fault models to image the same structures that were overlain by a TI (phenolite) slab. The symmetry axis of the TI slab was vertical, tilted or horizontal. In response to the symmetry axis orientations, spatial shifts and asymmetrical diffraction patterns in apparent reflections were observed in the acquired profiles. Given the different orientations of the symmetry axis, numerical manipulations showed that the imaged events could be well described by theoretical ray paths computed by the trial-and-error ray method and Fermat's principle (TERF) method. In addition, outputs of image restoration show that the imaging problems, i.e. spatial shift in the apparent reflections, can be properly handled by the ray-based anisotropic 2D Kirchhoff time migration (RAKTM) method.

Evidence of uplift near Charleston, South Carolina

USGS Publications Warehouse

Rhea, S.

1989-01-01

In spite of extensive research, the causal structure of the 1886 magnitude 7 earthquake near Charleston, South Carolina, has not been identified. In this study I analyzed digital surface topography and river morphology in light of earlier studies using seismic reflection, seismic refraction, earthquake seismology, and gravity and magnetic surveys. This analysis revealed an area approximately 400 km2 northwest of Charleston that may have been repeatedly uplifted by earthquakes. Geologic and seismic reflection data confirm alteration of formations at depth. Deformation of the surface is supported by observations on aerial and LANDSAT photographs. Therefore, the structure on which the 1886 earthquake occurred may be within the uplifted area defined in this report. -Author

The Flemish Cap - Goban Spur conjugate margins: New evidence of asymmetry

NASA Astrophysics Data System (ADS)

Gerlings, J.; Louden, K. E.; Minshull, T. A.; Nedimović, M. R.

2011-12-01

The combined results of deep multichannel seismic (MCS) and refraction/wide-angle reflection seismic (R/WAR) profiles across the Flemish Cap-Goban Spur conjugate margin pair will be presented to help constrain rifting and breakup processes. Both profiles cross magnetic anomaly 34 and extend into oceanic crust, which makes it possible to observe the complete extensional history from continental rifting through the formation of initial oceanic crust. Kirchhoff poststack time and prestack time and depth migration images of the Flemish Cap MCS data are produced using a velocity model constructed from the MCS and R/WAR data. These new images show improved continuity of the Moho under the thick continental crust of Flemish Cap. The basement morphology image is sharper and reflections observed in the thin crust of the transition zone are more coherent. A basement high at the seaward-most end of the transition zone now displays clear diapiric features. To compare the two margins, the existing migrated MCS data across Goban Spur has been time-to-depth converted using the R/WAR velocity model of the margin. These reimaged seismic profiles demonstrate asymmetries in continental rifting and breakup with a complex transition to oceanic spreading: (1) During initial phases of rifting, the Flemish Cap margin displays a sharper necking profile than that of the Goban Spur margin. (2) Within the ocean-continent-transition zone, constraints from S-wave velocities on both margins indentifies previously interpreted oceanic crust as thinned continental crust offshore Flemish Cap in contrast with primarily serpentinized mantle offshore Goban Spur. (3) Continental breakup and initial seafloor spreading occur in a complex, asymmetric manner where the initial ~50 km of oceanic crust appears different on the two margins. Offshore Flemish Cap, both R/WAR and MCS results indicate a sharp boundary immediately seaward of a ridge feature, where the basement morphology becomes typical of slow seafloor spreading. There are no significant changes in either reflectivity or velocity seaward toward magnetic anomaly 34. On the Goban Spur margin in marked contrast, the basement morphology landward of magnetic anomaly 34 is shallower and has lower relief, and the velocity model indicates a diffuse change between the transitional crust and seafloor spreading. The results from these two very different conjugate margins emphasize the importance of having both types of seismic data from both conjugate margins when interpreting the geodynamic processes.

Preliminary stratigraphic and hydrogeologic cross sections and seismic profile of the Floridan aquifer system of Broward County, Florida

USGS Publications Warehouse

Reese, Ronald S.; Cunningham, Kevin J.

2013-01-01

To help water-resource managers evaluate the Floridan aquifer system (FAS) as an alternative water supply, the U.S. Geological Survey initiated a study, in cooperation with the Broward County Environmental Protection and Growth Management Department, to refine the hydrogeologic framework of the FAS in the eastern part of Broward County. This report presents three preliminary cross sections illustrating stratigraphy and hydrogeology in eastern Broward County as well as an interpreted seismic profile along one of the cross sections. Marker horizons were identified using borehole geophysical data and were initially used to perform well-to-well correlation. Core sample data were integrated with the borehole geophysical data to support stratigraphic and hydrogeologic interpretations of marker horizons. Stratigraphic and hydrogeologic units were correlated across the county using borehole geophysical data from multiple wells. Seismic-reflection data were collected along the Hillsboro Canal. Borehole geophysical data were used to identify and correlate hydrogeologic units in the seismic-reflection profile. Faults and collapse structures that intersect hydrogeologic units were also identified in the seismic profile. The information provided in the cross sections and the seismic profile is preliminary and subject to revision.

Gas hydrate characterization from a 3D seismic dataset in the deepwater eastern Gulf of Mexico

DOE Office of Scientific and Technical Information (OSTI.GOV)

McConnell, Daniel; Haneberg, William C.

Seismic stratigraphic features are delineated using principal component analysis of the band limited data at potential gas hydrate sands, and compared and calibrated with spectral decomposition thickness to constrain thickness in the absence of well control. Layers in the abyssal fan sediments are thinner than can be resolved with 50 Hz seismic and thus comprise composite thin-bed reflections. Amplitude vs frequency analysis are used to indicate gas and gas hydrate reflections. Synthetic seismic wedge models show that with 50Hz seismic data, a 40% saturation of a Plio Pleistocene GoM sand in the hydrate stability zone with no subjacent gas canmore » produce a phase change (negative to positive) with a strong correlation between amplitude and hydrate saturation. The synthetic seismic response is more complicated if the gas hydrate filled sediments overlie gassy sediments. Hydrate (or gas) saturation in thin beds enhances the amplitude response and can be used to estimate saturation. Gas hydrate saturation from rock physics, amplitude, and frequency analysis is compared to saturation derived from inversion at several interpreted gas hydrate accumulations in the eastern Gulf of Mexico.« less

Long-term deformation in the Mississippi Embayment (Central USA) imaged by high-resolution seismic reflection data

NASA Astrophysics Data System (ADS)

Hao, Yanjun

Large magnitude intraplate earthquakes are a puzzling exception to plate tectonic theory. Unlike earthquakes occurring along plate boundaries, large continental intraplate earthquakes are a rare occurrence and are often distributed over broad regions. Albeit rare, their occurrence can cause widespread damage because of the low attenuation of seismic energy typical of plate interiors [Hanks and Johnston, 1992]. In the Central USA, most of the recent tectonic intraplate seismicity concentrates along the New Madrid seismic zone (NMSZ), where three large (M>7) earthquakes occurred between 1811--1812 [Johnston and Schweig, 1996]. Here the low surface deformation rates [Calais and Stein, 2009] conflict with the elevated instrument-recorded seismicity and the occurrence of historical and prehistorical large magnitude events [Tuttle et al., 2002]. One of the promising hypotheses proposed to reconcile this apparent contradiction is that intraplate earthquakes may be temporally clustered, episodic or cyclic, and may migrate spatially at the regional or continental scale across multiple faults or fault systems. In order to test this hypothesis and to understand how and where the long-term deformation is accommodated in the Mississippi Embayment, Central USA, I utilize high-resolution seismic reflection data acquired by the Mississippi River Project [Magnani and McIntosh, 2009] and by a 2010 survey across the Meeman-Shelby fault [Magnani, 2011; Hao et al., 2013]. To identify the location of Quaternary deformation and characterize deformation history, I acquired, processed, and interpreted the seismic reflection data and integrated them with other available geophysical (e.g. seismicity, crustal and lithospheric models) and geological (e.g. magmatism and borehole) data. For my research, I focus on three regions in the Mississippi Embayment: 1) the Meeman-Shelby fault west of Memphis, Tennessee, 2) the eastern Reelfoot rift margin north of Memphis, Tennessee, and 3) the area in southeastern Arkansas along the Alabama-Oklahoma transform zone. Quaternary deformation and prolonged history of activity of the imaged faults is documented at all sites. The results show that Quaternary seismic activity in the Mississippi Embayment is accommodated by faults additional to the NMSZ fault system, and that fault activity is controlled by certain paleotectonic structures inherited from the Proterozoic and Paleozoic history of the North American continent. The identification of Quaternary seismogenic faults outside the footprint of the NMSZ and of the lower crustal anomaly (i.e. "rift pillow") supports seismotectonic models that predict deformation over a large area (e.g. Forte et al., 2007) and calls into questions in models that predict concentration of strain in the NMSZ region (e.g. Pollitz et al., 2001). A comparison between the newly imaged faults and the NMSZ faults shows that the former are indistinguishable from the latter except for the occurrence of instrumental seismicity. Based on the analysis of the location and sense of displacement of Quaternary deformation in the northern Mississippi Embayment, I propose a new fault network to reconcile the wide distribution of Quaternary faults with concentration of instrumental seismicity along the NMSZ. The fault network consists of three distinct trends of faults: ~N45°E right-lateral strike-slip faults, ~N20°W reverse faults, and ~N25°E right-lateral strike-slip faults. Different faults in the fault network appear to have been active at different times across the northern embayment. The available age data suggest a northward migration of the deformation, with the NMSZ representing the latest and youngest fault system.

Artificial seismic acceleration

USGS Publications Warehouse

Felzer, Karen R.; Page, Morgan T.; Michael, Andrew J.

2015-01-01

In their 2013 paper, Bouchon, Durand, Marsan, Karabulut, 3 and Schmittbuhl (BDMKS) claim to see significant accelerating seismicity before M 6.5 interplate mainshocks, but not before intraplate mainshocks, reflecting a preparatory process before large events. We concur with the finding of BDMKS that their interplate dataset has significantly more fore- shocks than their intraplate dataset; however, we disagree that the foreshocks are predictive of large events in particular. Acceleration in stacked foreshock sequences has been seen before and has been explained by the cascade model, in which earthquakes occasionally trigger aftershocks larger than themselves4. In this model, the time lags between the smaller mainshocks and larger aftershocks follow the inverse power law common to all aftershock sequences, creating an apparent acceleration when stacked (see Supplementary Information).

Seismic transect across the Lomonosov and Mendeleev Ridges: Constraints on the geological evolution of the Amerasia Basin, Arctic Ocean

NASA Astrophysics Data System (ADS)

Jokat, Wilfried; Ickrath, Michele; O'Connor, John

2013-10-01

We report on seismic and petrological data that provide new constraints on the geological evolution of the Amerasia Basin. A seismic reflection transect across the Makarov Basin, located between the Mendeleev and Lomonosov Ridges, shows a complete undisturbed sedimentary section of Mesozoic/Cenozoic age. In contrast to the Mendeleev Ridge, the margin of the Lomonosov Ridge is wide and shows horst and graben structures. We suggest that the Mendeleev Ridge is most likely volcanic in origin and support this finding with a 40Ar/39Ar isotopic age for a tholeiitic basalt sampled from the central Alpha/Mendeleev Ridge. Seismic reflection data for the Makarov Basin show no evidence of compressional features, consistent with the Lomonosov Ridge moving as a microplate in the Cenozoic. We propose that the Amerasia Basin moved as a single tectonic plate during the opening of the Eurasia Basin.

Gas and gas hydrate distribution around seafloor seeps in Mississippi Canyon, Northern Gulf of Mexico, using multi-resolution seismic imagery

USGS Publications Warehouse

Wood, W.T.; Hart, P.E.; Hutchinson, D.R.; Dutta, N.; Snyder, F.; Coffin, R.B.; Gettrust, J.F.

2008-01-01

To determine the impact of seeps and focused flow on the occurrence of shallow gas hydrates, several seafloor mounds in the Atwater Valley lease area of the Gulf of Mexico were surveyed with a wide range of seismic frequencies. Seismic data were acquired with a deep-towed, Helmholz resonator source (220-820 Hz); a high-resolution, Generator-Injector air-gun (30-300 Hz); and an industrial air-gun array (10-130 Hz). Each showed a significantly different response in this weakly reflective, highly faulted area. Seismic modeling and observations of reversed-polarity reflections and small scale diffractions are consistent with a model of methane transport dominated regionally by diffusion but punctuated by intense upward advection responsible for the bathymetric mounds, as well as likely advection along pervasive filamentous fractures away from the mounds.

Image of the Moho across the continent-ocean transition, US east coast

DOE Office of Scientific and Technical Information (OSTI.GOV)

Holbrook, W.S.; Purdy, G.M.; Reiter, E.C.

1992-03-01

Strong wide-angle reflections from the Moho were recorded by ocean-bottom seismic instruments during the 1988 Carolina Trough multichannel seismic experiment, in an area where the Moho is difficult to detect with vertical-incidence seismic data. Prestack depth migration of these reflections has enabled the construction of a seismic image of the Moho across the continent-ocean transition of a sedimented passive margin. The Moho rises across the margin at a slope of 10{degree}-12{degree}, from a depth of about 33 km beneath the continental shelf to 20 km beneath the outer rise. This zone of crustal thinning defines a distinct, 60-70-km-wide continent-ocean transitionmore » zone. The authors interpret the Moho in the Carolina Trough as a Jurassic feature, formed by magmatic intrusion and underplating during the rifting of Pangea.« less

Continental Delamination of the Romanian Eastern Carpathians: A Lower Crustal Origin of the Vrancea Seismogenic Zone?

NASA Astrophysics Data System (ADS)

Fillerup, M. A.; Knapp, J. H.; Knapp, C. C.

2006-12-01

Two lithosphere-scale, explosive-source seismic reflection profiles (DRACULA I and DACIA PLAN), inclusive of the hinterland and foreland of the Romanian Eastern Carpathians, provide new evidence for the geodynamic origin of the Vrancea Seismogenic Zone (VSZ) of Romania. These data, collected to evaluate existing subduction-related and delamination geodynamic models proposed to explain the intermediate depth seismicity associated with the Vrancea zone, show evidence of continental crust extending continuously above the VSZ from the Carpathian foreland well into the Transylvanian hinterland. Crustal thicknesses inferred from these data based on reflectivity show a 40-45 km crust below the Transylvanian basin abruptly shallowing to 32 km for ~120 km beneath the fold and thrust belt of the main Carpathian orogen and thickening again to 38-42 km crust in the foreland. This thinned crust outlines an apparent lower crustal sub-orogenic cavity that is overlain by a relatively subhorizontal reflective fabric absent of dipping reflectivity. The northwest dipping Vrancea seismogenic body, a 30x70x200 km volume of intermediate depth earthquakes, is located on the eastern flank of the apparently thin crust beneath the Carpathian orogen. Amplitude decay curves show penetration of seismic energy to a depth of ~60 km in the vicinity of the sub-orogenic cavity, implying this non- reflective zone is a geologic signature. Rotation of the VSZ about a hinge beneath the foreland basin at a depth of ~50 km restores to fill the lower-crustal cavity under the orogen, suggesting the VSZ represents a portion of brittle lower crust delaminated during continental lithospheric delamination which may have caused regional uplift of the Transylvanian basin. The lack of through-going, dipping crustal-scale boundaries along this composite lithospheric transect would appear to preclude subduction as an explanation for seismicity in the VSZ, consistent with abundant surface geologic data. These seismic data advocate possible lower crustal continental lithospheric delamination as a mechanism for generating intermediate depth seismicity in the absence of a plate boundary.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Myers, S; Larsen, S; Wagoner, J

Seismic imaging and tracking methods have intelligence and monitoring applications. Current systems, however, do not adequately calibrate or model the unknown geological heterogeneity. Current systems are also not designed for rapid data acquisition and analysis in the field. This project seeks to build the core technological capabilities coupled with innovative deployment, processing, and analysis methodologies to allow seismic methods to be effectively utilized in the applications of seismic imaging and vehicle tracking where rapid (minutes to hours) and real-time analysis is required. The goal of this project is to build capabilities in acquisition system design, utilization of full three-dimensional (3D)more » finite difference modeling, as well as statistical characterization of geological heterogeneity. Such capabilities coupled with a rapid field analysis methodology based on matched field processing are applied to problems associated with surveillance, battlefield management, finding hard and deeply buried targets, and portal monitoring. This project, in support of LLNL's national-security mission, benefits the U.S. military and intelligence community. Fiscal year (FY) 2003 was the final year of this project. In the 2.5 years this project has been active, numerous and varied developments and milestones have been accomplished. A wireless communication module for seismic data was developed to facilitate rapid seismic data acquisition and analysis. The E3D code was enhanced to include topographic effects. Codes were developed to implement the Karhunen-Loeve (K-L) statistical methodology for generating geological heterogeneity that can be utilized in E3D modeling. The matched field processing methodology applied to vehicle tracking and based on a field calibration to characterize geological heterogeneity was tested and successfully demonstrated in a tank tracking experiment at the Nevada Test Site. A three-seismic-array vehicle tracking testbed was installed on site at LLNL for testing real-time seismic tracking methods. A field experiment was conducted over a tunnel at the Nevada Site that quantified the tunnel reflection signal and, coupled with modeling, identified key needs and requirements in experimental layout of sensors. A large field experiment was conducted at the Lake Lynn Laboratory, a mine safety research facility in Pennsylvania, over a tunnel complex in realistic, difficult conditions. This experiment gathered the necessary data for a full 3D attempt to apply the methodology. The experiment also collected data to analyze the capabilities to detect and locate in-tunnel explosions for mine safety and other applications. In FY03 specifically, a large and complex simulation experiment was conducted that tested the full modeling-based approach to geological characterization using E2D, the K-L statistical methodology, and matched field processing applied to tunnel detection with surface seismic sensors. The simulation validated the full methodology and the need for geological heterogeneity to be accounted for in the overall approach. The Lake Lynn site area was geologically modeled using the code Earthvision to produce a 32 million node 3D model grid for E3D. Model linking issues were resolved and a number of full 3D model runs were accomplished using shot locations that matched the data. E3D-generated wavefield movies showed the reflection signal would be too small to be observed in the data due to trapped and attenuated energy in the weathered layer. An analysis of the few sensors coupled to bedrock did not improve the reflection signal strength sufficiently because the shots, though buried, were within the surface layer and hence attenuated. Ability to model a complex 3D geological structure and calculate synthetic seismograms that are in good agreement with actual data (especially for surface waves and below the complex weathered layer) was demonstrated. We conclude that E3D is a powerful tool for assessing the conditions under which a tunnel could be detected in a specific geological setting. Finally, the Lake Lynn tunnel explosion data were analyzed using standard array processing techniques. The results showed that single detonations could be detected and located but simultaneous detonations would require a strategic placement of arrays.« less

Assessment of offshore New Jersey sources of Beach replenishment sand by diversified application of geologic and geophysical methods

USGS Publications Warehouse

Waldner, J.S.; Hall, D.W.; Uptegrove, J.; Sheridan, R.E.; Ashley, G.M.; Esker, D.

1999-01-01

Beach replenishment serves the dual purpose of maintaining a source of tourism and recreation while protecting life and property. For New Jersey, sources for beach sand supply are increasingly found offshore. To meet present and future needs, geologic and geophysical techniques can be used to improve the identification, volume estimation, and determination of suitability, thereby making the mining and managing of this resource more effective. Current research has improved both data collection and interpretation of seismic surveys and vibracore analysis for projects investigating sand ridges offshore of New Jersey. The New Jersey Geological Survey in cooperation with Rutgers University is evaluating the capabilities of digital seismic data (in addition to analog data) to analyze sand ridges. The printing density of analog systems limits the dynamic range to about 24 dB. Digital acquisition systems with dynamic ranges above 100 dB can permit enhanced seismic profiles by trace static correction, deconvolution, automatic gain scaling, horizontal stacking and digital filtering. Problems common to analog data, such as wave-motion effects of surface sources, water-bottom reverberation, and bubble-pulse-width can be addressed by processing. More than 160 line miles of digital high-resolution continuous profiling seismic data have been collected at sand ridges off Avalon, Beach Haven, and Barnegat Inlet. Digital multichannel data collection has recently been employed to map sand resources within the Port of New York/New Jersey expanded dredge-spoil site located 3 mi offshore of Sandy Hook, New Jersey. Multichannel data processing can reduce multiples, improve signal-to-noise calculations, enable source deconvolution, and generate sediment acoustic velocities and acoustic impedance analysis. Synthetic seismograms based on empirical relationships among grain size distribution, density, and velocity from vibracores are used to calculate proxy values for density and velocity. The seismograms are then correlated to the digital seismic profile to confirm reflected events. They are particularly useful where individual reflection events cannot be detected but a waveform generated by several thin lithologic units can be recognized. Progress in application of geologic and geophysical methods provides advantages in detailed sediment analysis and volumetric estimation of offshore sand ridges. New techniques for current and ongoing beach replenishment projects not only expand our knowledge of the geologic processes involved in sand ridge origin and development, but also improve our assessment of these valuable resources. These reconnaissance studies provide extensive data to the engineer regarding the suitability and quantity of sand and can optimize placement and analysis of vibracore samples.Beach replenishment serves the dual purpose of maintaining a source of tourism and recreation while protecting life and property. Research has improved both data collection and interpretation of seismic surveys and vibracore analysis for projects investigating sand ridges offshore of New Jersey. The New Jersey Geological Survey in cooperation with Rutgers University is evaluating the capabilities of digital seismic data to analyze sand ridges. The printing density of analog systems limits the dynamic range to about 24 dB. Digital acquisition systems with dynamic ranges about 100 dB can permit enhanced seismic profiles by trace static correction, deconvolution, automatic gain scaling, horizontal stacking and digital filtering.

A Community Seismic Experiment in the ENAM Primary Site

NASA Astrophysics Data System (ADS)

Van Avendonk, H. J.

2012-12-01

Eastern North America (ENAM) was chosen as a GeoPRISMS Rift Initiation and Evolution primary site because it represents a mature continental margin with onshore and offshore rift basins in which the record of extension and continental break-up is preserved. The degree to which syn-rift magmatism and preexisting lithospheric weaknesses controlled the evolution of the margin can be further investigated if we image its 3-D structure at small and large length scales with active-source and earthquake seismic imaging. In the Summer of 2012 we submitted a proposal to the US National Science Foundation for an ambitious plan for data acquisition on a 400 km wide section of the mid-Atlantic East Coast margin around Cape Hatteras, from unextended continental lithosphere onshore to mature oceanic lithosphere offshore. This area includes an important along-strike transition in the morphology of the margin from the Carolina Trough to the Baltimore Canyon Trough, and two major fracture zones that are associated with significant offsets at the modern Mid-Atlantic Ridge. The study area also covers several features representing the post-rift modification of the margin by slope instability and fluid flow. As the Earthscope Transportable Array reaches the East Coast of the US in 2013 and 2014, we will have an unprecedented opportunity to image the detailed structure of the rifted margin. To make effective use of the research infrastructure, including the seismic vessel R/V Marcus Langseth, the Earthscope seismic instrumentation, and US OBS Instrument Pool, we propose to collect a suite of seismic data at the mid-Atlantic margin in the context of a community-driven experiment with completely open data access. This multi-faceted seismic experiment offers an immense opportunity for education of young scientists. We propose an integrated education effort during and after acquisition. The science and field parties for data acquisition will largely consist of young scientists, who will be chosen by application. Following the cruise, we propose to hold two short courses on multi-channel seismic reflection and wide-angle reflection and refraction data processing using the new seismic data. The acquisition of all seismic data, archiving of the data in existing data bases, and distribution to the community will take two years. Afterwards, proposals developed by any member of the science community can be submitted for further data analysis and testing of current scientific hypotheses regarding the evolution and dynamics of the ENAM margin.

Improvement of real-time seismic magnitude estimation by combining seismic and geodetic instrumentation

NASA Astrophysics Data System (ADS)

Goldberg, D.; Bock, Y.; Melgar, D.

2017-12-01

Rapid seismic magnitude assessment is a top priority for earthquake and tsunami early warning systems. For the largest earthquakes, seismic instrumentation tends to underestimate the magnitude, leading to an insufficient early warning, particularly in the case of tsunami evacuation orders. GPS instrumentation provides more accurate magnitude estimations using near-field stations, but isn't sensitive enough to detect the first seismic wave arrivals, thereby limiting solution speed. By optimally combining collocated seismic and GPS instruments, we demonstrate improved solution speed of earthquake magnitude for the largest seismic events. We present a real-time implementation of magnitude-scaling relations that adapts to consider the length of the recording, reflecting the observed evolution of ground motion with time.

Archive of Digital Boomer and CHIRP Seismic Reflection Data Collected During USGS Field Activity 08LCA03 in Lake Panasoffkee, Florida, May 2008

USGS Publications Warehouse

Harrison, Arnell S.; Dadisman, Shawn V.; McBride, W. Scott; Flocks, James G.; Wiese, Dana S.

2009-01-01

In May of 2008, the U.S. Geological Survey (USGS) conducted geophysical surveys in Lake Panasoffkee, located in central Florida, as part of the USGS Lakes and Coastal Aquifers (LCA) study. This report serves as an archive of unprocessed digital boomer and Compressed High Intensity Radar Pulse (CHIRP)* seismic reflection data, trackline maps, navigation files, Field Activity Collection System (FACS) logs, Geographic Information System (GIS) files, and formal Federal Geographic Data Committee (FGDC) metadata. Filtered and gained (a relative increase in signal amplitude) digital images of the seismic profiles and geospatially corrected interactive profiles are also provided. Refer to the Acronyms page for expansions of acronyms and abbreviations used in this report. *Due to poor data acquisition conditions associated with the lake bottom sediments, only two CHIRP tracklines were collected during this field activity. The archived trace data are in standard Society of Exploration Geophysicists (SEG) SEG-Y format (Barry and others, 1975) and may be downloaded and processed with commercial or public domain software such as Seismic Unix (SU). Example SU processing scripts and USGS software for viewing the SEG-Y files (Zihlman, 1992) are provided. The USGS Florida Integrated Science Center (FISC) - St. Petersburg assigns a unique identifier to each cruise or field activity. For example, 08LCA03 tells us the data were collected in 2008 for the Lakes and Coastal Aquifers (LCA) study and the data were collected during the third field activity for that study in that calendar year. Refer to http://walrus.wr.usgs.gov/infobank/programs/html/definition/activity.html for a detailed description of the method used to assign the field activity ID. The naming convention used for each seismic line is as follows: yye##a, where 'yy' are the last two digits of the year in which the data were collected, 'e' is a 1-letter abbreviation for the equipment type (for example, b for boomer and c for CHIRP), '##' is a 2-digit number representing a specific track, and 'a' is a letter representing the section of a line if recording was prematurely terminated or rerun for quality or acquisition problems. The boomer plate is an acoustic energy source that consists of capacitors charged to a high voltage and discharged through a transducer in the water. The transducer is towed on a sled floating on the water surface and, when discharged, emits a short acoustic pulse, or shot, which propagates through the water, sediment column, or rock beneath. The acoustic energy is reflected at density boundaries (such as the seafloor, sediment, or rock layers beneath the seafloor), detected by the receiver, and recorded by a PC-based seismic acquisition system. This process is repeated at timed intervals (for example, 0.5 s) and recorded for specific intervals of time (for example, 100 ms). In this way, a two-dimensional (2-D) vertical profile of the shallow geologic structure beneath the ship track is produced. Figure 1 displays the boomer acquisition geometry. The EdgeTech SB-424 CHIRP system used for this survey has a vertical resolution of 4 - 8 cm, a penetration depth that is usually less than 2 m beneath the seafloor, and uses a signal of continuously varying frequency. The towfish is a sound source and receiver, which is typically towed 2 - 5 m above the seafloor. The acoustic energy is reflected at density boundaries (such as the seafloor or sediment layers beneath the seafloor), detected by a receiver, and recorded by a PC-based seismic acquisition system. This process is repeated at timed intervals (for example, 0.125 s) and recorded for specific intervals of time (for example, 50 ms); the resulting profile is a two-dimensional vertical image of the shallow geologic structure beneath the ship track. Figure 2 displays the acquisition geometry for the CHIRP system. Refer to table 1 for a summary of acquisition parameters and table 2 for trackline statistics.

The Waqf as Suwwan crater, Eastern Desert of Jordan: aspects of the deep structure of an oblique impact from reflection seismic and gravity data

NASA Astrophysics Data System (ADS)

Heinrichs, Till; Salameh, Elias; Khouri, Hani

2014-01-01

The deeply eroded Waqf as Suwwan ring structure was recently discovered to be a large impact, the first identified in the near east. Large-scale reflection seismic structure shows the impact situated high on the northeastern flank of the Jordan Uplift sloping into Wadi Sirhan Basin. If exhumation is linked to the Arabia-Eurasia collision, a likely time window for the impact event may be latest Eocene to Late Oligocene. Impact into a shallow sea seems an optional scenario. Old reflection seismic lines offer limited insight into the deep structure of the rim and part of the central uplift of the complex crater. An important structural clue is provided by a well-resolved seismic horizon of a yet tentative correlation with a Paleozoic black shale. The central gravity high is compatible with a mass surplus by the uplift of denser Paleozoic basement below the central uplift. The gravity model further indicates a ring of dense Paleozoic sediments rising from below into the ring syncline. Seismics show presumably radial synclines in the central uplift which are interpreted by centripetal constrictional flow during crater collapse. Beneath the final crater's outer boundary, a shallow-dip normal fault zone, subtle seismic structure in uncollapsed footwall segments reveal an asymmetry of strain. The asymmetry is attributed to the cratering flow by an oblique impact directed toward NE. The finding provides independent support to an earlier suggestion of impact obliquity based on vergency of folds exposed on the central uplift.

High-resolution seismic-reflection images across the ICDP-USGS Eyreville deep drilling site, Chesapeake Bay impact structure

USGS Publications Warehouse

Powars, D.S.; Catchings, R.D.; Goldman, M.R.; Gohn, G.S.; Horton, J. Wright; Edwards, L.E.; Rymer, M.J.; Gandhok, G.

2009-01-01

The U.S. Geological Survey (USGS) acquired two 1.4-km-long, high-resolution (??5 m vertical resolution) seismic-reflection lines in 2006 that cross near the International Continental Scientifi c Drilling Program (ICDP)-USGS Eyreville deep drilling site located above the late Eocene Chesapeake Bay impact structure in Virginia, USA. Five-meter spacing of seismic sources and geophones produced high-resolution images of the subsurface adjacent to the 1766-m-depth Eyreville core holes. Analysis of these lines, in the context of the core hole stratigraphy, shows that moderateamplitude, discontinuous, dipping reflections below ??527 m correlate with a variety of Chesapeake Bay impact structure sediment and rock breccias recovered in the cores. High-amplitude, continuous, subhorizontal reflections above ??527 m depth correlate with the uppermost part of the Chesapeake Bay impact structure crater-fi ll sediments and postimpact Eocene to Pleistocene sediments. Refl ections with ??20-30 m of relief in the uppermost part of the crater-fi ll and lowermost part of the postimpact section suggest differential compaction of the crater-fi ll materials during early postimpact time. The top of the crater-fi ll section also shows ??20 m of relief that appears to represent an original synimpact surface. Truncation surfaces, locally dipping reflections, and depth variations in reflection amplitudes generally correlate with the lithostratigraphic and sequence-stratigraphic units and contacts in the core. Seismic images show apparent postimpact paleochannels that include the fi rst possible Miocene paleochannels in the Mid-Atlantic Coastal Plain. Broad downwarping in the postimpact section unrelated to structures in the crater fi ll indicates postimpact sediment compaction. ?? 2009 The Geological Society of America.

Upper crust beneath the central Illinois basin, United States

USGS Publications Warehouse

McBride, J.H.; Kolata, Dennis R.

1999-01-01

Newly available industry seismic reflection data provide critical information for understanding the structure and origin of the upper crust (0-12 km depth) beneath the central Illinois basin and the seismic-tectonic framework north of the New Madrid seismic zone in the central Mississippi Valley. Mapping of reflector sequences furnishes the first broad three-dimensional perspective of the structure of Precambrian basement beneath the central United States Midcontinent. The highly coherent basement reflectivity is expressed as a synformal wedge of dipping and subhorizontal reflections situated beneath the center of the Illinois basin that thickens and deepens to the northeast (e.g., 0 to ???5.3 km thickness along a 123 km south to north line). The thickening trend of the wedge qualitatively mimics the northward thickening of the Late Cambrian Mt. Simon Sandstone; however, other Paleozoic units in the Illinois basin generally thicken southward into the basin center. The seismic data also reveal an anomalous subsequence defined by a spoon-shaped distribution of disrupted reflections located along the southern margin of the wedge. The boundaries of this subsequence are marked by distinct steeply dipping reflections (possible thrust faults?) that continue or project up to antiformal disruptions of lower Paleozoic marker reflectors, suggesting Paleozoic or possibly later tectonic reactivation of Precambrian structure. The areal extent of the subsequence appears to roughly correspond to an anomalous concentration of larger magnitude upper to middle crustal earthquakes. There are multiple hypotheses for the origin of the Precambrian reflectivity, including basaltic flows or sills interlayered with clastic sediments and/or emplaced within felsic igneous rocks. Such explanations are analogous to nearby Keweenawan rift-related volcanism and sedimentation, which initiated during Proterozoic rifting, and were followed eventually by reverse faulting along the rift margins caused by Grenville compression.

Seismic Rheological Model and Reflection Coefficients of the Brittle-Ductile Transition

NASA Astrophysics Data System (ADS)

Carcione, José M.; Poletto, Flavio

2013-12-01

It is well established that the upper—cooler—part of the crust is brittle, while deeper zones present ductile behaviour. In some cases, this brittle-ductile transition is a single seismic reflector with an associated reflection coefficient. We first develop a stress-strain relation including the effects of crust anisotropy, seismic attenuation and ductility in which deformation takes place by shear plastic flow. Viscoelastic anisotropy is based on the eigenstrain model and the Zener and Burgers mechanical models are used to model the effects of seismic attenuation, velocity dispersion, and steady-state creep flow, respectively. The stiffness components of the brittle and ductile media depend on stress and temperature through the shear viscosity, which is obtained by the Arrhenius equation and the octahedral stress criterion. The P- and S-wave velocities decrease as depth and temperature increase due to the geothermal gradient, an effect which is more pronounced for shear waves. We then obtain the reflection and transmission coefficients of a single brittle-ductile interface and of a ductile thin layer. The PP scattering coefficient has a Brewster angle (a sign change) in both cases, and there is substantial PS conversion at intermediate angles. The PP coefficient is sensitive to the layer thickness, unlike the SS coefficient. Thick layers have a well-defined Brewster angle and show higher reflection amplitudes. Finally, we compute synthetic seismograms in a homogeneous medium as a function of temperature.

High-resolution seismic-reflection data collected on R/V S.P. LEE: L9-84-CP, Marshall Islands to Hawaii

USGS Publications Warehouse

Schwab, William C.; Bailey, Norman G.

1984-01-01

The U.S. Geological Survey (USGS) R/V S.P. LEE (cruise L9-84-CP) left Majuro, Radak chain of the Marshall Islands on July 28, 1984, cruised over the Mid-Pacific Mountains, and reached Hawaii on August 15, 1984. The main objectives of the cruise were to study the distribution and composition of ferromanganese-oxide crusts in the Marshall Islands and to retrieve a current meter/sediment trap mooring deployed in October 1983 on Horizon Guyot, Mid-Pacific Mountains (USGS LS-83-HW cruise). The quality of the geophysical data collected is generally good. However, the declivity of some seamount, atoll, and guyot flanks are too large to allow high-quality resolution from the surface-towed systems that were used.The navigation system used was an integrated satellite-navigation/LORAN-C (in Mid-Pacific Mountains)/dead-reckoning system that was updated by radar when possible. A total of 5410 km of 12-kHz and 3.5-kHz seismic-reflection data and 730 km of 80-in3 to 148-in3 airgun seismic-reflection data were collected. The original records can be seen and studied at the USGS offices at Woods Hole, MA 02543. Microfilm copies of the seismic-reflection data can be purchased only from the National Geophysical Data Center, NOAA/EDIS/NGDC, 325 Broadway, Boulder, CO 80303.

Near-surface structure of the Central Scandinavian Caledonides in northern Trøndelag, Norway, from correlation of seismic and MT profiles using gravity and magnetic data

NASA Astrophysics Data System (ADS)

Ebbing, J.; Goerigk, L.; Nasuti, A.; Roberts, D.; Korja, T. J.; Smirnov, M.

2014-12-01

The deep geology of northern Trøndelag is somewhat speculative as the Central Scandinavian Caledonides are intersected by the Møre-Trøndelag Fault Complex (MTFC) and only a few depth-penetrating geophysical profiles exist. Here, we correlate the mapped geological units and faults between a seismic-reflection profile and a MT profile. The seismic-reflection data were acquired in 5 segments over the period 1986-1990. The westernmost section of the seismic profile is dominated by a complex pattern of reflections and diffractions. This type of pattern is typical of polydeformed terranes with a mixture of contrasting felsic and mafic lithologies. The two steeply-dipping strands of the MTFC (Hitra-Snåsa and Verran faults) that transect the profile do not show any distinctive signature in the seismic data. The MT data were acquired in 2007 from the Swedish border to the Norwegian coast. The conductivity profile shows some distinct vertical changes as well as changes from the near-surface to shallow depths. The strands of the MTFC show especially a distinctive change in conductivity. The two profiles are almost parallel but separated by 100 km. To correlate the structures seen on both profiles, we have applied lineament analysis and 3D modelling of the gravity and magnetic field. The tilt derivative of the magnetic and isostatic gravity anomaly clearly allows us to identify and link the main geological boundaries between the profiles and to trace the strands of the MTFC from one profile to the other. This trend analysis indicates that at least the Verran Fault visibly modifies the pattern of seismic reflections. However, the main change in crustal lithology occurs farther to the west, almost at the coast where the Tarva Fault intersects the MT profile. This integrated analysis shows the benefit of combining gravity and magnetic interpretations with MT and seismic data to enable us to understand the near-surface geology and structure in more detail.

Geophysical Studies Based on Gravity and Seismic Data of Tule Desert, Meadow Valley Wash, and California Wash Basins, Southern Nevada

USGS Publications Warehouse

Scheirer, Daniel S.; Page, William R.; Miller, John J.

2006-01-01

Gravity and seismic data from Tule Desert, Meadow Valley Wash, and California Wash, Nevada, provide insight into the subsurface geometry of these three basins that lie adjacent to rapidly developing areas of Clark County, Nevada. Each of the basins is the product of Tertiary extension accommodated with the general form of north-south oriented, asymmetrically-faulted half-grabens. Geophysical inversion of gravity observations indicates that Tule Desert and Meadow Valley Wash basins are segmented into subbasins by shallow, buried basement highs. In this study, basement refers to pre-Cenozoic bedrock units that underlie basins filled with Cenozoic sedimentary and volcanic units. In Tule Desert, a small, buried basement high inferred from gravity data appears to be a horst whose placement is consistent with seismic reflection and magnetotelluric observations. Meadow Valley Wash consists of three subbasins separated by basement highs at structural zones that accommodated different styles of extension of the adjacent subbasins, an interpretation consistent with geologic mapping of fault traces oblique to the predominant north-south fault orientation of Tertiary extension in this area. California Wash is a single structural basin. The three seismic reflection lines analyzed in this study image the sedimentary basin fill, and they allow identification of faults that offset basin deposits and underlying basement. The degree of faulting and folding of the basin-fill deposits increases with depth. Pre-Cenozoic units are observed in some of the seismic reflection lines, but their reflections are generally of poor quality or are absent. Factors that degrade seismic reflector quality in this area are rough land topography due to erosion, deformed sedimentary units at the land surface, rock layers that dip out of the plane of the seismic profile, and the presence of volcanic units that obscure underlying reflectors. Geophysical methods illustrate that basin geometry is more complicated than would be inferred from extrapolation of surface topography and geology, and these methods aid in defining a three-dimensional framework to understand groundwater storage and flow in southern Nevada.

Shear wave modelling of high resolution OBS data in a gas hydrate environment in the Danube deep-sea fan, Black Sea

NASA Astrophysics Data System (ADS)

Dannowski, A.; Bialas, J.; Zander, T.; Klaeschen, D.

2016-12-01

The Danube deep-sea fan, with his ancient channel-levee systems, hosts multiple bottom-simulating reflections (BSRs) observed in high-resolution reflection seismic data, indicating the occurrence of gas hydrates and free gas. To image the distribution of submarine gas hydrates and the occurrence of free gas in a channel-levee system, high-resolution 2D and 3D multichannel seismic reflection data were collected and fifteen ocean bottom seismometers (OBS) were deployed. The OBS data in particular reveal information about seismic P- and S-wave velocities of the subsurface. They record wave fields of a wide range of incidence angles. Both, P- and S-wave traveltime modelling cover a depth down to 1.5 km below the seafloor; thus, providing seismic velocity information far below the BSR. The seismic P-wave velocities increase with depth from 1600 m/s beneath the seafloor up to 2400 m/s at 1.5 km depth. The frequencies of the S-waves are much lower than the P-wave reflection signals. This is characteristic for shear waves in unconsolidated sediments where the S-wave attenuation is high. However, they travel much slower than P-waves and thus, show a higher resolution. The first S-wave appears at 0.7 s after the direct wave. Some of the S-phases can be traced up to 3.5 km in offset to the station. The seismic S-wave velocities increase from 240 m/s beneath the seafloor up to 1100 m/s at a depth of 1.5 km below the seafloor. From these observations, the P-to-S ratio can be derived. The P-to-S ratio might help to estimate the thickness of the zones with gas hydrates and free gas, while there will be a limited capability to constrain their concentrations.

Merging seismic and MT in Garden Valley, Nevada

DOE Office of Scientific and Technical Information (OSTI.GOV)

Telleen, K.E.

1986-04-01

In the northern part of Garden Valley, Nevada, a 1978 regional seismic program encountered a large area of poor to no-reflection data. Surface geology suggested that a large high structure might underlie the valley floor, and that shallowly buried basalts were causing the poor data. The implied strongly layered structure of electrical resistivity - resistive basalt on conductive Tertiary clastics on resistive paleozoic carbonates - formed an ideal theater for the magnetotelluric method. In 1984, Conoco acquired 48 magnetotelluric sites on about a half-mile grid. These data supported the presence of a buried high block in the Paleozoic rocks andmore » allowed confident mapping of its outlines. In addition, the magnetotelluric survey showed a thin, shallowly buried resistor coextensive with the seismic no-reflection area. In 1985, a high-effort repeat of the earlier no-reflection seismic line confirmed the high block, improved the fault interpretation, and provided weak guidance on the depth of the targeted Paleozoic rocks. Because Garden Valley's Paleozoic stratigraphy differs negligibly from that at nearby Grant Canyon field, the high block constitutes an attractive prospect - possibly the first one found in Nevada due largely to magnetotelluric surveying.« less

Cordilleran front range structural features in northwest Montana interpreted from vintage seismic reflection data

NASA Astrophysics Data System (ADS)

Porter, Mason C.; Rutherford, Bradley S.; Speece, Marvin A.; Mosolf, Jesse G.

2016-04-01

Industry seismic reflection data spanning the Rocky Mountain Cordillera front ranges of northwest Montana were reprocessed and interpreted in this study. Five seismic profiles represent 160 km of deep reflection data collected in 1983 that span the eastern Purcell anticlinorium, Rocky Mountain Trench (RMT), Rocky Mountain Basal Décollement (RMBD), and Lewis thrust. The data were reprocessed using modern techniques including refraction statics, pre-stack time migration (PSTM), and pre- and post-stack depth migration. Results indicate the RMBD is 8-13 km below the Earth's surface and dip 3-10° west. Evidence for the autochthonous Mesoproterozoic Belt and basal Cambrian rocks beneath the RMBD is present in all of the profiles and appears to extend east of the RMT. The Lewis thrust was identified in the seismic profiles and appears to sole into the RMBD east of the RMT. The RMT fault system has a dip displacement of 3-4 km and forms a half graben filled with 1 km of unconsolidated Tertiary sedimentary deposits. The RMT and adjacent Flathead fault systems are interpreted to be structurally linked and may represent a synthetic, en echelon fault system.

Digital Seismic-Reflection Data from Eastern Rhode Island Sound and Vicinity, 1975-1980

USGS Publications Warehouse

McMullen, K.Y.; Poppe, L.J.; Soderberg, N.K.

2009-01-01

During 1975 and 1980, the U.S. Geological Survey (USGS) conducted two seismic-reflection surveys in Rhode Island Sound (RIS) aboard the research vessel Asterias: cruise ASTR75-June surveyed eastern RIS in 1975 and cruise AST-80-6B surveyed southern RIS in 1980. Data from these surveys were recorded in analog form and archived at the USGS Woods Hole Coastal and Marine Science Center's Data Library. In response to recent interest in the geology of RIS and in an effort to make the data more readily accessible while preserving the original paper records, the seismic data from these cruises were scanned and converted to black and white Tagged Image File Format and grayscale Portable Network Graphics images and SEG-Y data files. Navigation data were converted from U.S. Coast Guard Long Range Aids to Navigation time delays to latitudes and longitudes that are available in Environmental Systems Research Institute, Inc., shapefile format and as eastings and northings in space-delimited text format. This report complements two others that contain analog seismic-reflection data from RIS (McMullen and others, 2009) and Long Island and Block Island Sounds (Poppe and others, 2002) and were converted into digital form.

Supra-salt normal fault growth during the rise and fall of a diapir: Perspectives from 3D seismic reflection data, Norwegian North Sea

NASA Astrophysics Data System (ADS)

Tvedt, Anette B. M.; Rotevatn, Atle; Jackson, Christopher A.-L.

2016-10-01

Normal faulting and the deep subsurface flow of salt are key processes controlling the structural development of many salt-bearing sedimentary basins. However, our detailed understanding of the spatial and temporal relationship between normal faulting and salt movement is poor due to a lack of natural examples constraining their geometric and kinematic relationship in three-dimensions. To improve our understanding of these processes, we here use 3D seismic reflection and borehole data from the Egersund Basin, offshore Norway, to determine the structure and growth of a normal fault array formed during the birth, growth and decay of an array of salt structures. We show that the fault array and salt structures developed in response to: (i) Late Triassic-to-Middle Jurassic extension, which involved thick-skinned, sub-salt and thin-skinned supra-salt faulting with the latter driving reactive diapirism; (ii) Early Cretaceous extensional collapse of the walls; and (iii) Jurassic-to-Neogene, active and passive diapirism, which was at least partly coeval with and occurred along-strike from areas of reactive diapirism and wall collapse. Our study supports physical model predictions, showcasing a three-dimensional example of how protracted, multiphase salt diapirism can influence the structure and growth of normal fault arrays.

Updated Tomographic Seismic Imaging at Kilauea Volcano, Hawaii

NASA Astrophysics Data System (ADS)

Okubo, P.; Johnson, J.; Felts, E. S.; Flores, N.

2013-12-01

Improved and more detailed geophysical, geological, and geochemical observations and measurements at Kilauea, along with prolonged eruptions at its summit caldera and east rift zone, are encouraging more ambitious interpretation and modeling of volcanic processes over a range of temporal and spatial scales. We are updating three-dimensional models of seismic wave-speed distributions within Kilauea using local earthquake arrival time tomography to support waveform-based modeling of seismic source mechanisms. We start from a tomographic model derived from a combination of permanent seismic stations comprising the Hawaiian Volcano Observatory (HVO) seismographic network and a dense deployment of temporary stations in the Kilauea caldera region in 1996. Using P- and S-wave arrival times measured from the HVO network for local earthquakes from 1997 through 2012, we compute velocity models with the finite difference tomographic seismic imaging technique implemented by Benz and others (1996), and applied to numerous volcanoes including Kilauea. Particular impetus to our current modeling was derived from a focused effort to review seismicity occurring in Kilauea's summit caldera and adjoining regions in 2012. Our results reveal clear P-wave low-velocity features at and slightly below sea level beneath Kilauea's summit caldera, lying between Halemaumau Crater and the north-facing scarps that mark the southern caldera boundary. The results are also suggestive of changes in seismic velocity distributions between 1996 and 2012. One example of such a change is an apparent decrease in the size and southeastward extent, compared to the earlier model, of the low VP feature imaged with the more recent data. However, we recognize the distinct possibility that these changes are reflective of differences in earthquake and seismic station distributions in the respective datasets, and we need to further populate the more recent HVO seismicity catalogs to possibly address this concern. We also look forward to more complete implementation at HVO of seismic imaging techniques that use ambient seismic noise retrieved from continuous seismic recordings, and to using earthquake arrival times and ambient seismic noise jointly to tomographically image Kilauea.

Multichannel Seismic Images of Cascadia Forearc Structure at the Oregon Margin

NASA Astrophysics Data System (ADS)

Han, S.; Carbotte, S. M.; Carton, H. D.; Canales, J.; Nedimovic, M. R.

2013-12-01

We present new Multichannel Seismic (MCS) images of the Cascadia forearc and downgoing Juan de Fuca plate offshore Oregon. The data were collected during the Cascadia Ridge-to-Trench experiment conducted in June-July 2012 aboard the R/V Langseth. 2D processing including geometry definition, filtering and editing, deconvolution, amplitude correction, velocity analysis, CMP stacking, and post-stack time migration, has been conducted. The new images confirm some previous observations on the location of the plate boundary and structure of the forearc and also reveal new features of the Oregon margin. West of the deformation front, the Juan de Fuca Plate has a dip of ~1.5o and sediment thickness is > 3 km. A bright Moho reflection and reflections from faults cutting through the crust are imaged. The subducting oceanic crust can be traced continuously landward at least to 15 km from the deformation front. One major forearc basin and a smaller basin 10 km from its west end are imaged. Sediments in both basins are folded with wavelengths of 4-6 km and several faults are identified in the larger basin. Beneath the major basin, a low-frequency reflection is imaged at 3.7 s TWTT similar to that imaged by Trehu et al (1995) and interpreted as originating from the top of Siletz terrane. About 70-80 km from the deformation front, a shallowly dipping reflection is imaged at 7.3 s, which likely corresponds to the top of the downgoing plate. Based on existing velocity models for the margin, the location of this reflection is approximately coincident with the July 2004 earthquake cluster interpreted to have occurred at the plate boundary. This bright reflection is presumably similar in origin to the 'bright spot' imaged from two prior multichannel and wide-angle seismic reflection surveys lines located 40 km and 60 km north of our line. The brightness of the reflection may reflect high pore fluid pressure at the plate interface. Just 4 km west of this presumed top-of-subducting plate reflection, there is another deep reflection at around 7 s dipping landward. This reflection may correspond to the base of the Siletz terrane, which would imply a subduction channel beneath the Siletz terrane. Alternatively, this reflection may be related to a subducted seamount identified from magnetic anomalies by Trehu et al (2012). In addition, we image several small diffractors at 5-7 s TWTT to the west, which are likely related to heterogeneities within the accretionary complex. MCS images of the Cascadia forearc at the Oregon margin illustrating these features will be presented and will be compared with the forearc structure imaged along our Washington MCS line from the same survey.

The sinkhole of Schmalkalden, Germany - Imaging of near-surface subrosion structures and faults

NASA Astrophysics Data System (ADS)

Wadas, Sonja H.; Tschache, Saskia; Polom, Ulrich; Krawczyk, Charlotte M.

2017-04-01

In November 2010 a sinkhole of 30 m diameter and 20 m depth opened in a residential area in the village Schmalkalden, Germany, which fortunately led to damage of buildings and property only. The collapse was caused by leaching of soluble rocks in the subsurface, called subrosion. For an improved understanding of the processes leading to subrosion and sinkhole development a detailed characterization of the subsurface structures and elastic parameters is required. We used shear wave reflection seismic, which has proven to be a suitable method for high-resolution imaging of the near-surface. The village Schmalkalden is located in southern Thuringia in Germany. Since the Upper Cretaceous the area is dominated by fault tectonics, fractures and joints, which increase the rock permeability. The circulating groundwater leaches the Permian saline deposits in the subsurface and forms upward migrating cavities, which can develop into sinkholes, if the overburden collapses. In the direct vicinity of the backfilled sinkhole, five 2-D shear wave reflection seismic profiles with total length of ca. 900 m and a zero-offset VSP down to 150 m depth were acquired. For the surface profiles a 120-channel landstreamer attached with horizontal geophones and an electrodynamic micro-vibrator, exciting horizontally polarized shear waves, were used. For the VSP survey an oriented borehole probe equipped with a 3C-geophone and electrodynamic and hydraulic vibrators, exciting compression- and shear waves, were utilized. The seismic sections show high-resolution images from the surface to ca. 100 m depth. They display heterogeneous structures as indicated by strong vertical and lateral variations of the reflectors. In the near-surface, depressions are visible and zones of low seismic velocities < 180 m/s show increased attenuation of the seismic wave field. These are probably the result of the fractured underground, due to fault tectonics and the ongoing subrosion. The unstable zones are additionally characterized by a low shear modulus < 120 MPa, which is derived from density and shear wave interval velocities. The results from the 2-D reflection seismics are supplemented with results of a VSP survey in a borehole near the former sinkhole. The VSP data shows anomalies of the Vp-Vs ratio with values above 2,5. This indicates unstable zones correlated with the anomalies revealed by the 2-D sections. Possible factors for the development of the Schmalkalden sinkhole in 2010 are the presence of soluble Permian deposits, the strongly fractured underground and the identified faults.

Comments on ``seismic properties of the Eltanin transform system, south Pacific'' by Emile A. Okal and Amy R. Langenhorst

NASA Astrophysics Data System (ADS)

Wessel, Paul; Kroenke, Loren W.

2001-03-01

Seismicity in the Eltanin transform system region reflects the current relative motion between the Pacific and Antarctica plates. As such, the seismicity provides little or no constraints on models for late Neogene Pacific absolute plate motion changes that in turn forced a synchronous change in relative plate motions resulting in the current relative plate motion.

Delineation of sediments below flood basalts by joint inversion of seismic and magnetotelluric data

NASA Astrophysics Data System (ADS)

Manglik, A.; Verma, Saurabh K.

A one-dimensional joint-inversion (JI) scheme considering seismic reflection and refraction, and MT data is developed. Its efficacy to resolve low velocity conducting sediments below high velocity resistive flood basalts is tested for a representative geological model considering noisy, incomplete data. The JI is found to provide improved results in comparison to those obtained by individual seismic and MT inversions.

Time-lapse CO2 monitoring using ambient-noise seismic interferometry: a feasibility study from Ketzin, Germany

NASA Astrophysics Data System (ADS)

Boullenger, Boris; Verdel, Arie; Paap, Bob; Thorbecke, Jan; Draganov, Deyan

2015-04-01

Seismic interferometry applied to ambient-noise measurements allows retrieval of the Green's function between two seismic receivers, by cross-correlating their recordings, as if from a source at one of the receivers. We propose to use ambient-noise seismic interferometry (ANSI) to retrieve reflection data. The time-lapse differences between different vintages of the retrieved data may help characterize property changes within a geologic reservoir with varying CO2 saturation. We test the feasibility of this time-lapse passive seismic method with numerical experiments based on the CO2-storage site of Ketzin, Germany. Ambient-noise recordings from Ketzin exhibit significant passive body-wave energy (from natural tremors or induced seismicity in the vicinity of the reservoir), which is advantageous to retrieve reflections with ANSI. The ANSI numerical experiments aim to understand what the requirements are for the recorded body-wave noise to retrieve the time-lapse reflection signal caused by an increase of CO2 saturation in the reservoir. For this purpose, we design two velocity scenarios at Ketzin: a base scenario before the injection of CO2, and a repeat scenario corresponding to a P-wave velocity decline in the reservoir by 20 percent. For both scenarios, we simulate passive seismic experiments of body-wave noise recordings that may take several days or months to record in the field. The passive recordings are obtained by modelling global (direct wave, internal and surface multiples) transmission responses from band-limited subsurface noise sources, randomly triggered in space and time. The time-lapse reflection signal is obtained by taking the differences between the base and the repeat retrieved reflection data (virtual common-shot gathers). We found that the time-lapse signal is still recovered with ANSI even if the base and repeat retrieved reflection data are partially polluted with artifacts. This means that uneven illumination of the array does not necessarily exclude acceptable time-lapse signal retrieval. Furthermore, the clarity of the time-lapse signal at the reservoir level increases with increasing repeatability of the two passive experiments. The increase in repeatability is achieved when the contributing noise sources form denser clusters that share analogous spatial coverage. To support the merits of the numerical experiments, we applied ANSI (by auto-correlation) to three days of Ketzin passive field-data and compare the retrieved responses with the modelling results. The data are recorded at a permanent array of sensors (hydrophones and geophones) installed above the injection site. We used the records from the buried line of the array that consists of sensors lying at 50-meters depth. These records are less contaminated with surface noise and preserve passive body-wave events better than surface-recorded data. The retrieved responses exhibit significant correspondence with the existing active-seismic field data as well as with our modelled ANSI and active responses. Key reflection events seem to be retrieved at the expected arrival times and support the idea that the settings and characteristics of the ambient noise at Ketzin offer good potential for time-lapse ANSI to monitor CO2 sequestration.

A comparison of Q-factor estimation methods for marine seismic data

NASA Astrophysics Data System (ADS)

Kwon, J.; Ha, J.; Shin, S.; Chung, W.; Lim, C.; Lee, D.

2016-12-01

The seismic imaging technique draws information from inside the earth using seismic reflection and transmission data. This technique is an important method in geophysical exploration. Also, it has been employed widely as a means of locating oil and gas reservoirs because it offers information on geological media. There is much recent and active research into seismic attenuation and how it determines the quality of seismic imaging. Seismic attenuation is determined by various geological characteristics, through the absorption or scattering that occurs when the seismic wave passes through a geological medium. The seismic attenuation can be defined using an attenuation coefficient and represented as a non-dimensional variable known as the Q-factor. Q-factor is a unique characteristic of a geological medium. It is a very important material property for oil and gas resource development. Q-factor can be used to infer other characteristics of a medium, such as porosity, permeability and viscosity, and can directly indicate the presence of hydrocarbons to identify oil and gas bearing areas from the seismic data. There are various ways to estimate Q-factor in three different domains. In the time domain, pulse amplitude decay, pulse rising time, and pulse broadening are representative. Logarithm spectral ratio (LSR), centroid frequency shift (CFS), and peak frequency shift (PFS) are used in the frequency domain. In the time-frequency domain, Wavelet's Envelope Peak Instantaneous Frequency (WEPIF) is most frequently employed. In this study, we estimated and analyzed the Q-factor through the numerical model test and used 4 methods: the LSR, CFS, PFS, and WEPIF. Before we applied these 4 methods to observed data, we experimented with the numerical model test. The numerical model test data is derived from Norsar-2D, which is the basis of the ray-tracing algorithm, and we used reflection and normal incidence surveys to calculate Q-factor according to the array of sources and receivers. After the numerical model test, we chose the most accurate of the 4 methods by comparing Q-factor through reflection and normal incidence surveys. We applied the method to the observed data and proved its accuracy.

Ambient seismic noise applications for Titan

NASA Astrophysics Data System (ADS)

Jackson, J. M.; Zhan, Z.; Clayton, R. W.; Helmberger, D. V.; Tsai, V. C.

2010-12-01

Titan is Saturn’s largest moon and is host to a myriad of surface, crustal, and perhaps interior dynamic processes (e.g., Lunine & Lorenz 2009; Sotin et al. 2009). Although recent gravity data put constraints on the nature of Titan’s deep interior (Iess et al. 2010), details regarding the layering and crustal structure remain poorly constrained. For example, the crustal thickness derived from modeling of the gravity data suggests a value ~100 km, but with a large uncertainty. There may exist a subsurface ocean or reservoirs of liquid that actively connects with Titan’s hyrdrocarbon-bearing lakes and atmosphere. Cross-correlation of ambient seismic noise is an emerging method to study crustal structures (e.g., Shapiro et al. 2005). Recent results show that under certain conditions, such as post-critical reflections, the Moho-reflected shear wave (SmS) can be clearly identified with ambient seismic noise [Zhan et al. 2010]. Titan may represent a plausible planetary body to apply the methods of ambient seismic noise, thereby providing a unique opportunity to better understand the interior of an icy body in our solar system. We will explore the use of ambient seismic noise on Titan and assess its application to determine interior structures, such as signals expected for different crust-(ocean)-mantle boundary depths. References: Iess, L. et al. (2010), Science 327: 1367-1369 Lunine, J.I. and Lorenz, R.D. (2009), Ann. Rev. Earth Planet. Sci. 37: 299-320. Shapiro et al. (2005), Science 307: 1615-1618. Sotin et al. (2009), in Titan from Cassini-Huygens: 61-73. R.H. Brown, J.-P. Lebreton, J. Hunter Waite, Eds. Zhan, Z. et al. (2010), Geophys. J. Int. doi: 10.1111/j/1365-246X.2010.04625.x Acknowledgments: Parts of this work grew out of discussions during a mini study at the Keck Institute for Space Studies, which is funded by the W. M. Keck Foundation.

The Sunda-Banda Arc Transition: New Insights From Marine Wide-Angle Seismic Data

NASA Astrophysics Data System (ADS)

Planert, L.; Shulgin, A.; Kopp, H.; Mueller, C.; Flueh, E.; Lueschen, E.; Engels, M.; Dayuf Jusuf, M.

2007-12-01

End of 2006, RV SONNE cruise SO190 SINDBAD (Seismic and Geoacoustic Investigations along the Sunda- Banda Arc Transition) went south of the Indonesian archipelago to acquire various geophysical datasets between 112 °E and 122 °E. The main goal of the project is to investigate the modifications of the lower plate (variability in the plate roughness, transition from oceanic to continental lower plate) and their effects on the tectonics of the upper plate (development of an outer high and forearc basin, accretionary and erosive processes). The tectonic style changes in neighboring margin segments from an oceanic plate-island arc subduction along the eastern Sunda margin to a continental plate-island arc collision along the Banda margin. Moreover, the character of the incoming oceanic plate varies from the rough topography in the area where the Roo Rise is subducting off eastern Java, to the smooth oceanic seafloor of the Argo- Abyssal Plain subducting off Bali, Lombok, and Sumbawa. In order to cover the entire variations of the lower plate, seven seismic refraction profiles were conducted along four major north-south oriented corridors of the margin, at 113 °E, 116 °E, 119 °E, and 121 °E, as well as three profiles running perpendicular to the major corridors. A total of 239 ocean bottom hydrophone and seismometer deployments were successfully recovered. Shooting was conducted along 1020 nm of seismic profiles using a G-gun cluster of 64 l. Here, we present velocity models obtained by applying a tomographic approach which jointly inverts for refracted and reflected phases. Additional geometry and velocity information for the uppermost layers, obtained by prestack depth migration of multichannel seismic reflection data (see poster of Mueller et al. in this session), is incorporated into our models and held fixed during the iterations. geomar.de/index.php?id=sindbad

High lateral resolution exploration using surface waves from noise records

NASA Astrophysics Data System (ADS)

Chávez-García, Francisco José Yokoi, Toshiaki

2016-04-01

Determination of the shear-wave velocity structure at shallow depths is a constant necessity in engineering or environmental projects. Given the sensitivity of Rayleigh waves to shear-wave velocity, subsoil structure exploration using surface waves is frequently used. Methods such as the spectral analysis of surface waves (SASW) or multi-channel analysis of surface waves (MASW) determine phase velocity dispersion from surface waves generated by an active source recorded on a line of geophones. Using MASW, it is important that the receiver array be as long as possible to increase the precision at low frequencies. However, this implies that possible lateral variations are discarded. Hayashi and Suzuki (2004) proposed a different way of stacking shot gathers to increase lateral resolution. They combined strategies used in MASW with the common mid-point (CMP) summation currently used in reflection seismology. In their common mid-point with cross-correlation method (CMPCC), they cross-correlate traces sharing CMP locations before determining phase velocity dispersion. Another recent approach to subsoil structure exploration is based on seismic interferometry. It has been shown that cross-correlation of a diffuse field, such as seismic noise, allows the estimation of the Green's Function between two receivers. Thus, a virtual-source seismic section may be constructed from the cross-correlation of seismic noise records obtained in a line of receivers. In this paper, we use the seismic interferometry method to process seismic noise records obtained in seismic refraction lines of 24 geophones, and analyse the results using CMPCC to increase the lateral resolution of the results. Cross-correlation of the noise records allows reconstructing seismic sections with virtual sources at each receiver location. The Rayleigh wave component of the Green's Functions is obtained with a high signal-to-noise ratio. Using CMPCC analysis of the virtual-source seismic lines, we are able to identify lateral variations of phase velocity inside the seismic line, and increase the lateral resolution compared with results of conventional analysis.

Investigation of sea-level changes and shelf break prograding sequences during the Late Quaternary offshore of Kusadasi (West Anatolia) and surroundings by high resolution seismic methods

NASA Astrophysics Data System (ADS)

Gurcay, Savas; Cifci, Gunay; Dondurur, Derman; Okay, Seda; Atgin, Orhan; Ozel, Ozkan; Mert Kucuk, Hilmi

2016-04-01

High Resolution multi-channel seismic reflection and Chirp data were collected by K. Piri Reis, research vessel of Dokuz Eylül University, in the central Aegean coast of the West Anatolia by research cruises carried out in 2005 and 2008, respectively. Submarine stratigraphic and structural features of Sıǧacık Gulf, Kuşadası Gulf and surroundings were investigated under this survey. The data were processed and interpreted in SeisLab, D.E.U. Marine Sciences and Technology seismic laboratory. Thirteen distinct unconformities can be traced below the study area that separate thirteen progradational stacked paleo-delta sequences (Lob1-Lob13) on seismic profiles following and cutting each other. As a result of comparison with the oxygen isotopic stages (δ18), these deltas (Lob1-L13) were interpreted that they have been deposited during the sea-level lowstands within Pleistocene glacial stages. In the study area the basement surface which observed as the lowest unconformity surface of the seismic sections was called 'Acoustic Basement'. This basement which traced approximately all of the seismic sections has generally quite wavy surface and underlain the upper seismic units. It was observed that these seismic units which terminated their formation in Pleistocene (Lob1-Lob13) and Holocene period were cut and uplifted by acoustic basement, like an intrusion. These type deformations were interpreted as a result of magmatic intrusion into these upper seismic units occurred in Late Pleistocene and Holocene period. Tectonic and structural interpretation was carried out to constitute the submarine active tectonic map of the study area by correlated active faults identified on seismic sections. Submarine active tectonic map and, basement topography and sediment thickness map were correlated together to present the relationship between tectonic deformation and stratigraphy.

Finite-Difference Modeling of Seismic Reflection Data in a Hard Rock Environment: An Example from the Mineralized Otago Schist, New Zealand

NASA Astrophysics Data System (ADS)

Leslie, A.; Gorman, A. R.

2004-12-01

The interpretation of seismic reflection data in non-sedimentary environments is problematic. In the Macraes Flat region near Dunedin (South Island, New Zealand), ongoing mining of mineralized schist has prompted the development of a seismic interpretation scheme that is capable of imaging a gold-bearing shear zone and associated mineralized structures accurately to the meter scale. The anisotropic and complex structural nature of this geological environment necessitates a cost-effective computer-based modeling technique that can provide information on the physical characteristics of the schist. Such a method has been tested on seismic data acquired in 1993 over a region that has since been excavated and logged. Correlation to measured structural data permits a direct comparison between the seismic data and the actual geology. Synthetic modeling utilizes a 2D visco-elastic finite difference routine to constrain the interpretation of observed seismic characteristics, including the velocity, anisotropy, and contrast, of the shear zone structures. Iterative refinements of the model result in a more representative synthetic model that most closely matches the seismic response. The comparison between the actual and synthetic seismic sections provides promising results that will be tested by new data acquisition over the summer of 2004/2005 to identify structures and zones of potential mineralization. As a downstream benefit, this research could also contribute to earthquake risk assessment analyses at active faults with similar characteristics.

New methods for engineering site characterization using reflection and surface wave seismic survey

NASA Astrophysics Data System (ADS)

Chaiprakaikeow, Susit

This study presents two new seismic testing methods for engineering application, a new shallow seismic reflection method and Time Filtered Analysis of Surface Waves (TFASW). Both methods are described in this dissertation. The new shallow seismic reflection was developed to measure reflection at a single point using two to four receivers, assuming homogeneous, horizontal layering. It uses one or more shakers driven by a swept sine function as a source, and the cross-correlation technique to identify wave arrivals. The phase difference between the source forcing function and the ground motion due to the dynamic response of the shaker-ground interface was corrected by using a reference geophone. Attenuated high frequency energy was also recovered using the whitening in frequency domain. The new shallow seismic reflection testing was performed at the crest of Porcupine Dam in Paradise, Utah. The testing used two horizontal Vibroseis sources and four receivers for spacings between 6 and 300 ft. Unfortunately, the results showed no clear evidence of the reflectors despite correction of the magnitude and phase of the signals. However, an improvement in the shape of the cross-correlations was noticed after the corrections. The results showed distinct primary lobes in the corrected cross-correlated signals up to 150 ft offset. More consistent maximum peaks were observed in the corrected waveforms. TFASW is a new surface (Rayleigh) wave method to determine the shear wave velocity profile at a site. It is a time domain method as opposed to the Spectral Analysis of Surface Waves (SASW) method, which is a frequency domain method. This method uses digital filtering to optimize bandwidth used to determine the dispersion curve. Results from testings at three different sites in Utah indicated good agreement with the dispersion curves measured using both TFASW and SASW methods. The advantage of TFASW method is that the dispersion curves had less scatter at long wavelengths as a result from wider bandwidth used in those tests.

High-resolution seismic imaging of the Kevitsa mafic-ultramafic Cu-Ni-PGE hosted intrusion, northern Finland

NASA Astrophysics Data System (ADS)

Malehmir, Alireza; Koivisto, Emilia; Wjins, Chris; Tryggvason, Ari; Juhlin, Christopher

2014-05-01

Kevitsa, in northern Finland, is a large nickel/copper ore body hosted by a massive mafic-ultramafic intrusion with measured and indicated resources of 240 million tons (cutoff 0.1%) grading 0.30% Ni and 0.41% Cu. Mining started in 2012 with an open pit that will extend down to about 550-600 m depth. The expected mine life is more than 20 years. Numerous boreholes are available in the area, but the majority of them are shallow and do not provide a comprehensive understanding of the dimensions of the intrusion. However, a number of boreholes do penetrate the basal contact of the intrusion. Most of these are also shallow and concentrated at the edge of the intrusion. A better knowledge of the geometry of the intrusion would provide a framework for near-mine and deep exploration in the area, but also a better understanding of the geology. Exact mapping of the basal contact of the intrusion would also provide an exploration target for the contact-type mineralization that is often more massive and richer in Ni-Cu than the disseminated mineralization away from the contact. With the objective of better characterizing the intrusion, a series of 2D profiles were acquired followed by a 3D reflection survey that covered an area of about 3 km by 3 km. Even though the geology is complex and the seismic P-wave velocity ranges between 5 to 8 km/s, conventional processing results show gently- to steeply-dipping reflections from depths of approximately 2 km to as shallow as 100 m. Many of these reflections are interpreted to originate from either fault systems or internal magmatic layering within the Kevitsa main intrusion. Correlations between the 3D surface seismic data and VSP data, based upon time shifts or phase changes along the reflections, support the interpretation that numerous faults are imaged in the volume. Some of these faults cross the planned open-pit mine at depths of about 300-500 m, and it is, therefore, critical to map them for mine planning. The seismic 3D volume better represents the geology around the mine and in the vicinity of the known deposit, while the 2D seismic profiles were designed to provide information on larger-scale structures in the area. Both the 2D and 3D seismic data were used to create a 3D lithological and structural model of the entire complex. Information on the dimensions of the ore-bearing Kevitsa intrusion can be used for more effective exploration in the area. The base of the intrusion is particularly clear in the northern and western sectors of the seismic data. Toward the east, the base is mostly defined by disruption of the reflectors internal to the intrusion. Recent tests using prestack migration methods on the 3D data show partial improvements in the image, especially at shallow depths. 3D seismic tomography has also been performed and the results indicate low velocity zones crossing the open pit that can be interpreted as zones of weakness. Future studies will focus on using the tomography results as the input velocity field for prestack depth migration of the 3D data and also improving the 3D geological model of the study area. Acknowledgments: FQM, GTK, HiSeis and Vibrometric

Accessing seismic data through geological interpretation: Challenges and solutions

NASA Astrophysics Data System (ADS)

Butler, R. W.; Clayton, S.; McCaffrey, B.

2008-12-01

Between them, the world's research programs, national institutions and corporations, especially oil and gas companies, have acquired substantial volumes of seismic reflection data. Although the vast majority are proprietary and confidential, significant data are released and available for research, including those in public data libraries. The challenge now is to maximise use of these data, by providing routes to seismic not simply on the basis of acquisition or processing attributes but via the geology they image. The Virtual Seismic Atlas (VSA: www.seismicatlas.org) meets this challenge by providing an independent, free-to-use community based internet resource that captures and shares the geological interpretation of seismic data globally. Images and associated documents are explicitly indexed by extensive metadata trees, using not only existing survey and geographical data but also the geology they portray. The solution uses a Documentum database interrogated through Endeca Guided Navigation, to search, discover and retrieve images. The VSA allows users to compare contrasting interpretations of clean data thereby exploring the ranges of uncertainty in the geometric interpretation of subsurface structure. The metadata structures can be used to link reports and published research together with other data types such as wells. And the VSA can link to existing data libraries. Searches can take different paths, revealing arrays of geological analogues, new datasets while providing entirely novel insights and genuine surprises. This can then drive new creative opportunities for research and training, and expose the contents of seismic data libraries to the world.

Stratigraphic Signatures of Forearc Basin Formation Mechanisms

NASA Astrophysics Data System (ADS)

Mannu, U.; Ueda, K.; Gerya, T.; Willett, S.; Strasser, M.

2014-12-01

Forearc basins are loci of active sedimentation above the landward portion of accretionary prisms. Although these basins typically remain separated from the frontal prism by a forearc high, their evolution has a significant impact on the structure and deformation of the entire wedge. Formation of forearc basins has been proposed as a consequence of changes in wedge stability due to an increase of slab dip in subduction zones. Another hypothesis attributes this to higher hinterland sedimentation, which causes the rear of the wedge to stabilize and eventually develop a forearc basin. Basin stratigraphic architecture, revealed by high-resolution reflection seismic data and borehole data allows interpretation of structural development of the accretionary prism and associated basins with the goal of determining the underlying driving mechanism(s) of basin formation. In this study we supplement data interpretation with thermo-mechanical numerical models including high-resolution isochronal surface tracking to visualize the developing stratigraphy of basins that develop in subduction zone and wedge dynamic models. We use a dynamic 2D thermo mechanical model incorporating surface processes, strain weakening and sediment subduction. The model is a modification of I2VIS model, which is based on conservative, fully staggered finite differences and a non-diffusive marker- in-cell technique capable of modelling mantle convection. In the model different driving mechanisms for basin formation can be explored. Stratigraphic simulations obtained by isochronal surface tracking are compared to reflection pattern and stratigraphy of seismic and borehole data, respectively. Initial results from a model roughly representing the Nankai Trough Subduction Zone offshore Japan are compared to available seismic and Integrated Ocean Drilling (IODP) data. A calibrated model predicting forearc basin stratigraphy will be used to discern the underlying process of basins formation and wedge dynamics.

Development of a technique for long-term detection of precursors of strong earthquakes using high-resolution satellite images

NASA Astrophysics Data System (ADS)

Soto-Pinto, C. A.; Arellano-Baeza, A. A.; Ouzounov, D. P.

2012-12-01

Among a variety of processes involved in seismic activity, the principal process is the accumulation and relaxation of stress in the crust, which takes place at the depth of tens of kilometers. While the Earth's surface bears at most the indirect sings of the accumulation and relaxation of the crust stress, it has long been understood that there is a strong correspondence between the structure of the underlying crust and the landscape. We assume the structure of the lineaments reflects an internal structure of the Earth's crust, and the variation of the lineament number and arrangement reflects the changes in the stress patterns related to the seismic activity. Contrary to the existing assumptions that lineament structure changes only at the geological timescale, we have found that the much faster seismic activity strongly affects the system of lineaments extracted from the high-resolution multispectral satellite images. Previous studies have shown that accumulation of the stress in the crust previous to a strong earthquake is directly related to the number increment and preferential orientation of lineament configuration present in the satellite images of epicenter zones. This effect increases with the earthquake magnitude and can be observed approximately since one month before. To study in details this effect we have developed a software based on a series of algorithms for automatic detection of lineaments. It was found that the Hough transform implemented after the application of discontinuity detection mechanisms like Canny edge detector or directional filters is the most robust technique for detection and characterization of changes in the lineament patterns related to strong earthquakes, which can be used as a robust long-term precursor of earthquakes indicating regions of strong stress accumulation.

High-resolution seismic-reflection profiles collected by the R/V Columbus Iselin, cruise CI 7807-1, in the Baltimore Canyon outer continental shelf area, offshore New Jersey

USGS Publications Warehouse

Robb, James M.

1980-01-01

High-resolution seismic-reflection profiles were collected by the U.S. Geological Survey (USGS) aboard R/V COLUMBUS ISELIN, cruise 7807-1, from 18 August to 4 September 1978 over the Continental Slope of the Eastern United States between Wilmington and Hudson Canyons. These data were acquired as part of a study to determine potential geologic hazards to petroleum development of the Baltimore Canyon trough area. On this cruise, the Continental Slope between Lindenkohl and Carteret Canyons was surveyed along lines spaced one-half nautical mile apart to study the size and distribution of mass-wasting features as a guide to assess the importance of mass wasting processes on the Continental Slope. The seismic-reflection profiles were placed to complement other data gathered previously by the USGS.Track-line distances totaled 2,050 km of 40-in3 air-gun (with wave shaper) profiles, 2,100 km of 800-J sparker data, and 2,100 km of 3 .5-kHz data. The air-gun and sparker profiles are of high quality, but the 3.5-kHz system did not function well and achieved no subbottom penetration. The side-scan sonar system was operated along the uppermost Continental Slope to investigate its potential for use in this environment. Data were acquired over 22 km of ship's track.Navigation was by Loran-C (5-minute fix interval).The original records can be examined at the U.S. Geological Survey offices in Woods Hole, Massachusetts 02543. Microfilm copies of the data are available for purchase from the National Geophysical and Solar-Terrestrial Data Center (NGSDC), Boulder, Colorado 80303.

TOMO3D: 3-D joint refraction and reflection traveltime tomography parallel code for active-source seismic data—synthetic test

NASA Astrophysics Data System (ADS)

Meléndez, A.; Korenaga, J.; Sallarès, V.; Miniussi, A.; Ranero, C. R.

2015-10-01

We present a new 3-D traveltime tomography code (TOMO3D) for the modelling of active-source seismic data that uses the arrival times of both refracted and reflected seismic phases to derive the velocity distribution and the geometry of reflecting boundaries in the subsurface. This code is based on its popular 2-D version TOMO2D from which it inherited the methods to solve the forward and inverse problems. The traveltime calculations are done using a hybrid ray-tracing technique combining the graph and bending methods. The LSQR algorithm is used to perform the iterative regularized inversion to improve the initial velocity and depth models. In order to cope with an increased computational demand due to the incorporation of the third dimension, the forward problem solver, which takes most of the run time (˜90 per cent in the test presented here), has been parallelized with a combination of multi-processing and message passing interface standards. This parallelization distributes the ray-tracing and traveltime calculations among available computational resources. The code's performance is illustrated with a realistic synthetic example, including a checkerboard anomaly and two reflectors, which simulates the geometry of a subduction zone. The code is designed to invert for a single reflector at a time. A data-driven layer-stripping strategy is proposed for cases involving multiple reflectors, and it is tested for the successive inversion of the two reflectors. Layers are bound by consecutive reflectors, and an initial velocity model for each inversion step incorporates the results from previous steps. This strategy poses simpler inversion problems at each step, allowing the recovery of strong velocity discontinuities that would otherwise be smoothened.