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Sample records for 2d seismic reflection

  1. 2D Seismic Reflection Data across Central Illinois

    SciTech Connect

    Smith, Valerie; Leetaru, Hannes

    2014-09-30

    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 necessary 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

  2. 2D seismic reflection tomography in strongly anisotropic media

    NASA Astrophysics Data System (ADS)

    Huang, Guangnan; Zhou, Bing; Li, Hongxi; Zhang, Hua; Li, Zelin

    2014-12-01

    Seismic traveltime tomography is an effective method to reconstruct underground anisotropic parameters. Currently, most anisotropic tomographic methods were developed under the assumption of weak anisotropy. The tomographic method proposed here can be implemented for imaging subsurface targets in strongly anisotropic media with a known tilted symmetry axis, since the adopted ray tracing method is suitable for anisotropic media with arbitrary degree. There are three kinds of reflection waves (qP, qSV and qSH waves) that were separately used to invert the blocky abnormal body model. The reflection traveltime tomographiy is developed here because a surface observation system is the most economical and practical way compared with crosswell and VSP. The numerical examples show that the traveltimes of qP reflection wave have inverted parameters {{c}11},{{c}13},{{c}33} \\text{and} {{c}44} successfully. Traveltimes of qSV reflection wave have inverted parameters {{c}11},{{c}33} \\text{and} {{c}44} successfully, with the exception of the {{c}13}, since it is less sensitive than other parameters. Traveltimes of qSH reflection wave also have inverted parameters {{c}44} \\text{and} {{c}66} successfully. In addition, we find that the velocity sensitivity functions (derivatives of phase velocity with respect to elastic moduli parameters) and raypath illuminating angles have a great influence on the qualities of tomograms according to the inversion of theoretical models. Finally, the numerical examples confirm that the reflection traveltime tomography can be applied to invert strongly anisotropic models.

  3. Geomorphological relationships through the use of 2-D seismic reflection data, Lidar, and aerial imagery

    NASA Astrophysics Data System (ADS)

    Alesce, Meghan Elizabeth

    Barrier Islands are crucial in protecting coastal environments. This study focuses on Dauphin Island, Alabama, located within the Northern Gulf of Mexico (NGOM) Barrier Island complex. It is one of many islands serving as natural protection for NGOM ecosystems and coastal cities. The NGOM barrier islands formed at 4 kya in response to a decrease in rate of sea level rise. The morphology of these islands changes with hurricanes, anthropogenic activity, and tidal and wave action. This study focuses on ancient incised valleys and and the impact on island morphology on hurricane breaches. Using high frequency 2-D seismic reflection data four horizons, including the present seafloor, were interpreted. Subaerial portions of Dauphin Island were imaged using Lidar data and aerial imagery over a ten-year time span, as well as historical maps. Historical shorelines of Dauphin Island were extracted from aerial imagery and historical maps, and were compared to the location of incised valleys seen within the 2-D seismic reflection data. Erosion and deposition volumes of Dauphin Island from 1998 to 2010 (the time span covering hurricanes Ivan and Katrina) in the vicinity of Katrina Cut and Pelican Island were quantified using Lidar data. For the time period prior to Hurricane Ivan an erosional volume of 46,382,552 m3 and depositional volume of 16,113.6 m3 were quantified from Lidar data. The effects of Hurricane Ivan produced a total erosion volume of 4,076,041.5 m3. The erosional and depositional volumes of Katrina Cut being were 7,562,068.5 m3 and 510,936.7 m3, respectively. More volume change was found within Pelican Pass. For the period between hurricanes Ivan and Katrina the erosion volume was 595,713.8 m3. This was mostly located within Katrina Cut. Total deposition for the same period, including in Pelican Pass, was 15,353,961 m3. Hurricane breaches were compared to ancient incised valleys seen within the 2-D seismic reflection results. Breaches from hurricanes from 1849

  4. Volcano growth mechanisms and the role of sub-volcanic intrusions: Insights from 2D seismic reflection data

    NASA Astrophysics Data System (ADS)

    Magee, Craig; Hunt-Stewart, Esther; Jackson, Christopher A.-L.

    2013-07-01

    Temporal and spatial changes in volcano morphology and internal architecture can determine eruption style and location. However, the relationship between the external and internal characteristics of volcanoes and sub-volcanic intrusions is often difficult to observe at outcrop or interpret uniquely from geophysical and geodetic data. We use high-quality 2D seismic reflection data from the Ceduna Sub-basin, offshore southern Australia, to quantitatively analyse 56, pristinely-preserved, Eocene-age volcanogenic mounds, and a genetically-related network of sub-volcanic sills and laccoliths. Detailed seismic mapping has allowed the 3D geometry of each mound to be reconstructed and distinct seismic facies within them to be recognised. Forty-six continental, basaltic shield volcanoes have been identified that have average flank dips of <12°, basal diameters of 1.94-18.89 km, central summits that are 0.02-1 km high and volumes that range from 0.06 to 57.21 km3. Parallel seismic reflections within the shield volcanoes are interpreted to represent interbedded volcanic and clastic material, suggesting that a series of temporally separate eruptions emanated from a central vent. The shield volcanoes typically overlie the lateral tips of sills and we suggest that the intermittent eruption phases correspond to the incremental emplacement of discrete magma pulses within the laterally extensive sill-complex. Eight volcanogenic hydrothermal vents, which are also associated with the lateral tips of sills, were also recognised, and these appear to have formed from the seepage of intrusion-related hydrothermal fluids onto the seafloor via emplacement-induced fractures. This work highlights that deformation patterns preceding volcanic eruptions may (i) be offset from the eruption site; (ii) attributed to intrusions with complex morphologies; and/or (iii) reflect magma movement along pre-existing fracture systems. These complexities should therefore be considered in eruption

  5. The seismic analyzer: interpreting and illustrating 2D seismic data.

    PubMed

    Patel, Daniel; Giertsen, Christopher; Thurmond, John; Gjelberg, John; Gröller, M Eduard

    2008-01-01

    We present a toolbox for quickly interpreting and illustrating 2D slices of seismic volumetric reflection data. Searching for oil and gas involves creating a structural overview of seismic reflection data to identify hydrocarbon reservoirs. We improve the search of seismic structures by precalculating the horizon structures of the seismic data prior to interpretation. We improve the annotation of seismic structures by applying novel illustrative rendering algorithms tailored to seismic data, such as deformed texturing and line and texture transfer functions. The illustrative rendering results in multi-attribute and scale invariant visualizations where features are represented clearly in both highly zoomed in and zoomed out views. Thumbnail views in combination with interactive appearance control allows for a quick overview of the data before detailed interpretation takes place. These techniques help reduce the work of seismic illustrators and interpreters.

  6. Modelling of a coal seam of the deposit Đurđevik (BiH) by means of 2D reflection seismic imaging

    NASA Astrophysics Data System (ADS)

    Arsenović, Siniša; Urošević, Milovan; Sretenović, Branislav; Cvetkov, Vesna; Životić, Dragana

    2016-06-01

    A low cost 2D reflection seismic survey was used to map the continuity of the main seams as well as the numerous faults at the Đurđevik sub-bituminous coal deposit (BiH). A 24-channel seismic data acquisition system was available for this survey. The natural high reflectivity of the coal seams and a favourable geometry of seismic profiles enabled the identification and correlation of major faults across the area. Rugged terrain presented challenges to both data acquisition and processing. Stacks of acceptable quality were obtained only after the application of surface consistent statics and careful application of multi-channel filtering. A set of recorded 2D lines was interpreted in a 3D environment. Inferred structural elements disrupting the seam continuity were identified and were in agreement with available drilling results and mine workings. The result of this work was used to reduce mining hazards and also to help optimise mine planning.

  7. 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

  8. Teaching Reflection Seismic Processing

    NASA Astrophysics Data System (ADS)

    Forel, D.; Benz, T.; Pennington, W. D.

    2004-12-01

    Without pictures, it is difficult to give students a feeling for wave propagation, transmission, and reflection. Even with pictures, wave propagation is still static to many. However, when students use and modify scripts that generate wavefronts and rays through a geologic model that they have modified themselves, we find that students gain a real feeling for wave propagation. To facilitate teaching 2-D seismic reflection data processing (from acquisition through migration) to our undergraduate and graduate Reflection Seismology students, we use Seismic Un*x (SU) software. SU is maintained and distributed by Colorado School of Mines, and it is freely available (at www.cwp.mines.edu/cwpcodes). Our approach includes use of synthetic and real seismic data, processing scripts, and detailed explanation of the scripts. Our real data were provided by Gregory F. Moore of the University of Hawaii. This approach can be used by any school at virtually no expense for either software or data, and can provide students with a sound introduction to techniques used in processing of reflection seismic data. The same software can be used for other purposes, such as research, with no additional expense. Students who have completed a course using SU are well equipped to begin using it for research, as well. Scripts for each processing step are supplied and explained to the students. Our detailed description of the scripts means students do not have to know anything about SU to start. Experience with the Unix operating system is preferable but not necessary -- our notes include Computer Hints to help the beginner work with the Unix operating system. We include several examples of synthetic model building, acquiring shot gathers through synthetic models, sorting shot gathers to CMP gathers, gain, 1-D frequency filtering, f-k filtering, deconvolution, semblance displays and velocity analysis, flattening data (NMO), stacking the CMPs, and migration. We use two real (marine) data sets. One

  9. 3D Reservoir Modeling of Semutang Gas Field: A lonely Gas field in Chittagong-Tripura Fold Belt, with Integrated Well Log, 2D Seismic Reflectivity and Attributes.

    NASA Astrophysics Data System (ADS)

    Salehin, Z.; Woobaidullah, A. S. M.; Snigdha, S. S.

    2015-12-01

    Bengal Basin with its prolific gas rich province provides needed energy to Bangladesh. Present energy situation demands more Hydrocarbon explorations. Only 'Semutang' is discovered in the high amplitude structures, where rest of are in the gentle to moderate structures of western part of Chittagong-Tripura Fold Belt. But it has some major thrust faults which have strongly breached the reservoir zone. The major objectives of this research are interpretation of gas horizons and faults, then to perform velocity model, structural and property modeling to obtain reservoir properties. It is needed to properly identify the faults and reservoir heterogeneities. 3D modeling is widely used to reveal the subsurface structure in faulted zone where planning and development drilling is major challenge. Thirteen 2D seismic and six well logs have been used to identify six gas bearing horizons and a network of faults and to map the structure at reservoir level. Variance attributes were used to identify faults. Velocity model is performed for domain conversion. Synthetics were prepared from two wells where sonic and density logs are available. Well to seismic tie at reservoir zone shows good match with Direct Hydrocarbon Indicator on seismic section. Vsh, porosity, water saturation and permeability have been calculated and various cross plots among porosity logs have been shown. Structural modeling is used to make zone and layering accordance with minimum sand thickness. Fault model shows the possible fault network, those liable for several dry wells. Facies model have been constrained with Sequential Indicator Simulation method to show the facies distribution along the depth surfaces. Petrophysical models have been prepared with Sequential Gaussian Simulation to estimate petrophysical parameters away from the existing wells to other parts of the field and to observe heterogeneities in reservoir. Average porosity map for each gas zone were constructed. The outcomes of the research

  10. Cross Gradient Based Joint Inversion of 2D Wide Angle Seismic Reflection/Refraction and Gravity Data Along the Profile Through the 2010 Ms 7.1 Yushu Earthquake, China

    NASA Astrophysics Data System (ADS)

    Xiang, S.; Zhang, H.

    2015-12-01

    2D wide-angle seismic reflection/refraction survey has been widely used to investigate crustal structure and Moho topography. Similarly gravity survey is also very important in the study of local and regional earth features. Seismic survey is sensitive to the seismic velocity parameters and interface variations. For gravity survey, it is sensitive to density parameters of the medium but the resolution along the vertical direction is relatively poor. In this study, we have developed a strategy to jointly invert for seismic velocity model, density model and interface positions using the gravity observations and seismic arrival times from different phases. For the joint inversion of seismic and gravity data, it often relies on the empirical relationship between seismic velocity and density. In comparison, our joint inversion strategy also includes the cross-gradient based structure constraint for seismic velocity and density models in addition to the empirical relationship between them. The objective function for the joint inversion includes data misfit terms for seismic travel times and gravity observations, the cross-gradient constraint, the smoothness terms for two models, and the data misfit term between predicted gravity data based on density model converted from velocity model using the empirical relationship. Each term has its respective weight. We have applied the new joint inversion method to the Riwoqe-Yushu-Maduo profile in northwest China. The profile crosses through the Qiangtang block and Bayan Har block from southwest to northeast, respectively. The 2010 Ms 7.1 Yushu earthquake is located on the profile, around the Ganzi-Yushu fault zone. The joint inversion produces the velocity and density models that are similar in structure and at the same time fit their respective data sets well. Compared to separate seismic inversion using seismic travel times, the joint inversion with gravity data gives a velocity model that better delineates the fault zones. Low

  11. West Flank Coso, CA FORGE Seismic Reflection

    DOE Data Explorer

    Doug Blankenship

    2016-05-16

    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).

  12. 3D constraints on a possible deep > 2.5 km massive sulphide mineralization from 2D crooked-line seismic reflection data in the Kristineberg mining area, northern Sweden

    NASA Astrophysics Data System (ADS)

    Malehmir, Alireza; Schmelzbach, Cedric; Bongajum, Emmanuel; Bellefleur, Gilles; Juhlin, Christopher; Tryggvason, Ari

    2009-12-01

    2D crooked-line seismic reflection surveys in crystalline environments are often considered challenging in their processing and interpretation. These challenges are more evident when complex diffraction signals that can originate from out-of-the-plane and a variety of geological features are present. A seismic profile in the Kristineberg mining area in northern Sweden shows an impressive diffraction package, covering an area larger than 25 km 2 in the subsurface at depths greater than 2.5 km. We present here a series of scenarios in which each can, to some extent, explain the nature of this extraordinarily large package of diffractions. Cross-dip analysis, diffraction imaging and modeling, as well as 3D processing of the crooked-line data provided constraints on the interpretation of the diffraction package. Overall, the results indicate that the diffraction package can be associated with at least four main short south-dipping diffractors in a depth range of 2.5-4.5 km. Candidate scenarios for the origin of the diffraction package are: (1) a series of massive sulphide deposits, (2) a series of mafic-ultramafic intrusions, (3) a major shear-zone and (4) multiple contact lithologies. We have also investigated the possible contribution of mode-converted scattered energy in the diffraction package using a modified converted-wave 3D prestack depth migration algorithm with the results indicating that a majority of the diffractions are P-wave diffractions. The 3D prestack migration of the data provided improved images of a series of steeply north-dipping mafic-ultramafic sill intrusions to a depth of about 4 km, where the diffractions appear to focus after the migration. The results and associated interpretations presented in this paper have improved our understanding of this conspicuous package of diffractions and may lead to re-evaluation of the 3D geological model of the Kristineberg mining area.

  13. Predicting abnormal pressure from 2-D seismic velocity modeling

    SciTech Connect

    Grauls, D.; Dunand, J.P.; Beaufort, D.

    1995-12-01

    Seismic velocities are the only data available, before drilling, on which to base a quantitative, present-day estimate of abnormal pressure. Recent advances in seismic velocity processing have enabled them to obtain, using an in-house approach, an optimized 2-D interval velocity field and consequently to better define the lateral extension of pressure regimes. The methodology, interpretation and quantification of overpressure-related anomalies are supported by case studies, selected in sand-shale dominated Tertiary basins, offshore West Africa. Another advantage of this approach is that it can also account for the presence of reservoir-potential intervals at great depth and thus provide significant insight, from a prospective standpoint, into very poorly explored areas. Although at the outset the 2-D seismic tool legitimately merits being favored, optimization of the final predictive pressure model, prior to drilling, will depend upon the success of its combined use with other concepts and approaches, pertaining to structural geology, sedimentology, rock mechanics and fluid dynamics.

  14. Shallow seismic reflection section -- Introduction

    SciTech Connect

    Steeples, D.W.

    1998-07-01

    For those interested in shallow seismic reflection (SSR) techniques, this special issues of Geophysics is likely to serve as a useful reference for years to come. The idea for this issue grew out of discussions that took place at the Shallow Seismic Reflection Workshop at the Lawrence Berkeley Laboratory, California, in September 1996. The content of those discussions is the subject of a published report elsewhere (Steeples et al., 1997). Several workshop participants and their colleagues contributed to the papers in this issue as authors and as reviewers. The articles include case histories, novel uses of the SSR technique, state-of-the-art planning considerations for 3-D SSR surveys, and some examples of problems unique to SSR surveying.

  15. Structure of the ophiolite-hosted Outokumpu Cu-Co-Zn-Ni-Ag-Au sulfide ore district revealed by combined 3D modelling and 2D high-resolution seismic reflection data

    NASA Astrophysics Data System (ADS)

    Saalmann, Kerstin; Laine, Eevaliisa

    2015-04-01

    -dipping faults , (iii) SW-NE to SSW-NNE striking faults which may have formed at an earlier stage and have been reactivated. The specific Outokumpu alteration assemblage around metaperidotite bodies combined with shear zones acting as pathways for fluids are the main vectors to mineralization. Seismic reflection data do not provide a simple tool to directly detect the sites of Outokumpu assemblage bodies at depth but they identify strong reflector zones which are characteristic for though not exclusive to the assemblage. Our approach shows that 3D modelling combining surface geology and geophysical data and a good knowledge about the structural evolution substantially improves the interpretation of reflectors and their assignments to rock units of interest. It thus enhances the chances for locating potentially economic bodies at depth and allows delineating target areas for detailed exploration.

  16. The development and testing of a 2D laboratory seismic modelling system for heterogeneous structure investigations

    NASA Astrophysics Data System (ADS)

    Mo, Yike; Greenhalgh, Stewart A.; Robertsson, Johan O. A.; Karaman, Hakki

    2015-05-01

    Lateral velocity variations and low velocity near-surface layers can produce strong scattered and guided waves which interfere with reflections and lead to severe imaging problems in seismic exploration. In order to investigate these specific problems by laboratory seismic modelling, a simple 2D ultrasonic model facility has been recently assembled within the Wave Propagation Lab at ETH Zurich. The simulated geological structures are constructed from 2 mm thick metal and plastic sheets, cut and bonded together. The experiments entail the use of a piezoelectric source driven by a pulse amplifier at ultrasonic frequencies to generate Lamb waves in the plate, which are detected by piezoelectric receivers and recorded digitally on a National Instruments recording system, under LabVIEW software control. The 2D models employed were constructed in-house in full recognition of the similitude relations. The first heterogeneous model features a flat uniform low velocity near-surface layer and deeper dipping and flat interfaces separating different materials. The second model is comparable but also incorporates two rectangular shaped inserts, one of low velocity, the other of high velocity. The third model is identical to the second other than it has an irregular low velocity surface layer of variable thickness. Reflection as well as transmission experiments (crosshole & vertical seismic profiling) were performed on each model. The two dominant Lamb waves recorded are the fundamental symmetric mode (non-dispersive) and the fundamental antisymmetric (flexural) dispersive mode, the latter normally being absent when the source transducer is located on a model edge but dominant when it is on the flat planar surface of the plate. Experimental group and phase velocity dispersion curves were determined and plotted for both modes in a uniform aluminium plate. For the reflection seismic data, various processing techniques were applied, as far as pre-stack Kirchhoff migration. The

  17. 2D Time-lapse Seismic Tomography Using An Active Time Constraint (ATC) Approach

    EPA Science Inventory

    We propose a 2D seismic time-lapse inversion approach to image the evolution of seismic velocities over time and space. The forward modeling is based on solving the eikonal equation using a second-order fast marching method. The wave-paths are represented by Fresnel volumes rathe...

  18. Carbonate platform-margins and reefs distribution using 2-D seismic analysis, Central Tunisia

    NASA Astrophysics Data System (ADS)

    Harzali, Makrem; Troudi, Habib; Ben Boubaker, Kamel; Ouali, Jamel

    2014-12-01

    The seismic characterization of sedimentary facies in a carbonate platform, comprising different types of reefs constructions, is based using two-dimensional (2-D) seismic and borehole data. Reefs of the Aptian Serdj carbonates are shown as mounds of strong chaotic amplitudes that have a high-amplitude continuous reflection at the top. They are sealed by Albian marl and claystone deposits characterized by mid- to low-amplitude, parallel and discontinuous to weak reflections. These buildups were restricted to the outer platform margin of Central Tunisia. Sea level oscillations associated with master fault rejuvenation governed the growth, the distribution and development of these reefs. Their distribution is largely controlled by deep-seated fault-related folds and the topography of underlying structures, representing local domal uplifts. Falls of sea level led to subaerial exposure and the development of a karstified denudation of the carbonate platform. Subsequently, reefs were partially or totally destroyed and then overlain, during the Albian, by marls and claystones of the Fahdene Formation. Their study indicates that reef buildups have important oil and gas exploration potential, not only onshore, but also in offshore, Central Tunisia.

  19. 2D seismic residual statics derived from refraction interferometry

    NASA Astrophysics Data System (ADS)

    Zhang, Chao; Zhang, Jie

    2016-07-01

    Refraction traveltimes have long been applied for deriving long-wavelength statics solutions. These traveltimes are also applied for the derivation of residual statics, but they must be sufficiently accurate at short wavelengths. In this study, we present a seismic residual statics method that applies interferometric theory to produce four stacked virtual refraction gathers with a significantly improved signal-to-noise ratio. These gathers are composed of forward and backward virtual refraction gathers for receivers and shots. By picking the first arrivals on these four gathers followed by the application of a set of refraction equations, reliable residual statics solutions can be derived. This approach can help deal with noisy data and also avoid using traveltime picks from shot gathers. We demonstrate the approach by applying it to synthetic data as well as real data.

  20. 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.

  1. High Resolution 2D Seismic Exploration of Poly-Metallic Massive Sulfide deposits at Garpenberg, Central Sweden

    NASA Astrophysics Data System (ADS)

    Ahmadi, O.; Juhlin, C.

    2012-04-01

    The Garpenberg mine is a VMS stratabound deposit in central Sweden which is located in the main mineralized part of a palaeoprotrozoic felsic magmatic province in the Baltic Shield. It has been mined for centuries and continues to date, therefore shallow deposits will soon be mined out. The seismic reflection method has been used recently in mineral exploration for imaging the subsurface by many researchers around the world. Therefore, to explore and evaluate the deeper potential, a 2D seismic profile was acquired over parts of the mining area. Due to the complexity in the structural geology of the area, a high resolution was desired along the profile and 5 meters spacing for shots and receivers was used. Underground activity and traffic on the surface generated significant noise, so that it was not possible to observe reflections on shot gathers easily. To attenuate coherent noise on shot gathers, an F-K filter was applied followed by deconvolution and a spectral weighting filter to improve the data quality. Most of the reflections on stacked section emanate from out of the plane and require a cross-dip correction to be imaged optimally. Velocity analysis, DMO and migration further improved the images. This study has shown that the reflection seismic method has potential in imaging complex structures in this challenging environment. The cross-dip correction is an important tool to enhance dipping and sub-horizontal seismic reflections and diffractions. Interpretation of the reflections shows that there is good correlation between the migrated seismic stacked section and some geological features.

  2. On the distribution of seismic reflection coefficients and seismic amplitudes

    SciTech Connect

    Painter, S.; Paterson, L.; Beresford, G.

    1995-07-01

    Reflection coefficient sequences from 14 wells in Australia have a statistical character consistent with a non-Gaussian scaling noise model based on the Levy-stable family of probability distributions. Experimental histograms of reflection coefficients are accurately approximated by symmetric Levy-stable probability density functions with Levy index between 0.99 and 1.43. These distributions have the same canonical role in mathematical statistics as the Gaussian distribution, but they have slowly decaying tails and infinite moments. The distribution of reflection coefficients is independent of the spatial scale (statistically self-similar), and the reflection coefficient sequences have long-range dependence. These results suggest that the logarithm of seismic impedance can be modeled accurately using fractional Levy motion, which is a generalization of fractional Brownian motion. Synthetic seismograms produced from the authors` model for the reflection coefficients also have Levy-stable distributions. These isolations include transmission losses, the effects of reverberations, and the loss of resolution caused by band-limited wavelets, and suggest that actual seismic amplitudes with sufficient signal-to-noise ratio should also have a Levy-stable distribution. This prediction is verified using post-stack seismic data acquired in the Timor Sea and in the continental USA. However, prestack seismic amplitudes from the Timor Sea are nearly Gaussian. They attribute the difference between prestack and poststack data to the high level of measurement noise in the prestack data.

  3. 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

  4. Seismic reflection imaging at a Shallow Site

    SciTech Connect

    Milligan, P.; Rector, J.; Bainer, R.

    1997-01-01

    The objective of our studies was to determine the best seismic method to image these sediments, between the water table at 3 m depth to the basement at 35 m depth. Good cross-correlation between well logs and the seismic data was also desirable, and would facilitate the tracking of known lithological units away from the wells. For instance, known aquifer control boundaries may then be mapped out over the boundaries, and may be used in a joint inversion with reflectivity data and other non-seismic geophysical data to produce a 3-D image containing quantitative physical properties of the target area.

  5. High-Resolution Seismic Reflection to Monitor Change

    NASA Astrophysics Data System (ADS)

    Miller, R. D.; Raef, A. E.; Lambrecht, J. L.; Byrnes, A. P.

    2006-05-01

    confinement failure of an oil field brine disposal well. In 1998, legacy 2-D seismic data showed the subsurface extent of collapse was approximately an order of magnitude larger than the sinkhole. A consistent pattern of growth, elongated parallel to the anticlinal structure responsible for the oil field, was interpreted on 2004 time-lapse 2-D data. Confinement of several aquifers overlying the salt was compromised when the 300 m of rocks overlying the salt collapsed, forming the sinkhole. This breach in confining layers provided a pathway to the salt for unsaturated brine fluids. Radial growth of the dissolution feature has slowed consistent with volumetric spreading of the dissolution front. The migration of the brine away from the dissolution front and out of the Hutchinson Salt interval has been relatively consistent in spite of changes in source waters. High-resolution seismic monitoring has a great deal of potential to monitor changes in fluid and structures, but requires a high degree of scrutiny and attention to detail for effective application.

  6. 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. 

  7. Seismic reflection profiling of Neoarchean cratons

    NASA Astrophysics Data System (ADS)

    van der Velden, Arie Jan

    Deep seismic reflection data from the Superior and Slave cratons in Canada and the Yilgarn craton in Australia are processed with similar processing flows and display parameters to facilitate comparative analysis. The profiles are characterized by subhorizontal to shallowly dipping reflection fabrics in the crust and upper mantle. These reflection fabrics are interpreted as ˜2.8-2.6 Ga ductile structural fabrics associated with peak orogenesis that led to cratonization. A re-evaluation of the seismic data has led to alternative interpretations compared to those published previously. In western Ontario, at Red Lake, divergent reflection patterns are interpreted as products of mainly collisional tectonics rather than extensional tectonics, and at Pickle Lake, mantle reflections connect to a mapped suture and strikeslip fault system. In western Quebec, steep structures are interpreted on the north flank of the Opatica domain. In the Kalgoorlie area of western Australia, subhorizontal upper crustal reflections are interpreted as pre-deformational layers within anticlines. A new tectonic model is presented for the western Slave Province in which divergent reflections at Yellowknife are interpreted to be associated with convergence between the Snare arc and the central Slave basement complex. Reflections that project from the reflection Moho into the upper mantle are observed on all profiles and are interpreted as relict subduction zones and/or major terrane-bounding structures. Listric mid-crustal reflections resembling roofing shingles are interpreted as products of underthrusting and subcretion. Strike-slip faults are manifested as near-vertical zones of reflection truncations. Greenstone belts are often poorly reflective. These reflection patterns are consistent with tectonic models in which greenstone belts form adjacent to protocratons and are thickened by protocontinent-dipping subduction, tectonic underplating, formation of nappes, and thrust-and-fold structures

  8. Seismic investigation of gas hydrates in the Gulf of Mexico: Results from 2013 high-resolution 2D and multicomponent seismic surveys

    NASA Astrophysics Data System (ADS)

    Haines, S. S.; Hart, P. E.; Shedd, W. W.; Frye, M.; Agena, W.; Miller, J. J.; Ruppel, C. D.

    2013-12-01

    In the spring of 2013, the U.S. Geological Survey led a 16-day seismic acquisition cruise aboard the R/V Pelican in the Gulf of Mexico to survey two established gas hydrate study sites. We used a pair of 105/105 cubic inch generator/injector airguns as the seismic source, and a 450-m 72-channel hydrophone streamer to record two-dimensional (2D) data. In addition, we also deployed at both sites an array of 4-component ocean-bottom seismometers (OBS) to record P- and S-wave energy at the seafloor from the same seismic source positions as the streamer data. At lease block Green Canyon 955 (GC955), we acquired 400 km of 2-D streamer data, in a 50- to 250-m-spaced grid augmented by several 20-km transects that provide long offsets for the OBS. The seafloor recording at GC955 was accomplished by a 2D array of 21 OBS at approximately 400-m spacing, including instruments carefully positioned at two of the three boreholes where extensive logging-while-drilling data is available to characterize the presence of gas hydrate. At lease block Walker Ridge 313 (WR313), we acquired 450 km of streamer data in a set of 11-km, 150- to 1,000-m-spaced, dip lines and 6- to 8-km, 500- to 1000-m-spaced strike lines. These were augmented by a set of 20-km lines that provide long offsets for a predominantly linear array of 25 400- to 800-m spaced OBS deployed in the dip direction in and around WR313. The 2D data provide at least five times better resolution of the gas hydrate stability zone than the available petroleum industry seismic data from the area; this enables considerably improved analysis and interpretation of stratigraphic and structural features including previously unseen faults and gas chimneys that may have considerable impact on gas migration. Initial processing indicates that the OBS data quality is good, and we anticipate that these data will yield estimates of P- and S-wave velocities, as well as PP (reflected) and PS (converted wave) images beneath each sensor location.

  9. Passive Seismic Reflectivity Imaging with Ocean-Bottom Cable Data

    NASA Astrophysics Data System (ADS)

    Hohl, D.; Mateeva, A.

    2005-12-01

    The idea of imaging the subsurface reflectivity distribution by correlating long traces of seismic ``noise'' (i.e. seismic data recorded without active sources) goes back more than 30 years [1]. To this day, passive seismic reflectivity imaging has not been exploited for business use in the E&P industry. The conditions for successful passive seismic reflection imaging have greatly improved over the past few years, and the prize of cheap continuous sourceless seismic imaging and possibly monitoring is still large. Nearly unlimited quantities of very high quality passive noise data are now available from permanent 4C ocean bottom cable (OBC) installations. In the present contribution, we report our initial results for single-line (2D) OBC data collected in the North Sea and GOM. The OBCs used for the experiment are of length 6-10 km with 4C receivers spaced 50 m apart. They are deployed in both shallow and deep water over large hydrocarbon reservoirs. Passive noise data were recorded for 8-24 h periods, sometimes several times, and months apart. In the analysis presented here only the hydrophone records are used, and the data from all recording periods are used together to produce a single 2D migrated reflectivity section. We observe that environmental noise (e.g. boat and rig activity) play an important role for imaging and usually requires pre-migration seismic processing steps to filter out unwanted signals. At the core of our image generation and processing sequence is the crosscorrelation of noise trace pairs and subsequent prestack time migration [1] with a velocity model established for the active-source OBC data processing. We compute 4 sec of lag time to either side of t=0. After removing unwanted signals (e.g. seafloor interface waves) from these ``virtual shot gathers'' one can clearly detect the linear-moveout direct water wave with velocity 1500 m/s, and a linear interface wave with velocity 2000 m/s. Other ``events'' with moveout are visible, but the

  10. Detecting low Velocity Anomalies Combining Seismic Reflection With First Arrival Seismic Tomography

    NASA Astrophysics Data System (ADS)

    Flecha, I.; Marti, D.; Carbonell, R.

    2002-12-01

    In the present study seismic reflection techniques and high resolution seismic tomography are combined to determine location and geometry of shallow low velocity anomalies. Underground cavities (mines), water flows (formation with loose sand), etc. are geologic features characterized by slow seismic velocities and are targets of considerable social interest. Theoretical considerations (Snell's law) suggest that low velocity anomalies are undersampled and therefore badly resolved by ray tracing methods. A series of synthetics simulations have been carried out to asses the resolving power of the different methodologies. A 400mx50m two dimensional velocity model consisting of a background velocity gradient in depth from 3000 to 4000 m/s which included a rectangular low velocity anomaly (300 m/s). This anomaly was placed between 10m and 30m in depth and between 180m and 220m in length. The synthetic data calculation and the tomographic inversion have been done with absolutely independent programs. The data has been created using a 2D finite differences wave propagation acoustic algorithm. The tomographic inversion has been performed using two different software packages. The first one uses a combination of ray tracing a finite differences schemes to estimate the forward problem and an iterative conjugate gradient matrix solver to calculate the inverse. The second software package uses a modified Vidale scheme (Eikonal equation) to solve the forward problem and a LSQR to solve the inverse problem. The synthetic data were used for the inversions and for the generation of a conventional stacked section simulating a high resolution seismic reflection transect along the velocity model. The conventional stack images the diffractions caused by the velocity anomaly, which provided the location and extent of the low velocity anomaly. The inversions schemes provided estimates of the velocities, however, the tomograms and the ray tracing diagrams indicated a low resolution for

  11. Can exposure to prenatal sex hormones (2D:4D) predict cognitive reflection?

    PubMed

    Bosch-Domènech, Antoni; Brañas-Garza, Pablo; Espín, Antonio M

    2014-05-01

    The Cognitive Reflection Test (CRT) is a test introduced by Frederick (2005). The task is designed to measure the tendency to override an intuitive response that is incorrect and to engage in further reflection that leads to the correct response. The consistent sex differences in CRT performance may suggest a role for prenatal sex hormones. A now widely studied putative marker for relative prenatal testosterone is the second-to-fourth digit ratio (2D:4D). This paper tests to what extent 2D:4D, as a proxy for the prenatal ratio of testosterone/estrogens, can predict CRT scores in a sample of 623 students. After controlling for sex, we observe that a lower 2D:4D (reflecting a relative higher exposure to testosterone) is significantly associated with a higher number of correct answers. The result holds for both hands' 2D:4Ds. In addition, the effect appears to be stronger for females than for males. We also control for patience and math proficiency, which are significantly related to performance in the CRT. But the effect of 2D:4D on performance in CRT is not reduced with these controls, implying that these variables are not mediating the relationship between digit ratio and CRT.

  12. 2-D Gaussian beam imaging of multicomponent seismic data in anisotropic media

    NASA Astrophysics Data System (ADS)

    Protasov, M. I.

    2015-12-01

    An approach for true-amplitude seismic beam imaging of multicomponent seismic data in 2-D anisotropic elastic media is presented and discussed. Here, the recovered true-amplitude function is a scattering potential. This approach is a migration procedure based on the weighted summation of pre-stack data. The true-amplitude weights are computed by applying Gaussian beams (GBs). We shoot a pair of properly chosen GBs with a fixed dip and opening angles from the current imaging point towards an acquisition system. This pair of beams is used to compute a true-amplitude selective image of a rapid velocity variation. The total true-amplitude image is constructed by superimposing selective images computed for a range of available dip angles. The global regularity of the GBs allows one to disregard whether a ray field is regular or irregular. P- and S-wave GBs can be used to handle raw multicomponent data without separating the waves. The use of anisotropic GBs allows one to take into account the anisotropy of the background model.

  13. Skeleton-migration: Applications in deep crustal reflection seismic profiling

    NASA Astrophysics Data System (ADS)

    Eaton, D. W.; Vasudevan, K.

    2009-12-01

    The reflection geometry of the sub-surface is three-dimensional in character. A 3-D seismic data acquisition and processing would be the ideal modus operandi for true seismic interpretation. However, almost all deep-crustal reflection profiles recorded on land follow quasi-linear geometry, for economic reasons. Although conventional processing of the lines accommodates crooked-line geometry, the migration algorithms used to produce seismic images for interpretation are generally 2-D in nature. Consequently, the effects of 3-D geometry are not usually well-accounted for. For example, the out-of-plane reflections lead to mislocation errors that increase with recording time. The events may be mislocated by 10’s of km and show spurious apparent dip after migration. In order to circumvent these problems and to gain insight into 3-D structures, we present an easy-to-implement “Skeleton-migration” algorithm. The skeleton-migration method follows a two-step procedure. In the first step, we introduce a fast skeletonization of the final pre-processed stack to generate a digital catalogue containing a variety of event attributes including two-way travel times and location information in UTM co-ordinates. In the second step, we apply ray-based migration to the catalogue of events or two-way travel times of the 2-D stack using an appropriate velocity model for the crust and upper mantle. Since often we do not know a priori the strike direction of the reflectors, we have implemented a fast visualization-based optimization procedure to determine the strike. In subsequent steps, we use visualization methods to view and interpret the skeleton-migration results. We illustrate the usefulness of the method with examples from both the synthetic and deep crustal seismic reflection data. For the synthetic examples, we consider physical models corresponding to a point-scatterer, a synform, a fault and a subducting slab. In all these instances, we use an elastic Kirchhoff algorithm

  14. Analysis of Cretaceous (Aptian) strata in central Tunisia, using 2D seismic data and well logs

    NASA Astrophysics Data System (ADS)

    Zouaghi, Taher; Ferhi, Issam; Bédir, Mourad; Youssef, Mohamed Ben; Gasmi, Mohamed; Inoubli, Mohamed Hédi

    2011-08-01

    This paper presents a structural and depositional model of lower Cretaceous (Aptian) strata in central Tunisia, using detailed facies relations in outcrops, seismic reflection data, and wells. The study interval (called the "Aptian supersequence") is subdivided into four seismic sequences containing third-order sequences. Sequence architecture was strongly affected by syndepositional tectonic movements, which controlled sequence position and distribution. Specifically, the seismic sections show irregular distribution of different zones of subsidence and uplift. The observed structures identified through the detailed mapping suggest that lower Cretaceous rifting created depressions and grabens that filled with strata characterized by divergent reflectors striking against dipping growth faults. The Aptian-Albian unconformity ("crisis") marked a change of the extensional stress field from NNW-SSE to NE-SW induced rotation of blocks and an evolution of sedimentary basin filling related to the regional tectonic deformation. Local salt tectonic movement accentuated the formation of asymmetric depocenters. The salt ascended at the junction of master faults, resulting in cross-cutting of the strata and local reworking of Triassic evaporites in Aptian strata. Basinward to landward variations of the thickness and facies associated with strata pinch-outs and unconformities are related to the main synsedimentary tectonic events that were synchronous with salt tectonic movements. Triassic salt domes and salt intrusions along faults accentuated the border elevations between basin depocenters and uplifts. These sedimentary phenomena in central Tunisia are interpreted as causally related aspects of a local and global tectonic event during the Aptian.

  15. 3D Seismic Reflection Experiment over the Galicia Deep Basin

    NASA Astrophysics Data System (ADS)

    Sawyer, D. S.; Jordan, B.; Reston, T. J.; Minshull, T. A.; Klaeschen, D.; Ranero, C.; Shillington, D. J.; Morgan, J. K.

    2014-12-01

    In June thru September, 2013, a 3D reflection and a long offset seismic experiment were conducted at the Galicia rifted margin by investigators from the US, UK, Germany, and Spain. The 3D multichannel experiment covered 64 km by 20 km (1280 km2), using the RV Marcus Langseth. Four streamers 6 km long were deployed at 12.5 m hydrophone channel spacing. The streamers were 200 m apart. Two airgun arrays, each 3300 cu in, were fired alternately every 37.5 m, to collectively yield a 400 m wide sail line consisting of 8 CMP lines at 50 m spacing. The long offset seismic experiment included 72 short period OBS's deployed below the 3D reflection survey box. Most of the instruments recorded all the shots from the airgun array shots. The 3D seismic box covered a variety of geologic features. The Peridotite Ridge (PR), is associated with the exhumation of upper mantle rocks to the seafloor during the final stage of the continental separation between the Galicia Bank and the Grand Banks of Newfoundland. The S reflector is present below most of the continental blocks under the deep Galicia basin. S is interpreted to be a low-angle detachment fault formed late in the rifting process, and a number of rotated fault block basins and ranges containing pre and syn-rift sediments. Initial observations from stacked 3D seismic data, and samples of 2D pre-stack time migrated (PSTM) 3D seismic data show that the PR is elevated above the present seafloor in the South and not exposed through the seafloor in the North. The relative smoothness of the PR surface for the entire 20 km N-S contrasts with the more complex, shorter wavelength, faulting of the continental crustal blocks to the east. The PR does not seem to show offsets or any apparent internal structure. The PSTM dip lines show substantial improvement for the structures in the deep sedimentary basin East of the PR. These seem to extend the S reflector somewhat farther to the West. The migrated data show a substantial network of

  16. Comparative 2D BRT and seismic modeling of CO2 plumes in deep saline reservoirs

    NASA Astrophysics Data System (ADS)

    Hagrey, Said Attia Al; Strahser, Matthias; Rabbel, Wolfgang

    2010-05-01

    The multi-disciplinary research project 'CO2 MoPa' (modeling and parameterization of CO2 storage in deep saline formations for dimensions and risk analysis) deals, among others, with the parameterization of virtual subsurface storage sites to characterize rock properties with modeling of processes related to CCS in deep saline reservoirs. The geophysical task is to estimate the sensitivity and the resolution of reflection seismic and geoelectrical time-lapses in order to determine the propagation of CO2 within the sediments and the development of the CO2 reservoir. Compared with seismic, borehole electric resistivity tomography (BRT) has lower resolution, but its permanent installation and continuous monitoring can make it an economical alternative or complement. Seismic and geoelectric applications to quantify changes of intrinsic aquifer properties with time are justified by the lower density and velocity and the higher electric resistivity of CO2 in comparison to pore brine. We present here modeling results on scenarios with realistic parameters of deep saline formations of the German Basin (candidate for CCS). The study focuses on effects of parameters related to depth (temperature, pressure), petrophysics (salinity, porosity), plume dimensions/saturations and data acquisition, processing and inversions. Both methods show stronger effects with increasing brine salinity, CO2 reservoir thickness, porosity and CO2 saturation in the pores. Both methods have a pronounced depth dependence due to the pressure and temperature dependence of the velocities, densities and resistivities of the host rock, brine and CO2. Increasing depth means also decreasing frequencies of the seismic signal and hence weaker resolution. Because of the expected limited thickness of the CO2 reservoir, the reflections from its top and bottom will most likely interfere with each other, making it difficult to determine the exact dimensions of the reservoir. In BRT, the resulting resistivity

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

    SciTech Connect

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

    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. On 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.

  18. Seismic reflection studies in eastern Nevada

    SciTech Connect

    Miller, J.J.; Grow, J.A.; Potter, C.J.

    1994-12-31

    The US Geological Survey has recently purchased over 600 km of multifold seismic reflection profiles in eastern Nevada in the vicinity of Railroad and White River Valleys to understand the regional structural setting of the Railroad Valley oil fields (35 million barrels produced through 1992). One profile extends west of Railroad Valley through the Pancake Range and into Big Sand Springs Valley; another line extends east of White River Valley into Cave, Muleshoe, and Lake valleys. Analysis of sonic logs from over 50 wells indicate that Miocene and younger valley-fill deposits vary from less than 7,000 ft/sec, average velocity in the center of Railroad Valley, to more than 16,000 ft/sec,/near the mountain fronts where conglomerates composed of Paleowic carbonate clasts occur. The conglomerates above and east of the Grand Canyon oil field (18 million barrels as of 1992) appear to have the highest velocities, and these may be due to cementation effects caused by hydrothermal upwelling. Normal faults are generally too steep to be seen as fault-plane reflections (>40{degree}), except in the vicinity of the prolific Grand Canyon oil field, where a low-angle normal fault (approx. 20{degree}) can be seen on two profiles. the overall extension in the study area appears to be in the range of 25--50% except beneath eastern Railroad Valley and the adjacent Grand Range where 80 to more than 100% extension probably has occurred.

  19. Analytical fundamentals of migration in reflection seismics

    NASA Astrophysics Data System (ADS)

    Ray, Arnab K.

    2016-06-01

    We consider migration in reflection seismics from a completely analytical perspective. We review the basic geometrical ray-path approach to understanding the subject of migration, and discuss the limitations of this method. We stress the importance of the linear differential wave equation in migration. We also review briefly how a wavefield, travelling with a constant velocity, is extrapolated from the differential wave equation, with the aid of Fourier transforms. Then we present a non-numerical treatment by which we derive an asymptotic solution for both the amplitude and the phase of a planar subsurface wavefield that has a vertical velocity variation. This treatment entails the application of the Wentzel-Kramers-Brillouin approximation, whose self-consistency can be established due to a very slow logarithmic variation of the velocity in the vertical direction, a feature that holds more firmly at increasingly greater subsurface depths. For a planar subsurface wavefield, we also demonstrate an equivalence between two apparently different migration algorithms, namely, the constant-velocity Stolt Migration algorithm and the stationary-phase approximation method.

  20. Monitoring of injected CO2 using the seismic full waveform inversion for 2-D elastic VTI media

    NASA Astrophysics Data System (ADS)

    Kim, W. K.; Min, D. J.; KIM, S.; Shin, Y.; Moon, S.

    2014-12-01

    To monitor the injected CO2 in the subsurface, seismic monitoring techniques are extensively applied because of its high resolution. Among the seismic monitoring techniques, seismic full waveform inversion (FWI) has high applicability because it can delineate parameter changes by injected CO2. When seismic FWIs are applied, subsurface media can be generally assumed to be isotropic. However, most subsurface media are not isotropic, and shale is a representative anisotropic medium, particularly vertical transversely isotropic (VTI) medium, which is often encountered as a barrier to injected CO2. Thus, anisotropic properties of subsurface media are important for monitoring of injected CO2. For these issues, we need to consider anisotropy of subsurface media when seismic FWIs are applied as a monitoring tool for CO2 sequestration. In this study, we performed seismic FWI for 2-D elastic VTI media to investigate the effects of anisotropic properties in CO2 monitoring. For this numerical test, we assumed a geological model, which copies after one of CO2 storage prospects in Korea. We also applied seismic FWI algorithm for 2-D elastic isotropic media for comparison. From this comparison, we noticed that we can obtain more reliable results when we apply the anisotropic FWI algorithm. Numerical examples indicate that we should apply the anisotropic FWI algorithm rather than the isotropic FWI algorithm when we interpret seismic monitoring data acquired in anisotropic media to increase the success of monitoring for injected CO2. Our numerical results can also be used as references for real seismic monitoring of the Korea CO2 sequestration projects in the near future. Acknowledgements This work was supported by the Human Resources Development program (No. 20134010200510) of the Korea Institute of Energy Technology Evaluation and Planning (KETEP) grant funded by the Korean government Ministry of Trade, Industry, and Energy and by the "Development of Technology for CO2 Marine

  1. A nearly analytic symplectically partitioned Runge-Kutta method for 2-D seismic wave equations

    NASA Astrophysics Data System (ADS)

    Ma, Xiao; Yang, Dinghui; Liu, Faqi

    2011-10-01

    In this paper, we develop a new nearly analytic symplectically partitioned Runge-Kutta (NSPRK) method for numerically solving elastic wave equations. In this method, we first transform the elastic wave equations into a Hamiltonian system, and use the nearly analytic discrete operator to approximate the high-order spatial differential operators, and then we employ the partitioned second-order symplectic Runge-Kutta method to numerically solve the resulted semi-discrete Hamiltonian ordinary differential equations (ODEs). We investigate in great detail on the properties of the NSPRK method that includes the stability condition for the P-SV wave in a 2-D homogeneous isotropic medium, the computational efficiency, and the numerical dispersion relation for the 2-D acoustic case. Meanwhile, we apply the NSPRK to simulate the elastic wave propagating in several multilayer models with both strong velocity contrasts and fluctuating interfaces. Both theoretical analysis and numerical results show that the NSPRK can effectively suppress the numerical dispersion resulted from the discretization of the wave equations, and more importantly, it preserves the symplecticity structure for long-time computation. In addition, numerical experiments demonstrate that the NSPRK is effective to combine the split perfectly matched layer boundary conditions to take care of the reflections from the artificial boundaries.

  2. Tectonics Of Eastern Offshore Trinidad Based On Integration Of BOLIVAR 2D Seismic Lines With Industry 3D Seismic Surveys

    NASA Astrophysics Data System (ADS)

    Soto, M. D.; Mann, P.; Wood, L. J.

    2004-12-01

    New MCS lines in the eastern offshore area of Trinidad augmented by existing 3D seismic surveys by industry provide new insights into complex, strain partitioning produced along this segment of the South America-Caribbean plate boundary. Two major tectonosequences are imaged separated by a Middle Miocene angular unconformity known from wells and mapping in Trinidad. A thick section of deep-marine carbonate and clastic rocks are cleanly truncated by the Middle Miocene unconformity and are chaotically deformed along vertical to northwest-dipping thrust faults. This shortening event reflects a major pulse of pre-Middle Miocene southeastward overthrusting of the Caribbean arc over the passive margin of South America. An upper 2-7-km-thick tectonosequence consisting of late Miocene-Quaternary shelf-related sandstone and shale was deposited by the nearby Orinoco delta. This section is folded to lesser degree and deformed by the sub-vertical, right-lateral Central Range fault zone (CRFZ), known from GPS studies to accommodate 12 mm/yr, of the total 20 mm/yr of interplate motion. Deep, continuous reflec-tors are observed at a depth of 12-17 km beneath eastern Trinidad are correlated with authochthonous, late Cretaceous-early Tertiary carbonate and clastic rocks of the South American passive margin. The Darien fault southeast of the CRFZ accommodates active shortening, elevates passive margin rocks to the surface in Trinidad, and forms the northeastern limit of a large, 12-km-thick foreland basin (Columbus basin) that extends onshore.

  3. 2D time-domain finite-difference modeling for viscoelastic seismic wave propagation

    NASA Astrophysics Data System (ADS)

    Fan, Na; Zhao, Lian-Feng; Xie, Xiao-Bi; Ge, Zengxi; Yao, Zhen-Xing

    2016-07-01

    Real Earth media are not perfectly elastic. Instead, they attenuate propagating mechanical waves. This anelastic phenomenon in wave propagation can be modeled by a viscoelastic mechanical model consisting of several standard linear solids. Using this viscoelastic model, we approximate a constant Q over a frequency band of interest. We use a four-element viscoelastic model with a tradeoff between accuracy and computational costs to incorporate Q into 2D time-domain first-order velocity-stress wave equations. To improve the computational efficiency, we limit the Q in the model to a list of discrete values between 2 and 1000. The related stress and strain relaxation times that characterize the viscoelastic model are pre-calculated and stored in a database for use by the finite-difference calculation. A viscoelastic finite-difference scheme that is second-order in time and fourth-order in space is developed based on the MacCormack algorithm. The new method is validated by comparing the numerical result with analytical solutions that are calculated using the generalized reflection/transmission coefficient method. The synthetic seismograms exhibit greater than 95 per cent consistency in a two-layer viscoelastic model. The dispersion generated from the simulation is consistent with the Kolsky-Futterman dispersion relationship.

  4. Reflection Seismics for Ore Exploration: A Case Study From Vihanti, Finland

    NASA Astrophysics Data System (ADS)

    Heinonen, S. E.; Snyder, D. B.; Heikkinen, P. J.; Kukkonen, I. T.; Kousa, J.

    2009-05-01

    Applicability of the reflection seismic soundings for ore exploration is tested in the HIRE-project of the Geological Survey of Finland (GTK). Seismic data were acquired in 15 mining camps and exploration targets in Finland. One of the targets is the Vihanti Zn mining area in western Finland. Area is mainly composed of the Paleoproterozoic intrusive rocks and lower and upper Svecofennian supracrustal rocks. In Vihanti volcanic rocks and volcaniclastic sediments form layers of intermediate to felsic volcanites, tuffites and calc-silicate rocks. The multi-phased deformation history varies among crustal blocks delimited by the faults and shear zones. The mined Vihanti VHMS deposit (total production 28 Mt massive sulphide ore) is located in an anticline. The lateral extend of Vihanti-type rocks sequence is estimated to be 60 km. The HIRE Vihanti survey consisted of 8 Vibroseis (total of 90 km) and 4 explosion (total of 30 km) survey lines. Preliminary processing using a 6.25 m CMP interval revealed prominent reflectors associated with the Lampinsaari formation, hosting the mined ore bodies in Vihanti. These reflectors can be traced southward to another former drill target. Known SE-trending faults within the survey area were also clearly visible in seismic sections. The 2D reflection seismic images suggest that potential host rocks of sulphide deposits may be much more common in the area than previously anticipated. Conventional processing of the Vihanti high resolution reflection seismic data illuminated the subsurface structures of the area, but in order to create more reliable depth and attribute estimation for reflectors, further processing was found necessary. Previous studies have shown that special attention should be paid for the static corrections in the hard rock areas, where variation of the thickness and seismic velocity in overburden cause substantial time delays to seismic signal. Velocity analysis is also challenging in hard-rock surveys, and preliminary

  5. Combined analysis of 2-D electrical resistivity, seismic refraction and geotechnical investigations for Bukit Bunuh complex crater

    NASA Astrophysics Data System (ADS)

    Azwin, I. N.; Saad, Rosli; Saidin, Mokhtar; Nordiana, M. M.; Anderson Bery, Andy; Hidayah, I. N. E.

    2015-01-01

    Interest in studying impact crater on earth has increased tremendously due to its importance in geologic events, earth inhabitant history as well as economic value. The existences of few shock metamorphism and crater morphology evidences are discovered in Bukit Bunuh, Malaysia thus detailed studies are performed using geophysical and geotechnical methods to verify the type of the crater and characteristics accordingly. This paper presents the combined analysis of 2-D electrical resistivity, seismic refraction, geotechnical SPT N value, moisture content and RQD within the study area. Three stages of data acquisition are made starting with regional study followed by detailed study on West side and East side. Bulk resistivity and p-wave seismic velocity were digitized from 2-D resistivity and seismic sections at specific distance and depth for corresponding boreholes and samples taken. Generally, Bukit Bunuh shows the complex crater characteristics. Standard table of bulk resistivity and p-wave seismic velocity against SPT N value, moisture content and RQD are produce according to geological classifications of impact crater; inside crater, rim/slumped terrace and outside crater.

  6. Deep seismic reflection profiling and continental growth curves

    NASA Technical Reports Server (NTRS)

    Klemperer, Simon L.

    1988-01-01

    The results of deep seismic reflection profiling is discussed which shows that the lower crust is prominently layered, in many continental areas, regardless of the age of the surface rocks. The seismic Moho is commonly shallower than the petrological Moho, leading to the question of the nature and origin of this prominent reflector in the deep crust. The lower crust is much less well defined in Phanerozoic and Proterozoic accreted terranes, suggesting possible differences in types of lower crusts.

  7. Deep Seismic Reflectivity at Volcanic Margins: Reflections from the Petrological Moho or from within the Mantle?

    NASA Astrophysics Data System (ADS)

    Kusznir, Nick; Roberts, Alan; Bellingham, Paul

    2015-04-01

    Advances in deep long-offset seismic-reflection acquisition and processing now frequently provide imaging of strong and laterally continuous reflectors in the TWTT range of 10 to 14 seconds. While an initial interpretation might be that these reflectors correspond to the crust-mantle interface, this interpretation may in some cases be incorrect or over-simplistic. Do these deep reflectors correspond to the petrological Moho or could they be located within the mantle? Examples of deep laterally-coherent reflectivity can be seen within the ocean-continent transition of the Argentine, Uruguayan and S Brazilian volcanic margins of the S Atlantic. An initial qualitative interpretation of the seismic data suggests the presence of deep crustal "keels" or crustal roots underlying well developed seaward dipping reflectors (SDRs). Joint inversion of the PSTM time-domain seismic reflection and gravity anomaly data has been used to determine the average interval density and seismic velocity between base sediment and the deep seismic reflectivity. Joint inversion densities and seismic velocities for this depth interval reach values in excess of 3000 kg/m3 and 7.0 km/sec for the entire thickness of the interval, substantially in excess of densities and velocities observed for normal oceanic and continental crust. The high densities determined from joint seismic-gravity inversion under the SDR regions are also consistent with results from flexural subsidence analysis. We consider two interpretations of these results. One interpretation is that the strong deep reflectivity corresponds to the base of the petrological crust and that the crust has an abnormally high average density and seismic velocity due to high-temperature mantle-plume-related magmatism. An alternative interpretation is that the deep seismic reflectivity is located within the mantle beneath the petrological Moho, and that the high density and seismic velocity result from averaging of both crustal basement (~2850

  8. Estimation of Random Medium Parameters from 2D Post-Stack Seismic Data and Its Application in Seismic Inversion

    NASA Astrophysics Data System (ADS)

    Yang, X.; Zhu, P.; Gu, Y.; Xu, Z.

    2015-12-01

    Small scale heterogeneities of subsurface medium can be characterized conveniently and effectively using a few simple random medium parameters (RMP), such as autocorrelation length, angle and roughness factor, etc. The estimation of these parameters is significant in both oil reservoir prediction and metallic mine exploration. Poor accuracy and low stability existed in current estimation approaches limit the application of random medium theory in seismic exploration. This study focuses on improving the accuracy and stability of RMP estimation from post-stacked seismic data and its application in the seismic inversion. Experiment and theory analysis indicate that, although the autocorrelation of random medium is related to those of corresponding post-stacked seismic data, the relationship is obviously affected by the seismic dominant frequency, the autocorrelation length, roughness factor and so on. Also the error of calculation of autocorrelation in the case of finite and discrete model decreases the accuracy. In order to improve the precision of estimation of RMP, we design two improved approaches. Firstly, we apply region growing algorithm, which often used in image processing, to reduce the influence of noise in the autocorrelation calculated by the power spectrum method. Secondly, the orientation of autocorrelation is used as a new constraint in the estimation algorithm. The numerical experiments proved that it is feasible. In addition, in post-stack seismic inversion of random medium, the estimated RMP may be used to constrain inverse procedure and to construct the initial model. The experiment results indicate that taking inversed model as random medium and using relatively accurate estimated RMP to construct initial model can get better inversion result, which contained more details conformed to the actual underground medium.

  9. Seismic Reflection Processing With Special Reference to Anisotropy

    NASA Astrophysics Data System (ADS)

    Burns, Dan

    Seismic reflection data are used extensively in petroleum exploration and development to provide subsurface images and estimates of rock and fluid properties. Data acquisition, processing, and interpretation methodologies have progressed over the past 30 years to allow high-resolution three-dimensional imaging, pore fluid and lithology prediction, and, in certain situations, time-lapse monitoring of reservoir production. Exploration seismology experiences and applications are also finding their way into whole-Earth imaging problems (and vice versa) with great success.Into this long and successful history, S. K. Upadhyay's book, Seismic Reflection Processing With Special Reference to Anisotropy, is introduced.

  10. Seismic reflection processing for characterization of a hazardous waste site

    SciTech Connect

    Liu, Z.-M.; Doll, W.E.

    1997-03-01

    Seismic reflection data have been acquired by the Kansas Geological Survey near the Oak Ridge K-25 Plant on the Oak Ridge Reservation, Tennessee, to assist in the selection of ground water monitoring well locations. The data were recorded in uncorrelated format to allow flexibility in enhancement of stacked images. During the summer of 1996, five of the thirteen seismic reflection lines acquired were processed. An unconventional correlation procedure, ``Vibroseis Whitening`` (VSW) (Coruh and Costain, 1983) has been applied to produce improved seismic sections. Refraction statics corrections, which remove the detrimental effect of an irregular weathered layer, have also been utilized to improve the seismic sections. The seismic data were stacked using the velocities obtained from a standard semblance velocity analysis tool. Locations and orientations of faults or fault zones can be interpreted from these stacked sections, and they are in agreement with the interpretations of the surface mapping in the area. This paper concludes that VSW and refraction statics can be important to near-surface swept source seismic data processing.

  11. Contourlet based seismic reflection data non-local noise suppression

    NASA Astrophysics Data System (ADS)

    Li, Qiang; Gao, Jinghuai

    2013-08-01

    In this paper, we propose a non-local, transform domain noise suppression framework to improve the quality of seismic reflection data. The original non-local means (NLM) algorithm measures similarities in the data domain and we generalize it in the nonsubsampled contourlet transform (NSCT) domain. NSCT gives a multiscale, multiresolution and anisotropy representation of the noisy input. The redundancy information in NSCT subbands can be utilized to enhance the structures in the original seismic data. Like the wavelet transform, NSCT coefficients in each subband follow the generalized Gaussian distribution and the parameters can be estimated using appropriate techniques. These parameters are used to construct our proposed NSCT domain filtering algorithm. Applications for synthetic and real seismic data of the proposed algorithm demonstrate its effectiveness on seismic data random noise suppression.

  12. Mapping bedrock beneath glacial till using CDP seismic reflection methods

    SciTech Connect

    Keiswetter, D.; Black, R.; Steeples, D.

    1994-03-01

    This paper is a case history demonstrating the applicability of the common depth point (CDP) seismic reflection method to image bedrock beneath glacial till in northwestern Iowa. Reflections from the base of the 40-m thick glacial till are clearly observable on field files at around 45 to 50 ms two-way traveltime and possess a dominant frequency of around 100 Hz. The bedrock reflection is confirmed by drill data. The seismic data are of sufficient quality to detect local bedrock topographic changes and to interpret discontinuities along the till-bedrock interface. Finite-difference synthetic seismograms substantiate the interpreted reflections and the diffraction signatures from faults observed on the field files. At some locations along the seismic line, intra-till reflections are apparent on the field files. These intra-till features are on the order of tens of meters in length along the line traverse and reflections from them are not enhanced by common depth point processing. Intra-till reflections could be indicative of gravels or other alluvial materials that may serve as local aquifers.

  13. 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.

  14. Seismic reflection imaging of mixing processes in Fram Strait

    NASA Astrophysics Data System (ADS)

    Sarkar, Sudipta; Sheen, Katy L.; Klaeschen, Dirk; Brearley, J. Alexander; Minshull, Timothy A.; Berndt, Christian; Hobbs, Richard W.; Naveira Garabato, Alberto C.

    2015-10-01

    The West Spitsbergen Current, which flows northward along the western Svalbard continental slope, transports warm and saline Atlantic water (AW) into the Arctic Ocean. A combined analysis of high-resolution seismic images and hydrographic sections across this current has uncovered the oceanographic processes involved in horizontal and vertical mixing of AW. At the shelf break, where a strong horizontal temperature gradient exists east of the warmest AW, isopycnal interleaving of warm AW and surrounding colder waters is observed. Strong seismic reflections characterize these interleaving features, with a negative polarity reflection arising from an interface of warm water overlying colder water. A seismic-derived sound speed image reveals the extent and lateral continuity of such interleaving layers. There is evidence of obliquely aligned internal waves emanating from the slope at 450-500 m. They follow the predicted trajectory of internal S2 tidal waves and can promote vertical mixing between Atlantic and Arctic-origin waters.

  15. Reconstruction of 2D seismic wavefield from Long-Period Seismogram and Short-Period Seismogram Envelope by Seismic Gradiometry applied to the Hi-net Array

    NASA Astrophysics Data System (ADS)

    Maeda, Takuto; Nishida, Kiwamu; Takagi, Ryota; Obara, Kazushige

    2016-04-01

    The high-sensitive seismograph network (Hi-net) operated by National Research Institute for Earth Science and Disaster Prevention (NIED) has about 800 stations with average separation of 20 km all over the Japanese archipelago. Although it is equipped with short-period seismometers, we also can observe long-period seismic wave up to 100 s in periods for significantly large earthquakes. In this case, we may treat long-period seismic waves as a 2D wavefield with station separations shorter than wavelength rather than individual traces at stations. In this study, we attempt to reconstruct 2D wavefield and obtain its propagation properties from seismic gradiometry (SG) method. The SG estimates the wave amplitude and its spatial derivative coefficients from discrete station record by the Taylor series approximation with an inverse problem. By using spatial derivatives in horizontal directions, we can obtain properties of propagating wave packet such as the arrival direction, slowness, geometrical spreading and radiation pattern. In addition, by using spatial derivatives together with free-surface boundary condition, we may decompose the vector elastic 2D wavefield estimated by the SG into divergence and rotation components. First, we applied the seismic gradiometry to a synthetic long-period (20-50 s) seismogram dataset computed by numerical simulation in realistic 3D medium at the Hi-net station layout as a feasibility test. We confirmed that the wave amplitude and its spatial derivatives are very well reproduced with average correlation coefficients higher than 0.99 in this period range. Applications to a real large earthquakes show that the amplitude and phase of the wavefield are well reconstructed with additional information of arrival direction and its slowness. The reconstructed wavefield contained a clear contrast in slowness between body and surface waves, regional non-great-circle-path wave propagation which may be attributed to scattering. Slowness

  16. Seismic crosshole curved ray reflection plus transmission tomography

    SciTech Connect

    Wu, L.; Song, W.; Zhang, M.

    1994-12-31

    This paper provides a new seismic crosshole tomography method, Curved Ray Reflection + Transmission Tomography (CCRTT). The method could enhance the resolution of oil and gas reservoir beds tomography image, and it is suitable for the area with thin reservoir beds and high velocity contrast between the adjacent beds.

  17. Seismic architecture of the Chalk Group from onshore reflection data in eastern Denmark

    NASA Astrophysics Data System (ADS)

    Moreau, Julien; Anderskouv, Kresten; Boldreel, Lars Ole; Boussaha, Myriam; Nielsen, Lars; Stemmerik, Lars; Surlyk, Finn; Thibault, Nicolas

    2013-04-01

    The Upper Cretaceous-Danian chalk is well exposed in the 14 km long coastal cliff of Stevns Klint (eastern Denmark). The cliff is a world renowned for its spectacular exposure of the Cretaceous-Palaeogene boundary. Based on regional geological knowledge of the field and cores, the characteristics of the Chalk Group have been well constrained. Distinct sedimentary facies have been encountered; the sedimentology, the biostratigraphy, the diagenesis and the reservoir properties have been thoroughly investigated and reported. Stimulated by the intensive geological research, the field studies have been completed with the acquisition of an extensive set of subsurface data. The data include high resolution 2D multichannel seismics onshore and offshore, a seismic refraction profile, two entirely cored boreholes including wireline logs, GPR cross-hole tomography, thermographic analysis, etc. We intend to compile and merge the geological and geophysical datasets to investigate the variation of the Chalk Group properties and their signature in the subsurface. In this communication, the seismic reflection data are being analysed. Very high resolution litho-, bio- and cyclostratigraphy can be correlated with the seismic stratigraphy. Several seismic facies are identified in the Chalk Group: the 'transparent' (white chalk), the stratified (marl-chalk alternations), the crudely stratified (flint-rich chalk) and the hummocky (bryozoan mounds). The units notably vary in thickness at a relatively small scale. The variations confirm the complex shelf organisation which was highly influenced by bottom currents. In addition to the stratigraphic observations, peculiar deformation structures can be recognised. The area has been supposedly tectonically stable since deposition as the coastal cliff lacks fault offset but the succession has been uplifted of c. 1 km. The main fracture patterns are associated with the recent unloading of the ice, opening shallow horizontal fractures

  18. Fault zone structure and seismic reflection characteristics in zones of slow slip and tsunami earthquakes

    NASA Astrophysics Data System (ADS)

    Bell, Rebecca; Henrys, Stuart; Sutherland, Rupert; Barker, Daniel; Wallace, Laura; Holden, Caroline; Power, William; Wang, Xiaoming; Morgan, Joanna; Warner, Michael; Downes, Gaye

    2015-04-01

    Over the last couple of decades we have learned that a whole spectrum of different fault slip behaviour takes place on subduction megathrust faults from stick-slip earthquakes to slow slip and stable sliding. Geophysical data, including seismic reflection data, can be used to characterise margins and fault zones that undergo different modes of slip. In this presentation we will focus on the Hikurangi margin, New Zealand, which exhibits marked along-strike changes in seismic behaviour and margin characteristics. Campaign and continuous GPS measurements reveal deep interseismic coupling and deep slow slip events (~30-60 km) at the southern Hikurangi margin. The northern margin, in contrast, experiences aseismic slip and shallow (<10-15 km) slow slip events (SSE) every 18-24 months with equivalent moment magnitudes of Mw 6.5-6.8. Updip of the SSE region two unusual megathrust earthquakes occurred in March and May 1947 with characteristics typical of tsunami earthquakes. The Hikurangi margin is therefore an excellent natural laboratory to study differential fault slip behaviour. Using 2D seismic reflection, magnetic anomaly and geodetic data we observe in the source areas of the 1947 tsunami earthquakes i) low amplitude interface reflectivity, ii) shallower interface relief, iii) bathymetric ridges, iv) magnetic anomaly highs and in the case of the March 1947 earthquake v) stronger geodetic coupling. We suggest that this is due to the subduction of seamounts, similar in dimensions to seamounts observed on the incoming Pacific plate, to depths of <10 km. We propose a source model for the 1947 tsunami earthquakes based on geophysical data and find that extremely low rupture velocities (c. 300 m/s) are required to model the observed large tsunami run-up heights (Bell et al. 2014, EPSL). Our study suggests that subducted topography can cause the nucleation of moderate earthquakes with complex, low velocity rupture scenarios that enhance tsunami waves, and the role of

  19. 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.

  20. Seismic Waves Reflected from Discontinuities within Earth's Upper Mantle.

    PubMed

    Engdahl, E R; Flinn, E A

    1969-01-10

    Precursors to normtial seismic waves of the PKPPKP type in the distance range of 55 degrees to 75 degrees are ascribed to reflection of this phase from within the earth's upper mantle. The new observations confirm the existence of a sharply defined transition zone, probably worldwide in extent, at a depth of approximately 650 kilometers. These data are shown to be a useful tool for the study of upper mantle structure on a global basis.

  1. Mapping of active faults based on the analysis of high-resolution seismic reflection profiles in offshore Montenegro

    NASA Astrophysics Data System (ADS)

    Vucic, Ljiljana; Glavatovic, Branislav

    2014-05-01

    High-resolution seismic-reflection data analysis is considered as important tool for mapping of active tectonic faults, since seismic exploration methods on varied scales can image subsurface structures of different depth ranges. Mapping of active faults for the offshore area of Montenegro is performed in Petrel software, using reflection database consist of 2D profiles in length of about 3.500 kilometers and 311 square kilometers of 3D seismics, acquired from 1979 to 2003. Montenegro offshore area is influenced by recent tectonic activity with numerous faults, folded faults and over trusts. Based on reflection profiles analysis, the trust fault system offshore Montenegro is reveled, parallel to the coast and extending up to 15 kilometers from the offshore line. Then, the system of normal top carbonate fault planes is mapped and characterized on the southern Adriatic, with NE trending. The tectonic interpretation of the seismic reflection profiles in Montenegro point toward the existence of principally reverse tectonic forms in the carbonate sediments, covered by young Quaternary sandy sediments of thickness 1-3 kilometers. Also, reflective seismic data indicate the active uplifting of evaporite dome on about 10 kilometers of coastline.

  2. Source rock potential analysis using rock physics approach and 2D seismic data inversion: case study of Great Australian Bight

    NASA Astrophysics Data System (ADS)

    Shulakova, V.

    2015-12-01

    The quantity of total organic carbon (TOC) and its type determine the ability of source rocks to generate hydrocarbons. Thus, the quantification of TOC content is an essential part of any reservoir characterisation project. Traditionally TOC is estimated from geochemical analysis of core samples. In this case the results are limited spatially by a well location as well as vertically by a number of tested samples. At the same time TOC vertical variability might be very high, changing every 1-3 m. The several methods have been deployed to estimate TOC from well-log data which provides continuous vertical profile estimations. The basin wide information might be provided by the utilization of seismic surveys. The methodology of mapping source rocks based on seismic data has been lately reported to be successful for the thick source rocks (>20 m) with relatively high TOC values up to 3-4% (Løseth et al., 2011). We employ the described approach and demonstrate our findings for a case study from Ceduna Basin (Great Australian Bight, Australia). The reported TOC values estimated from the cores go up to only 1.3%. The organic matter is contained in thin layers of claystones interlayered with sandstones. The workflow included TOC estimation from the well-log data and then seismic data inversion performed in JasonTM software. The inverted acoustic impedance decreases nonlinearly with increasing TOC content. The obtained results comprises 2D section of TOC distribution. The calculated TOC values are in a good agreement with the results of laboratory measurements. The results of this study show that TOC can be successfully estimated from seismic data inversion even in the case of low organic matter values. Further work has to be done to understand whether this approach works for different types of organic matter and stages of its maturation. Løseth H., Wensaas L., Gading M., Duffaut K., Springer M. 2001. Can hydrocarbon source rocks be identified on seismic data? Geology 39/12.

  3. Well log and 2D seismic data character of the Wilcox Group in south-central Louisiana

    USGS Publications Warehouse

    Enomoto, Catherine B.

    2014-01-01

    The Wilcox Group is productive in updip areas of Texas and Louisiana from fluvial, deltaic, and near-shore marine shelf sandstones. The reported presence of porous sandstones at 29,000 feet within the Wilcox Group containing about 200 feet of gas in the Davy Jones 1 discovery well in the offshore Louisiana South Marsh Island area illustrates a sand-rich system developed during the Paleocene and early Eocene. This study describes some of the well log and reflection seismic data characteristics of the slope and basin-floor reservoirs with gas-discovery potential that may be in the area between the producing trend onshore Louisiana and the offshore discovery.

  4. Seismic Velocity Structure Across the Quebrada and Gofar Oceanic Transform Faults from 2D Refraction Tomography - A Comparison of Faults with High and Low Seismic Slip Deficits

    NASA Astrophysics Data System (ADS)

    Roland, E. C.; McGuire, J. J.; Collins, J. A.; Lizarralde, D.

    2009-12-01

    We perform two 2-D tomographic inversions using data collected as a part of the Quebrada-Discovery-Gofar (QDG) Transform Fault Active/Passive Experiment. The QDG transform faults are located in the southern Pacific Ocean and offset the East Pacific Rise (EPR) at approximately 4° south. In the spring of 2008, two ~100 km refraction profiles were collected, each using 8 short period Ocean Bottom Seismometers (OBS) from OBSIP and over 900 shots from the RV Marcus Langseth, across the easternmost segments of the Quebrada and Gofar transform faults. The two refraction profiles are modeled using a 2-D tomographic code that allows joint inversion of the Pg, PmP, and Pn arrivals (Korenaga et al., 2000). Variations in crustal velocity and thickness, as well as the width and depth extent of a significant low velocity zone within and below the transform valley provide some insight into the material properties of each of the fault-zones. Reduced seismic velocities that are 0.5 to over 1.0 km/s slower than velocities associated with the oceanic crust outside the fault zone may indicate the highly fractured fault zone lithology. The low velocity zone associated with the Quebrada fault also extends to the south of the active fault zone, beneath a fossil fault trace. Because Gofar is offset by an intratransform spreading center, we are able to compare ‘normal’ oceanic crust produced at the EPR to the south of the fault with crust associated with the ~15 km intratransform spreading center to the north. These two high slip rate (14 cm/yr) faults look similar morphologically and demonstrate comparable microseismicity characteristics, however their abilities to generate large earthquakes differ significantly. Gofar generates large earthquakes (Mw ~6) regularly every few years, but in the past 24 years only one large (Mw 5.6) event has been reliably located on Quebrada. The contrasting seismic behavior of these faults represents the range of behavior observed in the global

  5. Attenuation (1/Q) estimation in reflection seismic records

    NASA Astrophysics Data System (ADS)

    Raji, Wasiu; Rietbrock, Andreas

    2013-08-01

    Despite its numerous potential applications, the lack of a reliable method for determining attenuation (1/Q) in seismic data is an issue when utilizing attenuation for hydrocarbon exploration. In this paper, a new method for measuring attenuation in reflection seismic data is presented. The inversion process involves two key stages: computation of the centroid frequency for the individual signal using a variable window length and fast Fourier transform; and estimation of the difference in the centroid frequency and travel time for paired incident and transmitted signals. The new method introduces a shape factor and a constant which allows several spectral shapes to be used to represent a real seismic signal without altering the mathematical model. Application of the new method to synthetic data shows that it can provide reliable estimates of Q using any of the spectral shapes commonly assumed for real seismic signals. Tested against two published methods of Q measurement, the new method shows less sensitivity to interference from noise and change of frequency bandwidth. The method is also applied to a 3D data set from the Gullfaks field, North Sea, Norway. The trace length is divided into four intervals: AB, BC, CD, and DE. Results show that interval AB has the lowest 1/Q value, and that interval BC has the highest 1/Q value. The values of 1/Q measured in the CDP stack using the new method are consistent with those measured using the classical spectral ratio method.

  6. Neotectonic structure in the central new madrid seismic zone: Evidence from multimode seismic-reflection data

    USGS Publications Warehouse

    Woolery, E.W.; Street, R.L.; Wang, Z.; Harris, J.B.; McIntyre, J.

    1999-01-01

    Approximately 14.5 km of conventional P-wave and 2.2 km of horizontally polarized shear-wave seismic-reflection data acquired in the Kentucky Bend area of the central New Madrid Seismic Zone provide evidence of extensive neotectonic near-surface structure. The style and geometry of the deformation are consistent with documented historical geomorphic features, contemporary geomorphic features, and contemporary seismicity. The data image high-angle transpressional faults that strike between N30??W and N50??W. The fault planes exhibit apparent northeast and southwest dips. The opposing high-angle planes represent secondary splay or imbricate faults that responded to torsional bending of a lower-angle master fault.

  7. 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.

  8. Seismic Reflectivity of the Crust in the Northern Salton Trough

    NASA Astrophysics Data System (ADS)

    Bauer, K.; Fuis, G. S.; Goldman, M.; Persaud, P.; Ryberg, T.; Langenheim, V. E.; Scheirer, D. S.; Rymer, M. J.; Hole, J. A.; Stock, J. M.; Catchings, R.

    2015-12-01

    The Salton Trough in southern California is a tectonically active pull-apart basin that was formed by migrating step-overs between strike-slip faults, of which the San Andreas Fault (SAF) and the Imperial Fault are the current, northernmost examples. The Salton Seismic Imaging Project (SSIP) was undertaken to improve our knowledge of fault geometry and seismic velocities within the sedimentary basins and underlying crystalline crust around the SAF. Such data are useful as input for modeling scenarios of strong ground shaking in the surrounding high-population areas. We used pre-stack depth migration of line segments from shot gathers in several seismic profiles that were acquired in the northern part of the SSIP study area (Lines 4 - 7). Our migration approach can be considered as an infinite-frequency approximation of the Fresnel volume pre-stack depth migration method. We use line segments instead of the original waveform data. We demonstrate the method using synthetic data and analyze real data from Lines 4 - 7 to illustrate the relationship between distinct phases in the time domain and their resulting image at depth. We show both normal-moveout reflections from sub-horizontal interfaces and reverse-moveout reflections from steep interfaces, such as faults. Migrated images of dipping faults, such as the SAF and the Pinto Mountain Fault, are presented in this way. The SAF is imaged along Line 4, through the Mecca Hills, as a number of steeply dipping fault segments that collectively form a flower structure, above 5 km depth, that sole into a moderately NE-dipping fault below that depth. The individual migrated reflection packages correlate with mapped surface fault traces in the Mecca Hills. A similar geometry is seen on Line 6, from Palm Springs through Yucca Valley, where fault splays sole or project into a moderately dipping SAF below 10-km depth. We also show and discuss the reflectivity pattern of the middle and lower crust for Lines 4 - 7.

  9. Evolution of seismic layer 2B across the Juan de Fuca Ridge from hydrophone streamer 2-D traveltime tomography

    NASA Astrophysics Data System (ADS)

    Newman, Kori R.; Nedimović, Mladen R.; Canales, J. Pablo; Carbotte, Suzanne M.

    2011-05-01

    How oceanic crust evolves has important implications for understanding both subduction earthquake hazards and energy and mass exchange between the Earth's interior and the oceans. Although considerable work has been done characterizing the evolution of seismic layer 2A, there has been little analysis of the processes that affect layer 2B after formation. Here we present high-resolution 2-D tomographic models of seismic layer 2B along ˜300 km long multichannel seismic transects crossing the Endeavour, Northern Symmetric, and Cleft segments of the Juan de Fuca Ridge. These models show that seismic layer 2B evolves rapidly following a different course than layer 2A. The upper layer 2B velocities increase on average by 0.8 km/s and reach a generally constant velocity of 5.2 ± 0.3 km/s within the first 0.5 Myr after crustal formation. This suggests that the strongest impact on layer 2B evolution may be that of mineral precipitation due to "active" hydrothermal circulation centered about the ridge crest and driven by the heat from the axial magma chamber. Variations in upper layer 2B velocity with age at time scales ≥0.5 Ma show correlation about the ridge axis indicating that in the long term, crustal accretion processes affect both sides of the ridge axis in a similar way. Below the 0.5 Ma threshold, differences in 2B velocity are likely imprinted during crustal formation or early crustal evolution. Layer 2B velocities at propagator wakes (5.0 ± 0.2 km/s), where enhanced faulting and cracking are expected, and at areas that coincide with extensional or transtensional faulting are on average slightly slower than in normal mature upper layer 2B. Analysis of the layer 2B velocities from areas where the hydrothermal patterns are known shows that the locations of current and paleohydrothermal discharge and recharge zones are marked by reduced and increased upper layer 2B velocities, respectively. Additionally, the distance between present up-flow and down-flow zones is

  10. 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.

  11. A deep reflection seismic line across the Northern Rhine Graben

    NASA Astrophysics Data System (ADS)

    Wenzel, F.; Brun, J.-P.; Ecors-Dekorp Working Group

    1991-06-01

    Two reflection seismic lines across the Tertiary Rhine Graben in Central Europe were recorded in 1988 as a joint venture of the French ECORS and the German DEKORP deep seismic reflection programs. In this paper the line across the northern graben is presented. The main results are: The asymmetry of the graben as documented by the sedimentary fill is accompanied by asymmetric features throughout the entire deep crystalline crust: a thin (3.7 s TWT) reflective lower crust in the east—a thick (5.5 s TWT), relatively transparent lower crust in the west, total crustal thicknesses of 8.7 s TWT in the east vs. 10.5 s TWT in the west. Provided a laterally homogeneous crust existed prior to rifting significant differences in upper and lower crustal thinning must be postulated. Extension occurred along localized shear zones that are located in the upper crust and at the crust/mantle boundary. The entire lower crustal layer acts as a decoupling zone.

  12. Seismic Waves within Earth's Outer Core: Multiple Reflection.

    PubMed

    Engdahl, E R

    1968-07-19

    Seismic waves reflected as many as four times within Earth's outer core are routinely recorded from large earthquakes. Observations of these waves are confined to rays near grazing incidence on the core-mantle boundary, in agreement with theoretical expectation. Minor adjustments to outer-core velocities may be necessary to account for certain of these arrivals that are not predicted by present core models. A change of 10 kilometers or more in the currently accepted core radius, 3473 kilometers, is not corroborated by the new data.

  13. Fracture Detection in Alluvial Fan Deposits Using Near-Surface Seismic Reflection Techniques

    NASA Astrophysics Data System (ADS)

    Black, R. A.; Miller, B.

    2012-12-01

    In this study we document the observation of probable extensive shallow vertical fracture systems in unprocessed 2-D source gathers from near-surface seismic reflection surveys conducted over unconsolidated materials in alluvial fans environments. Mapping of fracture and fault systems within the sedimentary sections at hydrocarbon exploration scales has become common practice. This is due to the advent of post-stack attribute analysis of 3-D seismic images worldwide. However, examples of fracture detection and imaging in the near-surface are currently lacking in the literature. In addition, examples of fracture detection and mapping in the pre-stack domain are also lacking. In this study, unprocessed seismic source gathers from very high-resolution reflection surveys over alluvial fan deposits in tectonically active areas appear to display distinct patterns of amplitude drop off, geometrically similar to patterns expected for vertical fracture systems. The patterns can also be extracted by attribute analysis using techniques such as envelope and coherency analyses. Simple standard processing steps such as trace editing, muting, and bandpass filtering enhance interpretability. The patterns appear to be consistent and spatially fixed in the subsurface from source location to source location. These are observed in areas of obvious recent local large-scale fault movement. Examples are given from two areas, eastern Queen Valley in California and eastern Fish Lake Valley in Nevada. The stratigraphic and sedimentation patterns are quite complicated in both areas, and sediment characteristics vary considerably between sites. The surface sediments in the Queen Valley case are, in general, much coarser with many more boulder-sized clasts in the shallow subsurface. The seismic source consisted of a 30-06 rifle fired downhole at a depth of 0.5m. While the boulders interfered with seismic source operations, the record quality was excellent. The alluvial materials, especially

  14. Investigating a clay landslide site using 3D P-wave reflection seismics in Lilla Edet, Sweden

    NASA Astrophysics Data System (ADS)

    Lundberg, E.; Malehmir, A.; Juhlin, C.; Bastani, M.

    2012-04-01

    Landslides are one of the most commonly occurring natural disasters. Global damages range in the billions of dollars and cost hundreds of lives each year; Sweden is not an exception. The main objectives of this geohazard-related project are (1) to improve the understanding of the geometrical shape and structure of clay areas, (2) to develop tools for monitoring changes in their geometry and physical properties as critical factors for landslide triggering, and (3) to provide robust analytical methods for assessing risks associated with clay landslides both in short and long terms. The project is sponsored by the Geoscientists Without Borders (GWB) Program of the Society of Exploration Geophysicists and is multidisciplinary, involving several geophysical methods such as ground gravity and magnetics, geoelectrics, controlled source/radio magnetotellurics, as well as reflection/refraction seismic methods (both P- and S-wave source and receivers). The test site is located on the shoreline of the Göta river that runs from lake Vänern to Göteborg on the southwest coast. The Göta river is the largest river in Sweden and follows the Götaälv Zone, which is an approximately 4 km wide fault zone dipping towards the west. The 3D seismic survey covers a large landslide scar that occurred about 30-40 years ago. The main objective of the 3D seismic is to image the bedrock topography in detail and possibly define layering in the sediments above. The 3D seismic data were acquired in September 2011 using a weight-drop source, 4 m geophone spacing and 20 m line spacing with the source activated at most geophone positions. Ten lines with 60 geophones on each line were shot in two overlapping patches. The preliminary results are encouraging and depict the bedrock topography at 100-150 ms or about 70-100 m. The central line in the 3D seismic survey is overlapped by a longer 2D reflection seismic profile, acquired using a dynamite source. The 2D reflection stack, as well as a travel

  15. Reconstructing the birth, life and death of ancient monogenetic basalt volcanoes using seismic reflection data

    NASA Astrophysics Data System (ADS)

    Magee, C.; Jackson, C. A. L.; Hunt-Stewart, E.

    2014-12-01

    Temporal and spatial changes in monogenetic volcano morphology and internal architecture can determine eruption style and location. However, the relationships between the external and internal characteristics of volcanoes, and sub-volcanic intrusions, are often difficult to observe at outcrop or interpret uniquely from geophysical and geodetic data. This compromises our understanding of the birth, life and death of monogenetic basalt volcanoes. To address this, we use high-quality 2D seismic reflection data from the Ceduna Sub-basin, offshore southern Australia, to quantitatively analyse 46, pristinely-preserved, Eocene-age volcanoes and a genetically-related network of sub-volcanic sills and laccoliths. Detailed seismic mapping has allowed the 3D geometry of each volcano to be reconstructed and distinct seismic facies within them to be recognised. The volcanoes have average flank dips of <10.3°, basal diameters of 1.94-18.89 km, central summits that are 0.02-1 km above the contemporaneous palaeosurface, and volumes that range from 0.06-57.21 km3. Parallel, outward-dipping seismic reflections within the shield volcanoes are interpreted to represent interbedded volcanic and clastic material, suggesting that a series of temporally separate eruptions emanated from a central vent. The shield volcanoes typically overlie the lateral tips of sills and we suggest that the intermittent eruption phases correspond to the incremental emplacement of discrete magma pulses within the laterally extensive sill-complex. This work highlights that deformation patterns preceding volcanic eruptions may: (i) be offset from the eruption site; and (ii) attributed to intrusions with complex morphologies.

  16. Mesozoic and Cenozoic plate tectonics in the High Arctic: new 2D seismic data and geodynamic models

    NASA Astrophysics Data System (ADS)

    Nikishin, Anatoly; Kazmin, Yuriy; Glumov, Ivan; Petrov, Eugene; Poselov, Viktor; Burov, Evgueni; Gaina, Carmen

    2014-05-01

    Our paper is mainly based on the interpretation of 2D seismic lines, obtained from Arctic-2001 and Arctic-2012 projects. We also analyzed all available open-source data concerning Arctic geology. Three domains are distinguished in the abyssal part of Arctic Ocean: (1) Canada Basin, (2) Lomonosov-Podvodnikov-Alpha-Mendeleev-Nautilus-Chukchi Plateau (LPAMNCP) area, (3) Eurasia Basin. Canada Basin has oceanic and transitional crust of different structure. The formation time of this oceanic basin is probably 134-117 Ma. New seismic data for LPAMNCP area shows numerous rift structures parallel to the Lomonosov Ridge and Mendeleev Ridge. These rift structures are also nearly orthogonal to the Canada Basin spreading axis, and this may indicate either a different mechanism for the formation of the LPAMNCP region and Canada Basin, or a very complicated basin architecture formed by processes we do not yet understand. We also observe at the base of the LPAMNCP area sedimentary cover packages of bright reflectors, they were interpreted as basalt flows probably related to the Cretaceous plume volcanism. Approximate time of the volcanism is about 125 Ma. After this event, the area experienced stretching and transtension as documented by large scale rifting structures. The younger Eurasian Basin has oceanic crust of Eocene to Recent age, and our new seismic data confirms that Gakkel Ridge has typical ultraslow-spreading zone topography. Perhaps, Eurasia Basin crust was partly formed by exhumed and serpentinized mantle. Lomonosov and Alpha-Mendeleev Ridges has typical present-day basin and range topography with Oligocene to Recent faults. It means, that all LPAMNCP area was subjected to regional intra-plate stretching during Neogene to Recent time. We assume, that this intra-plate stretching was related to the Gakkel Ridge extension. We suppose, that the deep-water part of Arctic Ocean was formed during three main stages: (1) Valanginian - Early Aptian: formation of Canada Basin

  17. Shallow Seismic Reflection Survey at Garner Valley Digital Array

    NASA Astrophysics Data System (ADS)

    Lawrence, Z. S.; Brackman, T. B.; Bodin, P.; Stephenson, W. J.; Steidl, J. H.; Gomberg, J.

    2004-12-01

    The Garner Valley Digital Array (GVDA) site is a NEES-sponsored facility in a small, sediment-filled, intermountain valley in Southern California, established for the purpose of investigating ground motion site response and soil-structure interaction, in situ. The site has been well-characterized geotechnically, and is thoroughly instrumented with both surface and downhole instrumentation of various types. Nevertheless, a borehole recently drilled into lake bed sediments and deeply weathered granitic rocks that comprise the valley fill at GVDA encountered hard, unweathered bedrock at an unexpected depth, suggesting an apparent 38 meter offset in the unweathered bedrock between two wells 40 meters apart. The apparent offset can be most easily explained either by faulting, or as a buried erosional surface. The Hot Springs fault, a strand of the San Jacinto fault zone, runs through Garner Valley, although its inferred location is several hundred meters east of GVDA. To better characterize the subsurface strata, particularly the existence and configuration of faulting that may disturb them; we conducted a 120-meter long, 12-fold shallow seismic reflection common midpoint (CMP) survey at GVDA using a 24-channel seismograph, vertical 4.5 Hz geophones at 2-meter intervals and a sledgehammer seismic source. Preliminary processing reveals strong refractors and surface waves that may mask reflections, although reflections are visible in some raw shot records. Semi-continuous reflections seen in the CMP section from a shallow reflector may coincide with the water table. There are also deeper, discontinuous reflectors obscured by bands of coherent noise. We plan to present a fully migrated and interpreted CMP record section.

  18. 3D Seismic Reflection Experiment Over the Galicia Deep Basin

    NASA Astrophysics Data System (ADS)

    Sawyer, Dale; Jordan, Brian; Tesi Sanjurjo, Mari; Alexanian, Ara; Morgan, Julia; Shillington, Donna; Reston, Timothy; Minshull, Timothy; Klaeschen, Dirk; Ranero, César

    2014-05-01

    In June thru September, 2013, a 3D reflection and a long offset seismic experiment were conducted at the Galicia rifted margin by investigators from the US, UK, Germany, and Spain. The 3D multichannel experiment covered 64 km by 20 km (1280 km2), using the RV Marcus Langseth. Four streamers 6 km long were deployed at 12.5 m hydrophone channel spacing. The streamers were 200 m apart. Two airgun arrays, each 3300 cu in, were fired alternately every 37.5 m, to collectively yield a 400 m wide sail line consisting of 8 CMP lines at 50 m spacing. The long offset seismic experiment included 72 short period OBS's deployed below the 3D reflection survey box. Most of the instruments recorded all the shots from the airgun array shots. The 3D seismic box covered a variety of geologic features. The Peridotite Ridge (PR), is associated with the exhumation of upper mantle rocks to the seafloor during the final stage of the continental separation between the Galicia Bank and the Grand Banks of Newfoundland. The S reflector is present below most of the continental blocks under the deep Galicia basin. S is interpreted to be a low-angle detachment fault formed late in the rifting process, and a number of rotated fault block basins and ranges containing pre and syn-rift sediments. Initial observations from stacked, but not yet migrated, 3D seismic data show that the PR is elevated above the present seafloor in the South and not exposed through the seafloor in the North. The relative smoothness of the PR surface for the entire 20 km N-S contrasts with the more complex, shorter wavelength, faulting of the continental crustal blocks to the east. The PR does not seem to show offsets or any apparent internal structure. However, migration will be required to see internal structure of the PR. Between the PR and the western most rifted continental crustal blocks, is a sedimentary basin about as wide as the PR and very different from the sedimentary basins bounded by the continental crustal

  19. 2D THz and GHz signature for identification of explosive on reflected THz signal

    NASA Astrophysics Data System (ADS)

    Trofimov, Vyacheslav A.; Varentsova, Svetlana A.; Chen, Jian

    2010-11-01

    The method of THz spectrum dynamics analysis (SDA - Spectral dynamics analysis - method) is applied for the detection and identification of substances by using the signal reflected from sample. It allows to obtain the spectrogram - composite Fourier spectrum dynamics - of the signal and to analyze the dynamics of many spectral lines simultaneously, even if the measurements are made on short time interval (less than 50 ps). The efficiency of the SDA method used for longer time intervals (more than 100 ps) is discussed also. The Fourier-Gabor sliding window method is used for obtaining the spectrogram. We consider the examples of finding the pure RDX and harmless materials (L-Tartaric Acid, Sucrose, PTFE) or their mixture in pellets by using a THz pulse reflected from them. A THz pulse with a few cycles falls on the sample and reflects from it. The receiver makes the discrete measurements of electric field strength of signal reflected from the sample. To restore the signal to the required accuracy the SVD - Single Value Decomposition - technique is used. Our investigations show that the spectrograms and dynamics of several spectral lines of the THz pulse reflected differ from the corresponding spectrograms and dynamics of spectral lines for the reference pulse under certain conditions and hence it is possible to detect the presence of the material in the sample of interest. The comparison of the Fourier spectrum of the substance with the corresponding spectrum calculated on the base of using an autocorrelation function for obtaining the spectrum shows that the AC-spectrum gives us essential less information about substance. From our consideration follows that in some cases the analysis of reflected signal on the short time interval (less than 50 ps) is insufficient for the reliable identification. It is necessary to analyze the response on the long time interval (about 300 - 400 ps). The analysis of spectrogram and spectral lines dynamics on the long time intervals

  20. Tunable Plasmonic Reflection by Bound 1D Electron States in a 2D Dirac Metal.

    PubMed

    Jiang, B-Y; Ni, G X; Pan, C; Fei, Z; Cheng, B; Lau, C N; Bockrath, M; Basov, D N; Fogler, M M

    2016-08-19

    We show that the surface plasmons of a two-dimensional Dirac metal such as graphene can be reflected by linelike perturbations hosting one-dimensional electron states. The reflection originates from a strong enhancement of the local optical conductivity caused by optical transitions involving these bound states. We propose that the bound states can be systematically created, controlled, and liquidated by an ultranarrow electrostatic gate. Using infrared nanoimaging, we obtain experimental evidence for the locally enhanced conductivity of graphene induced by a carbon nanotube gate, which supports this theoretical concept. PMID:27588873

  1. Tunable Plasmonic Reflection by Bound 1D Electron States in a 2D Dirac Metal

    NASA Astrophysics Data System (ADS)

    Jiang, B.-Y.; Ni, G. X.; Pan, C.; Fei, Z.; Cheng, B.; Lau, C. N.; Bockrath, M.; Basov, D. N.; Fogler, M. M.

    2016-08-01

    We show that the surface plasmons of a two-dimensional Dirac metal such as graphene can be reflected by linelike perturbations hosting one-dimensional electron states. The reflection originates from a strong enhancement of the local optical conductivity caused by optical transitions involving these bound states. We propose that the bound states can be systematically created, controlled, and liquidated by an ultranarrow electrostatic gate. Using infrared nanoimaging, we obtain experimental evidence for the locally enhanced conductivity of graphene induced by a carbon nanotube gate, which supports this theoretical concept.

  2. The limits of seaward spreading and slope instability at the continental margin offshore Mt Etna, imaged by high-resolution 2D seismic data

    NASA Astrophysics Data System (ADS)

    Gross, Felix; Krastel, Sebastian; Geersen, Jacob; Behrmann, Jan Hinrich; Ridente, Domenico; Chiocci, Francesco Latino; Bialas, Jörg; Papenberg, Cord; Cukur, Deniz; Urlaub, Morelia; Micallef, Aaron

    2016-01-01

    Mount Etna is the largest active volcano in Europe. Instability of its eastern flank is well documented onshore, and continuously monitored by geodetic and InSAR measurements. Little is known, however, about the offshore extension of the eastern volcano flank, defining a serious shortcoming in stability models. In order to better constrain the active tectonics of the continental margin offshore the eastern flank of the volcano, we acquired a new high-resolution 2D reflection seismic dataset. The data provide new insights into the heterogeneous geology and tectonics at the continental margin offshore Mt Etna. The submarine realm is characterized by different blocks, which are controlled by local- and regional tectonics. A compressional regime is found at the toe of the continental margin, which is bound to a complex basin system. Both, the clear link between on- and offshore tectonic structures as well as the compressional regime at the easternmost flank edge, indicate a continental margin gravitational collapse as well as spreading to be present at Mt Etna. Moreover, we find evidence for the offshore southern boundary of the moving flank, which is identified as a right lateral oblique fault north of Catania Canyon. Our findings suggest a coupled volcano edifice/continental margin instability at Mt Etna, demonstrating first order linkage between on- and offshore tectonic processes.

  3. 2D attenuated total reflectance infrared spectroscopy reveals ultrafast vibrational dynamics of organic monolayers at metal-liquid interfaces

    NASA Astrophysics Data System (ADS)

    Kraack, Jan Philip; Lotti, Davide; Hamm, Peter

    2015-06-01

    We present two-dimensional infrared (2D IR) spectra of organic monolayers immobilized on thin metallic films at the solid liquid interface. The experiments are acquired under Attenuated Total Reflectance (ATR) conditions which allow a surface-sensitive measurement of spectral diffusion, sample inhomogeneity, and vibrational relaxation of the monolayers. Terminal azide functional groups are used as local probes of the environment and structural dynamics of the samples. Specifically, we investigate the influence of different alkyl chain-lengths on the ultrafast dynamics of the monolayer, revealing a smaller initial inhomogeneity and faster spectral diffusion with increasing chain-length. Furthermore, by varying the environment (i.e., in different solvents or as bare sample), we conclude that the most significant contribution to spectral diffusion stems from intra- and intermolecular dynamics within the monolayer. The obtained results demonstrate that 2D ATR IR spectroscopy is a versatile tool for measuring interfacial dynamics of adsorbed molecules.

  4. 2D attenuated total reflectance infrared spectroscopy reveals ultrafast vibrational dynamics of organic monolayers at metal-liquid interfaces.

    PubMed

    Kraack, Jan Philip; Lotti, Davide; Hamm, Peter

    2015-06-01

    We present two-dimensional infrared (2D IR) spectra of organic monolayers immobilized on thin metallic films at the solid liquid interface. The experiments are acquired under Attenuated Total Reflectance (ATR) conditions which allow a surface-sensitive measurement of spectral diffusion, sample inhomogeneity, and vibrational relaxation of the monolayers. Terminal azide functional groups are used as local probes of the environment and structural dynamics of the samples. Specifically, we investigate the influence of different alkyl chain-lengths on the ultrafast dynamics of the monolayer, revealing a smaller initial inhomogeneity and faster spectral diffusion with increasing chain-length. Furthermore, by varying the environment (i.e., in different solvents or as bare sample), we conclude that the most significant contribution to spectral diffusion stems from intra- and intermolecular dynamics within the monolayer. The obtained results demonstrate that 2D ATR IR spectroscopy is a versatile tool for measuring interfacial dynamics of adsorbed molecules.

  5. Theory of reflectivity blurring in seismic depth imaging

    NASA Astrophysics Data System (ADS)

    Thomson, C. J.; Kitchenside, P. W.; Fletcher, R. P.

    2016-05-01

    A subsurface extended image gather obtained during controlled-source depth imaging yields a blurred kernel of an interface reflection operator. This reflectivity kernel or reflection function is comprised of the interface plane-wave reflection coefficients and so, in principle, the gather contains amplitude versus offset or angle information. We present a modelling theory for extended image gathers that accounts for variable illumination and blurring, under the assumption of a good migration-velocity model. The method involves forward modelling as well as migration or back propagation so as to define a receiver-side blurring function, which contains the effects of the detector array for a given shot. Composition with the modelled incident wave and summation over shots then yields an overall blurring function that relates the reflectivity to the extended image gather obtained from field data. The spatial evolution or instability of blurring functions is a key concept and there is generally not just spatial blurring in the apparent reflectivity, but also slowness or angle blurring. Gridded blurring functions can be estimated with, for example, a reverse-time migration modelling engine. A calibration step is required to account for ad hoc band limitedness in the modelling and the method also exploits blurring-function reciprocity. To demonstrate the concepts, we show numerical examples of various quantities using the well-known SIGSBEE test model and a simple salt-body overburden model, both for 2-D. The moderately strong slowness/angle blurring in the latter model suggests that the effect on amplitude versus offset or angle analysis should be considered in more realistic structures. Although the description and examples are for 2-D, the extension to 3-D is conceptually straightforward. The computational cost of overall blurring functions implies their targeted use for the foreseeable future, for example, in reservoir characterization. The description is for scalar

  6. Reinterpretation of seismic reflection data over the East Pacific Rise

    SciTech Connect

    Hale, L.D.; Morton, C.J.; Sleep, N.H.

    1982-09-10

    Multichannel seismic reflection data over the axial region of the East Pacific Rise are depth migrated using detailed velocity information from laboratory measurements of ophiolite samples. The data are from the Lamont Doherty Geological Observatory's line 17 shot across the rise at 9/sup 0/N. The migrated data are interpreted to show the structure of the seafloor and what we believe is the magma chamber roof. The polarity and apparent root mean squared velocity of the magma chamber roof are asymmetric with respect to the topographic axis of the ridge. The asymmetry is probably real and not an artifact of data collection. Modeling of the magnetic data gathered along the line shows that spreading has not been proceeding normally. A reasonable explanation for the asymmetry is the possibility that the line intersects a transform fault or an abandoned ridge segment near the ridge axis. The shape of the roof reflection is convex upward with an approximate slope of 10/sup 0/ and a width of 4 km. If extrapolated symmetrically to the other side of the ridge axis, the magma chamber roof event is consistent with the funnel-shaped chamber proposed by Pallister and Hopson (1981) for the Samail ophiolite. If the chamber roof steepens rapidly beyond the extent of the reflection, it would be consistent with the mush-filled model of Sleep (1975, 1978) and Dewey and Kidd (1977).

  7. An asymptotic model of seismic reflection from a permeable layer

    SciTech Connect

    Silin, D.; Goloshubin, G.

    2009-10-15

    Analysis of compression wave propagation in a poroelastic medium predicts a peak of reflection from a high-permeability layer in the low-frequency end of the spectrum. An explicit formula expresses the resonant frequency through the elastic moduli of the solid skeleton, the permeability of the reservoir rock, the fluid viscosity and compressibility, and the reservoir thickness. This result is obtained through a low-frequency asymptotic analysis of Biot's model of poroelasticity. A review of the derivation of the main equations from the Hooke's law, momentum and mass balance equations, and Darcy's law suggests an alternative new physical interpretation of some coefficients of the classical poroelasticity. The velocity of wave propagation, the attenuation factor, and the wave number, are expressed in the form of power series with respect to a small dimensionless parameter. The absolute value of this parameter is equal to the product of the kinematic reservoir fluid mobility and the wave frequency. Retaining only the leading terms of the series leads to explicit and relatively simple expressions for the reflection and transmission coefficients for a planar wave crossing an interface between two permeable media, as well as wave reflection from a thin highly-permeable layer (a lens). Practical applications of the obtained asymptotic formulae are seismic modeling, inversion, and at-tribute analysis.

  8. Seismic reflectivity effects from seasonal seafloor temperature variation

    NASA Astrophysics Data System (ADS)

    Wood, Warren T.; Martin, Kylara M.; Jung, Wooyeol; Sample, John

    2014-10-01

    The effects of seasonal temperature variation on sound speed contrasts at the seafloor are usually considered negligible in the analysis of seismic data but may be significant at large incidence angles (offsets) important for inversion of sediment elastic properties, or long-range acoustic transmission. In coastal areas, the maximum annual seafloor temperature variation can be several degrees Celsius or more, corresponding to a sound speed variation of 30 m/s or more. Thermal pulses propagate via conduction several meters into the seafloor resulting in a damped quasi-sinusoidal temperature profile with predictable wave number characteristics. The oscillating seasonal and spatial character of this signal creates a time- and frequency-dependent effect on the elastic seafloor reflectivity. Results of numerical simulations show that the expected temperature profile for most sediment types and porosities will have the strongest affect on frequencies between about 60 and 600 Hz, at incidence angles greater than about 50°.

  9. Detailed Seismic Reflection Images of the Central American Volcanic Arc

    NASA Astrophysics Data System (ADS)

    McIntosh, K. D.; Fulthorpe, C. S.

    2005-12-01

    New high-resolution seismic reflection profiles across the Central American volcanic arc (CAVA) reveal an asymmetric deformation pattern with large-scale folding and uplift of basinal strata in the forearc contrasted by intrusive bodies, normal faults, and possible strikes-slip faults in the backarc. Since Miocene times the CAVA has migrated seaward, apparently impinging on the Sandino forearc basin and creating or modifying the low-lying Nicaragua depression, which contains the backarc and much of the arc. However the structural nature of the depression and its possible relationship to forearc sliver movement is poorly known. In November-December 2004 we recorded a large, high-resolution, seismic reflection dataset largely on the Pacific shelf (forearc) area of Central America, extending from NW Costa Rica to the SE edge of El Salvador's territorial waters. We seized an opportunity to study the nature of the CAVA by recording data into the Gulf of Fonseca, a large embayment at the intersection of Nicaragua, Honduras, and El Salvador. With 3 GI airguns and a 2100 m streamer we recorded data with typical penetration of 2-3 seconds in the Sandino basin and frequency content of ~10-250 Hz (at shallow levels). Penetration was limited over the arc summit with high velocity volcanic rocks encountered at depths as shallow as a few hundred meters. To the NE the edge of the Nicaragua depression occurs abruptly; our data show a well-developed sedimentary basin 1.5-3 km thick separated by numerous steeply-dipping faults. The broadband signal and good penetration of this dataset will help us determine the chronology of arc development in this position and the styles of deformation in the forearc, arc, and backarc areas. In turn, this will help us understand the regional tectonic and stratigraphic development of this margin due to the profound affects of the arc.

  10. Seismic reflection exploration of geothermal reservoir at Naval Air Station (NAS) Fallon, Nevada

    NASA Astrophysics Data System (ADS)

    Alay G., Gebregiorgis

    The Primary objective of this study is to increase geologic and tectonic understanding of the geothermal resources at the Naval Air Station (NAS) Fallon, Nevada. The seismic reflection method is employed to study faults, fractures and other tectonic structures in the subsurface in order to identify geothermal drill targets. The efficiency of geothermal systems is strongly dependent on water circulation. Discrete faults may be permeable and provide pathways for water flow depending on the fracture density. It is therefore desirable to detect and map faults and fracture zones and characterize their physical properties when evaluating a geothermal prospect. The seismic data for this project were provided by the NAS environmental research program in Ridgecrest, CA. However, the data collection information was not available so the work includes determining the line geometry and mapping shot points to field files in order to process the data. ProMAX 2D(TM) is the software used to determine the geometry and to process the data. Data processing includes eliminating noise, datum and refraction statics, trace muting, bandpass filter, automatic gain control, amplitude recovery, CMP sorting, velocity analysis and NMO correction, stacking and migration. The results of this study indicate the presence of thick basin fill including Tertiary and Quaternary sediments underlain by Tertiary basalts which are interpreted to be capping rocks for the geothermal reservoirs. This seismic reflection study also reveals the presence of strongly fractured pre-Tertiary basement complex with their top at about 1500m on the north and west and about 900 m on the eastern and southern part of the study area.

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

    SciTech Connect

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

    2001-05-01

    The Earth Sciences and Resources Institute, University of South Carolina is conducting a 14 month proof of concept study to determine the location and distribution of subsurface Dense Nonaqueous Phase Liquid (DNAPL) carbon tetrachloride (CCl{sub 4}) contamination at the 216-Z-9 crib, 200 West area, Department of Energy (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 a noninvasive means towards site characterization and direct free-phase DNAPL detection. This report covers the results of Task 3 and change of scope of Tasks 4-6. 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 designed to image areas of probable high concentration of DNAPL. Task 3 is the processing and interpretation of the 2-D data. Task 4, 5, and 6 were designing, acquiring, processing, and interpretation of a three dimensional seismic survey (3D) at the Z-9 crib area at 200 west area, Hanford.

  12. Multiple attenuation to reflection seismic data using Radon filter and Wave Equation Multiple Rejection (WEMR) method

    SciTech Connect

    Erlangga, Mokhammad Puput

    2015-04-16

    Separation between signal and noise, incoherent or coherent, is important in seismic data processing. Although we have processed the seismic data, the coherent noise is still mixing with the primary signal. Multiple reflections are a kind of coherent noise. In this research, we processed seismic data to attenuate multiple reflections in the both synthetic and real seismic data of Mentawai. There are several methods to attenuate multiple reflection, one of them is Radon filter method that discriminates between primary reflection and multiple reflection in the τ-p domain based on move out difference between primary reflection and multiple reflection. However, in case where the move out difference is too small, the Radon filter method is not enough to attenuate the multiple reflections. The Radon filter also produces the artifacts on the gathers data. Except the Radon filter method, we also use the Wave Equation Multiple Elimination (WEMR) method to attenuate the long period multiple reflection. The WEMR method can attenuate the long period multiple reflection based on wave equation inversion. Refer to the inversion of wave equation and the magnitude of the seismic wave amplitude that observed on the free surface, we get the water bottom reflectivity which is used to eliminate the multiple reflections. The WEMR method does not depend on the move out difference to attenuate the long period multiple reflection. Therefore, the WEMR method can be applied to the seismic data which has small move out difference as the Mentawai seismic data. The small move out difference on the Mentawai seismic data is caused by the restrictiveness of far offset, which is only 705 meter. We compared the real free multiple stacking data after processing with Radon filter and WEMR process. The conclusion is the WEMR method can more attenuate the long period multiple reflection than the Radon filter method on the real (Mentawai) seismic data.

  13. 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.

  14. Late Palezoic structure of the southern part of the Uinta Basin, Utah, from seismic reflection data

    SciTech Connect

    Potter, C.J. ); Tang, R. ); Hainsworth, T.J.

    1991-01-01

    A network of oil-industry seismic reflections lines that reveal buried Pennsylvanian and Permian faulting patterns is presented and discussed. The fault patterns have not been reactivated during the Mesozoic and Cenozoic. Four seismic reflection lines are presented in detail.

  15. Imaging Enhancement on Deep Seismic Reflection with Petrel and Ocean Working Environment

    NASA Astrophysics Data System (ADS)

    Yu, P.; Huang, D.; Feng, X.; Li, L.; Liu, W.; Wang, Y.; Zhao, Q.

    2011-12-01

    SinoProbe has been initiated to enhance understanding of earth deep structure, resources and geological disasters forecasting throughout Chinese continent. Besides traditional deep exploration methods, various state-of-the-art technologies have been carried out in order to acquire data and jointly utilize all possible information reflecting deep crust and mantle structures and evolution.Petrel, a powerful software application developed by Schlumberger, has been successfully applied to the O&G industry. It is now a complete seismic-to-simulation application for 3D and 2D seismic interpretation. However, it has a great potential to allow the user to extend utilization with multiple types of data sets to deal with much deeper geophysical information. Petrel all-in-one concept, that functionally comprises of massive data integration, multiple domains experts participation and 3D geological object-oriented etc., will come benefit to the deep earth study. Currently, there is no special tool designed for this purpose so that Petrel is required to extend its potential to cope with not only O&G area but also a larger area with unique requests of deeper objects.Ocean, a software framework for Petrel, provides an open development environment offering seamless integration of developer intellectual contribution to the Petrel mainstream workflow. It is able to accelerate the development and deployment of user's Petrel-like workflows to resolve complex problems. It can be implemented by means of plug-ins utilities although there is additional challenge to write a robust code with Ocean framework. Deep seismic reflection profiling is a well recognized technique to reveal the fine structure of lithosphere. Moreover, it can perform a significant role for prospective evaluation of O&G and mineral resources, and geological disasters. Its near-vertical deep seismic reflection method can enhance broad band seismic observations for imaging of the deep crust and continental geodynamics

  16. Urban shear-wave reflection seismics: Reconstruction support by combined shallow seismic and engineering geology investigations

    NASA Astrophysics Data System (ADS)

    Polom, U.; Guenther, A.; Arsyad, I.; Wiyono, P.; Krawczyk, C. M.

    2009-12-01

    After the big 2004 Sumatra-Andaman earthquake, the massive reconstruction activities in the Aceh province (Northern Sumatra) were promoted by the Republic of Indonesia and the Federal Ministry of Economic Cooperation and Development. The aims of the project MANGEONAD (Management of Georisk Nanggroe Aceh Darussalam). are to establish geoscientific on the ground support for a sustainable development and management of save building constructions, lifelines, infrastructure and also natural resources. Therefore, shallow shear-wave reflection seismics was applied in close combination to engineering geology investigations in the period between 2005-2009 since depth and internal structure of the Krueng Aceh River delta (mainly young alluvial sediments) were widely unknown. Due to the requirements in the densely populated Banda Aceh region, lacking also traffic infrastructure, a small and lightweight engineering seismic setup of high mobility and high subsurface resolution capability was chosen. The S-wave land streamer system with 48 channels was applied successfully together with the ELVIS vibratory source using S- and P-waves on paved roads within the city of Banda Aceh. The performance of the S-wave system enabled the detailed seismic investigation of the shallow subsurface down to 50-150 m depth generating shaking frequencies between 20 Hz to 200 Hz. This also provides depth information extending the maximum depths of boreholes and Standard Penetrometer Testings (SPT), which could only be applied to max. 20 m depth. To integrate the results gained from all three methods, and further to provide a fast statistical analysis tool for engineering use, the Information System Engineering Geology (ISEG, BGR) was developed. This geospatial information tool includes the seismic data, all borehole information, geotechnical SPT and laboratory results from samples available in the investigation area. Thereby, the geotechnical 3D analysis of the subsurface units is enabled. The

  17. The Northwestern Atlantic Moroccan Margin From Deep Multichannel Seismic Reflection

    NASA Astrophysics Data System (ADS)

    Malod, J. A.; Réhault, J. P.; Sahabi, M.; Géli, L.; Matias, L.; Zitellini, N.; Sismar Group

    The NW Atlantic Moroccan margin, a conjugate of the Nova Scotia margin, is one of the oldest passive margins of the world. Continental break up occurred in the early Jurassic and the deep margin is characterized by a large salt basin. The SISMAR cruise (9 April to 4 May 2001) acquired 3667 km of 360 channel seismic reflection profiles. In addition, refraction data were recorded by means of 48 OBH/OBS deployments. Simultaneously, some of the marine profiles were extended onshore with 16 portable seismic land stations. WNW-ESE profiles 4 and 5 off El Jadida show a good section of the margin. The crustal thinning in this region is fairly abrupt. These profiles image the crust above a strong seismic reflector at about 12 s.twt., interpreted as the Moho. The crust exhibits several different characteristics from the continent towards the ocean.: - highly diffractive with a thickness larger than 25 km beneath the shelf. - stratified at a deep level and topped by few "tilted blocks" with a diffractive acoustic facies and for which 2 hypotheses are proposed: either continental crust tilted during the rifting or large landslides of crustal and sedimentary material slid down later. Liassic evapor- ites are present but seem less thick than to the south. - layered with seaward dipping reflectors: this type of crust correlates with the magnetic anomaly S1 and corresponds to the continent-ocean transition. - diffractive with an oceanic character. Oceanwards, the crust becomes more typically oceanic, but shows internal reflectors that may be re- lated to compressional reactivation during the Tertiary attested by large scale inverted basins. Our results allow us to discuss the nature and location of the continent-ocean transition at a regional scale and the rifting to spreading evolution of the very ma- ture continental margin off El Jadida. This provide us with some constraints for the initial reconstruction between Africa, North America and Iberia. Moreover, these re- sults help

  18. 2D Seismic interpretation of strike-slip faulting, salt tectonics, and Cretaceous unconformities, Atlas Mountains, central Tunisia

    NASA Astrophysics Data System (ADS)

    Zouaghi, Taher; Bédir, Mourad; Inoubli, Mohamed Hédi

    2005-11-01

    The Cretaceous deposits in central Tunisia blocks were studied by sequence stratigraphy, 2D seismic interpretation calibrated to the well and associated outcrop data. The constructing and comparing histories of the northern and southern blocks of the Gafsa master fault was the establishment of platform to basin stratigraphic configuration based on the major unconformity surfaces. Three important basin zones mark subsurface structures: Gafsa to the south, Souinia-Majoura to the northeast and Sidi Aïch-Mèjel Bel Abbès to the northwest. Basin depocenters and upthrown blocks are bounded by the N120° Gafsa and Majoura and N180° Sidi Ali Ben Aoun wrench fault salt-intruded tectonic corridors and subdivided by the associated N60° and N90° trending second-order fault corridors. The Mèjel Bel Abbès block is characterized by brittle structures associated with a deep asymmetric geometry that is organized into depressions and uplifts. Halokinesis of Triassic salt began in the Jurassic and continued during the Cretaceous periods. During extensional deformations, salt movement controlled sedimentation distribution and location of pre-compressional structures. During compressional deformations, salt remobilization accentuated the folded uplifts. The Triassic salt facies constitutes a level of decollement at the base of the Mesozoic deposits during the later displacements. The coeval dextral strike-slip motion along the three northwest-southeast bounding master faults (Gafsa, Sehib-Alima and Majoura-Mech) suggests a pull-apart opening of the Gafsa basin. Synchronous movements of the Gafsa first-order dextral strike-slip fault with the Sidi Ali Ben Aoun sinistral wrench fault caused formation of tectonic obstacles that are shown first by the sealed structures, then by development of the local compressive stress that caused formation of the south overturned folds and the syncline depressions. The transcurrent fault systems caused formation of Turonian and Senonian

  19. Seismic Reflectivity Evolution Beneath Sakurajima Volcano, Japan, from 2009 through 2014, Revealed with Rounds of Controlled-source Seismic Experiments

    NASA Astrophysics Data System (ADS)

    Tsutsui, T.; Iguchi, M.; Tameguri, T.; Nakamichi, H.

    2015-12-01

    Evolution in seismic reflectivity is detected beneath an active volcano, Sakurajima Volcano, from 2009 through 2014 with using controlled seismic experiments . The reflectivity variation is interpreted to associate with discharging magma. Sakurajima Volcano is the target of this study, which is one of the most active volcanoes in Japan. Seven rounds of the seismic experiment with controlled sources have been conducted annually in the volcano. Two seismic reflection profiles tied up are obtained from the datasets under successful reproduction during rounds. Clear annual variation in seismic reflectivity at 6.2km depth is detected in the northeastern part of Sakurajima during the rounds. The reflectivity marked its maximum on December 2009 on the first intrusion of magma and decreased gradually until December 2013, which coincides with inflation and following deflation in Sakurajima Volcano. The active reflector at 6.2km depth occupies a part of embedded clear reflector. A sandwich structure is invoked as the reflector model. Intrusion of fresh and high temperature magma into the intermediate layer of the model and its decline explains the variation range of reflectivity successfully. Our study presents one of new approaches for sensing magma properties instantaneously and for monitoring active volcanoes.

  20. Application of 3D reflection seismic methods to mineral exploration

    NASA Astrophysics Data System (ADS)

    Urosevic, Milovan

    2013-04-01

    Seismic exploration for mineral deposits is often tested by excessively complex structures, regolith heterogeneity, intrinsically low signal to noise ratio, ground relief and accessibility. In brown fields, where the majority of the seismic surveys have been conducted, existing infrastructure, old pits and tailings, heavy machinery in operation, mine drainage and other mine related activities are further challenging the application of seismic methods and furthermore increasing its cost. It is therefore not surprising that the mining industry has been reluctant to use seismic methods, particularly 3D for mineral exploration, primarily due to the high cost, but also because of variable performance, and in some cases ambiguous interpretation results. However, shallow mineral reserves are becoming depleted and exploration is moving towards deeper targets. Seismic methods will be more important for deeper investigations and may become the primary exploration tool in the near future. The big issue is if we have an appropriate seismic "strategy" for exploration of deep, complex mineral reserves. From the existing case histories worldwide we know that massive ore deposits (VMS, VHMS) constitute the best case scenario for the application of 3D seismic. Direct targeting of massive ore bodies from seismic has been documented in several case histories. Sediment hosted deposits could, in some cases, can also produce a detectable seismic signature. Other deposit types such as IOCG and skarn are much more challenging for the application of seismic methods. The complexity of these deposits requires new thinking. Several 3D surveys acquired over different deposit types will be presented and discussed.

  1. The tectonostratigraphic evolution of the offshore Gippsland Basin, Victoria, Australia---results from 3D seismic interpretation and 2D section restoration

    NASA Astrophysics Data System (ADS)

    Weller, Mitchell

    The Gippsland Basin is located primarily offshore Victoria, Australia (between the Australian mainland and Tasmania) approximately 200 km east of Melbourne. The formation of the east-west trending Gippsland Basin is associated with the break-up of Gondwana during the late Jurassic/early Cretaceous and the basin has endured multiple rifting and inversion events. Strong tectonic control on the sedimentary development of the basin is reflected in the deposition of several major, basin scale sequences ranging in age from the early Cretaceous to Neogene, which are usually bounded by angular unconformities. Schlumberger's Petrel software package has been used to structurally and stratigraphically interpret a basin-wide 3D seismic data set provided by the Australian Government (Geoscience Australia) and four 2D kinematic reconstruction/restorations through the basin have been completed with Midland Valley's Move software to achieve a better understanding of the structural evolution of the Gippsland Basin. Rift phase extension calculated from the restorations (5.0--10.5%) appears anomalously low to accommodate the amount of sediment that has been deposited in the basin (>10km). Distributed extension on small faults and subsidence history from backstripping are employed to answer this anomaly. The 2D restorations completed illustrate structural time relationships across the basin and allow for a minimum estimate of erosion that has occurred along the inverted northern basin margin. Differences between previous work completed by Power et al. (2001) and this study as well as several extension models and associated implications are discussed as they relate to the interpretation carried out in this study. Extension calculated from section restorations ranged from approximately 5.0--10.5%. These measured extensional values appear too low to wholly accommodate the accumulated sediment thickness in the basin. Subsidence modelling and backstripping estimates approximately 50

  2. 2-D finite difference time domain model of ultrasound reflection from normal and osteoarthritic human articular cartilage surface.

    PubMed

    Kaleva, Erna; Liukkonen, Jukka; Toyras, Juha; Saarakkala, Simo; Kiviranta, Panu; Jurvelin, Jukka

    2010-04-01

    Quantitative high-frequency ultrasonic evaluation of articular cartilage has shown a potential for the diagnosis of osteoarthritis, where the roughness of the surface, collagen and proteoglycan contents, and the density and mechanical properties of cartilage change concurrently. Experimentally, these factors are difficult to investigate individually and thus a numerical model is needed. The present study is the first one to use finite difference time domain modeling of pulse-echo measurements of articular cartilage. Ultrasound reflection from the surface was investigated with varying surface roughness, material parameters (Young's modulus, density, longitudinal, and transversal velocities) and inclination of the samples. The 2-D simulation results were compared with the results from experimental measurements of the same samples in an identical geometry. Both the roughness and the material parameters contributed significantly to the ultrasound reflection. The angular dependence of the ultrasound reflection was strong for a smooth cartilage surface but disappeared for the samples with a rougher surface. These results support the findings of previous experimental studies and indicate that ultrasound detects changes in the cartilage that are characteristic of osteoarthritis. In the present study there are differences between the results of the simulations and the experimental measurements. However, the systematic patterns in the experimental behavior are correctly reproduced by the model. In the future, our goal is to develop more realistic acoustic models incorporating inhomogeneity and anisotropy of the cartilage. PMID:20378451

  3. Multicomponent, 3-D, and High-Resolution 2-D Seismic Characterization of Gas Hydrate Study Sites in the Gulf of Mexico

    NASA Astrophysics Data System (ADS)

    Haines, S. S.; Hart, P. E.; Ruppel, C. D.; Collett, T. S.; Shedd, W.; Lee, M. W.; Miller, J.

    2012-12-01

    High saturations of gas hydrates have been identified within coarse-grained sediments in the Green Canyon 955 and Walker Ridge 313 lease blocks of the deepwater northern Gulf of Mexico. The thickness, lateral extent, and hydrate saturations in these deposits are constrained by geological and geophysical data and state-of-the-art logging-while-drilling information obtained in multiple boreholes at each site during a 2009 expedition. Presently lacking are multicomponent seismic data that can provide a thorough understanding of the in-situ compressional and shear seismic properties of the hydrate-bearing sediments. Such data may represent an important tool for future characterization of gas hydrate resources. To address this data gap, the U.S. Geological Survey, the U.S. Department of Energy, and the Bureau of Ocean Energy Management will collaborate on a 20-day research expedition to acquire wide-angle ocean bottom seismometer and high-resolution vertical incidence 2-D seismic data at the study sites. In preparation for this mid-2013 expedition, we have analyzed existing industry 3-D seismic data, along with numerically modeled multicomponent data. The 3-D seismic data allow us to identify and rank specific survey targets and can be combined with the numerical modeling results to determine optimal survey line orientation and acquisition parameters. Together, these data also provide a more thorough understanding of the gas hydrate systems at these two sites.

  4. Smooth 2-D ocean sound speed from Laplace and Laplace-Fourier domain inversion of seismic oceanography data

    NASA Astrophysics Data System (ADS)

    Blacic, Tanya M.; Jun, Hyunggu; Rosado, Hayley; Shin, Changsoo

    2016-02-01

    In seismic oceanography, processed images highlight small temperature changes, but inversion is needed to obtain absolute temperatures. Local search-based full waveform inversion has a lower computational cost than global search but requires accurate starting models. Unfortunately, most marine seismic data have little associated hydrographic data and the band-limited nature of seismic data makes extracting the long wavelength sound speed trend directly from seismic data inherently challenging. Laplace and Laplace-Fourier domain inversion (LDI) can use rudimentary starting models without prior information about the medium. Data are transformed to the Laplace domain, and a smooth sound speed model is extracted by examining the zero and low frequency components of the damped wavefield. We applied LDI to five synthetic data sets based on oceanographic features and recovered smoothed versions of our synthetic models, showing the viability of LDI for creating starting models suitable for more detailed inversions.

  5. Seismic investigation of gas hydrates in the Gulf of Mexico: 2013 multi-component and high-resolution 2D acquisition at GC955 and WR313

    USGS Publications Warehouse

    Haines, Seth S.; Hart, Patrick E.; Shedd, William W.; Frye, Matthew

    2014-01-01

    The U.S. Geological Survey led a seismic acquisition cruise at Green Canyon 955 (GC955) and Walker Ridge 313 (WR313) in the Gulf of Mexico from April 18 to May 3, 2013, acquiring multicomponent and high-resolution 2D seismic data. GC955 and WR313 are established, world-class study sites where high gas hydrate saturations exist within reservoir-grade sands in this long-established petroleum province. Logging-while-drilling (LWD) data acquired in 2009 by the Gulf of Mexico Gas Hydrates Joint Industry Project provide detailed characterization at the borehole locations, and industry seismic data provide regional- and local-scale structural and stratigraphic characterization. Significant remaining questions regarding lithology and hydrate saturation between and away from the boreholes spurred new geophysical data acquisition at these sites. The goals of our 2013 surveys were to (1) achieve improved imaging and characterization at these sites and (2) refine geophysical methods for gas hydrate characterization in other locations. In the area of GC955 we deployed 21 ocean-bottom seismometers (OBS) and acquired approximately 400 km of high-resolution 2D streamer seismic data in a grid with line spacing as small as 50 m and along radial lines that provide source offsets up to 10 km and diverse azimuths for the OBS. In the area of WR313 we deployed 25 OBS and acquired approximately 450 km of streamer seismic data in a grid pattern with line spacing as small as 250 m and along radial lines that provide source offsets up to 10 km for the OBS. These new data afford at least five times better resolution of the structural and stratigraphic features of interest at the sites and enable considerably improved characterization of lithology and the gas and gas hydrate systems. Our recent survey represents a unique application of dedicated geophysical data to the characterization of confirmed reservoir-grade gas hydrate accumulations.

  6. Subsurface mapping in the Iberian Pyrite Belt using seismic reflection profiling and potential-field data

    NASA Astrophysics Data System (ADS)

    Carvalho, João; Inverno, Carlos; Matos, João Xavier; Rosa, Carlos; Granado, Isabel; Branch, Tim; Represas, Patrícia; Carabaneanu, Livia; Matias, Luís; Sousa, Pedro

    2016-06-01

    The Iberian Pyrite Belt (IPB) hosts world-class massive sulphide deposits, such as Neves-Corvo in Portugal and Rio Tinto in Spain. In Portugal, the Palaeozoic Volcanic-Sedimentary Complex (VSC) hosts these ore deposits, extending from the Grândola-Alcácer region to the Spanish border with a NW-SE to WNW-ESE trend. In the study area, between the Neves-Corvo mine region and Alcoutim (close to the Spanish border), the VSC outcrops only in a small horst near Alcoutim. Sparse exploration drill-hole data indicate that the depth to the top of the VSC varies from several 100 m to about 1 km beneath the Mértola Formation Flysch cover. Mapping of the VSC to the SE of Neves-Corvo mine is an important exploration goal and motivated the acquisition of six 2D seismic reflection profiles with a total length of approximately 82 km in order to map the hidden extension of the VSC. The data, providing information deeper than 10 km at some locations, were integrated in a 3D software environment along with potential-field, geological and drill-hole data to form a 3D structural framework model. Seismic data show strong reflections that represent several long Variscan thrust planes that smoothly dip to the NNE. Outcropping and previously unknown Late Variscan near-vertical faults were also mapped. Our data strongly suggest that the structural framework of Neves-Corvo extends south-eastwards to Alcoutim. Furthermore, the VSC top is located at depths that show the existence within the IPB of new areas with good potential to develop exploration projects envisaging the discovery of massive sulphide deposits of the Neves-Corvo type.

  7. 2D multi-parameter elastic seismic imaging by frequency-domain L1-norm full waveform inversion

    NASA Astrophysics Data System (ADS)

    Brossier, Romain; Operto, Stéphane; Virieux, Jean

    2010-05-01

    Full waveform inversion (FWI) is becoming a powerful and efficient tool to derive high-resolution quantitative models of the subsurface. In the frequency-domain, computationally efficient FWI algorithms can be designed for wide-aperture acquisition geometries by limiting inversion to few discrete frequencies. However, FWI remains an ill-posed and highly non-linear data-fitting procedure that is sensitive to noise, inaccuracies of the starting model and definition of multiparameter classes. The footprint of the noise in seismic imaging is conventionally mitigated by stacking highly redundant multifold data. However, when the data redundancy is decimated in the framework of efficient frequency-domain FWI, it is essential to assess the sensitivity of the inversion to noise. The impact of the noise in FWI, when applied to decimated data sets, has been marginally illustrated in the past and least-squares minimisation has remained the most popular approach. We investigate in this study the sensitivity of frequency-domain elastic FWI to noise for realistic onshore and offshore synthetic data sets contaminated by ambient random white noise. Four minimisation functionals are assessed in the framework of frequency domain FWI of decimated data: the classical least-square norm (L2), the least-absolute-values norm (L1), and some combinations of both (the Huber and the so-called Hybrid criteria). These functionals are implemented in a massively-parallel, 2D elastic frequency-domain FWI algorithm. A two-level hierarchical algorithm is implemented to mitigate the non-linearity of the inversion in complex environments. The first outer level consists of successive inversions of frequency groups of increasing high-frequency content. This level defines a multi-scale approach while preserving some data redundancy by means of simultaneous inversion of multiple frequencies. The second inner level used complex-valued frequencies for data preconditioning. This preconditioning controls the

  8. Imaging of reflection seismic energy for mapping shallow fracture zones in crystalline rocks

    SciTech Connect

    Kim, J.D.; Moon, W.M. ); Lodha, G.; Serzu, M.; Soonawala, N. )

    1994-05-01

    The high-resolution reflection seismic technique is being used increasingly to address geologic exploration and engineering problems. There are, however, a number of problems in applying reflection seismic techniques in a crystalline rock environment. The reflection seismic data collected over a fractured crystalline rock environment are often characterized by low signal-to-noise (S/N) and inconsistent reflection events. Thus it is important to develop data processing strategies and correlation schemes for the imaging of fracture zones in crystalline rocks. Two sets of very low S/N, high-resolution seismic data, previously collected by two different contractors in Pinawa, Canada, and the island of Aespoe, Sweden, were reprocessed and analyzed, with special emphasis on the shallow reflection events occurring at depths as shallow as 60--100 m.

  9. Basement blocks and basin inversion structures mapped using reprocessed Gulfrex 2D seismic data, Caribbean-South American oblique collisional zone

    NASA Astrophysics Data System (ADS)

    Escalona, A.; Sena, A.; Mann, P.

    2003-12-01

    We have reprocessed and reinterpreted more than 10,000 km of "Gulfrex" multi-channel 2D seismic reflection lines collected by Gulf Oil Corporation in 1972 along the northern margin of South America (offshore Venezuela and Trinidad). These digital data were donated to the University of Texas Institute for Geophysics and represent the largest single, digital reflection survey of the region. Reprocessing of these data included: format correction, filtering, post-stack multiple suppression, and fk migration. Reprocessed data were loaded and interpreted on a workstation. The data straddle a 2,000,000 km2 zone of Paleocene-Recent, time-transgressive, oblique collision between the Caribbean arc system and the passive continental margin of northern South America. Free-air, satellite gravity data shows the remarkable 1000-km-scale continuity of four basement ridges between the uncollided part of the Caribbean arc system (NS-trending Lesser Antilles arc) and the EW-trending collisional area north of Venezuela. The basement ridges involved in the Venezuelan collisional zone include: 1) Aruba-Bonaire-Curacao ridge that can be traced as a continuous feature to the Aves ridge remnant arc of the Lesser Antilles; 2) the partially inverted Blanquilla-Bonaire basin that can be traced into the Grenada back-arc basin; 3) Margarita-Los Testigos platform that can be traced to the Lesser Antilles volcanic arc; and 4) foreland basins and fold-thrust belts of eastern Venezuela (Serrania del Interior and Maturin basin) that can be traced to the Tobago forearc basin and Barbados accretionary prism. Gulfrex data document the progressive change of basinal fault systems from NS-striking normal faults formed in extensional, Lesser Antilles intra-arc settings to rotated and inverted, NE and EW-striking normal faults deformed in the collisional area north of Venezuela. Age of initial shortening of basinal areas and inversion of normal faults setting does not follow the simple, expected pattern of

  10. Are Deep Seismic Reflections at Volcanic Margins from the Petrological Moho or from within the Mantle?

    NASA Astrophysics Data System (ADS)

    Harkin, C. J.; Kusznir, N. J.; Roberts, A. M.; Bellingham, P.; Manatschal, G.

    2015-12-01

    Deep long-offset seismic-reflection now frequently provide imaging of strong and laterally continuous reflectors in the TWTT range of 10 to 14 seconds. Examples of deep laterally-coherent reflectivity can be seen within the ocean-continent transition of the Argentine, Uruguayan and S Brazilian volcanic margins of the S Atlantic. Qualitative interpretation of the seismic data suggests the presence of deep crustal "keels" or crustal roots underlying well developed seaward dipping reflectors (SDRs). While an initial interpretation might be that these reflectors correspond to the crust-mantle interface, this interpretation may in some cases be incorrect or over-simplistic. Do these deep reflectors correspond to the petrological Moho or could they be located within the mantle? Joint inversion of the PSTM time-domain seismic reflection and gravity anomaly data has been used to determine the average interval density and seismic velocity between base sediment and the deep seismic reflectivity. Joint inversion densities and seismic velocities for this depth interval reach values in excess of 3000 kg/m3 and 7.0 km/sec for the entire thickness of the interval, substantially in excess of densities and velocities observed for normal oceanic and continental crust. The high densities determined from joint seismic-gravity inversion under the SDR regions are also consistent with results from flexural subsidence analysis. We consider two interpretations of these results. One interpretation is that the strong deep reflectivity corresponds to the base of the petrological crust and that the crust has an abnormally high average density and seismic velocity due to high-temperature mantle-plume-related magmatism. An alternative interpretation is that the deep seismic reflectivity is located within the mantle beneath the petrological Moho, and that the high density and seismic velocity result from averaging of both crustal basement (~2850 kg/m3) and mantle (~3300 kg/m3) values. In some

  11. Aniso2D

    2005-07-01

    Aniso2d is a two-dimensional seismic forward modeling code. The earth is parameterized by an X-Z plane in which the seismic properties Can have monoclinic with x-z plane symmetry. The program uses a user define time-domain wavelet to produce synthetic seismograms anrwhere within the two-dimensional media.

  12. An analysis of a seismic reflection from the base of a gas hydrate zone, offshore Peru

    USGS Publications Warehouse

    Miller, J.J.; Lee, M.W.; Von Huene, R.

    1991-01-01

    Seismic reflection data recorded near ODP Site 688, offshore Peru, exhibit a persistent bottom-simulating reflector (BSR) from a depth corresponding to the theoretical base of the gas hdyrate stability field. To carry out a quantitative analysis of the BSR, the seismic data were reprocessed using signature deconvolution and true amplitude recovery techniques. Results indicate the BSR is discontinuous laterally. -from Authors

  13. A Three-dimensional Reflection Seismic Survey In The Earstern Nankai Accretionary Prism.

    NASA Astrophysics Data System (ADS)

    Ike, T.; Tokuyama, H.; Kuramoto, S.; Matsushima, J.; Yokota, T.; Pascal, G.; Lalememant, S.

    The Three-Dimensional Multi-Channel Seismic (3D-MCS) reflection survey using a tuned air gun source was held in the eastern Nankai accretionary prism from June to July 2000. The crustal deformation of the eastern Nankai accretionary prism is affected by a nearby collision between the Izu-Bonin arc and the central Japan. Sev- eral active fault systems were described by many high-resolution seismic data, and proposed that the Tokai and Kodaiba fault systems were derived from a decollement plane. From the deformation style in the Nankai Trough, we concern about the oc- currence of a great earthquake in recent years. The main objective of our experiment is to resolve the structural image of the plate boundary and identify the up-dip limit of seismogenic zone. The 3-D survey covers 45km long and 5km wide area with 51 seismic lines, located about 50km southwest from Omaezaki. We applied the non- iterative Kirchhoff pre-stack time migration method (Matsushima et.,al 2001) with stacking velocity analysis to our 3-D data. The derived 3-D prestack time migra- tion profile shows a better development at the deep structure on the top of oceanic crust, compared with preliminary 2-D prestack time migration processed profile. The processed 3-D data gives us a significantly clear image of the thrust faults and the relationship between sediment deformation and thrust activity. A preliminary 3-D in- terpretation was conducted and leaded the following results.1) The Tokai and Kodaiba thrusts are confirmed to be sets of out-of-sequence thrusts. 2) Both thrusts are ac- tive fault that revealed by the structure of the deformation of surface sediments. 3) A strong and low frequency reflector can be identified in the entire profile at two-way- time 7-7.5sec that should be a decollement plane. 4)Tokai and Kodaiba fault systems merged to the decollement plane at same depth. The contact area of the thrust faults to the decollement corresponds to south end of seismic coupling region presumed

  14. 2D and 3D seismic measurements to evaluate the collapse risk of an important prehistoric cave in soft carbonate rock

    NASA Astrophysics Data System (ADS)

    Leucci, Giovanni; De Giorgi, Lara

    2015-02-01

    The southern part of the Apulia region (the Salento peninsula) has been the site of at least fifteen collapse events due to sinkholes in the last twenty years. The majority of these occurred in "soft" carbonate rocks (calcarenites). Man-made and/or natural cavities are sometimes assets of historical and archaeological significance. This paper provides a methodology for the evaluation of sinkhole hazard in "soft" carbonate rocks, combining seismic and mine engineering methods.Acase study of a natural cavity which is called Grotta delle Veneri is illustrated. For this example the approach was: i) 2D and 3D seismic methods to study the physical-mechanical characteristics of the rock mass that constitutes the roof of the cave; and ii) scaled span empirical analysis in order to evaluate the instability of the crown pillar's caves.

  15. 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.

  16. 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.

  17. Applications of shallow high-resolution seismic reflection to various environmental problems

    USGS Publications Warehouse

    Miller, R.D.; Steeples, D.W.

    1994-01-01

    Shallow seismic reflection has been successfully applied to environmental problems in a variety of geologic settings. Increased dynamic range of recording equipment and decreased cost of processing hardware and software have made seismic reflection a cost-effective means of imaging shallow geologic targets. Seismic data possess sufficient resolution in many areas to detect faulting with displacement of less than 3 m and beds as thin as 1 m. We have detected reflections from depths as shallow as 2 m. Subsurface voids associated with abandoned coal mines at depths of less than 20 m can be detected and mapped. Seismic reflection has been successful in mapping disturbed subsurface associated with dissolution mining of salt. A graben detected and traced by seismic reflection was shown to be a preferential pathway for leachate leaking from a chemical storage pond. As shown by these case histories, shallow high-resolution seismic reflection has the potential to significantly enhance the economics and efficiency of preventing and/or solving many environmental problems. ?? 1994.

  18. Seismic reflection evidence against a shallow detachment beneath Yucca Mountain, Nevada

    USGS Publications Warehouse

    Brocher, Thomas M.; Hunter, W. Clay

    1996-01-01

    Intermediate-depth seismic reflection profile across Crater Flat and Yucca Mountain is obtained. The aim of the seismic profiling are discrimination the subsurface geometry of faults and imaging of the boundary between the pre-Tertiary sedimentary strata and the Miocene volcanic rocks of Yucca Mountain. Of major interest is the existence and geometry of a postulated west-dipping detachment fault beneath Yucca Mountain. These reflection profiles provide critical input to efforts to evaluate tectonic models, probabilistic seismic hazards, and potential volcanic hazards near Yucca Mountain, site of investigations for a potential permanent repository for high-level nuclear waste.

  19. Thermohaline fine structure in an oceanographic front from seismic reflection profiling.

    PubMed

    Holbrook, W Steven; Páramo, Pedro; Pearse, Scott; Schmitt, Raymond W

    2003-08-01

    We present acoustic images of oceanic thermohaline structure created from marine seismic reflection profiles across the major oceanographic front between the Labrador Current and the North Atlantic Current. The images show that distinct water masses can be mapped, and their internal structure imaged, using low-frequency acoustic reflections from sound speed contrasts at interfaces across which temperature changes. The warm/cold front is characterized by east-dipping reflections generated by thermohaline intrusions in the uppermost 1000 meters of the ocean. Our results imply that marine seismic reflection techniques can provide excellent spatial resolution of important oceanic phenomena, including thermohaline intrusions, internal waves, and eddies.

  20. Geostatistical Evaluation of the Mechanical Properties of Rock Mass for TBM Tunnelling by Seismic Reflection Method

    NASA Astrophysics Data System (ADS)

    Aoki, K.; Mito, Y.; Yamamoto, T.; Shirasagi, S.

    2007-12-01

    The evaluation of the rock mass mechanical properties by the seismic reflection method and TBM driving is proposed for TBM tunnelling. The relationship between the reflection number derived from the three-dimensional seismic reflection method and the rock strength index ( RSI) derived from TBM driving data is examined, and the methodology of conversion from the reflection number to the RSI is proposed. Furthermore a geostatistical prediction methodology to provide a three-dimensional geotechnical profile ahead of the tunnel face is proposed. The performance of this prediction method is verified by actual field data.

  1. Proposed criteria for recognizing intrastratal deformation features in marine high resolution seismic reflection profiles

    USGS Publications Warehouse

    O'Leary, D. W.; Laine, E.

    1996-01-01

    Intrastratal deformation of marine strata is ordinarily recorded in high-resolution seismic reflection profiles as acoustically transparent or "chaotic" intervals marked by hyperbolic echoes. Intrastratal deformation is easily confused with buried slump or slide deposits formed initially at the sea floor. Correct identification of intrastratal deformation depends on the presence of a warped continuously reflective layer overlying a chaotic/transparent layer. Decollement is the key criterion for identification in seismic reflection profiles. Other criteria include intrusive structures or faults rooted in a chaotic/transparent layer and thickening and thinning of a chaotic/transparent layer with transitions to reflective intervals.

  2. Integrating Reflection Seismic, Gravity and Magnetic Data to Reveal the Structure of Crystalline Basement: Implications for Understanding Rift Development

    NASA Astrophysics Data System (ADS)

    Lenhart, Antje; Jackson, Christopher A.-L.; Bell, Rebecca E.; Duffy, Oliver B.; Fossen, Haakon; Gawthorpe, Robert L.

    2016-04-01

    Numerous rifts form above crystalline basement containing pervasive faults and shear zones. However, the compositional and mechanical heterogeneity within crystalline basement and the geometry and kinematics of discrete and pervasive basement fabrics are poorly understood. Furthermore, the interpretation of intra-crustal structures beneath sedimentary basins is often complicated by limitations in the depth of conventional seismic imaging, the commonly acoustically transparent nature of basement, limited well penetrations, and complex overprinting of multiple tectonic events. Yet, a detailed knowledge of the structural and lithological complexity of crystalline basement rocks is crucial to improve our understanding of how rifts evolve. Potential field methods are a powerful but perhaps underutilised regional tool that can decrease interpretational uncertainty based solely on seismic reflection data. We use petrophysical data, high-resolution 3D reflection seismic volumes, gridded gravity and magnetic data, and 2D gravity and magnetic modelling to constrain the structure of crystalline basement offshore western Norway. Intra-basement structures are well-imaged on seismic data due to relatively shallow burial of the basement beneath a thin (<3.5 km) sedimentary cover. Variations in basement composition were interpreted from detailed seismic facies analysis and mapping of discrete intra-basement reflections. A variety of data filtering and isolation techniques were applied to the original gravity and magnetic data in order to enhance small-scale field variations, to accentuate formation boundaries and discrete linear trends, and to isolate shallow and deep crustal anomalies. In addition, 2D gravity and magnetic data modelling was used to verify the seismic interpretation and to further constrain the configuration of the upper and lower crust. Our analysis shows that the basement offshore western Norway is predominantly composed of Caledonian allochthonous nappes

  3. Seismic-reflection evidence that the hayward fault extends into the lower crust of the San Francisco Bay Area, California

    USGS Publications Warehouse

    Parsons, T.

    1998-01-01

    This article presents deep seismic-reflection data from an experiment across San Francisco Peninsula in 1995 using large (125 to 500 kg) explosive sources. Shot gathers show a mostly nonreflective upper crust in both the Franciscan and Salinian terranes (juxtaposed across the San Andreas fault), an onset of weak lower-crustal reflectivity beginning at about 6-sec two-way travel time (TWTT) and bright southwest-dipping reflections between 11 and 13 sec TWTT. Previous studies have shown that the Moho in this area is no deeper than 25 km (~8 to 9 sec TWTT). Three-dimensional reflection travel-time modeling of the 11 to 13 sec events from the shot gathers indicates that the bright events may be explained by reflectors 15 to 20 km into the upper mantle, northeast of the San Andreas fault. However, upper mantle reflections from these depths were not observed on marine-reflection profiles collected in San Francisco Bay, nor were they reported from a refraction profile on San Francisco Peninsula. The most consistent interpretation of these events from 2D raytracing and 3D travel-time modeling is that they are out-of-plane reflections from a high-angle (dipping ~70??to the southwest) impedance contrast in the lower crust that corresponds with the surface trace of the Hayward fault. These results suggest that the Hayward fault truncates the horizontal detachment fault suggested to be active beneath San Francisco Bay.

  4. 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).

  5. pySeismicFMM: Python based travel time calculation in regular 2D and 3D grids in Cartesian and geographic coordinates using Fast Marching Method

    NASA Astrophysics Data System (ADS)

    Polkowski, Marcin

    2016-04-01

    Seismic wave travel time calculation is the most common numerical operation in seismology. The most efficient is travel time calculation in 1D velocity model - for given source, receiver depths and angular distance time is calculated within fraction of a second. Unfortunately, in most cases 1D is not enough to encounter differentiating local and regional structures. Whenever possible travel time through 3D velocity model has to be calculated. It can be achieved using ray calculation or time propagation in space. While single ray path calculation is quick it is complicated to find the ray path that connects source with the receiver. Time propagation in space using Fast Marching Method seems more efficient in most cases, especially when there are multiple receivers. In this presentation a Python module pySeismicFMM is presented - simple and very efficient tool for calculating travel time from sources to receivers. Calculation requires regular 2D or 3D velocity grid either in Cartesian or geographic coordinates. On desktop class computer calculation speed is 200k grid cells per second. Calculation has to be performed once for every source location and provides travel time to all receivers. pySeismicFMM is free and open source. Development of this tool is a part of authors PhD thesis. National Science Centre Poland provided financial support for this work via NCN grant DEC-2011/02/A/ST10/00284.

  6. 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.

  7. The structure and stratigraphy of the sedimentary succession in the Swedish sector of the Baltic Basin: New insights from vintage 2D marine seismic data

    NASA Astrophysics Data System (ADS)

    Sopher, Daniel; Erlström, Mikael; Bell, Nicholas; Juhlin, Christopher

    2016-04-01

    We present five interpreted regional seismic profiles, describing the full sedimentary sequence across the Swedish sector of the Baltic Sea. The data for the study are part of an extensive and largely unpublished 2D seismic dataset acquired between 1970 and 1990 by the Swedish Oil Prospecting Company (OPAB). The Baltic Basin is an intracratonic basin located in northern Europe. Most of the Swedish sector of the basin constitutes the NW flank of a broad synclinal depression, the Baltic Basin. In the SW of the Swedish sector lies the Hanö Bay Basin, formed by subsidence associated with inversion of the Tornquist Zone during the Late Cretaceous. The geological history presented here is broadly consistent with previously published works. We observe an area between the Hanö Bay and the Baltic Basin where the Palaeozoic strata has been affected by transpression and subsequent inversion, associated with the Tornquist Zone during the late Carboniferous-Early Permian and Late Cretaceous, respectively. We propose that the Christiansø High was a structural low during the Late Jurassic, which was later inverted in the Late Cretaceous. We suggest that a fan shaped feature in the seismic data, adjacent to the Christiansø Fault within the Hanö Bay Basin, represents rapidly deposited, coarse-grained sediments eroded from the inverted Christiansø High during the Late Cretaceous. We identify a number of faults within the deeper part of the Baltic Basin, which we also interpret to be transpressional in nature, formed during the Caledonian Orogeny in the Late Silurian-Early Devonian. East of Gotland a number of sedimentary structures consisting of Silurian carbonate reefs and Ordovician carbonate mounds, as well as a large Quaternary glacial feature are observed. Finally, we use the seismic interpretation to infer the structural and stratigraphic history of the Baltic and Hanö Bay basins within the Swedish sector.

  8. Deep Seismic Reflection Profiling in the Source Region of the 1923 Kanto Earthquake

    NASA Astrophysics Data System (ADS)

    Sato, H.; Hirata, N.; Iwasaki, T.; Koketsu, K.; Ito, T.; Kasahara, K.; Ito, K.; Kawamura, T.; Ikawa, T.; Onishi, M.; Kawanaka, T.; Abe, S.

    2003-12-01

    The location and geometry of the source fault, and crustal velocity structure, provide the basic information for more precise estimation of strong ground motions with devastative earthquakes. The deep seismic profiling around Metropolitan Tokyo (Kanto area) began from 2002 under the project named `Regional Characterization of the Crust in Metropolitan Areas for Prediction of Strong Ground Motion' as five year's project. Deep seismic profiling was performed along the Sagami (Sagami 2003) and Tokyo Bay (Tokyo Bay 2003), to obtain an image of the source fault of the Kanto earthquake of 1923 (M7.9), upper surface of the Philippine Sea plate, and deeper extension of inland active faults. In Sagami 2003, seismic reflection data were acquired along a 75-km-long seismic line from the flank of the Hakone volcano to Tokyo Bay through the coast of Sagami Bay. The seismic source was four vibroseis trucks and air guns (1500 cu. inch). The seismic signals were recorded by geophones (10 Hz) on land along the coast with 20 33-km-long spread. The seismic data was processed by standard CMP-reflection method. The obtained seismic section portrays the east dipping reflectors beneath Odawara at depth ca. 4 km to Kamakura at depth ca. 13 km for 40-km-distance forming a narrow (< 1 km) concentrated zone of reflectors. The location and geometry of reflectors are almost coincidence with the source fault model (model II) proposed by MatsuOura et al. (1980) for the Kanto earthquake using a inverse method from geodetic data. Thus, it is interpreted that the source fault of the earthquake is in the narrow zone of the concentrated reflectors. The deeper extension of the Kozu-Matsuda Fault, showing the one of the highest slip rates (3 mm/y: vertical component) among active faults in Japan and was assessed high seismic risk, merges to the east dipping reflectors at ca. 6.5 km in depth beneath the Oiso hills. In the Tokyo Bay 2003, seismic reflection data were acquired along a 71-km

  9. 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.

  10. Pseudo-reflection imaging of the Lunar Moho beneath the Apollo seismic stations using deep-moonquake seismic interferometry

    NASA Astrophysics Data System (ADS)

    Nishitsuji, Yohei; Rowe, Charlotte; Wapenaar, Kees; Draganov, Deyan

    2016-04-01

    In 30 years following NASA's Apollo missions, numerous geophysical methods have been applied to determine the depth of the Lunar Moho. These methods, such as travel-time analysis and gravity inversion, have yielded inconsistent estimates. Here, we apply a seismic interferometry technique using body waves. We use deep moonquakes recorded by the Apollo stations to retrieve zero-offset reflection responses beneath each seismic station on the Nearside of the Moon. We call this application deep-moonquake seismic interferometry (DMSI). We present here the first pseudo-reflection imaging of the Lunar Moho, which we interpret to reside at around 50 km depth. Our interpretation agrees with JAXA's SELENE result, and with earlier travel-time studies. Our DMSI results also show lateral inhomogeneity beneath the Moho, suggesting strong scattering within a zone characterized by seismic velocity that exhibits little variation at our resolution scale (0.2-2.0 Hz). This zone is where most of the shallow moonquakes are presumed to be occurring.

  11. Origin of deep crystal reflections: seismic profiling across high-grade metamorphic terranes in Canada

    USGS Publications Warehouse

    Green, A.; Milkereit, B.; Percival, J.; Davidson, A.; Parrish, R.; Cook, F.; Geis, W.; Cannon, W.; Hutchinson, D.; West, G.; Clowes, R.

    1990-01-01

    In an attempt to better understand the origin of deep crustal reflections LITHOPROBE has sponsored or co-sponsored Seismic reflection surveys across tracts of high-grade metamorphic rock in the Archean Superior craton, the Proterozoic Grenville orogen and the Phanerozoic Cordilleran orogen. Common to these three diverse terranes are near-surface zones of prominent Seismic reflectivity that are typically associated with velocity discontinuities at highly strained contacts between gneissic rocks of varying lithology. At some locations the reflective layering resulted from transposition and rearrangement of previously layered rocks (stratified assemblages, sills, etc.), whereas in other regions it was generated by extreme attenuation, stretching and ductile flow of weakly layered or irregularly organized rocks. It seems likely that compositionally layered gneissic rock is a common source of reflections in the deep crust, with reflections originating at lithological boundaries and zones of mylonite. ?? 1990.

  12. Deep seismic reflection profiling of the subduction megathrust across the Sagimi trough and Tokyo bay, Japan

    NASA Astrophysics Data System (ADS)

    Sato, Hiroshi; Iwasaki, Takaya; Abe, Susumu; Saito, Hideo; Kawanaka, Taku; Hirata, Naoshi

    2010-05-01

    Beneath the metropolitan Tokyo, the Philippine Sea plate, in particular the fore arc portion of the Izu-Bonin island arc, has been subducted. Subduction megathrust beneath Tokyo generated M-8 class earthquakes, such as the 1923 Kanto (M7.9) and 1703 Genroku (M8.0) earthquakes. Due to the buyant subduction of the Izu-Bonin arc, the megathrust lies very shallow part of the crust. The Kozu-Matsuda fault, probable spray fault from the megathrust, emerged at the surface. In 2009, we acquired the deep seismic reflection data across the toe of the thrust system to reveal the connectivity of the probable spray fault to the megathrust. Together with the deep seismic section acquired in 2003, we show a 120-km-long deep seismic reflection profile from the front to 30 km in depth and discuss the geometry and characteristics of the thrust system. We performed deep seismic profiling across the Sagami trough for a 70-km-long seismic line in September 2009, using two ships for offshore seismic data acquisition: a gun-ship with a 3020 cu. inch air-gun and a cable-ship with a 2-km-long, streamer cable and a 480 cu. inch air-gun. The seismic signals were recorded at Miura and Izu peninsulas located both ends of the seismic line. At both sides of the onshore line, off-line recorders were deployed along total 20-km-long seismic lines at a 50m interval. Seismic reflection data were acquired by different offset of ships making large-offset gathers. The northeast end of the seismic line connected with the 2003 Tokyo bay seismic line (Sato et al., 2005: Science). The obtained seismic sections portray the detailed geometry of the spray faults, suggesting an emergent thrust with 4 km thick landward dipping strata. It merges to the megathrust at 6-7 sec (TWT). Judging from the geometry of fault-related fold in the trough fill sediments, the tip of the megathrust is located at 3 sec (TWT) beneath the trough axis. According to the co-seismic crustal deformation, the slip of the 1923 Kanto

  13. Seismic reflection imaging of underground cavities using open-source software

    SciTech Connect

    Mellors, R J

    2011-12-20

    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 impact 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.

  14. Pen Branch fault program: Interim report on the High Resolution, Shallow Seismic Reflection surveys

    SciTech Connect

    Stieve, A.L.

    1991-01-31

    The Pen Branch fault was identified in the subsurface at the Savannah River Site in 1989 based upon the interpretation of earlier seismic reflection surveys and other geologic investigations. A program was initiated at that time to further define the fault in terms of its capability to release seismic energy. The High-Resolution, Shallow Seismic Reflection survey recently completed at SRS was initiated to determine the shallowest extent of the fault and to demonstrate the presence of flat-lying sediments in the top 300 feet of sediments. Conclusions at this time are based upon this shallow seismic survey and the Conoco deep seismic survey (1988--1989). Deformation related to the Pen Branch fault is at least 200 milliseconds beneath the surface in the Conoco data and at least 150 milliseconds in the shallow seismic reflection data. This corresponds to approximately 300 feet below the surface. Sediments at that depth are lower Tertiary (Danian stage) or over 60 million years old. This indicates that the fault is not capable.

  15. Constraints on the geometry of the Suasselkä post-glacial fault, northern Finland, based on reflection seismic imaging

    NASA Astrophysics Data System (ADS)

    Abdi, Amir; Heinonen, Suvi; Juhlin, Christopher; Karinen, Tuomo

    2015-05-01

    Unloading of the ice during the last glacial period in northern Fennoscandia is believed to have generated major faulting. These faults, often referred to as post-glacial faults, typically have clear surface exposures, but their geometry at depth is poorly known. In order to better understand the geometry at depth of the Suasselkä post-glacial fault in Finland, three high resolution 2D reflection seismic profiles over the fault were reprocessed. Their total profile length is about 60 km and they were acquired as part of a major effort in Finland to map the uppermost crust in mining areas. The reprocessing led to significantly improved images that could be used to map the fault at depth. Two approximately N-S striking profiles and one E-W striking profile were reprocessed. The different azimuths and the crooked nature of the profiles allowed the fault geometry to be relatively well constrained. Clear reflections from the fault, dipping towards the SE, can be traced from the shallow subsurface down to about 3 km. The strike and dip of two sets of dipping reflections in the stacked data along with geometrical constraints and cross-dip analysis give a consistent dip of about 35-45° towards the SE for the fault. The strike and dip vary from N55E with a dip of 35° in the east to a strike of N48E with a dip of 45° in the west. Existence of the two sets of reflections indicates that the fault surface is non-planar. Aside from allowing the geometry of the fault to be determined, the seismic data show a complex reflectivity pattern in the area and indications of both reverse and normal movement along fault planes with similar orientation to the Suasselkä post-glacial fault. These images can be used as a basis for better characterizing the 3D geology of the area.

  16. Blind test of methods for obtaining 2-D near-surface seismic velocity models from first-arrival traveltimes

    USGS Publications Warehouse

    Zelt, Colin A.; Haines, Seth; Powers, Michael H.; Sheehan, Jacob; Rohdewald, Siegfried; Link, Curtis; Hayashi, Koichi; Zhao, Don; Zhou, Hua-wei; Burton, Bethany L.; Petersen, Uni K.; Bonal, Nedra D.; Doll, William E.

    2013-01-01

    Seismic refraction methods are used in environmental and engineering studies to image the shallow subsurface. We present a blind test of inversion and tomographic refraction analysis methods using a synthetic first-arrival-time dataset that was made available to the community in 2010. The data are realistic in terms of the near-surface velocity model, shot-receiver geometry and the data's frequency and added noise. Fourteen estimated models were determined by ten participants using eight different inversion algorithms, with the true model unknown to the participants until it was revealed at a session at the 2011 SAGEEP meeting. The estimated models are generally consistent in terms of their large-scale features, demonstrating the robustness of refraction data inversion in general, and the eight inversion algorithms in particular. When compared to the true model, all of the estimated models contain a smooth expression of its two main features: a large offset in the bedrock and the top of a steeply dipping low-velocity fault zone. The estimated models do not contain a subtle low-velocity zone and other fine-scale features, in accord with conventional wisdom. Together, the results support confidence in the reliability and robustness of modern refraction inversion and tomographic methods.

  17. Piedmont seismic reflection study: A program integrated with tectonics to probe the cause of eastern seismicity

    SciTech Connect

    Glover, L. III; Coruh, C.; Costain, J.K.; Bollinger, G.A. . Dept. of Geological Sciences)

    1992-03-01

    A new tectonic model of the Appalachian orogen indicates that one, not two or more, terrane boundaries is present in the Piedmont and Blue Ridge of the central and southern Appalachians. This terrane boundary is the Taconic suture, it has been transported in the allochthonous Blue Ridge/Piedmont crystalline thrust nappe, and it is repeated at the surface by faulting and folding associated with later Paleozoic orogenies. The suture passes through the lower crust and lithosphere somewhere east of Richmond. It is spatially associated with seismicity in the central Virginia seismic zone, but is not conformable with earthquake focal planes and appears to have little causal relation to their localization.

  18. 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.

  19. Estimation of Q factors from reflection seismic data for a band-limited and stabilized inverse Q filter driven by an average-Q model

    NASA Astrophysics Data System (ADS)

    Chen, Zengbao; Chen, Xiaohong; Wang, Yanghua; Li, Jingye

    2014-02-01

    Reliable Q estimation is desirable for model-based inverse Q filtering to improve seismic resolution. On the one hand, conventional methods estimate Q from the amplitude spectra or frequency variations of individual wavelets at different depth (or time) levels, which is vulnerable to the effects of spectral interference and ambient noise. On the other hand, most inverse Q filtering algorithms are sensitive to noise, in order not to boost them, sometimes at the expense of degrading compensation effect. In this paper, the average-Q values are obtained from reflection seismic data based on the Gabor transform spectrum of a seismic trace. We transform the 2-D time-variant frequency spectrum into the 1-D spectrum, and then estimate the average-Q values based on the amplitude attenuation and compensation functions, respectively. Driven by the estimated average-Q model, we also develop a modified inverse Q filtering algorithm by incorporating a time-variant bandpass filter (TVBF), whose high cut off frequency follows a hyperbola along the traveltime from a specified time. Finally, we test this modified inverse Q filtering algorithm on synthetic data and perform the Q estimation procedure on a real reflection seismic data, followed by applying the modified inverse Q filtering algorithm. The synthetic data test and the real data example demonstrate that the algorithm driven by average-Q model may enhance the seismic resolution, without degrading the signal-to-noise ratio.

  20. 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

  1. USING RECENT ADVANCES IN 2D SEISMIC TECHNOLOGY AND SURFACE GEOCHEMISTRY TO ECONOMICALLY REDEVELOP A SHALLOW SHELF CARBONATE RESERVOIR: VERNON FIELD, ISABELLA COUNTY, MI.

    SciTech Connect

    James R. Wood; T.J. Bornhorst; William B. Harrison; W. Quinlan

    2002-04-01

    The fault study continues to find more faults and develop new techniques to visualize them. Data from the Dundee Formation has been used to document 11 major faults in the Michigan Basin which have now been verified using data from other horizons. These faults control the locations of many of the large anticlinal structures in the Michigan Basin and likely controlled fluid movements as well. The surface geochemistry program is also moving along well with emphasis on measuring samples collected last sampling season. The new GC laboratory is now functional and has been fully staffed as of December. The annual project review was held March 7-9 in Tampa, Florida. Contracts are being prepared for drilling the Bower's prospects in Isabella County, Michigan, this spring or summer. A request was made to extend the scope of the project to include the Willison Basin. A demonstration well has been suggested in Burke County, N. Dakota, following a review of 2D seismic and surface geochem. A 3D seismic survey is scheduled for the prospect.

  2. Seismic reflection imaging of a geothermal aquifer in an urban setting

    SciTech Connect

    Liberty, L.

    1998-07-01

    A seismic reflection survey that was conducted in downtown Boise, Idaho, to help city planners site a new well for injection of spent geothermal water illustrates some methods to safely and successfully employ a seismic reflection survey in an urban setting. The objective of the seismic survey was to estimate the depth and continuity of a basalt and rhyolite volcanic sequence. Well siting was based on geothermal aquifer depth, location of interpreted faults, projected thermal impact of injection on existing wells, surface pipe extension costs, and public land availability. Seismic acquisition tests and careful processing were used to ensure high-quality data while minimizing the potential for damage along city streets. A video camera placed in a sewer and a blast vibration monitor were used to confirm that energy from the seismic source (a 75-in{sup 3} land air gun) did not damage nearby buildings, street surfaces, or buried utilities along the survey lines. Walkaway seismic tests were also used to compare signal quality of the air-gun source to an explosive source for imaging targets up to 800 m depth. These tests show less signal bandwidth from the air-gun source compared to the buried explosive source, but the air-gun signal quality was adequate to meet imaging objectives. Seismic reflection results show that the top of this rhyolite/basalt sequence dips ({approximately}8--1{degree}) southwest away from the Boise foothills at depths of 200 to 800 m. Seismic methods enabled interpretation of aquifer depths along the profiles and located fault zones where injected water may encounter fracture permeability and optimally benefit the existing producing system. The acquisition and processing techniques used to locate the Boise injection well may succeed for other hydrogeologic and environmental studies in urban settings.

  3. 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.

  4. A pseudo-spectral method for the simulation of poro-elastic seismic wave propagation in 2D polar coordinates using domain decomposition

    SciTech Connect

    Sidler, Rolf; Carcione, José M.; Holliger, Klaus

    2013-02-15

    We present a novel numerical approach for the comprehensive, flexible, and accurate simulation of poro-elastic wave propagation in 2D polar coordinates. An important application of this method and its extensions will be the modeling of complex seismic wave phenomena in fluid-filled boreholes, which represents a major, and as of yet largely unresolved, computational problem in exploration geophysics. In view of this, we consider a numerical mesh, which can be arbitrarily heterogeneous, consisting of two or more concentric rings representing the fluid in the center and the surrounding porous medium. The spatial discretization is based on a Chebyshev expansion in the radial direction and a Fourier expansion in the azimuthal direction and a Runge–Kutta integration scheme for the time evolution. A domain decomposition method is used to match the fluid–solid boundary conditions based on the method of characteristics. This multi-domain approach allows for significant reductions of the number of grid points in the azimuthal direction for the inner grid domain and thus for corresponding increases of the time step and enhancements of computational efficiency. The viability and accuracy of the proposed method has been rigorously tested and verified through comparisons with analytical solutions as well as with the results obtained with a corresponding, previously published, and independently benchmarked solution for 2D Cartesian coordinates. Finally, the proposed numerical solution also satisfies the reciprocity theorem, which indicates that the inherent singularity associated with the origin of the polar coordinate system is adequately handled.

  5. Limitations of quantitative analysis of deep crustal seismic reflection data: Examples from GLIMPCE

    USGS Publications Warehouse

    Lee, Myung W.; Hutchinson, Deborah R.

    1992-01-01

    Amplitude preservation in seismic reflection data can be obtained by a relative true amplitude (RTA) processing technique in which the relative strength of reflection amplitudes is preserved vertically as well as horizontally, after compensating for amplitude distortion by near-surface effects and propagation effects. Quantitative analysis of relative true amplitudes of the Great Lakes International Multidisciplinary Program on Crustal Evolution seismic data is hampered by large uncertainties in estimates of the water bottom reflection coefficient and the vertical amplitude correction and by inadequate noise suppression. Processing techniques such as deconvolution, F-K filtering, and migration significantly change the overall shape of amplitude curves and hence calculation of reflection coefficients and average reflectance. Thus lithological interpretation of deep crustal seismic data based on the absolute value of estimated reflection strength alone is meaningless. The relative strength of individual events, however, is preserved on curves generated at different stages in the processing. We suggest that qualitative comparisons of relative strength, if used carefully, provide a meaningful measure of variations in reflectivity. Simple theoretical models indicate that peg-leg multiples rather than water bottom multiples are the most severe source of noise contamination. These multiples are extremely difficult to remove when the water bottom reflection coefficient is large (>0.6), a condition that exists beneath parts of Lake Superior and most of Lake Huron.

  6. Seismic Reflections Within the Water Column South of South Africa: Indications for the Agulhas Retroflection

    NASA Astrophysics Data System (ADS)

    Uenzelmann-Neben, G.; Klaeschen, D.; Krahmann, G.; Reston, T.; Visbeck, M.

    2006-12-01

    With the publication of Holbrook et al. (2003) the field of seismic oceanography experienced a major momentum. Several authors since then (Nandi et al., 2004; Holbrook and Fer, 2005; Paramo and Holbrook, 2005) could show that those reflections within the water column correspond to thin layers with strong vertical temperature gradients. Those reflections hence represent a chance to trace those temperature gradients over large distances. Weak seismic reflections within the water column south of South Africa gave rise to the question whether here traces of the Agulhas Current or Agulhas Retroflection can be observed. A careful reprocessing of the data led to the imaging of fields of reflections pointing towards a 135 km broad and about 1000 m deep reaching well stratified area with strong reflection amplitudes and several weaker reflections extending down to at least 1500 m water depth over the whole area of investigation. To image both the boundaries between the water masses as reflections and the different properties of the long wavelength velocity variations in depth special imaging technigues like prestack depth migration analysis were performed. Further, the temperature gradients from the short wavelength properties as velocity and density contrasts were determind by a two step inversion of acoustic amplitude versus angle analysis to better quantify the variations of the water masses of the Agulhas Current. References: Holbrook, W.S., and I. Fer, Ocean internal wave spectra inferred from seismic reflection transects, 2005, Geophys. Res. Lett., 32, L15604, doi:10.1029/2005GL023733. Nandi, P., W.S. Holbrook, S. Pearse, P. Paramo, and R.W. Schmitt, 2004, Seismic reflection imaging of Norwegian Sea water mass boundaries, Geophys. Res. Lett., 31, L23311, doi:10.1029/2004GL021325. Paramo, P., and W. S. Holbrook, 2005, Temperature contrasts in the water column inferred from amplitude-versus-offset analysis of acoustic reflections, Geophys. Res. Lett., v. 32, L24611, doi

  7. Impact and implications of the Afro-Eurasian collision south of Cyprus from reflection seismic data

    NASA Astrophysics Data System (ADS)

    Klimke, Jennifer; Ehrhardt, Axel

    2014-06-01

    The Cyprus Arc in the Eastern Mediterranean represents the active collision front between the African and Eurasian (Anatolian) Plates. Along the Cyprus Arc, the Eratosthenes Seamount is believed to have been blocking the northward motion of the African Plate since the Late Pliocene-Early Pleistocene. Based on a dense grid of 2D reflection seismic profiles covering the Eratosthenes Seamount and western Levant Basin offshore Cyprus, new observations regarding the Cyprus Arc collision front at the triple transition zone Eratosthenes Seamount-Levant Basin-Hecataeus Rise are presented. The data show that the Levant Basin is filled with ~ 10 km of sediments of Early Mesozoic (probably Jurassic) to Plio-Quaternary age with only a localized deformation affecting the Miocene-Oligocene rock units. The sediments onlap directly against the steep eastern flank of the Eratosthenes Seamount to the west and the southern flank of the Hecataeus Rise to the north. The sediments show no deformation that could be associated with collision and are undeformed even very close to the two prominent structures. Pinching out of the Base Miocene reflector in the Levant Basin due to onlapping of the Middle Miocene reflector indicates uplift of the Eratosthenes Seamount and the Hecataeus Rise. In contrast to the Messinian Evaporites north of the Eratosthenes Seamount, the salt in the Levant Basin, even close to the Hecataeus Rise, is tectonically undeformed. It is proposed that the Eratosthenes Seamount, the western Levant Basin and the Hecataeus Rise act as one tectonic unit. This implies that the collision front is located north of this unit and that the Hecataeus Rise shields the sediments south of it from deformation associated with collision of the African and Anatolian Plates.

  8. Downhole seismic logging for high-resolution reflection surveying in unconsolidated overburden

    SciTech Connect

    Hunter, J.A.; Pullan, S.E.; Burns, R.A.; Good, R.L.; Harris, J.B.; Pugin, A.; Skvortsov, A.; Goriainov, N.N.

    1998-07-01

    Downhole seismic velocity logging techniques have been developed and applied in support of high-resolution reflection seismic surveys. Data obtained from downhole seismic logging can provide accurate velocity-depth functions and directly correlate seismic reflections to depth. The methodologies described in this paper are designed for slimhole applications in plastic-cased boreholes (minimum ID of 50 mm) and with source and detector arrays that yield similar frequency ranges and vertical depth resolutions as the surface reflection surveys. Compressional- (P-) wave logging uses a multichannel hydrophone array with 0.5-m detector spacings in a fluid-filled borehole and a high-frequency, in-hole shotgun source at the surface. Overlapping array positions downhole results in redundant first-arrival data which can be processed to provide accurate interval velocities. The data also can be displayed as a record suite, showing reflections and directly correlating reflection events with depths. Example applications include identification of gas zones, lithological boundaries within unconsolidated sediments, and the overburden-bedrock interface. Shear- (S-) wave logging uses a slimhole, well-locked, three-component (3-C) geophone pod and a horizontally polarized, hammer-and-loaded-plate source at ground surface. In unconsolidated sediments, shear-wave velocity contrasts can be associated with changes in material density or dynamic shear modulus, which in turn can be related to consolidation. Example applications include identification of a lithological boundary for earthquake hazard applications and mapping massive ice within permafrost materials.

  9. Seismic reflection applied to sedimentology and gas discovery in the Gulf of Cadiz

    SciTech Connect

    Delaplanche, J.; Lafet, Y.; Sineriz, B.G.; Remon Gil, M.A.

    1982-02-01

    In the Gulf of Cadiz, a Tertiary basin became filled by clastic series during Miocene and Pliocene times. This terrigenous influx, derived from the Iberic Meseta in the north, is characterized by a sandy episode during the Tortonian and Messinian. The sand deposits were probably connected with uplift and major erosion of the Meseta during the sliding of the olistostrome, which occupied the south of the basin from late Helvetian to middle Tortonian. High-resolution seismic techniques produced a good picture of the stratigraphy and of the depositional environment of the sands. A further study, using the amplitude of the reflections, inversion of seismic traces into acoustic impedance traces, and modeling, provides a remarkable example of the possibilities of seismic stratigraphy for depicting the lateral evolution of facies and localizing hydrocarbon occurrences. Out of seven exploratory wells based upon seismic information, six encountered gas-bearing sands with economic potential.

  10. Application of Hilbert-Huang transform based instantaneous frequency to seismic reflection data

    NASA Astrophysics Data System (ADS)

    Zhou, Yanhui; Chen, Wenchao; Gao, Jinghuai; He, Yongqiang

    2012-07-01

    Empirical mode decomposition (EMD) is designed to decompose non-stationary, nonlinear data into a series of intrinsic mode functions (IMFs) adaptively. This procedure is automatic, data-driven and time-variant. And then a Hilbert transform is applied to these IMFs. The combination of EMD with a Hilbert transform is known as Hilbert-Huang transform (HHT). HHT can be used to calculate meaningful multi-resolution instantaneous frequency (HHT based instantaneous frequency). Currently, the application of EMD and HHT to seismic data is performed mainly for noise attenuation. In this paper, we demonstrate new insights of EMD and HHT to seismic data analysis. We first extend the research of Flandrin et al. and analyze how EMD behaves on a Gaussian band-pass signal; we then employ HHT based instantaneous frequency on wedge model and real seismic data to delineate thickness variations. Numerical examples of Gaussian band-pass noise indicate that EMD acts as an adaptive, multi-band overlapping filter bank. The analysis of a wedge model and 2D real seismic data illustrates that HHT based instantaneous frequency is more effective than conventional Hilbert transform based instantaneous frequency in delineating the thickness variation of seismic thin bed.

  11. 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, T.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

  12. 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

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

    SciTech Connect

    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, 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

  14. Continuous seismic reflection profiling of hydrogeologic features beneath New River, Camp Lejeune, North Carolina

    USGS Publications Warehouse

    Cardinell, A.P.; Harned, D.A.; Berg, S.A.

    1990-01-01

    A medium-power, wide-frequency seismic system was used to collect more than 100 miles of continuous seismic reflection profiling data over a 4- day period along a 24-mile segment of the New River estuary and Intracoastal Waterway. The seismic reflection data were evaluated to determine the continuity of aquifer sediments and correlation with existing borehole geophysical well-log data at the Base. Results indicate that the Castle Hayne aquifer, the major source of freshwater for the military base and surrounding area, and deeper aquifers are continuous beds that gently dip to the southeast. However, immediately above the Castle Hayne aquifer, the survey showed that sediment beds are thin and discontinuous. This not only allows rainfall to more easily percolate and recharge the aquifer, but also makes the Castle Hayne more vulnerable to contamination.

  15. Variable post-Paleozoic deformation detected by seismic reflection profiling across the northwestern "prong" of New Madrid seismic zone

    USGS Publications Warehouse

    McBride, J.H.; Pugin, Andre J.M.; Nelson, W.J.; Larson, T.H.; Sargent, S.L.; Devera, J.A.; Denny, F.B.; Woolery, E.W.

    2003-01-01

    High-resolution shallow seismic reflection profiles across the northwesternmost part of the New Madrid seismic zone (NMSZ) and northwestern margin of the Reelfoot rift, near the confluence of the Ohio and Mississippi Rivers in the northern Mississippi embayment, reveal intense structural deformation that apparently took place during the late Paleozoic and/or Mesozoic up to near the end of the Cretaceous Period. The seismic profiles were sited on both sides of the northeast-trending Olmsted fault, defined by varying elevations of the top of Mississippian (locally base of Cretaceous) bedrock. The trend of this fault is close to and parallel with an unusually straight segment of the Ohio River and is approximately on trend with the westernmost of two groups of northeast-aligned epicenters ("prongs") in the NMSZ. Initially suspected on the basis of pre-existing borehole data, the deformation along the fault has been confirmed by four seismic reflection profiles, combined with some new information from drilling. The new data reveal (1) many high-angle normal and reverse faults expressed as narrow grabens and anticlines (suggesting both extensional and compressional regimes) that involved the largest displacements during the late Cretaceous (McNairy); (2) a different style of deformation involving probably more horizontal displacements (i.e., thrusting) that occurred at the end of this phase near the end of McNairy deposition, with some fault offsets of Paleocene and younger units; (3) zones of steeply dipping faults that bound chaotic blocks similar to that observed previously from the nearby Commerce geophysical lineament (CGL); and (4) complex internal deformation stratigraphically restricted to the McNairy, suggestive of major sediment liquefaction or landsliding. Our results thus confirm the prevalence of complex Cretaceous deformations continuing up into Tertiary strata near the northern terminus of the NMSZ. ?? 2003 Elsevier Science B.V. All rights reserved.

  16. IPOD-USGS multichannel seismic reflection profile from Cape Hatteras to the Mid-Atlantic Ridge

    USGS Publications Warehouse

    Grow, John A.; Markl, Rudi G.

    1977-01-01

    A 3,400-km-long multichannel seismic-reflection profile from Cape Hatteras to the Mid-Atlantic Ridge was acquired commercially under contract to the National Science Foundation and the U.S. Geological Survey. These data show evidence for massive erosion of the continental slope, diapirs at the base of the continental slope, and mantle reflections beneath the Hatteras Abyssal Plain.

  17. First-arrival traveltime tomography of regional-scale seismic-reflection data to image near-surface Quaternary and Tertiary sediments in Northern Switzerland

    NASA Astrophysics Data System (ADS)

    Hofstetter, Florian; Schmelzbach, Cedric; Horstmeyer, Heinrich; Hertrich, Marian; Buechi, Marius W.

    2014-05-01

    Regional-scale seismic-reflection data have usually a limited potential for imaging the shallow (<100 m) subsurface. However, resolving near-surface units is of significant interest for various purposes such as weathering-layer corrections in seismic-reflection processing but also to study Quaternary sediments and their geologic history. In this study, we inverted the first-arrival traveltimes of a recently acquired regional-scale seismic-exploration data set from Northern Switzerland. The overall motivation was to complement the seismic-reflection investigations and to image the shallow subsurface with seismic-refraction tomography. Whereas the surface distribution of the Quaternary and Tertiary sediments is mapped in detail in the investigation area, the highly variable thickness of the Quaternary sediments (up to 150 m) is only constrained at a few borehole locations. We focused on a ~9 km long stretch of a 2-D seismic-reflection profile that was acquired with short source and receiver intervals varying between 6 and 12 m. A total of 450'000 traveltimes was picked from mostly Vibroseis and few dynamite data with varying quality due to partly strong sweep-correlation noise and the data were inverted using a regularized inversion scheme. The robustness of the velocity models was assessed based on traveltime residuals, start model and free-parameter variation, and ray coverage. The final tomograms image the subsurface down to a depth of ~700 m. Shallow low (< 2000 m/s) seismic velocity zones correlate well with mapped Quaternary sediment units in the valleys. Geological and seismic-velocity information from three boreholes allows to correlate a distinct velocity increase at ~50 to 100 m depth with the Quaternary-Tertiary sediment interface. Velocity isolines allow tracing the Quaternary-sediment thickness away from the boreholes and significantly aid in updating a pre-existing Quaternary-sediment thickness model. An extensive about 100 m thick body with very low

  18. 3D crustal seismic velocity model for the Gulf of Cadiz and adjacent areas (SW Iberia margin) based on seismic reflection and refraction profiles

    NASA Astrophysics Data System (ADS)

    Lozano, Lucía; Cantavella, Juan Vicente; Barco, Jaime; Carranza, Marta; Burforn, Elisa

    2016-04-01

    The Atlantic margin of the SW Iberian Peninsula and northern Morocco has been subject of study during the last 30 years. Many seismic reflection and refraction profiles have been carried out offshore, providing detailed information about the crustal structure of the main seafloor tectonic domains in the region, from the South Portuguese Zone and the Gulf of Cadiz to the Abyssal Plains and the Josephine Seamount. The interest to obtain a detailed and realistic velocity model for this area, integrating the available data from these studies, is clear, mainly to improve real-time earthquake hypocentral location and for tsunami and earthquake early warning. Since currently real-time seismic location tools allow the implementation of 3D velocity models, we aim to generate a full 3D crustal model. For this purpose we have reviewed more than 50 profiles obtained in different seismic surveys, from 1980 to 2008. Data from the most relevant and reliable 2D seismic velocity published profiles were retrieved. We first generated a Moho depth map of the studied area (latitude 32°N - 41°N and longitude 15°W - 5°W) by extracting Moho depths along each digitized profile with a 10 km spacing, and then interpolating this dataset using ordinary kriging method and generating the contour isodepth map. Then, a 3D crustal velocity model has been obtained. Selected vertical sections at different distances along each profile were considered to retrieve P-wave velocity values at each interface in order to reproduce the geometry and the velocity gradient within each layer. A double linear interpolation, both in distance and depth, with sampling rates of 10 km and 1 km respectively, was carried out to generate a (latitude, longitude, depth, velocity) matrix. This database of all the profiles was interpolated to obtain the P-wave velocity distribution map every kilometer of depth. The new 3D velocity model has been integrated in NonLinLoc location program to relocate several representative

  19. Overdeepened glacigenic landforms in Lake Thun (Switzerland) revealed by a multichannel reflection seismic survey

    NASA Astrophysics Data System (ADS)

    Fabbri, Stefano; Herwegh, Marco; Schlunegger, Fritz; Hübscher, Christian; Weiss, Benedikt J.; Schmelzbach, Cédric; Horstmeyer, Heinrich; Buechi, Marius W.; Anselmetti, Flavio S.

    2016-04-01

    Recently acquired high-resolution multibeam bathymetry, in combination with a 2D multichannel reflection seismic campaign on perialpine Lake Thun (Switzerland) reveals new insights into the diverse geometry of the lake basin and a so far unknown subaquatic moraine crest with unprecedented clarity. These new data will improve our comprehension concerning the retreat phases of the Aare glacier, the morphology of its proximal deposits and the facies architecture of the subglacial units. The overdeepened basin of Lake Thun was formed by a combination of tectonically predefined weak zones and glacial erosion during the last glacial periods. The new data indicate that below the outermost edge of a morphologically distinct platform in the south eastern part of the lake basin, a ridge structure marked by strong reflection amplitudes occurs. This structure is interpreted as a subaquatic terminal moraine crest, most likely created by a slightly advancing or stagnant grounded Aare glacier during its major retreating phase. The terminal moraine smoothly transforms downstream into well distinguishable foresets with internally recognisable layering, which dip steeply towards the deepest part of the basin, eventually transforming into bottomsets. This depositional sequence formed by the fore- and bottomsets represents ˜50% of the overall sediment volume that fills the basin and was deposited while the glacier was stagnant, interpreted to represent a rather short period of time of a few hundreds of years. This sequence is overlain by lacustrine deposits formed by late-glacial and Holocene laminated muds comprising intercalated turbidites (Wirth et al. 2011). Little is known about the exact timing and behaviour of retreating glaciers between their recessional phase from the Alpine foreland to the deglaciation of the inner-Alpine ice cap, mostly due to the lack of well-developed moraines that indicate glacial stabilization or slight readvance. Findings from pollen analyses by

  20. Seismic reflection characteristics of glacial and glacimarine sediment in the Gulf of Alaska and adjacent fjords

    USGS Publications Warehouse

    Carlson, P.R.

    1989-01-01

    Glaciation together with tectonism have been dominant factors affecting sedimentation in the Gulf of Alaska area from at least the late Miocene throughout the Quaternary. The effects of tectonism are apparent in high mountains that border the gulf, raised terraces of Middleton Island and the eastern gulf coastal zone, and numerous active faults and related earthquakes. Glacial evidence includes magnificent glaciers and their onshore deposits, spectacular fjords, large sea valleys incised in the continental shelf, submarine morainal ridges at mouths of bays and sea valleys, and thick glacimarine sedimentary sequences (diamicts) that are exposed onshore and at the sea floor along the outer shelf. Seismic-reflection profiling and sampling of the uppermost marine sedimentary sequences in the Gulf of Alaska and adjacent fjords and bays have allowed identification of three discrete glacially related stratigraphic units. These units were delineated on the basis of seismic signature, geometry, physiographic location, stratigraphic position, and sedimentologic characteristics. The oldest unit, a Quaternary diamict, is portrayed on seismic profiles by irregular, discontinuous reflections. This unit probably includes till, outwash and glacimarine sediment. A geographically restricted unit, one incorporating Holocene end moraines at bay mouths and associated with some sea valleys, consists of jumbled masses of discontinuous reflections and very irregular surface morphology. The youngest unit, a blanket of Holocene sand to clayey silt prograding as a sediment wedge across the shelf, contains nearly horizontal, parallel reflections except where disrupted by mass movement. Although seismic-reflection data alone cannot provide definitive proof of the presence of glacial sediment, when combined with sea-floor sampling, seismic profiling is a powerful tool for determining the continuity of marine sedimentary units and relationships to past and modern glaciers. ?? 1989.

  1. FWT2D: A massively parallel program for frequency-domain full-waveform tomography of wide-aperture seismic data—Part 1: Algorithm

    NASA Astrophysics Data System (ADS)

    Sourbier, Florent; Operto, Stéphane; Virieux, Jean; Amestoy, Patrick; L'Excellent, Jean-Yves

    2009-03-01

    This is the first paper in a two-part series that describes a massively parallel code that performs 2D frequency-domain full-waveform inversion of wide-aperture seismic data for imaging complex structures. Full-waveform inversion methods, namely quantitative seismic imaging methods based on the resolution of the full wave equation, are computationally expensive. Therefore, designing efficient algorithms which take advantage of parallel computing facilities is critical for the appraisal of these approaches when applied to representative case studies and for further improvements. Full-waveform modelling requires the resolution of a large sparse system of linear equations which is performed with the massively parallel direct solver MUMPS for efficient multiple-shot simulations. Efficiency of the multiple-shot solution phase (forward/backward substitutions) is improved by using the BLAS3 library. The inverse problem relies on a classic local optimization approach implemented with a gradient method. The direct solver returns the multiple-shot wavefield solutions distributed over the processors according to a domain decomposition driven by the distribution of the LU factors. The domain decomposition of the wavefield solutions is used to compute in parallel the gradient of the objective function and the diagonal Hessian, this latter providing a suitable scaling of the gradient. The algorithm allows one to test different strategies for multiscale frequency inversion ranging from successive mono-frequency inversion to simultaneous multifrequency inversion. These different inversion strategies will be illustrated in the following companion paper. The parallel efficiency and the scalability of the code will also be quantified.

  2. Seismic reflection structure of intracratonic palmyride fold-thrust belt and surrounding Arabian platform, Syria

    SciTech Connect

    McBride, J.H.; Barazangi, M.; Best, J. ); Al-Saad, D.; Sawaf, T.; Al-Otri, M.; Gebran, A. )

    1990-03-01

    Seismic reflection and drill-hole data from central Syria provide a detailed view of the subsurface structure (10-15 km depth) of the relatively little-studied intracratonic Palmyride fold and thrust belt. The data set, together with surface geologic mapping, constrains a structural/stratigraphic section spanning the northeast sector of the belt and the surrounding subprovinces of the Arabian platform. The seismic reflection and drill-hole data show Mesozoic stratigraphic sequences thickening abruptly into the Palmyrides from the adjacent, arched Paleozoic platforms Neogene (alpine) folding and thrusting of the Mesozoic basin, as documented on the seismic data, are sharply restricted to the narrow width of the belt ({approximately}100 km), in contrast to the relatively undeformed Phanerozoic strata of the platforms to the north and south. The seismic and drill-hole data support the hypothesis that the palmyrides began as a Permian-Triassic failed rift connected to the Levantine passive continental margin, which was inverted and complexly deformed by the interfering effects of Cenozoic movements along the Dead Sea transform fault system and the Turkish Bitlis convergent zone. The seismic data provide a first view into the extent and depth of the early basin formation and subsequent compressional deformation, and as such represent a necessary element for constraining reconstructions of northern Middle East plate motions. 20 figs.

  3. Use of 2D images of depth and integrated reflectivity to represent the severity of demineralization in cross-polarization optical coherence tomography

    PubMed Central

    Chan, Kenneth H.; Chan, Andrew C.; Fried, William A.; Simon, Jacob C.; Darling, Cynthia L.; Fried, Daniel

    2015-01-01

    Several studies have demonstrated the potential of cross-polarization optical coherence tomography (CP-OCT) to quantify the severity of early caries lesions (tooth decay) on tooth surfaces. The purpose of this study is to show that 2D images of the lesion depth and the integrated reflectivity can be used to accurately represent the severity of early lesions. Simulated early lesions of varying severity were produced on tooth samples using simulated lesion models. Methods were developed to convert the 3D CP-OCT images of the samples to 2D images of the lesion depth and lesion integrated reflectivity. Calculated lesion depths from OCT were compared with lesion depths measured from histological sections examined using polarized light microscopy. The 2D images of the lesion depth and integrated reflectivity are well suited for visualization of early demineralization. Polarized light micrographs (PLM) of one of the histological sections from a tooth exposed to demineralization for 48 hrs. (A) PLM image of entire thin section (B) magnified PLM image of region of interest. PMID:24307350

  4. Solution of the 2-D steady-state radiative transfer equation in participating media with specular reflections using SUPG and DG finite elements

    NASA Astrophysics Data System (ADS)

    Le Hardy, D.; Favennec, Y.; Rousseau, B.

    2016-08-01

    The 2D radiative transfer equation coupled with specular reflection boundary conditions is solved using finite element schemes. Both Discontinuous Galerkin and Streamline-Upwind Petrov-Galerkin variational formulations are fully developed. These two schemes are validated step-by-step for all involved operators (transport, scattering, reflection) using analytical formulations. Numerical comparisons of the two schemes, in terms of convergence rate, reveal that the quadratic SUPG scheme proves efficient for solving such problems. This comparison constitutes the main issue of the paper. Moreover, the solution process is accelerated using block SOR-type iterative methods, for which the determination of the optimal parameter is found in a very cheap way.

  5. Apalachicola Bay interpreted seismic horizons and updated IRIS chirp seismic-reflection data

    USGS Publications Warehouse

    Cross, V.A.; Twichell, D.C.; Foster, D.S.; O'Brien, T.F.

    2012-01-01

    Apalachicola Bay and St. George Sound contain the largest oyster fishery in Florida, and the growth and distribution of the numerous oyster reefs here are the combined product of modern estuarine conditions and the late Holocene evolution of the bay. A suite of geophysical data and cores were collected during a cooperative study by the U.S. Geological Survey, the National Oceanic and Atmospheric Administration Coastal Services Center, and the Apalachicola National Estuarine Research Reserve to refine the geology of the bay floor as well as the bay's Holocene stratigraphy. Sidescan-sonar imagery, bathymetry, high-resolution seismic profiles, and cores show that oyster reefs occupy the crests of sandy shoals that range from 1 to 7 kilometers in length, while most of the remainder of the bay floor is covered by mud. The sandy shoals are the surficial expression of broader sand deposits associated with deltas that advanced southward into the bay between 6,400 and 4,400 years before present. The seismic and core data indicate that the extent of oyster reefs was greatest between 2,400 and 1,200 years before present and has decreased since then due to the continued input of mud to the bay by the Apalachicola River. The association of oyster reefs with the middle to late Holocene sandy delta deposits indicates that the present distribution of oyster beds is controlled in part by the geologic evolution of the estuary.

  6. Seismic Reflection Signatures of Internal Waves and Thermohaline Intrusions in the Norwegian Sea

    NASA Astrophysics Data System (ADS)

    Nandi, P.; Holbrook, W. S.; Pearse, S.; Paramo, P.; Schmitt, R. W.

    2004-12-01

    Water-column reflections acquired on a seismic survey in the Norwegian Sea and corroborated by 35 XBTs at an average spacing of 5 km and 2 XCTDs at both ends of a 172 km line suggest that temperature fine structure from internal wave strains and thermohaline intrusions have distinct seismic signatures. The survey images reflections from temperature fine structure sensitive to changes as small as 0.03 °C at the water mass boundary between the Norwegian Atlantic Current (NwAC) and Norwegian Sea Deep Water (NSDW). Internal wave strains appear in XCTD data from the eastern part of the seismic line near the Norwegian coast showing congruent changes in temperature and density. Reflections in this region have relatively small amplitudes and slope across isotherms corresponding to changes of several degrees Celsius. In contrast, an XCTD taken from the western seaward side of the profile shows several depths where density does not vary with temperature. Salinity is compensating for changes in temperature; thus reflections in this region likely correspond to irreversible fine structure caused by thermohaline intrusions. These reflections have high amplitudes and closely follow isotherms. These results indicate that studying these signatures can provide information about the structure of the internal wave field and isopycnal stirring processes over the lateral and vertical extent of the water column.

  7. 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.

  8. 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.

  9. Development of a Seismic Snow Streamer and Use of Multi- Offset Reflection for Determining Glacier Ice Properties

    NASA Astrophysics Data System (ADS)

    Velez Gonzalez, Jose A.

    seismic signal while the wind and signal analysis revealed that the best snow-streamer configuration was a combination of aluminum plates with vertical geophones. Using these results a second 480m full scale snow-streamer was tested in the Thwaites Glacier Antarctica. The snow-streamer data was simultaneously collected with a mirrored arrangement of surface planted and buried geophones. The trace by trace comparison revealed higher signal to noise in the data collected using the snow-streamer when compared to the surface planted and buried geophones. The full scale snow-streamer was easy to maneuver, very light and could be pulled in speeds up to 15 km/h. The use of the snow-streamer proved to be an efficient data acquisition tool, yielding high quality data. Therefore the use of snow-streamers can represent a significant improvement in the efficiency of seismic data acquisition in polar environments opening the possibility of determining important ice column properties for areas of interest. An important parameter affecting glacier flow is preferred ice crystal orientation. Seismic waves in ice travel up to 5% faster along the c-axis than when travelling perpendicular to it. Therefore, reflected seismic wave slowness (inverse of the velocity) variability as a function of angle of incidence can be used to detect anisotropy in ice crystal orientation. By combining the multi-offset seismic reflection data set acquired with the experimental snow-streamer and a 2D seismic reflection profile simultaneously collected for the same location, we investigated the presence of preferred ice crystal orientation for the area of study on the Jakobshavn Glacier. The combination of both data sets allowed the approximation of the average ray velocity as a function of angle of incidence. Given that the seismic velocity varies as a function of ice crystal orientation, we can use an existing model to relate the variation of seismic velocity as a function of offset to estimate the mean ice

  10. Gravity and multichannel seismic reflection constraints on the lithospheric structure of the Canary Swell

    NASA Astrophysics Data System (ADS)

    Ranero, C. R.; Torne, M.; Banda, E.

    1995-12-01

    Deep penetrating multichannel seismic reflection and gravity data have been used to study the lithospheric structure of the Canary Swell. The seismic reflection data show the transition from undisturbed Jurassic oceanic crust, away from the Canary Islands, to an area of ocean crust strongly modified by the Canary volcanism (ACV). Outside the ACV the seismic records image a well layered sedimentary cover, underlined by a bright reflection from the top of the igneous basement and also relatively continuous reflections from the base of the crust. In the ACV the definition of the boundary between sedimentary cover and igneous basement and the crust-mantle boundary remains very loose. Two-dimensional gravity modelling in the area outside the influence of the Canary volcanism, where the reflection data constrain the structure of the ocean crust, suggests a thinning of the lithosphere. The base of the lithosphere rises from 100 km, about 400 km west of the ACV, to 80 km at the outer limit of the ACV. In addition, depth conversion of the seismic reflection data and unloading of the sediments indicate the presence of a regional depth anomaly of an extension similar to the lithospheric thinning inferred from gravity modelling. The depth anomaly associated with the swell, after correction for sediment weight, is about 500 m. We interpret the lithospheric thinning as an indication of reheating of old Mesozoic lithosphere beneath the Canary Basin and along with the depth anomaly as indicating a thermal rejuvenation of the lithosphere. We suggest that the most likely origin for the Canary Islands is a hot spot.

  11. Combined analysis of surface reflection imaging and vertical seismic profiling at Yucca Mountain, Nevada

    SciTech Connect

    Daley, T.M.; Majer, E.L.; Karageorgi, E.

    1994-08-01

    This report presents results from surface and borehole seismic profiling performed by the Lawrence Berkeley Laboratory (LBL) on Yucca Mountain. This work was performed as part of the site characterization effort for the potential high-level nuclear waste repository. Their objective was to provide seismic imaging from the near surface (200 to 300 ft. depth) to the repository horizon and below, if possible. Among the issues addressed by this seismic imaging work are location and depth of fracturing and faulting, geologic identification of reflecting horizons, and spatial continuity of reflecting horizons. The authors believe their results are generally positive, with tome specific successes. This was the first attempt at this scale using modem seismic imaging techniques to determine geologic features on Yucca Mountain. The principle purpose of this report is to present the interpretation of the seismic reflection section in a geologic context. Three surface reflection profiles were acquired and processed as part of this study. Because of environmental concerns, all three lines were on preexisting roads. Line 1 crossed the mapped surface trace of the Ghost Dance fault and it was intended to study the dip and depth extent of the fault system. Line 2 was acquired along Drill Hole wash and was intended to help the ESF north ramp design activities. Line 3 was acquired along Yucca Crest and was designed to image geologic horizons which were thought to be less faulted along the ridge. Unfortunately, line 3 proved to have poor data quality, in part because of winds, poor field conditions and limited time. Their processing and interpretation efforts were focused on lines 1 and 2 and their associated VSP studies.

  12. 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

  13. USING RECENT ADVANCES IN 2D SEISMIC TECHNOLOGY AND SURFACE GEOCHEMISTRY TO ECONOMICALLY REDEVELOP A SHALLOW SHELF CARBONATE RESERVOIR: VERNON FIELD, ISABELLA COUNTY, MI

    SciTech Connect

    James R. Wood; A. Wylie; W. Quinlan

    2004-10-01

    One of the principal objectives of this demonstration project is to test surface geochemical techniques for detecting trace amounts of light hydrocarbons in pore gases as a means of reducing risk in hydrocarbon exploration and production. During this reporting period, microbial samples were collected from the Trusty Steed prospect area in Grand Traverse County, Michigan. The samples were analyzed using the Microbial Oil Surveying Technique (MOST) technique and revealed only a local (1-point) anomaly. A decision to resample over that point is pending, but drilling has been postponed for the time being. The main news this reporting period is that in the Bear Lake area, northwest Michigan, Federated Oil & Gas Properties' Charlich-Fauble 2-9HD horizontal lateral, has cumulative production of more than 72,000 barrels of oil and is still producing 50 to 75 bopd from a Silurian Niagaran reef reservoir eighteen months after the well was completed. Surface geochemical surveys conducted in the demonstration area were consistent with production results although the ultimate decision to drill was based on interpretation of conventional subsurface and 2D seismic data. The surface geochemical techniques employed were Solid Phase MicroExtraction (SPME) and MOST. The geochemical results have been submitted to World Oil for publication. New geochemical surveys are planned for November in the Springdale quadrangle in Manistee County, Michigan. These surveys will concentrate on sampling over the trace of the proposed horizontal wells rather than a broad grid survey.

  14. 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

  15. Seismic reflection survey in the geothermal field of the Rotorua Caldera, New Zealand

    SciTech Connect

    Lamarche, G. )

    1992-04-01

    This paper discusses a seismic reflection survey conducted in the southern part of the Rotorua geothermal field (New Zealand). Geological structures were interpreted along the two profiles to a depth of about 300 m. A seismic image of the Mamaku Ignimbrite is obtained and appears to show normal faulting. Depth of the top of the Mamaku Ignimbrite corroborates data from boreholes. Thickness of the Ignimbrite sheet may reach 280 m near Rotorua City. It is suggested that the Rotorua caldera boundary is not a single fault but a fault zone consisting of at least 4 faults. The displacement on any one fault is no greater than 30 m. The near surface cold-warm thermal boundary, at the northern boundary of the Whakarewarewa thermal area, is also shown in the seismic section.

  16. Modelling study of challenges in sinkhole detection with shear wave reflection seismics

    NASA Astrophysics Data System (ADS)

    Burschil, Thomas; Krawczyk, CharLotte M.

    2016-04-01

    The detection of cavities with reflection seismics is a difficult task even if high impedance contrasts are assumed. Especially the shear wave reflection method with a higher resolution potential trough lower velocities and short wavelength has come into focus of investigation. But shear wave propagation fails if material exists that partially has no shear strength. The shear wave does not propagate into or through those voids. Here, we evaluate the influence of a possible fracture zone above a cavity. We simulate shear wave propagation with finite difference modelling for two reference models, with and without cavity, and various sets of input models with a fracture zone above the cavity. Reflections and multiples of the reference models image the subsidence structure and the cavity. For the fracture input models, we implemented a fracture network, derived from numerical crack propagation modelling (Schneider-Löbens et al., 2015). The cracks possess the minimum possible aperture of one grid point (i.e. 0.1 m) and no shear stiffness. The seismic modelling exhibits that the shear wave does not pass through the fracture zone and shadows the subjacent cavity. Sequences of randomly discontinuous cracks, cf. displacement discontinuity model with zero crack stiffness, approximate partially seismic connected rock on both sides of the crack. The amount of these seismic pathways determines whether a reflection of the cavity can be detected at the surface or not. Cracks with higher aperture, e.g. two or three grid points, need a higher amount of intact rock/defective cracks, since more connected grid points are necessary to create seismic pathways. Furthermore, it turns out that the crack filling is important for shear wave transmission. While a mineralized fracture zone, implemented with high velocity, facilitate shear wave propagation, water or air-filled cracks avoid shear wave transmission. Crack orientation affects the shear wave propagation through the geometry. A

  17. 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

  18. 3-component HR seismic reflection, a new paradigm for near surface exploration of aquifers and aquitards

    NASA Astrophysics Data System (ADS)

    Pugin, A.; Pullan, S. E.; Oldenborger, G. A.; Crow, H.; Hunter, J. A.; Near Surface Geophysics

    2011-12-01

    sealed by thick till aquitards. In southeastern Manitoba, a 3-C seismic survey combined with geophysical dowhole logs has provided critical depth calibrations for a 1000 square-km airborne EM data that has highlighted the presence of a three dimensional network of buried valleys. The high rate of production of 3-C high resolution S-wave and P-wave seismic reflection combined with other geophysical techniques provides very reliable depths, structural evidence and a better characterisation of the physical property of aquifers and aquitards present in unconsolidated sediments.

  19. Q estimation from reflection seismic data for hydrocarbon detection using a modified frequency shift method

    NASA Astrophysics Data System (ADS)

    Li, Fangyu; Zhou, Huailai; Jiang, Nan; Bi, Jianxia; Marfurt, Kurt J.

    2015-08-01

    As a powerfully diagnostic tool for structural interpretation, reservoir characterization, and hydrocarbon detection, quality factor Q provides useful information in seismic processing and interpretation. Popular methods, like the spectral ratio (SR) method, central frequency shift (CFS) method and peak frequency shift (PFS) method, have their respective limitations in dealing with field seismic data. The lack of a reliable method for estimating Q from reflection seismic data is an issue when utilizing the Q value for hydrocarbon detection. In this article, we derive an approximate equation and propose a dominant and central frequency shift (DCFS) method by combining the quality factor Q, the travel time, and dominant and central frequencies of two successive seismic signals along the wave propagating direction. Based on multi-layered analysis, we then proposed a method to obtain continuous volumetric Q estimation results. A test using synthetic data and statistical experiments showed the proposed method can achieve higher accuracy and robustness compared with existing methods. Application of field data also shows its potential and effectiveness to estimate seismic attenuation.

  20. 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).

  1. 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

  2. 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.

  3. Pen Branch fault program: Consolidated report on the seismic reflection surveys and the shallow drilling

    SciTech Connect

    Stieve, A.L.; Stephenson, D.E.; Aadland, R.K.

    1991-03-23

    The Pen Branch fault was identified in the subsurface at the Savannah River Site (SRS) in 1989 based upon interpretation of earlier seismic reflection surveys and other geologic investigations (Seismorgraph Services Incorp., 1973; Chapman and DiStefano, 1989; Snipes, Fallaw and Price, 1989). A program was initiated at that time to determine the capability of the fault to release seismic energy (Price and others, 1989) as defined in the Nuclear Regulatory Commission regulatory guidelines, 10 CFR 100 Appendix A. This report presents the results of the Pen Branch fault investigation based on data acquired from seismic reflection surveys and shallow drilling across the fault completed at this time. The Earth Science Advisory Committee (ESAC) has reviewed the results of these investigations and unanimously agrees with the conclusion of Westinghouse Savannah River Company (WSRC) that the Pen Branch fault is a non-capable fault. ESAC is a committee of 12 earth science professionals from academia and industry with the charter of providing outside peer review of SRS geotechnical, seismic, and ground water modeling programs.

  4. Geological Structures of the South Okinawa Trough based on Seismic Reflection Data

    NASA Astrophysics Data System (ADS)

    Fan, M.; Liu, C.; Teng, L. S.

    2011-12-01

    The Southern Okinawa Trough (SOT) located offshore northeastern Taiwan is an extensional basin north of the Ryukyu Island Arc that opens toward Taiwan. In order to better understand the geological processes in the Southern Okinawa Trough, we collect all the available multi-channel seismic reflection data, reprocess some of them to improve the data quality, and interpret 22 seismic reflection profiles. A structural map, which shows the distribution of fault structures and submarine volcanoes in the study area, is compiled with the aid of seismic sequence analysis. We found that normal faults developed in both the northern and southern flanks of the SOT, and also in the axial area where volcanic extrusions are abundant, suggesting that the SOT is presently undergoing active extension. Some deeply rooted compressional structures are observed below the younger normal faults, which may indicate that the area offshore northern Taiwan was once in a convergent tectonic environment. We use seismic and bathymetry data to discuss the fault activities and related tectonic processes, also examine the volcanic activities and their geological environment.

  5. Seismic Reflection - Focusing on Muting Jacquelyn Daves University of Colorado - Boulder SAGE 2014

    NASA Astrophysics Data System (ADS)

    Daves, J.

    2014-12-01

    The SAGE 2014 survey was conducted directly west of the Santo Domingo Pueblo, along Borrego Canyon Road. This survey is a continuation of the SAGE 2010 and 2011 investigations. The survey was aimed to locate a previously mapped fault running orthogonal to the road. The SAGE 2014 seismic line ran 5.6 km long with 20 meter geophone spacing. 8-80 Hz sweeps were utilized with 10 s sweeps and 4 s of listening. Once the data was converted into the proper file type, preprocesses was conducted. After the preprocessing was complete, various processing methods were used to obtain the final Common Midpoint (CMP) stack. Two CMP stacks were created-one containing the muting method and one without. The ideal result would be to interpret stratigraphic structures and potential faults. The Rio Grande Rift is a Cenozoic continental rift zone that extends approximately 1000 km from Leadville, Colorado to west Texas and Chihuahua, Mexico. The Northern most extent of the rift separates the Great Plains from the Colorado Plateau. The rift consists of a series of interconnected grabbens that lie in an asymmetric pattern (Baldridge, 1989). Basins involved with this rifting are a distinct features along with faults that bound one or both sides. SAGE has been investigating these for over a decade to interpolate the complex structures. By examining Borrego Canyon, we were able to add to the investigation. Various geophysical methods were utilized to study Borrego Canyon. AMT, MT, TEM, gravity, seismic reflection and seismic refraction were individually used to understand the subsurface and were subsequently integrated together in order to have a full spectrum of subsurface depths. Each method has unique processing steps and are critical in order to analyze the gathered data. As such, this paper will focus on processing seismic reflection with an emphasis on muting. Each technique used in processing the SAGE 2014 seismic reflection data will be explained. Next, this paper will validate muting

  6. Reflection seismic mapping of shallow quick-clay landslides in Sweden - new insights from shear-wave surveying

    NASA Astrophysics Data System (ADS)

    Polom, U.; Krawczyk, C. M.; Malehmir, A.; Bastani, M.

    2012-04-01

    As part of a joint project studying clay-related landslides in Nordic countries, we successfully tested the use of shear wave reflection seismics to survey shallow structures that are known to be related to quick-clay landslide processes. Co-sponsored via the Society of Exploration Geophysicists (SEG) program 'Geoscientists Without Borders (GWB)', several international groups apply a suite of applied geophysical and geotechnical methods to understand structural and physical conditions and the conditioning of this type of liquefaction. For this purpose, three 2D profiles were recorded in Frastadt, southern Sweden, above the main slide plane area. Using a 120 m long streamer of 120 SH-geophones at 1 m spacing, and the ELVIS micro-vibrator as source, shear-wave data of very high quality were gathered. The longest profile along a paved road shows clear internal structuring of the up to 50 m thick marine sediments as well as strong undulations of top basement underneath. The sedimentary shear wave velocities suggest extremely low values of 100-120 m/s, which geotechnically prohibits building areas. In addition, test measurements on a stubble field showed the first time that the suppression of Love waves is not only restricted to paved surfaces and may also be achieved if reflection contrasts and low dispersion allow a suitable data processing. This opens new possibilities for a wide range of applications and specialized equipment adaptions.

  7. Geostatistical inversion of seismic and ground-penetrating radar reflection images: What can we actually resolve?

    NASA Astrophysics Data System (ADS)

    Irving, James; Holliger, Klaus

    2010-11-01

    Estimation of the spatial statistics of subsurface velocity heterogeneity from surface-based geophysical reflection survey data is a problem of significant interest in seismic and ground-penetrating radar (GPR) research. A method to effectively address this problem has been recently presented, but our knowledge regarding the resolution of the estimated parameters is still inadequate. Here we examine this issue using an analytical approach that is based on the realistic assumption that the subsurface velocity structure can be characterized as a band-limited scale-invariant medium. Our work importantly confirms recent numerical findings that the inversion of seismic or GPR reflection data for the geostatistical properties of the probed subsurface region is sensitive to the aspect ratio of the velocity heterogeneity and to the decay of its power spectrum, but not to the individual values of the horizontal and vertical correlation lengths.

  8. Analysis and modeling of high-resolution multicomponent seismic reflection data

    NASA Astrophysics Data System (ADS)

    Guy, Erich D.

    The facts that seismic body-wave types are sensitive to different physical properties, seismic sources radiate polarized waves, and seismic receivers are sensitive to the polarization of scattered body-waves and coherent noise, mean that it is important to consider recording and analyzing different wave-types and data components prior to high-resolution reflection surveys. In this dissertation, important aspects of elastic-wave propagation relevant to high-resolution multicomponent surveying have been analyzed experimentally and numerically, and methodologies have been tested and developed that will improve near-surface imaging and characterization. Factors affecting the ability of common-mode P- and S-wave reflection surveys for mapping features in the near-surface are described and illustrated through analyses of experimental field data and modeling. It is demonstrated through comparisons of known subsurface conditions and processed stacked sections, that combined P- and S-wave common-mode reflection information can allow a geologic sequence to be imaged more effectively than by using solely P- or S-wave reflection information. Near-surface mode-converted seismic reflection imaging potential was tested experimentally and evaluated through modeling. Modeling results demonstrate that potential advantages of near-surface mode-conversion imaging can be realized in theory. Analyses of acquired multicomponent data however demonstrate that mode-conversion imaging could not be accomplished in the field study area, due to the low amplitudes of events and the presence of noise in field data. Analysis methods are presented that can be used for assessing converted-wave imaging potential in future reflection studies. Factors affecting the ability of SH-wave reflection measurements for allowing near-surface interfaces and discontinuities to be effectively imaged are described. A SH-wave reflection data analysis workflow is presented that provides a methodology for delineating

  9. 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

  10. Intra-oceanic crustal seismic reflecting zone below the dipping reflectors on Lofoten margin

    SciTech Connect

    Sellevoll, M.A.; Mokhtari, M.

    1988-07-01

    Multichannel seismic reflection measurements off Lofoten, Northern Norway, show an uneven, discontinuous reflector within the crystalline oceanic crust at a depth of 7-8 s (two-way travel time). This intra-oceanic crustal reflector is observed seaward as well as beneath sub-basement dipping reflectors, which are of disputed (oceanic or continental) origin. These observations indicate that the dipping reflectors are an integrated part of the oceanic crust.

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

    SciTech Connect

    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 effectiveness 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

  12. Characterization of the upper surface of the Philippine Sea plate beneath Kanto, central Japan: insight from seismic reflection profiling

    NASA Astrophysics Data System (ADS)

    Sato, H.; Abe, S.; Iwasaki, T.; Kurashimo, E.; Okaya, D. A.; Sakai, S.; Kawanaka, T.; Hirata, N.

    2010-12-01

    Beneath metropolitan Tokyo, the Philippine Sea plate (PHS) has been subducted on the Pacific plate (PAC). Due to shallow subduction of Philippine Sea plate (PHS), intraslab earthquake of PHS can also produce significant damage of Tokyo metropolitan area. To construct source fault models, we have carried out seismic reflection profiling since 2002 and acquired seismic reflection data from 9 seismic lines, including 2009 Sagami trough and 2010 Kujukuri seismic survey. Due to strong impedance contrast of plate interface, the upper surface of PHS was imaged down to maximum 40 km in depth. The obtained seismic profiles portrayed the shallow geometry of the PHS. The combined seismic section from Izu peninsula to Tokyo (2009 Sagami trough and 2003 Tokyo bay seismic sections) shows strong reflectivity in the deeper part (17 to 27 km) and also shallower part (5 to 10 km). Base on the co-seismic displacement of the 1923 Kanto earthquake (M7.9) and slip-deficit rate determined by GPS observations, the asperity zone is clearly identified along the combined seismic line. By comparison, the zone of asperity is marked by the area of low reflectivity, relatively flat geometry and Vp > 6 km/sec. The subducted PHS slab beneath Kanto consists of fore-arc and volcanic-arc of young geologic age. The slab geometry obtained by seismic reflection suggests strong deformation. Three seismic lines across the north to northwestern part of the Izu collision zone demonstrate the ridge shaped antiform of the PHS slab. Judging from overall geometry of PHS slab beneath Kanto, the deformation of the slab probably produced by the northward subduction of PHS (> 1 Ma) and interaction with underlying cold PAC slab.

  13. 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.

  14. Feasibility study of the seismic reflection method in Amargosa Desert, Nye County, Nevada

    SciTech Connect

    Brocher, T.M.; Hart, P.E.; Carle, S.F.

    1990-11-01

    The US Geological Survey (USGS) working under an Interagency agreement with the Department of Energy is engaged in a broad geoscience program to assess and identify a potential repository for high level nuclear waste at Yucca Mountain, Nye County, Nevada. The USGS program, referred to as the Yucca Mountain Project, or YMP, consists of integrated geologic, hydrologic and geophysical studies which range in nature from site specific to regional. This report is an evaluation of different acquisition methods for future regional seismic reflection studies to be conducted in the vicinity of Yucca Mountain, located in the southwestern corner of the Nevada Test Site (NTS). In January 1988, field studies were conducted to investigate the feasibility of using the common-depth point (CDP) seismic reflection method to map subsurface geological horizons within the Amargosa Desert, Nye County, Nevada. The goal of the field study was to investigate which seismic reflection method(s) should be used for mapping shallow to lower-crustal horizons. Therefore, a wide-variety of field acquisition parameters were tested, included point versus linear receiver group arrays; Vibroseis (service and trademark of Conoco, Inc.) versus explosive sources; Vibroseis array patterns; and Vibroseis sweep and frequency range. 31 refs., 33 figs., 8 tabs.

  15. Fine-scale thermohaline ocean structure retrieved with 2-D prestack full-waveform inversion of multichannel seismic data: Application to the Gulf of Cadiz (SW Iberia)

    NASA Astrophysics Data System (ADS)

    Dagnino, D.; Sallarès, V.; Biescas, B.; Ranero, C. R.

    2016-08-01

    This work demonstrates the feasibility of 2-D time-domain, adjoint-state acoustic full-waveform inversion (FWI) to retrieve high-resolution models of ocean physical parameters such as sound speed, temperature and salinity. The proposed method is first described and then applied to prestack multichannel seismic (MCS) data acquired in the Gulf of Cadiz (SW Iberia) in 2007 in the framework of the Geophysical Oceanography project. The inversion strategy flow includes specifically designed data preconditioning for acoustic noise reduction, followed by the inversion of sound speed in the shotgather domain. We show that the final sound speed model has a horizontal resolution of ˜ 70 m, which is two orders of magnitude better than that of the initial model constructed with coincident eXpendable Bathy Thermograph (XBT) data, and close to the theoretical resolution of O(λ). Temperature (T) and salinity (S) are retrieved with the same lateral resolution as sound speed by combining the inverted sound speed model with the thermodynamic equation of seawater and a local, depth-dependent T-S relation derived from regional conductivity-temperature-depth (CTD) measurements of the National Oceanic and Atmospheric Administration (NOAA) database. The comparison of the inverted T and S models with XBT and CTD casts deployed simultaneously to the MCS acquisition shows that the thermohaline contrasts are resolved with an accuracy of 0.18oC for temperature and 0.08 PSU for salinity. The combination of oceanographic and MCS data into a common, pseudo-automatic inversion scheme allows to quantitatively resolve submeso-scale features that ought to be incorporated into larger-scale ocean models of oceans structure and circulation.

  16. Reflection and transmission of seismic waves at an interface between two saturated soils

    NASA Astrophysics Data System (ADS)

    Yang, Jun; Wu, Shi-Ming

    1997-01-01

    Based on the modified Biot model for asturated soils, taking the compressibilities of the grains and the pore fluid as well as the viscous coupling into account, the reflection and transmission of seismic aves at an interface between two saturated soils are studied in this paper. A formula is derived for calculation of the amplitude reflection and transmission coefficients of various waves. A aumerical investigation of the dependence of the coefficients on the angle of incidence and the frequency is performed. This study is of a value for seismological studies and geophysical exploration.

  17. REPROCESSING OF SHALLOW SEISMIC REFLECTION DATA TO IMAGE FAULTS NEAR A HAZARDOUS WASTE SITE ON THE OAK RIDGE RESERVATION, TENNESSEE

    SciTech Connect

    DOLL, W.E.

    1997-12-30

    Shallow seismic reflection data from Bear Creek Valley on the Oak Ridge Reservation demonstrates that spectral balancing and tomographic refraction statics can be important processing tools for shallow seismic data. At this site, reprocessing of data which had previously yielded no useable CMP stacked sections was successful after application of these processing techniques.

  18. Comparison of geoelectric and seismic reflection models of the Zambezi Valley basins, northern Zimbabwe

    NASA Astrophysics Data System (ADS)

    Bailey, David; Whaler, Kathy; Zengeni, Teddy

    2000-09-01

    The Mana Pools and Lower Zambezi Karoo sedimentary basins lie within the Zambezi mobile belt in northern Zimbabwe. The subsurface apparent resistivities measured at both locations are extremely low. Magnetotelluric (MT) data along a profile across part of the Lower Zambezi basin have been inverted using Rapid Relaxation Inversion (Smith & Booker 1991) to find the minimum structure needed to fit the data and compare with an earlier forward model. The resistivity models of both the Mana Pools and the Lower Zambezi basins are then compared with their structure revealed from seismic reflection data. The resistivity structure of the Mana Pools basin is well modelled as a series of different resistivity layers whose boundaries are defined by the seismic data. However, the resistivity structure of the Lower Zambezi basin cannot be matched easily to the seismic structure; additional structure with no seismic expression is required. There is a conductive feature in the two basins in the Upper Karoo sandstone layer that extends below the seismic basement beneath the Lower Zambezi basin. This indicates that the conductors may represent different types of features in the two basins, consistent with their proposed different tectonic origins. A resistive unit is present within the sediments in the Lower Zambezi basin that may represent intercalated basalt dykes, giving an anisotropic MT response. It has been suggested that there might be similar thin basalt layers within the sediments of the Mana Pools basin, but these could not be resolved by MT methods. The low resistivity of the basement, particularly beneath the Lower Zambezi basin, is remarkable and may result from a high degree of either chemical or tectonic alteration to the underlying rocks due to metamorphic processes and tectonic disruption during rift formation. The presence of the Lower Zambezi basin conductor at depths greater than the seismic basement is consistent with observations to the west, in the adjacent

  19. Avalon terane in eastern coastal Maine: seismic refraction-wide- angle reflection data

    USGS Publications Warehouse

    Luetgert, J.; Mann, C.E.

    1990-01-01

    A 145-km-long seismic refraction line recorded parallel to the eastern coastline of Maine within the Avalon terrane provides information about the crustal velocity structure within the Avalon block and its relation to other Appalachian terranes. A crustal velocity model for the upper 8 km shows that, except for a thin surficial layer of velocity 5.0-5.3 km/s, upper crustal granites and country rocks have velocities in the range 6.0-6.3 km/s and gabbros have a 6.5 km/s velocity. To determine the lower crustal structure, deep reflections were analyzed by applying normal moveout corrections routinely used in reflection data processing. Major reflective boundaries at approximately 3-4, 7, and 10-11 s two-way traveltime are easily distinguished, and are similar to those observed in a near-vertical seismic reflection survey crossing the refraction profile at its southwestern end. The deepest reflections correspond to the crust-mantle boundary at a depth of 34-35 km. -from Authors

  20. An Evaluation of Seismic Reflection Studies in the Yucca Mountain Area, Nevada Test Site

    USGS Publications Warehouse

    McGovern, Thomas F.; Introduction by Pankratz, L. W.; Ackermann, H.D.

    1983-01-01

    As part of a total geophysical evaluation of Yucca Mountain for use as a Nuclear Waste Repository the seismic reflection technique has been applied. This study has been conducted to analyze the historical and technical efforts which have been used by three geophysical contractors employing a wide variety of techniques ranging from the most simple to very elaborate 3-D surveys. In each case elaborate noise studies were conducted, and based upon their evaluation parameters were chosen for multifold CDP recording. In every case, the signal-to-noise ratio was such that no reflections were discernable. Since the reflections cannot be separated from the noise even using very elaborate noise suppression techniques and up to 384 fold multiplicity it is apparent that in this volcanic terrain reflection surveys, can not work.

  1. Decoupling of deformation in the Upper Rhine Graben sediments. Seismic reflection and diffraction on 3-component Vertical Seismic Profiling (Soultz-sous-Forêts area)

    NASA Astrophysics Data System (ADS)

    Place, Joachim; Diraison, Marc; Naville, Charles; Géraud, Yves; Schaming, Marc; Dezayes, Chrystel

    2010-07-01

    A contribution to the definition of the structural pattern of the Soultz-sous-Forêts EGS (Enhanced Geothermal System) is presented here. After reprocessing, the PHN84J seismic reflection profile highlights the tilted blocks of the Merkwiller-Péchelbronn oilfield. In the Soultz-sous-Forêts horst, complex fault patterns are observed: the Hermerswiller normal fault flattens at depth and is rooted in decollements occurring in Triassic salt or clay series, while other steep normal faults affect underlying sedimentary formations and basement. Some methods for the exploitation of a seismic diffraction recorded by multi-component Vertical Seismic Profiling (VSP) are also illustrated to locate the diffractor without specific data processing. Polarisation and travel time analysis of a diffraction event recorded in the GPK1 borehole are analysed, and its exploitation combined with seismic reflection helps defining a tilted block geometry.

  2. Seismic slip propagation along a fault in the Shimanto accretionary prism detected by vitrinite reflectance studies

    NASA Astrophysics Data System (ADS)

    Kitamura, M.; Mukoyoshi, H.; Hirose, T.

    2011-12-01

    Quantitative assessment of heat generation along faults during fault movement is of primary importance in understanding the dynamics of earthquakes. Last several years localized heat anomaly in a fault zone due to rapid seismic sliding has been detected by various analyses of fault zone materials, such as ferromagnetic resonance signal (Fukuchi et al., 2005), trace elements and isotopes (e.g., Ishikawa et al., 2008) and mineralogical change of clay (e.g., Hirono et al., 2008) and vitrinite reflectance (O'Hara, 2004). Here we report a heat anomaly found in a fault zone in the Shimanto accretionary complex by vitrinite reflectance measurements. Mature faults in nature mostly experience multiple seismic events, resulting in integrated heat anomaly. Thus, in addition to vitrinite reflectance measurements across natural faults, we performed high-velocity friction experiments on a mixture of quartz and vitrinite grains to evaluate how multiple rapid-slip events affect vitrinite reflectance in a fault zone. A localized heat anomaly is found in one of fault zones which are developed within a mélange unit in the Cretaceous Shimanto belt, SW Japan. A principle slip zone with thickness of ~5 mm forms within cataclastic damage zone with thickness of ~3 m. The slip zone is mainly composed of well-foliated clay minerals. Host rocks are characterized by a block-in-matrix texture: aligned sandstone and chert blocks embedded in mudstone matrix. We measured vitrinite reflectance across the fault zone by the same method as reported in Sakaguchi et al., (2011). The measurement reveals that the principle slip zone underwent localized temperature of more than 220°C, while background temperature of both damage zone and host rocks is ~170°C. Since fault motion along most active faults occurs seismological, that inevitably generates frictional heat, the localized heat anomaly is possibly caused by the rapid seismic slip. In order to evaluate the change in vitrinite reflectance by

  3. Red Sea isolation history suggested by Plio-Pleistocene seismic reflection sequences

    NASA Astrophysics Data System (ADS)

    Mitchell, Neil C.; Ligi, Marco; Rohling, Eelco J.

    2015-11-01

    High evaporation rates in the desert climate of the Red Sea ensure that, during glacial sea level lowstands when water exchange with the Indian Ocean was more restricted, water salinity and δ18 O became unusually extreme. Modeling of the effect on Red Sea sedimentary δ18 O has been used previously to reconstruct relative sea level to 500 ka and now poses the question of whether that sea-level model could be extended if continuous core material of older sediment became available. We attempt to address this question here by examining seismic reflection data. The upper Pleistocene hemipelagic sediments in the Red Sea contain intervals of inorganic aragonite precipitated during supersaturated conditions of sea-level lowstands. Seismic impedance changes associated with boundaries to those aragonite-rich layers appear to explain seismic reflection sequences. A segment of Chirp sediment profiler data from the central Red Sea reveals prominent reflections at ∼1, ∼5, ∼23, ∼26 and ∼36 ms two-way travel time (TWT) from the seabed. Based on depths to the glacial marine isotope stages (MIS) in cores, we relate the upper three reflections to the tops of aragonite-rich layers and hence the sea level rises immediately following MIS 2, 6 and 12. The reflection at 26 ms is related to an unusually rapid fall into MIS 12 predicted by one sea level reconstruction, which may have created an abrupt lower boundary to the MIS 12 aragonite-rich layer. With the aid of seismogram modeling, we tentatively associate the ∼36 ms reflection with the top of an aragonite-rich layer formed during MIS 16. Furthermore, some segments of lower frequency (airgun and sparker) seismic data from the central and southern Red Sea show a lower (earlier) Plio-Pleistocene (PP) interval that is less reflective than the upper (late) PP interval. This implies less variability in sediment impedance and that extreme variability in water salinity did not develop; water exchange with the Indian Ocean

  4. 3-D Tomography Study of Seismic Refraction/Wide-Angle Reflection Data Across the Variscides, SW Ireland

    NASA Astrophysics Data System (ADS)

    O'Reilly, B. M.; Landes, M.; Readman, P. W.; Shannon, P. M.; Prodehl, C.

    2002-12-01

    The VARNET-96 seismic experiment acquired three seismic refraction/wide-angle reflection profiles in order to examine the crustal structure in the south-west of Ireland. 170 seismic stations were used on 300 recording sites. The shotpoint geometry was designed to allow for both in-line and off-line fan shot recordings on the three profiles. A total of 34 water shots was fired. Results from 3-D raytrace and inversion modelling illustrate the pervasive lateral heterogeneity of the study area south of the Shannon Estuary. Palaeozoic strata at the south coast are about 5-6 km thick associated with the sedimentary infill of the Munster and South Munster Basins. To the north, shallow upper crust in the vicinity of the Killarney-Mallow Fault Zone is followed by a 3-4 km thick sedimentary succession in the Dingle-Shannon Basin. A zone of high-velocity upper crust (6.4-6.6 km/s) beneath the South Munster Basin correlates with a gravity high between the Kenmare-Killarney and the Leinster Granite gravity lows. Other high-velocity zones were found beneath Dingle Bay and the Kenmare River region and may be associated with the deep traces of the Killarney-Mallow Fault Zone and the Cork-Kenmare Line. The 3-D velocity model was taken as a basis for the computation of PmP reflected arrivals from the crust-mantle boundary. The Moho depth varies from about 28-29 km at the south coast to about 32-33 km beneath the Dingle-Shannon Basin, the region where the 2-D inline model shows a south-dipping reflector in the upper mantle. Pervasive Variscan deformation appears to be confined to the sedimentary and upper crustal structure and has not deformed the entire crust supporting a thin-skinned tectonic model for Variscan deformation. Deep-crustal variations only occur where they can be correlated with major tectonic features such as the Caledonian Iapetus Suture near the Shannon Estuary. The shallowing of the Moho towards the coast may result from Mesozoic crustal extension in the adjacent

  5. BASIN STRUCTURE FROM TWO-DIMENSIONAL SEISMIC REFLECTION DATA, CRAZY MOUNTAINS BASIN, MONTANA

    SciTech Connect

    David J. Taylor

    2003-08-01

    Some 140 miles of multichannel seismic reflection data, acquired commercially in the 1970's, were reprocessed by the U.S. Geological Survey in late 2000 and early 2001 to interpret the subsurface geology of the Crazy Mountains Basin, an asymmetric Laramide foreland basin located in south-central Montana. The seismic data indicate that the northwestern basin margin is controlled by a thrust fault that places basement rocks over a thick (22,000 feet) sequence of Paleozoic and Mesozoic sedimentary rocks to the south. From the deep basin trough, Paleozoic through Tertiary rocks slope gently upward to the south and southeast. The northern boundary of the basin, which is not imaged well by the seismic data, appears to be folded over a basement ridge rather than being truncated against a fault plane. Seismic data along the basin margin to the south indicate that several fault controlled basement highs may have been created by thin-skinned tectonics where a series of shallow thrust faults cut Precambrian, Paleozoic, and early Mesozoic rocks, whereas, in contrast, Cretaceous and Tertiary strata are folded. The data are further interpreted to indicate that this fault-bounded asymmetric basin contains several structures that possibly could trap hydrocarbons, provided source rocks, reservoirs, and seals are present. In addition, faults in the deep basin trough may have created enough fracturing to enhance porosity, thus developing ''sweet spots'' for hydrocarbons in basin-centered continuous gas accumulations.

  6. 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

  7. 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

  8. High-resolution seismic reflection to delineate shallow gas in Eastern Kansas

    USGS Publications Warehouse

    Miller, R.D.; Watney, W.L.; Begay, D.K.; Xia, J.

    2000-01-01

    Unique amplitude characteristics of shallow gas sands within Pennsylvanian clastic-carbonate dominated sequences are discernible on high-resolution seismic reflection data in eastern Kansas. Upward grading sequences of sand into shale represent a potential gas reservoir with a low-impedence acoustic contrast at the base of the encasing layer. The gas sand and encasing shale, which define the gas reservoir studied here, are part of an erosional incised valley where about 30 m of carbonates and shale have been replaced by sandstone and shale confined to the incised valley. These consolidated geologic settings would normally possess high impedence gas sand reservoirs as defined by abrupt contacts between the gas sand and encasing shale. Based orr core and borehole logs, the gas sand studied here grades from sand into shale in a fashion analogous to that observed in classic low-impedance environments. Amplitude and phase characteristics of high-resolution seismic data across this approximately 400-m wide gas sand are indicative of a low-impedance reservoir. Shot gathers possess classic amplitude with offsett-dependent characteristics which are manifeted on the stacked section as "bright spots." Dominant Frequencies of around 120 Hz allow detection of several reflectors within the 30+ meters of sand/shale that make up this localized gas-rich incised valley fill. The gradational nature of the trapping mechanism observed in this gas reservoir would make detection with conventional seismic reflection methods unlikely.

  9. The Northern end of the Dead Sea Basin: Geometry from reflection seismic evidence

    USGS Publications Warehouse

    Al-Zoubi, A. S.; Heinrichs, T.; Qabbani, I.; ten Brink, U.S.

    2007-01-01

    Recently released reflection seismic lines from the Eastern side of the Jordan River north of the Dead Sea were interpreted by using borehole data and incorporated with the previously published seismic lines of the eastern side of the Jordan River. For the first time, the lines from the eastern side of the Jordan River were combined with the published reflection seismic lines from the western side of the Jordan River. In the complete cross sections, the inner deep basin is strongly asymmetric toward the Jericho Fault supporting the interpretation of this segment of the fault as the long-lived and presently active part of the Dead Sea Transform. There is no indication for a shift of the depocenter toward a hypothetical eastern major fault with time, as recently suggested. Rather, the north-eastern margin of the deep basin takes the form of a large flexure, modestly faulted. In the N-S-section along its depocenter, the floor of the basin at its northern end appears to deepen continuously by roughly 0.5??km over 10??km distance, without evidence of a transverse fault. The asymmetric and gently-dipping shape of the basin can be explained by models in which the basin is located outside the area of overlap between en-echelon strike-slip faults. ?? 2007 Elsevier B.V. All rights reserved.

  10. 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.

  11. A seismic reflection image for the base of a tectonic plate.

    PubMed

    Stern, T A; Henrys, S A; Okaya, D; Louie, J N; Savage, M K; Lamb, S; Sato, H; Sutherland, R; Iwasaki, T

    2015-02-01

    Plate tectonics successfully describes the surface of Earth as a mosaic of moving lithospheric plates. But it is not clear what happens at the base of the plates, the lithosphere-asthenosphere boundary (LAB). The LAB has been well imaged with converted teleseismic waves, whose 10-40-kilometre wavelength controls the structural resolution. Here we use explosion-generated seismic waves (of about 0.5-kilometre wavelength) to form a high-resolution image for the base of an oceanic plate that is subducting beneath North Island, New Zealand. Our 80-kilometre-wide image is based on P-wave reflections and shows an approximately 15° dipping, abrupt, seismic wave-speed transition (less than 1 kilometre thick) at a depth of about 100 kilometres. The boundary is parallel to the top of the plate and seismic attributes indicate a P-wave speed decrease of at least 8 ± 3 per cent across it. A parallel reflection event approximately 10 kilometres deeper shows that the decrease in P-wave speed is confined to a channel at the base of the plate, which we interpret as a sheared zone of ponded partial melts or volatiles. This is independent, high-resolution evidence for a low-viscosity channel at the LAB that decouples plates from mantle flow beneath, and allows plate tectonics to work.

  12. A seismic reflection image for the base of a tectonic plate.

    PubMed

    Stern, T A; Henrys, S A; Okaya, D; Louie, J N; Savage, M K; Lamb, S; Sato, H; Sutherland, R; Iwasaki, T

    2015-02-01

    Plate tectonics successfully describes the surface of Earth as a mosaic of moving lithospheric plates. But it is not clear what happens at the base of the plates, the lithosphere-asthenosphere boundary (LAB). The LAB has been well imaged with converted teleseismic waves, whose 10-40-kilometre wavelength controls the structural resolution. Here we use explosion-generated seismic waves (of about 0.5-kilometre wavelength) to form a high-resolution image for the base of an oceanic plate that is subducting beneath North Island, New Zealand. Our 80-kilometre-wide image is based on P-wave reflections and shows an approximately 15° dipping, abrupt, seismic wave-speed transition (less than 1 kilometre thick) at a depth of about 100 kilometres. The boundary is parallel to the top of the plate and seismic attributes indicate a P-wave speed decrease of at least 8 ± 3 per cent across it. A parallel reflection event approximately 10 kilometres deeper shows that the decrease in P-wave speed is confined to a channel at the base of the plate, which we interpret as a sheared zone of ponded partial melts or volatiles. This is independent, high-resolution evidence for a low-viscosity channel at the LAB that decouples plates from mantle flow beneath, and allows plate tectonics to work. PMID:25653000

  13. 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.

  14. Neotectonic analysis of upper klamath lake, oregon: New insights from seismic reflection data

    USGS Publications Warehouse

    Liberty, L.M.; Pratt, T.L.; Lyle, M.; Madin, I.P.

    2009-01-01

    We present marine high-resolution seismic reflection data from Upper Klamath Lake, Oregon, to discern the underlying structure and estimate Quaternary slip rates in this actively extending Basin and Range system. The sediment patterns and structures imaged on our seismic profiles reveal a complex geologic system that reflects a changing climate record, shallow water conditions, growth faulting, contrasting sediment sources, and high slip rates. We observe that Upper Klamath Lake is a sedimentsaturated environment, and sediment accumulation rates are therefore controlled by basin subsidence rather than sediment supply. Published slip rates for Holocene extension are greater than our determined late Quaternary slip rates, assuming reasonable rates of deposition. The apparent increased Holocene fault-slip rates may be in part an artifact of long recurrence intervals between major earthquakes, with recent seismicity accommodating long-term strain. The quantity of observed faults below the lake is at least an order of magnitude greater than those mapped outside the lake, suggesting that many hidden faults throughout the region may be unaccounted for when estimating Basin and Range extension rates. Copyright ?? 2009 The Geological Society of America. All rights reserved.

  15. Seismic reflection images of the Moho underlying melt sills at the East Pacific Rise.

    PubMed

    Singh, S C; Harding, A J; Kent, G M; Sinha, M C; Combier, V; Bazin, S; Tong, C H; Pye, J W; Barton, P J; Hobbs, R W; White, R S; Orcutt, J A

    2006-07-20

    The determination of melt distribution in the crust and the nature of the crust-mantle boundary (the 'Moho') is fundamental to the understanding of crustal accretion processes at oceanic spreading centres. Upper-crustal magma chambers have been imaged beneath fast- and intermediate-spreading centres but it has been difficult to image structures beneath these magma sills. Using three-dimensional seismic reflection images, here we report the presence of Moho reflections beneath a crustal magma chamber at the 9 degrees 03' N overlapping spreading centre, East Pacific Rise. Our observations highlight the formation of the Moho at zero-aged crust. Over a distance of less than 7 km along the ridge crest, a rapid increase in two-way travel time of seismic waves between the magma chamber and Moho reflections is observed, which we suggest is due to a melt anomaly in the lower crust. The amplitude versus offset variation of reflections from the magma chamber shows a coincident region of higher melt fraction overlying this anomalous region, supporting the conclusion of additional melt at depth.

  16. 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

  17. Crustal structure beneath the Rif Cordillera, North Morocco, from the RIFSIS wide-angle reflection seismic experiment

    NASA Astrophysics Data System (ADS)

    Gil, Alba; Gallart, Josep; Diaz, Jordi; Carbonell, Ramon; Torne, Montserrat; Levander, Alan; Harnafi, Mimoun

    2014-12-01

    different geodynamic models proposed since the late 1990s to account for the complex evolution of the Gibraltar Arc System lack definite constraints on the crustal structure of the Rif orogen. Here we present the first well-resolved P-wave velocity crustal models of the Rif Cordillera and its southern continuation toward the Atlas made using controlled-source seismic data. Two 300+ km-long wide-angle reflection profiles crossed the Rif along NS and EW trends. The profiles recorded simultaneously five land explosions of 1Tn each using ˜850 high frequency seismometers. The crustal structure revealed from 2-D forward modeling delineates a complex, laterally varying crustal structure below the Rif domains. The most surprising feature, seen on both profiles, is a ˜50 km deep crustal root localized beneath the External Rif. To the east, the crust thins rapidly by 20 km across the Nekkor fault, indicating that the fault is a crustal scale feature. On the NS profile the crust thins more gradually to 40 km thickness beneath Middle Atlas and 42 km beneath the Betics. These new seismic results are in overall agreement with regional trends of Bouguer gravity and are consistent with recent receiver function estimates of crustal thickness. The complex crustal structure of the Rif orogen in the Gibraltar Arc is a consequence of the Miocene collision between the Iberian and African plates. Both the abrupt change in crustal thickness at the Nekkor fault and the unexpectedly deep Rif crustal root can be attributed to interaction of the subducting Alboran slab with the North African passive margin at late Oligocene-early Miocene times.

  18. Digital seismic-reflection data from western Rhode Island Sound, 1980

    USGS Publications Warehouse

    McMullen, K.Y.; Poppe, L.J.; Soderberg, N.K.

    2009-01-01

    During 1980, the U.S. Geological Survey (USGS) conducted a seismic-reflection survey in western Rhode Island Sound aboard the Research Vessel Neecho. Data from this survey were recorded in analog form and archived at the USGS Woods Hole Science Center's Data Library. Due to recent interest in the geology of Rhode Island Sound and in an effort to make the data more readily accessible while preserving the original paper records, the seismic data from this cruise were scanned and converted to Tagged Image File Format (TIFF) images and SEG-Y data files. Navigation data were converted from U.S. Coast Guard Long Range Aids to Navigation (LORAN-C) time delays to latitudes and longitudes, which are available in Environmental Systems Research Institute, Inc. (ESRI) shapefile format and as eastings and northings in space-delimited text format.

  19. Recent faulting in western Nevada revealed by multi-scale seismic reflection

    USGS Publications Warehouse

    Frary, Roxanna N.; Louie, John N.; Stephenson, William J.; Odum, Jackson K.; Kell, Annie; Eisses, Amy; Kent, Graham M.; Driscoll, Neal W.; Karlin, Robert; Baskin, Robert L.; Pullammanappallil, Satish; Liberty, Lee M.

    2011-01-01

    The main goal of this study is to compare different reflection methods used to image subsurface structure within different physical environments in western Nevada. With all the methods employed, the primary goal is fault imaging for structural information toward geothermal exploration and seismic hazard estimation. We use seismic CHIRP (a swept-frequency marine acquisition system), weight drop (an accelerated hammer source), and two different vibroseis systems to characterize fault structure. We focused our efforts in the Reno metropolitan area and the area within and surrounding Pyramid Lake in northern Nevada. These different methods have provided valuable constraints on the fault geometry and activity, as well as associated fluid movement. These are critical in evaluating the potential for large earthquakes in these areas, and geothermal exploration possibilities near these structures.

  20. Recent faulting in western Nevada revealed by multi-scale seismic reflection

    USGS Publications Warehouse

    Frary, R.N.; Louie, J.N.; Stephenson, W.J.; Odum, J.K.; Kell, A.; Eisses, A.; Kent, G.M.; Driscoll, N.W.; Karlin, R.; Baskin, R.L.; Pullammanappallil, S.; Liberty, L.M.

    2011-01-01

    The main goal of this study is to compare different reflection methods used to image subsurface structure within different physical environments in western Nevada. With all the methods employed, the primary goal is fault imaging for structural information toward geothermal exploration and seismic hazard estimation. We use seismic CHIRP a swept-frequency marine acquisition system, weight drop an accelerated hammer source, and two different vibroseis systems to characterize fault structure. We focused our efforts in the Reno metropolitan area and the area within and surrounding Pyramid Lake in northern Nevada. These different methods have provided valuable constraints on the fault geometry and activity, as well as associated fluid movement. These are critical in evaluating the potential for large earthquakes in these areas, and geothermal exploration possibilities near these structures. ?? 2011 Society of Exploration Geophysicists.

  1. The tectonic puzzle of the Messina area (Southern Italy): Insights from new seismic reflection data

    PubMed Central

    Doglioni, Carlo; Ligi, Marco; Scrocca, Davide; Bigi, Sabina; Bortoluzzi, Giovanni; Carminati, Eugenio; Cuffaro, Marco; D'Oriano, Filippo; Forleo, Vittoria; Muccini, Filippo; Riguzzi, Federica

    2012-01-01

    The Messina Strait, that separates peninsular Italy from Sicily, is one of the most seismically active areas of the Mediterranean. The structure and seismotectonic setting of the region are poorly understood, although the area is highly populated and important infrastructures are planned there. New seismic reflection data have identified a number of faults, as well as a crustal scale NE-trending anticline few km north of the strait. These features are interpreted as due to active right-lateral transpression along the north-eastern Sicilian offshore, coexisting with extensional and right-lateral transtensional tectonics in the southern Messina Strait. This complex tectonic network appears to be controlled by independent and overlapping tectonic settings, due to the presence of a diffuse transfer zone between the SE-ward retreating Calabria subduction zone relative to slab advance in the western Sicilian side. PMID:23240075

  2. Crustal imaging using old industry seismic reflection data across the Coast Ranges and the Great Valley in Central Californa, USA

    NASA Astrophysics Data System (ADS)

    Gutjahr, Stine; Buske, Stefan

    2014-05-01

    We make use of the old industry seismic reflection data set SJ-6 in order to image middle and lower crustal structures beneath the California Coast Ranges and the Great Valley in Central California. For this purpose we use advanced imaging techniques in combination with a local 3D tomographic velocity model in order to map the reflectivity structure of the crust in particular across the San Andreas fault zone. The SJ-6 data set is so far the only active seismic data set crossing the San Andreas fault where the transitional fault segment approaches into the locked segment that last ruptured during the 1857 M7.9 Fort Tejon earthquake. This particular region shows major non volcanic tremor activity that is related directly to and at close range to the deep San Andreas fault zone. The SJ-6 data have been recorded along a crooked profile line that changes its predominating orientation from SW-NE to W-E after crossing the San Andreas fault surface trace. For this reason the imaging technique is implemented in 3D in order to account for the true source and receiver locations. We use a Prestack Kirchhoff type migration method called Fresnel Volume migration that spatializes the recorded reflection energy to the vicinity of the actual reflector elements according to the subsurface model. The results are high quality seismic images of improved signal- to noise ratio compared to standard Prestack Kirchhoff migration techniques. In order to extract reflection signals recorded from the deep crust we extend the record length of the data by adding zeros to the original field data and then crosscorrelate the latter with the source sweep signal. Several adjustments are applied to the migration and stacking schemes in order to obtain final 2D depth sections that represent the reflectivity structure directly beneath the crooked acquisition line. The most prominent feature southwest of the San Andreas fault is a bundle of strong northeast dipping reflectors within the lower crust of

  3. Investigating possible earthquake-related structure beneath the southern Illinois Basin from seismic reflection

    USGS Publications Warehouse

    McBride, J.H.; Sargent, M.L.; Potter, C.J.

    1997-01-01

    The relationship between seismicity and faults observed on seismic reflection profiles from the New Madrid Seismic Zone (NMSZ) in the central Mississippi Valley has been intensively studied for the past 15 years. However, comparable studies relating reflector sequences and earthquakes in the southern Illinois Basin, located northeast of the NMSZ, have not been undertaken. This study investigates the possible relationship between the source parameters of the November 9, 1968, magnitude (mbLg) 5.5 earthquake (a NNE-trending, previously interpreted west-dipping reverse fault at 21.2 ?? 5.4 km depth) in southern Illinois, and a zone of moderately dipping reflectors in crystalline (?) basement observed on a nearby high-quality seismic reflection profile. The 1968 event was the twentieth century's largest magnitude earthquake in the southern Illinois region. The zone of dipping basement reflectors is part of a broad prominent sequence, in which reflectors are subhorizontal or inclined with a strong west-dipping component, that appears beneath the Wabash Valley Fault System and extends to the west beneath the Illinois Basin where it steepens and plunges deeper into the crust over the 1968 hypocenter. More than one interpretation of the dipping reflector zone is admissible, including intrusion of igneous sills or thrust faults or both within a localized shear zone. The dipping reflector zone cannot be traced from the basement into the overlying Phanerozoic sedimentary section or associated directly with any particular previously mapped fault. If a tectonic interpretation is correct, the correlation between the 1968 reverse fault event and the reflector zone may mean that such quakes are nucleating along a blind compressional structure in the crystalline basement of southern Illinois, possibly analogous to the recent destructive southern California earthquakes.

  4. Integrated test plan for a shallow high resolution compressional seismic reflection demonstration

    SciTech Connect

    Narbutovskih, S.M.

    1994-08-04

    This integrated test plan describes the demonstration of a surface high resolution seismic reflection acquisition system using swept source technology. Compressional wave data will be collected along a previously occupied seismic line associated with a recent seismic survey north of the 300 Area. The swept source system will be employed testing two very different high resolution vibrator sources, one with a frequency range from 10 to 500 Hz and a smaller unit with a range from 20 to 1,500 Hz. This will enable a precursory comparison of two vibrator data sets with standard impulse data. The data will be evaluated for the presence of reflected energy, signal strength, frequency content and signal-to-noise ratio. If the water table can be distinguished from the Hanford/Ringold formation contact, then the high permeability Hanford-filled channels can be mapped. Next, if details on the configuration of the Ringold middle mud can be discerned, this will allow detecting fluid pathway through the mud and confirm the depositional nature of this unit. Finally, by mapping the extent of the lower confining mud unit, areas where the polluted unconfined and lower confined aquifers communicate might be located. Another source and acquisition method will also be tested by gathering data along the same seismic line. This system uses a lightweight source that produces a high-velocity shock wave that strikes the earth`s surface causing an acoustic wave to propagate downward. The acquisition method is nonconventional and is reported to eliminate obstructing noise such as groundroll and air blast. It is unexpected that this system will have the imaging ability of the vibratory systems. However it could prove to be economical for shallow applications when only compressional energy is needed.

  5. Possible modes of coral-reef development at Molokai, Hawaii, inferred from seismic-reflection profiling

    USGS Publications Warehouse

    Barnhardt, W.A.; Richmond, B.M.; Grossman, E.E.; Hart, P.

    2005-01-01

    High-resolution, seismic-reflection data elucidate the late Quaternary development of the largest coral-reef complex in the main Hawaiian Islands. Six acoustic facies were identified from reflection characteristics and lithosome geometry. An extensive, buried platform with uniformly low relief was traced beneath fore-reef and marginal shelf environments. This highly reflective surface dips gently seaward to ???130 m depth and locally crops out on the seafloor. It probably represents a wave-cut platform or ancient reef flat. We propose alternative evolutionary models, in which sea-level changes have modulated the development of reef systems, to explain the observed stratigraphic relationships. The primary difference between the models is the origin of the underlying antecedent surface, which arguably could have formed during either regression/lowstand or subsequent transgression. ?? Springer-Verlag 2005.

  6. New multichannel seismic reflection data along the eastern part of Lomonosov Ridge, Arctic Ocean

    NASA Astrophysics Data System (ADS)

    Sauermilch, Isabel; Jokat, Wilfried

    2015-04-01

    During the RV Polarstern cruise ARK XXVIII/4 in summer 2014, multichannel seismic reflection data were collected along the eastern part of the Lomonosov Ridge with the aim to provide an appropriate database for an IODP drilling proposal as well as to enhance the knowledge of sedimentary and tectonic processes in this area. Depending on the sea ice conditions and required resolution of the data, four survey set-ups with different streamer settings (300 m, 600 m, 3000 m) and airgun clusters (3, 4 G-Guns, 2 GI-Guns) were used. The dataset contains more than 3000 km of seismic profiles, including one transect along as well as several profiles across the ridge and two detailed networks close to the proposed drilling sites. An erosional unconformity, whose presence has been confirmed first by Moran et al. (2006) by scientific drilling at the Lomonosov Ridge in 2004, is visible in the entire seismic dataset as a continuous prominent reflector band. In the seismic data, this unconformity can be found over the entire length of the investigated ridge. Below, the strata show folded and slightly disturbed Mesozoic sediments, which are lying on top of the basement with intensive faulting. These structures might be created by two past rifting events which are significant for the evolution of the Arctic Ocean. The basement faults might be as old as the Mesozoic formation of the Amerasia Basin, and may have been overprinted during the subsequent unconformity-forming event that initiated the Amundsen Basin and the final ridge's break-up. Within the southern seismic survey additional data were gathered around the primary IODP drilling location. Aim of the drilling program is to reach layers of Oligocene and older sediment. Although, the Miocene sediment cover in this area has an almost constant thickness, at the northern end of a topographic channel the seismic data imaged a 500 m high slide scarp where the entire sedimentary column is exposed down to the proposed Oligocene. This

  7. Correlations of Scientific Drillcores and Seismic Reflection Data from Lake Malawi, Africa

    NASA Astrophysics Data System (ADS)

    Lyons, R. P.; Scholz, C. A.; King, J. W.; Johnson, T. C.; Cohen, A. S.

    2005-12-01

    Lake Malawi is one of the world's largest lakes, extending ~580km along the East Africa Rift System from 9-14 degrees S. The 700m deep lake has a permanently stratified water column that is anoxic below 250m. The water budget is dominated by evaporation and direct rainfall onto its surface; accordingly lake level is highly sensitive to minor shifts in climate. Three high-resolution, high-density single-channel seismic reflection surveys were collected on Lake Malawi between 1992 and 2001. These studies revealed a series of prograding lowstand delta deposits in the North Basin located in as much as 500m of water. The four deltas are define paleo-lakeshore geography and are located up to ~20km offshore today. Over the past ~1Ma, we observe evidence for a progression of major lowstand shorelines at 500m, 350m, 500m, and 200m below modern lake level. These back-stepping deltas document lake-level changes that occurred nearly instantaneously, suggesting large volumes of water were removed or added to the lake over time frames of a few hundred to a few thousand years. In February 2005, the Lake Malawi Scientific Drilling Project recovered 623m of continuous drillcore from Lake Malawi. Toplap and downlap surfaces from the lowstand deltas are correlated to the two drill site locations, one in the North Basin, and one in the Central Basin, using lithologic and physical properties logs from the recovered drillcores. At the North Basin drill site (site #2) in 359m water depth, we observe a sharp boundary ~37m below lake floor. This boundary demonstrates a transition from well sorted medium-grained sand to finely laminated muds. It correlates to the downlap surface of the 200m lowstand observed in the seismic reflection data set. Physical property logs such as magnetic susceptibility, GRAPE density, natural gamma, and p-wave velocity are posted on the seismic data and correlated to the lowstand surfaces. Using the density and p-wave velocity logs, synthetic seismograms are

  8. Seismic-reflection and ground penetrating radar for environmental site characterization. 1998 annual progress report

    SciTech Connect

    Steeples, D.W.; Plumb, R.

    1998-06-01

    'The project''s goals are threefold: (1) to examine the complementary site-characterization capabilities of modern, three-component shallow-seismic techniques and ground-penetrating radar (GPR) methods at depths ranging from 2 to 8 m at an existing test site; (2) to demonstrate the usefulness of the two methods when used in concert to characterize, in three-dimensions, the cone of depression of a pumping well, which will serve as a proxy site for fluid-flow at an actual, polluted site; and (3) to use the site as an outdoor mesoscale laboratory to validate existing three-dimensional ground-penetrating radar and seismic-reflection computer models developed at the Univ. of Kansas. To do this, useful seismic and GPR data are being collected along the same line(s) and within the same depth range. The principal investigators selected a site in central Kansas as a primary location and, although the site itself is not environmentally sensitive, the location chosen offers particularly useful attributes for this research and will serve as a proxy site for areas that are contaminated. As part of an effort to evaluate the strengths of each method, the authors will repeat the seismic and GPR surveys on a seasonal basis to establish how the complementary information obtained varies over time. Because the water table fluctuates at this site on a seasonal basis, variations in the two types of data over time also can be observed. Such noninvasive in-situ methods of identifying and characterizing the hydrologic flow regimes at contaminated sites support the prospect of developing effective, cost-conscious cleanup strategies in the near future. As of the end of May 1998, the project is on schedule. The first field work was conducted using both of the geophysical survey methods in October of 1997, and the second field survey employed both methods in March of 1998. One of the stated tasks is to reoccupy the same survey line on a quarterly basis for two years to examine change in both

  9. Robust, spatially scanning, open-path TDLAS hygrometer using retro-reflective foils for fast tomographic 2-D water vapour concentration field measurements

    NASA Astrophysics Data System (ADS)

    Seidel, A.; Wagner, S.; Dreizler, A.; Ebert, V.

    2014-12-01

    We have developed a fast, spatially direct scanning tunable diode laser absorption spectrometer (dTDLAS) that combines four polygon-mirror based scanning units with low-cost retro-reflective foils. With this instrument, tomographic measurements of absolute 2-D water vapour concentration profiles are possible without any calibration using a reference gas. A spatial area of 0.8 m × 0.8 m was covered, which allows for application in soil physics, where greenhouse gas emission from certain soil structures shall be monitored. The whole concentration field was measured with up to 2.5 Hz. In this paper, we present the setup and spectroscopic performance of the instrument regarding the influence of the polygon rotation speed and mode on the absorption signal. Homogeneous H2O distributions were measured and compared to a single channel, bi-static reference TDLAS spectrometer for validation of the instrument. Good accuracy and precision with errors of less than 6% of the absolute concentration and length and bandwidth normalized detection limits of up to 1.1 ppmv · m · √Hz-1 were achieved. The spectrometer is a robust and easy to set up instrument for tomographic reconstructions of 2-D-concentration fields that can be considered a good basis for future field measurements in environmental research.

  10. Robust, spatially scanning, open-path TDLAS hygrometer using retro-reflective foils for fast tomographic 2-D water vapor concentration field measurements

    NASA Astrophysics Data System (ADS)

    Seidel, A.; Wagner, S.; Dreizler, A.; Ebert, V.

    2015-05-01

    We have developed a fast, spatially scanning direct tunable diode laser absorption spectrometer (dTDLAS) that combines four polygon-mirror based scanning units with low-cost retro-reflective foils. With this instrument, tomographic measurements of absolute 2-D water vapor concentration profiles are possible without any calibration using a reference gas. A spatial area of 0.8 m x 0.8 m was covered, which allows for application in soil physics, where greenhouse gas emission from certain soil structures shall be monitored. The whole concentration field was measured with up to 2.5 Hz. In this paper, we present the setup and spectroscopic performance of the instrument regarding the influence of the polygon rotation speed and mode on the absorption signal. Homogeneous H2O distributions were measured and compared to a single channel, bi-static reference TDLAS spectrometer for validation of the instrument. Good accuracy and precision with errors of less than 6% of the absolute concentration and length and bandwidth normalized detection limits of up to 1.1 ppmv . m (Hz)-0.5 were achieved. The spectrometer is a robust and easy to set up instrument for tomographic reconstructions of 2-D-concentration fields that can be considered as a good basis for future field measurements in environmental research.

  11. Reprocessing of multi-channel seismic-reflection data collected in the Chukchi Sea

    USGS Publications Warehouse

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

    2001-01-01

    Contained on this set of two CD-ROMs are stacked and migrated multi-channel seismic-reflection data for 44 lines recorded in the Chukchi Sea, northern Alaska, by the United States Geological Survey in 1977, 1978, and 1980. All data were reprocessed by the USGS in 2000 using updated methods. The resulting final data have both increased temporal and spatial resolution thus providing improved interpretability. An added benefit of these CD-ROMs is that they are a more stable, long-term archival medium for the data.

  12. Seismic-reflection signature of cretaceous continental breakup on the wilkes land margin, antarctica.

    PubMed

    Eittreim, S L; Hampton, M A; Childs, J R

    1985-09-13

    The passive (rifted) continental margin of Wilkes Land, Antarctica, is characterized on seismic reflection records by (i) in the south, a block-faulted sequence of highly stratified continental beds overlain by two distinct unconformities; (ii) a transitional, greatly thinned continental crust overlain by material interpreted to be flood basalt; and (iii) in the north, oceanic crust with a boundary ridge at its edge. The Mohorovicić discontinuity can be followed across the continent-ocean boundary and shows a progressive thinning of continental crust to a minimum of 2.5 kilometers at its northern edge.

  13. Deep seismic reflection study of a passive margin, southeatern Gulf of Guinea

    SciTech Connect

    Rosendahl, B.R.; Groschel-Becker, H.; Meyers, J.; Kaczmarick, K. )

    1991-04-01

    A large grid of deep-imaging, marine seismic reflection data has been acquired in the Gulf of Guinea. The data show that the architecture of old Atlantic igneous crust and upper mantle is highly variable, particularly if reflection Moho is taken to be the base of the crust. Most abrupt changes in oceanic basement thickness and depth to Moho can be correlated with fracture-zone crossings, but significant variations can occur between fracture zones and along flow lines, especially near the ocean-continent transition. Reflection Moho is usually continuous from ocean to continent and does not display any systematic changes in character, continuity, or reflection time even beneath the innermost shelf areas. There are several varieties of intracrustal reflectors, including those that mark different levels within the oceanic gabbroic complex and events that diagonally link the top of oceanic seismic layer 2 and Moho. Different types of sub-Moho dipping reflections also are observed. Some are associated with fracture zones, some originate within continental crust and dip toward the ocean, dissecting Moho without offsetting it, and still others originate at the oceanic Moho and dip toward the continent. The transition from oceanic to continental crust is generally quite sharp north of lat 1{degree}S, but the exact nature of the transition ranges from rift-block geology to abrupt juxtapositions of oceanic and continental crustal rocks. South of about lat 1{degree}S, the transition to continental crust is more gradual, involving a progressive thickening of oceanic crust toward land. This difference may relate to the occurrence of much more oblique initial rifting north of 1{degree}S.

  14. Poisson's ratio model derived from P- and S-wave reflection seismic data at the CO2CRC Otway Project pilot site, Australia

    NASA Astrophysics Data System (ADS)

    Beilecke, Thies; Krawczyk, Charlotte M.; Tanner, David C.; Ziesch, Jennifer; Research Group Protect

    2014-05-01

    Compressional wave (P-wave) reflection seismic field measurements are a standard tool for subsurface exploration. 2-D seismic measurements are often used for overview measurements, but also as near-surface supplement to fill gaps that often exist in 3-D seismic data sets. Such supplementing 2-D measurements are typically simple with respect to field layout. This is an opportunity for the use of shear waves (S-waves). Within the last years, S-waves have become more and more important. One reason is that P- and S-waves are differently sensitive to fluids and pore fill so that the additional S-wave information can be used to enhance lithological studies. Another reason is that S-waves have the advantage of higher spatial resolution. Within the same signal bandwidth they typically have about half the wavelength of P-waves. In near-surface unconsolidated sediments they can even enhance the structural resolution by one order of magnitude. We make use of these capabilities within the PROTECT project. In addition to already existing 2-D P-wave data, we carried out a near surface 2-D S-wave field survey at the CO2CRC Otway Project pilot site, close to Warrnambool, Australia in November 2013. The combined analysis of P-wave and S-wave data is used to construct a Poisson's Ratio 2-D model down to roughly 600 m depth. The Poisson's ratio values along a 1 km long profile at the site are surprisingly high, ranging from 0.47 in the carbonate-dominated near surface to 0.4 at depth. In the literature, average lab measurements of 0.22 for unfissured carbonates and 0.37 for fissured examples have been reported. The high values that we found may indicate areas of rather unconsolidated or fractured material, or enhanced fluid contents, and will be subject of further studies. This work is integrated in a larger workflow towards prediction of CO2 leakage and monitoring strategies for subsurface storage in general. Acknowledgement: This work was sponsored in part by the Australian

  15. Application of stacking and inversion techniques to three-dimensional wide-angle reflection and refraction seismic data of the Eastern Alps

    NASA Astrophysics Data System (ADS)

    Behm, Michael; Brückl, Ewald; Chwatal, Werner; Thybo, Hans

    2007-07-01

    We present new methods for the interpretation of 3-D seismic wide-angle reflection and refraction data with application to data acquired during the experiments CELEBRATION, 2000 and ALP 2002 in the area of the Eastern Alps and their transition to the surrounding tectonic provinces (Bohemian Massif, Carpathians, Pannonian domain, Dinarides). Data was acquired on a net of arbitrarily oriented seismic lines by simultaneous recording on all lines of seismic waves from the shots, which allows 2-D and 3-D interpretations. Much (80%) of the data set consists of crossline traces. Low signal to noise (S/N) ratio in the area of the young orogens decreases the quality of travel time picks. In these seismically heterogeneous areas it is difficult to assign clearly defined arrivals to the seismic phases, in particular on crossline record sections. In order to enhance the S/N ratio, signal detection and stacking techniques have been applied to enhance the Pg-, Pn- and PmP phases. Further, inversion methods have been developed for the interpretation of WAR/R-data, based on automated 1-D inversion (Pg) and the application of the delay time concept (Pn). The results include a 3-D velocity model of the crust based on Pg waves, time and depth maps of the Moho and a Pn-velocity map. The models based on stacked data are robust and provide a larger coverage, than models based on travel time picks from single-fold (unstacked) traces, but have relatively low resolution, especially near the surface. They were used as the basis for constructing models with improved resolution by the inversion of picks from single-fold data. The results correlate well with geological structures and show new prominent features in the Eastern Alps area and their surrounds. The velocity distribution in the crust has strong lateral variations and the Moho in the investigation area appears to be fragmented into three parts.

  16. Subsurface Structure of the Suspicious Hsiaokangshan Fault in Southern Taiwan From Seismic Reflection Images and Core Borings

    NASA Astrophysics Data System (ADS)

    Fu, C.; Shih, R.; Wang, W.; Lee, Y.; Chen, W.; Liu, Y.

    2008-12-01

    The Hsiaokangshan fault in southern Taiwan was suspected as an active fault, which strikes in NS direction for about 8 km long. Existence of the Hsiaokangshan fault was originally proposed from its geomorphic characteristics, several lineation structures were found situated at west of the Dakangshan anticline. From evidences of regional seismic reflection surveys, gravity anomaly and borehole lithology, the Dakangshan anticline was thought formed by intrusion of a mud diaper. Since the area nearby the Hsiaokangshan fault was over developed, barely any geologic evidence was able to find to verify the fault. Currently, several boreholes were drilled by the Central Geological Survey of Taiwan to across one of the lineation structures, the borehole records show that the shallowest bedrock (Pleistocene mud formation) was reached at 36m deep and deepened westward. The Holocene marine environment sediments were laid down above the unconformity. In this paper, we will show our studies of the fault by using shallow seismic reflection method, core borings and regional subsurface seismic reflection images. To collect the shallow seismic reflection data, we used 96-channel data acquisition system to collect the seismic data and used a mini impactor, JMS Mini65 to generate seismic wave. To image the shallow unconformity, we deployed the geophone groups at every 5 m and set the minimum nearest offset at 5m. Although there is no reflection signal appeared in the mud formation, we are able to trace the unconformity and image the reflections of marine environmental sediments down to 1000m deep. Combining the shallow seismic reflection images, regional subsurface structures, and core borings, we are able to illustrate the detailed structures across the suspicious Hsiaokangshan fault and clarify the relationship between those lineation structures and the Dakangshan anticline.

  17. Crustal Deformation Styles Along the Reprocessed Deep Seismic Reflection Transect of the Central Iberian Zone (Iberian Peninsula)

    NASA Astrophysics Data System (ADS)

    Ehsan, Siddique Akhtar; Carbonell, Ramon; Ayarza, Puy; Marti, David; Martinez-Poyatos, David; Simancas, Jose Fernando; Azor, Antonio; Marzan, Ignacio; Mansilla, Luis; Perez-Estaun, Andres

    2014-05-01

    The multichannel normal incidence deep seismic reflection profile ALCUDIA was acquired in summer 2007 and is 230 km long. This transect samples an intracontinental Variscan orogenic crust going across, from north to south, the major crustal domain (the Central Iberian Zone) and a suture zone with the Ossa-Morena Zone (the Central Unit) that build up the southwestern part of the Iberian Peninsula basement. The multichannel deep seismic high resolution (60-90 fold) profile images 20 s (TWTT), about 70 km depth. The reassessment of this data aims to provide better structural constraints on the shallow and deep structures. The ALCUDIA seismic image shows an upper crust c. 13 km thick decoupled from the comparatively reflective lower crust. The shallow reflectivity of the upper crust can be correlated with surface geological features mapped in the field whereas the deep reflectivity suggests imbricate thrust systems and listric extensional faults. The reflectivity of the mid-lower crust is relatively continuous, revealing high amplitude, and horizontal to arcuate reflection events delineating boudinage shaped geometries. A transpressional flower structure can be interpreted from the seismic image which involves a subcrustal mantle wedge. The ALCUDIA seismic image reveals a laminated c. 1.5 km thick, subhorizontal to flat Moho indicating an average crustal thickness of 31-33 km. The seismic signature of the Moho varies along the transect being highly reflective beneath the Central Iberian Zone (CIZ) and discontinuous and diffuse below the Ossa-Morena Zone (OMZ). The gravity response across the ALCUDIA transect suggests relatively high density bodies in the mid-lower crust of the southern half of the transect. The seismic results suggest two major horizontal limits/discontinuities, a horizontal discontinuity at c. 13-15 km (the Conrad discontinuity) and the Moho discontinuity located at a depth of c. 31 km.

  18. 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).

  19. Seismic reflection imaging of two megathrust shear zones in the northern Cascadia subduction zone.

    PubMed

    Calvert, Andrew J

    2004-03-11

    At convergent continental margins, the relative motion between the subducting oceanic plate and the overriding continent is usually accommodated by movement along a single, thin interface known as a megathrust. Great thrust earthquakes occur on the shallow part of this interface where the two plates are locked together. Earthquakes of lower magnitude occur within the underlying oceanic plate, and have been linked to geochemical dehydration reactions caused by the plate's descent. Here I present deep seismic reflection data from the northern Cascadia subduction zone that show that the inter-plate boundary is up to 16 km thick and comprises two megathrust shear zones that bound a >5-km-thick, approximately 110-km-wide region of imbricated crustal rocks. Earthquakes within the subducting plate occur predominantly in two geographic bands where the dip of the plate is inferred to increase as it is forced around the edges of the imbricated inter-plate boundary zone. This implies that seismicity in the subducting slab is controlled primarily by deformation in the upper part of the plate. Slip on the shallower megathrust shear zone, which may occur by aseismic slow slip, will transport crustal rocks into the upper mantle above the subducting oceanic plate and may, in part, provide an explanation for the unusually low seismic wave speeds that are observed there.

  20. Fault Architecture of the Salton Sea through multi-scale Seismic Reflection Surveys

    NASA Astrophysics Data System (ADS)

    Kell, A. M.; Driscoll, N. W.; Kent, G.; Harding, A. J.; Baskin, R. L.

    2011-12-01

    Two sets of seismic reflection images collected in the Salton Sea, California in May 2010 and April 2011 highlight a longstanding episode of extension-related deformation within the Salton Sea pull-apart system. These data are part of a continued multi-scale network of seismic studies of the faults within the Salton Trough. In 2010, we collected ~350 line-km of data using a 75-m-long, 24-channel streamer and a 1.6kJ "sparker" source fired at 1.2 sec intervals. These images document a series of south-east dipping normal faults that are related to the current pull-apart geometry; this configuration appears to persist for only the past 20-40 ka. Newly acquired low fold images (~150 line-km) collected using a 300-m-long, 48-channel streamer and a Generator Injector (GI) airgun source firing at 1 min intervals show that the same structures seen in the higher resolution (2010) data as well as high-resolution seismic CHIRP images collected in 2007 (Brothers et al., 2009, 2010) continue to depths of >2.5 km. From this deeper imagery, we infer that the structures seen in the very shallow CHIRP data are through-going to seismogenic depths and play a dominant role in strain partitioning from the Imperial Fault to the San Andreas Fault through the Brawley Seismic Zone. The 2011 reflection and refraction data are part of a larger collaborative project involving Cal Tech, Virginia Tech, the USGS, University of Nevada, Reno and Scripps Institution of Oceanography. Within this study we seek to understand the mechanisms of how crustal thinning and rifting develops. The fault dip imaged at both scales is ~50-60° and show vertical offsets (sub-meter to tens of meters) distinguishable to the limits of our imaging resolution. These multi-scale data offer a unique opportunity to calculate the timing and mode of motion in the most actively deforming portion of the Salton Trough. The insights gained through these data allow a greater understanding of the tectonics and seismic hazards

  1. Thrust fault growth within accretionary wedges: New Insights from 3D seismic reflection data

    NASA Astrophysics Data System (ADS)

    Orme, H.; Bell, R. E.; Jackson, C. A. L.

    2015-12-01

    The shallow parts of subduction megathrust faults are typically thought to be aseismic and incapable of propagating seismic rupture. The 2011 Tohoku-Oki earthquake, however, ruptured all the way to the trench, proving that in some locations rupture can propagate through the accretionary wedge. An improved understanding of the structural character and physical properties of accretionary wedges is therefore crucial to begin to assess why such anomalously shallow seismic rupture occurs. Despite its importance, we know surprisingly little regarding the 3D geometry and kinematics of thrust network development in accretionary prisms, largely due to a lack of 3D seismic reflection data providing high-resolution, 3D images of entire networks. Thus our current understanding is largely underpinned by observations from analogue and numerical modelling, with limited observational data from natural examples. In this contribution we use PSDM, 3D seismic reflection data from the Nankai margin (3D Muroto dataset, available from the UTIG Academic Seismic Portal, Marine Geoscience Data System) to examine how imbricate thrust fault networks evolve during accretionary wedge growth. Previous studies have reported en-echelon thrust fault geometries from the NW part of the dataset, and have related this complex structure to seamount subduction. We unravel the evolution of faults within the protothrust and imbricate thrust zones by interpreting multiple horizons across faults and measuring fault displacement and fold amplitude along-strike; by doing this, we are able to investigate the three dimensional accrual of strain. We document a number of local displacement minima along-strike of faults, suggesting that, the protothrust and imbricate thrusts developed from the linkage of smaller, previously isolated fault segments. We also demonstrate that the majority of faults grew upward from the décollement, although there is some evidence for downward fault propagation. Our observations

  2. 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.

  3. Interpretation of shallow crustal structure of the Imperial Valley, California, from seismic reflection profiles

    SciTech Connect

    Severson, L.K.

    1987-05-01

    Eight seismic reflection profiles (285 km total length) from the Imperial Valley, California, were provided to CALCRUST for reprocessing and interpretation. Two profiles were located along the western margin of the valley, five profiles were situated along the eastern margin and one traversed the deepest portion of the basin. These data reveal that the central basin contains a wedge of highly faulted sediments that thins to the east. Most of the faulting is strike-slip but there is evidence for block rotations on the scale of 5 to 10 kilometers within the Brawley Seismic Zone. These lines provide insight into the nature of the east and west edges of the Imperial Valley. The basement at the northwestern margin of the valley, to the north of the Superstition Hills, has been normal-faulted and blocks of basement material have ''calved'' into the trough. A blanket of sediments has been deposited on this margin. To the south of the Superstition Hills and Superstition Mountain, the top of the basement is a detachment surface that dips gently into the basin. This margin is also covered by a thick sequence sediments. The basement of the eastern margin consists of metamorphic rocks of the upper plate of the Chocolate Mountain Thrust system underlain by the Orocopia Schist. These rocks dip to the southeast and extend westward to the Sand Hills Fault but do not appear to cross it. Thus, the Sand Hills Fault is interpreted to be the southern extension of the San Andreas Fault. North of the Sand Hills Fault the East Highline Canal seismicity lineament is associated with a strike-slip fault and is probably linked to the Sand Hills Fault. Six geothermal areas crossed by these lines, in agreement with previous studies of geothermal reservoirs, are associated with ''faded'' zones, Bouguer gravity and heat flow maxima, and with higher seismic velocities than surrounding terranes.

  4. Paleozoic continent-ocean transition in the ouachita mountains imaged from PASSCAL wide-angle seismic reflection-refraction data

    SciTech Connect

    Keller, G.R. ); Braile, L.W. ); McMechan, G.A.; Chang, Wen-Fong ); Thomas, W.A. ); Harder, S.H. ); Jardine, W.G. )

    1989-02-01

    A wide-angle reflection-reflection experiment, sponsored by the Program for Array Seismic Studies of the Continental Lithosphere (PASSCAL), was conducted in the Ouachita Mountains area of southwestern Arkansas and northwestern Louisiana. This experimental employed 400 state-of-the-art seismic recorders and overlapped the southern one-third of the COCORP (Consortium for Continental Reflection Profiling) deep seismic reflection profile in the area. A wide variety of data processing and interpretation techniques was employed to derive an Earth model from these data. The model depicts a preserved early Paleozoic continental margin buried beneath allochthonous Paleozoic strata and younger sedimentary rocks. The southern part of the model indicates the presence of oceanic or highly extended continental crust overlain by about 15 km of mostly Paleozoic sedimentary rock. These results are consistent with little if any shortening of crystalline continental crust during the Ouachita orogeny.

  5. Seismic tomography and ambient noise reflection interferometry on Reykjanes, SW Iceland

    NASA Astrophysics Data System (ADS)

    Jousset, Philippe; Verdel, Arie; Ágústsson, Kristján; Blanck, Hanna; Franke, Steven; Metz, Malte; Ryberg, Trond; Weemstra, Cornelius; Hersir, Gylfi; Bruhn, David

    2016-04-01

    Recent advances in volcano-seismology and seismic noise interferometry have introduced new processing techniques for assessing subsurface structures and controls on fluid flow in geothermal systems. We present tomographic results obtained from seismic data recorded around geothermal reservoirs located both on-land Reykjanes, SW-Iceland and offshore along Reykjanes Ridge. We gathered records from a network of 234 seismic stations (including 24 Ocean Bottom Seismometers) deployed between April 2014 and August 2015. In order to determine the orientation of the OBS stations, we used Rayleigh waves planar particle motions from large magnitude earthquakes. This method proved suitable using the on-land stations: orientations determined using this method with the orientations measured using a giro-compass agreed. We obtain 3D velocity images from two fundamentally different tomography methods. First, we used local earthquakes to perform travel time tomography. The processing includes first arrival picking of P- and S- phases using an automatic detection and picking technique based on Akaike Information Criteria. We locate earthquakes by using a non-linear localization technique, as a priori information for deriving a 1D velocity model. We then computed 3D velocity models of velocities by joint inversion of each earthquake's location and lateral velocity anomalies with respect to the 1D model. Our models confirms previous models obtained in the area, with enhanced details. Second, we performed ambient noise cross-correlation techniques in order to derive an S velocity model, especially where earthquakes did not occur. Cross-correlation techniques involve the computation of cross- correlation between seismic records, from which Green's functions are estimated. Surface wave inversion of the Green's functions allows derivation of an S wave velocity model. Noise correlation theory furthermore shows that zero-offset P-wave reflectivity at selected station locations can be

  6. Strike fault links mountain building from top to deep: evidence from the deep seismic reflection profiles

    NASA Astrophysics Data System (ADS)

    Gao, R.; Wang, H.; Lu, Z.; Wang, C.; Klemperer, S. L.; Yin, A.

    2013-12-01

    The formation of mountains was influenced by large-scale strike-slip faults in Tibet. At the south and north borders of the Tibetan Plateau, the Karakorum and Kunlun strike-slip faults cut the Himalayas and the Kunlun Mountains crust respectively. Based on the detection results of deep seismic reflection profiles, we report the structures of these strike-slip faults and shear deformation depth. The Karakoram fault and Indus-Yarlung suture (IYS) zone are two important structures in southwest and south Tibet, associated with the collision between India and Eurasia. SinoProbe has acquired two deep seismic reflection profiles with 210 km length. The northwestern profile spans 120 km and crosses the southeast part of the Karakoram fault where dextrally sheared mylonite and mylonitized gneiss-granite are exposed along the fault. The southeastern profile spans 90km and crosses the ophiolite belt of the western IYS. Our preliminary images show: Moho reflections appear at ~ 24 s (TWT) beneath both lines. Flower-structures imaged at the Karakoram fault zone are suggestive of strike-slip structure. There are significant differences in lower-crustal structure between the two lines. Many north and south dipping reflections in the lower crust form v-shaped structures along the northwest line. On the southeastern line, there are many north-dipping but few south-dipping reflections in the lower crust. Kunlun seismic profile crosses the active left-slip Kunlun fault, which is ~1000-km long and was inferred to merge downward with a continental subduction zone. The fault was initiated at 15-8 Ma, moved at a rate of 5-16 mm/year, and has a total slip of 65-120 km. The results of our seismic-reflection study across northeastern Tibet show that the actively deforming middle Tibetan crust is dominated by discrete sub-horizontal simple-shear zones that terminate the subvertical, left-slip Kunlun fault above. The flat shear zones appear to act as roof and floor thrusts of large duplex

  7. Comparison of the bedrock depth from array measurements of Rayleigh waves associated with microtremor and seismic profile obtained the Seismic Reflection Data, Eskisehir Basin, Turkey

    NASA Astrophysics Data System (ADS)

    Tün, Muammer; Karabulut, Savaş; Özel, Oğuz

    2015-04-01

    Ground motion estimation for future earthquakes is one of the most challenging problems in seismology and earthquake engineering. The bedrock depth has a considerable seismic risk for the urban area of Eskişehir. In this study, multiple station microtremor measurement methods which are more practical, non-distructive, fast and economical compared to seismic reflection method were implemented. These method using microtremor recordings have become a very useful data for microzonation studies because of their simple acquisition and analysis. Extensive ambient noise measurements were performed in the basin of Eskisehir from June 2010 to spring 2012. We use data recorded by a broadband seismometer and digitizer CMG-6TD, Guralp seismometer. Some of the measurement locations, the CMG-6TD sensor was located into 30 cm-deep holes in the ground to avoid strongly wind-generated, long-period noise. Dominant frequency (f), bed-rock depth (h) and shear-wave velocity (Vs) were determined from Spatial Autocorrelation (SPAC) methods. With the SPAC Method, it is possible to constrain the velocity structure underlying the site using microtremor array measurements. The results obtained were compared to the 96-channel seismic reflection data with explosive energy source. Several seismic reflection surveys with P-Gun seismic source have been performed on the same place with array measurements. We used two types of seismic sources: 36 cartridge Gun. Shot interval was 10 meters, group interval (one geophone per group, 48 geophones in total) was 10 meters, near offset was 10 meters, far offset was 480 meters, CDP interval was 5 meters. We adapted the 'Off-End Spread' technique while using the Gun. Reflection images within the sedimentary section correlate well with the velocity structure obtained from SPAC.

  8. Active Tectonics of off-Hokuriku, Central Japan, by two ships seismic reflection profiling

    NASA Astrophysics Data System (ADS)

    Kato, Naoko; Sato, Hiroshi; Ishiyama, Tatsuya; Abe, Susumu; Shiraishi, Kazuya

    2015-04-01

    Along the southern to eastern margin of the Sea of Japan, active faults are densely distributed. These submarine active faults produced tsunami disasters, such as 1983 Nihonkai-chubu earthquake (M7.7) and 1993 Hokkaido Nansei-oki earthquake (M7.8). To estimate tsunami hazards, we performed deep seismic reflection profiling to obtain the information of tsunami source faults, off-Hokuriku area in the central part of Honshu, Japan. The survey is carried out as a part of research project named "the integrated research project on seismic and tsunami hazards around the Sea of Japan" funded by MEXT. To obtain long offset data in busy marine activity area, we used two vessels; a gun-ship with 3020 cu. inch air-gun and a cable-ship with a 2-km-long, streamer cable with 156 channels and 480 cu. inch air-gun. Common-midpoint reflection data were acquired using two ships at 4 km offset. The survey area consists of stretched continental crust associated with rifting and opening of the Sea of Japan in early Miocene and is marked by densely distributed syn-rift normal faults. Fault reactivation of normal faults as reverse faults is common. Two phases of fault reactivation are identified from the seismic sections after termination of opening of the Sea of Japan. One is the late Miocene NS trending shortening deformation. This is produced by NS-trending convergence of the Shikoku basin (15 Ma), which belongs to the Philippine Sea plate (PHS) to SW Japan at Nankai trough (Kimura et al., 2005). After the initiation of the subduction of PHS at Nankai trough, the strong shortening deformation is terminated and the fold-and-thrust belt was unconformably covered by sub-horizontal Pliocene sediments. Some horizons of unconformities represent multiple events of shortening driven from the subduction interface. Some normal faults reactivated as active strike-slip and reverse faults in Quaternary. Well observed example is the 2007 Noto peninsula earthquake (M6.8). The 2007 Noto peninsula

  9. Geostatistics applied to cross-well reflection seismic for imaging carbonate aquifers

    NASA Astrophysics Data System (ADS)

    Parra, Jorge; Emery, Xavier

    2013-05-01

    Cross-well seismic reflection data, acquired from a carbonate aquifer at Port Mayaca test site near the eastern boundary of Lake Okeechobee in Martin County, Florida, are used to delineate flow units in the region intercepted by two wells. The interwell impedance determined by inversion from the seismic reflection data allows us to visualize the major boundaries between the hydraulic units. The hydraulic (flow) unit properties are based on the integration of well logs and the carbonate structure, which consists of isolated vuggy carbonate units and interconnected vug systems within the carbonate matrix. The vuggy and matrix porosity logs based on Formation Micro-Imager (FMI) data provide information about highly permeable conduits at well locations. The integration of the inverted impedance and well logs using geostatistics helps us to assess the resolution of the cross-well seismic method for detecting conduits and to determine whether these conduits are continuous or discontinuous between wells. A productive water zone of the aquifer outlined by the well logs was selected for analysis and interpretation. The ELAN (Elemental Log Analysis) porosity from two wells was selected as primary data and the reflection seismic-based impedance as secondary data. The direct and cross variograms along the vertical wells capture nested structures associated with periodic carbonate units, which correspond to connected flow units between the wells. Alternatively, the horizontal variogram of impedance (secondary data) provides scale lengths that correspond to irregular boundary shapes of flow units. The ELAN porosity image obtained by cokriging exhibits three similar flow units at different depths. These units are thin conduits developed in the first well and, at about the middle of the interwell separation region, these conduits connect to thicker flow units that are intercepted by the second well. In addition, a high impedance zone (low porosity) at a depth of about 275 m, after

  10. 3-Component Reflection Seismic Survey Across the Seismogenic Coupling Zone in Chile (Project TIPTEQ)

    NASA Astrophysics Data System (ADS)

    Micksch, U.; Gross, K.; Buske, S.; Krawczyk, C. M.; Stiller, M.; Wigger, P.; Araneda, M.; Bataille, K.; Bribach, J.; Lüth, S.; Mechie, J.; Schulze, A.; Shapiro, S. A.; Ziegenhagen, T.

    2005-12-01

    The TIPTEQ project (from The Incoming Plate to mega-Thrust EarthQuake processes) studies processes which generate mega-thrust earthquakes at convergent plate margins, with the Chilean subduction zone as natural laboratory. The seismogenic coupling zones at convergent margin plate interfaces harbour some 90% of the global seismicity, and in the case of Chile, the hypocenter of the largest historically recorded earthquake in 1960 (Mw = 9.5). The rupture started at 38° S with a hypocentral depth of some 30 km below the continental forearc and continued towards the south for approximately 1000 km. The active seismic experiment component of TIPTEQ crosses the 1960 earthquake hypocenter. The survey consists of a 95 km long near-vertical reflection seismic profile shot in January 2005. 180 three-component geophones were deployed along an 18 km long spread, moving 4.5 km in a daily roll-along. Explosive shots, with a spacing of 1.5 km, allow an up to 8-fold CDP coverage. The W-E trending line runs across part of the Central Valley and continues over the coastal cordillera towards the Pacific. The seismic line shows good reflectivity and internal structures of the accretionary wedge and the plate interface. The down-going plate is clearly visible at c. 8 s TWT near the coast, reaching 17 s TWT at the eastern end of the profile. Two more experiment configurations were applied in addition: An expanding spread profiling setup aims at the down-dip limit of the seismogenic coupling zone at 30-50 km depth to image the hypocenter of the 1960 earthquake in more detail (10-fold coverage); a SH experiment configuration (1-fold coverage) served as a pilot study to test SH-wave generation in a crustal regime. Using the three component data, S-wave images could yield an improved picture of the petrophysical contrasts within the subduction zone. We present the results from poststack- and prestack-migration of the near-vertical reflection experiment, as well as a first interpretation of

  11. A simple deep-towed vertical array for high-resolution reflection seismic profiling

    NASA Astrophysics Data System (ADS)

    Herber, R.; Nuppenau, V.; Weigel, W.; Wong, H. K.

    1986-06-01

    A simple, low cost, deep-towed system for high-resolution reflection seismic profiling is described. It consists of a vertical array with two hydrophones having a separation of 2.2 m and rigidly mounted onto streamlined tow bodies. Improvement of the signal-to-noise ratio is attained by simple stacking of the hydrophone outputs after signal conditioning and travel time corrections. The suppression of side echoes and surface reflections is achieved by an analog procedure which in effect improves the directional characteristics of the array. A circuit for automatic gain control is included to enhance weak signals as well as to suppress ringing. Results in Kiel Bay and over the crest of the Jan Mayen Ridge (northern Atlantic) suggest that this simple vertical array may supplement air gun systems better than conventional, surface pinger-type equipment.

  12. Interferometric techniques in seismic reflection imaging and the principle of stationary phase

    NASA Astrophysics Data System (ADS)

    Snieder, R.

    2005-05-01

    Interferometric imaging where the Green's function is constructed using the correlation of complex wavefields recorded at two receivers is a rapidly emerging field. The methodology has been justified based on assumptions of equiparitioning of the normal modes of the system, as well as on various versions of the representation theorem applied to time-reversed waves. I will present another point of view that is based on stationary phase arguments. This complementary formulation of interferometric imaging gives insight in the physics of the emergence of the Green's function, and of the limitations that are encountered when applying this technique to data. Issues that will be covered are the relation between ensemble averaging and time averaging, and interferometric imaging of reflected waves. This example is of particular interest for exploration seisology since it shows that interferometric imaging may introduce spurious multiple reflections. I will show that these "multiples" have a clear physical interpretation and do not form a problem in seismic imaging.

  13. High-resolution seismic reflection survey at the Manson crater, Iowa

    NASA Technical Reports Server (NTRS)

    Keiswetter, D. A.; Black, R.; Steeples, D. W.; Anderson, R. R.

    1993-01-01

    Approximately 17.4 km of high-resolution reflection data were acquired along an east-west radius of the Manson Impact Structure (MIS) to delineate the shallow (upper 300 m) subsurface structural configuration. The geometry of the shallow structure is poorly known due to a 30-90 m thick Pleistocene till cover. The resolution of the new seismic data is roughly 5-10 times that of existing Vibroseis data. Data quality varies rapidly along the line from exceptional to poor, due primarily to velocity variations associated with the geological complexity of the area. Preliminary results indicate subsurface structural blocks previously envisioned to be several hundreds of meters in size are actually an order of magnitude smaller and more complex. A seismogram-by-seismogram analysis is necessary to confidently identify intricate stratigraphic and structural relationships seen on preliminary CDP sections, as numerous faults, diffractions, and complicated reflection patterns create potential pitfalls.

  14. Seismic Shear Wave Reflection Imaging at the Former Fort Ord, Monterey, California

    USGS Publications Warehouse

    Haines, Seth S.; Burton, Bethany L.; Hunter, Lewis E.

    2007-01-01

    At the former Fort Ord in Monterey County, California, contamination threatens an aquifer that provides drinking water for local communities. Assessment and remediation require accurate hydrological modeling, which in turn require a thorough understanding of aquifer stratigraphy. In order to help guide remediation efforts at the site, the U.S. Geological Survey, in cooperation with the U.S. Army Corps of Engineers, has undertaken seismic reflection surveys, testing compressional (P) and horizontally polarized shear (SH) waves. Sledgehammer-source SH data show reflections from interfaces up to approximately 60 m deep, which correspond with the major boundaries between aquifers and aquitards. In contrast, P-wave data show only the reflection from the water table at approximately 30 m depth. We collected SH data along two transects and processed these data to produce reflection images. The interpreted SH-wave images agree with available well information, constrain the geology for ground-water models, and provide guidance for future geophysical studies. These favorable results demonstrate the effectiveness of SH reflection methods for imaging unconsolidated aquifer layers at the former Fort Ord and at other sites with similar geologic conditions.

  15. The Crustal Structure of the Central Iberian Zone form the ALCUDIA Deep Seismic Reflection transect.

    NASA Astrophysics Data System (ADS)

    Martí, D.

    2009-04-01

    The ALCUDIA transect is a 250 km long, vertical incidence Vibroseis seismic reflection profile acquired in 2007. It extends IBERSEIS transect to the N and NE imaging from within the Ossa Morena Zone (OMZ) to the Central Iberian Zone (CIZ) from 20 km south of Fuenteovejuna in the S to Toledo in the N. The southern part of the transect samples the suture zone between the OMZ and the CIZ. It continues in a N-NE direction crossing the Pedroches batholith and a series of relatively long wavelength synclinal structures limited by sub-vertical and relatively narrow folds (e.g. the Almaden syncline, the Alcudia anticline). Lower Paleozoic quartzites and slates cover most of these synclynal structures. Farther to the N, the profile crosses several major faults system (e.g Santa Elena and Toledo) . The acquisition parameters, 35 m station spacing, 70 m VP spacing resulted in a 60-90 fold high resolution seismic reflection image. A 20 s long Vibroseis sweep with frequencies between 8-120 Hz was recorded by a 400 station recording cable a long a 14 km long split spread configuration. The new processing sequence significantly increased the signal-to-noise ratio. It includes: crooked line geometry, geometrical divergence corrections, elevation statics, surface-wave attenuation, surface consistent zero-phase spiking deconvolution, time-variant band pass filtering., refraction and residual static corrections velocity analysis, NMO, surface consistent amplitude balancing, CMP stacking F-X deconvolution. The seismic image reveals the geometry of the suture between the OMZ and the CIZ. This is a reworked transpression suture (the Badajoz-Cordoba Sherar zone) includes the Central Unit (CU) as a north dipping wedge structure limited by two bands of reflectors that reach the middle crust (5 s twtt). This CU includes amphibolites with some oceanic affinity, orthogneisses, paragneisses, schists and minor amounts of peridotites. To the north the upper crust shows a moderate reflectivity

  16. Orogenic structure of the Eastern Alps, Europe, from TRANSALP deep seismic reflection profiling

    NASA Astrophysics Data System (ADS)

    Lüschen, Ewald; Lammerer, Bernd; Gebrande, Helmut; Millahn, Karl; Nicolich, Rinaldo; Transalp Working Group

    2004-09-01

    The TRANSALP Group, comprising of partner institutions from Italy, Austria and Germany, acquired data on a 340 km long deep seismic reflection line crossing the Eastern Alps between Munich and Venice. Although the field work was split into four campaigns, between fall 1998 and summer 2001, the project gathered for the first time a continuous profile across the Alps using consistent field acquisition and data processing parameters. These sections span the orogen itself, at its broadest width, as well as the editor Fred Davey and the two adjacent basins. Vibroseis and explosion data, complementary in their depth penetration and resolution characteristics, were obtained along with wide-angle and teleseismic data. The profile shows a bi-vergent asymmetric structure of the crust beneath the Alpine axis which reaches a maximum thickness of 55 km, and 80-100 km long transcrustal ramps, the southward dipping 'Sub-Tauern-Ramp' and the northward-dipping 'Sub-Dolomites-Ramp'. Strongly reflective patterns of these ramps can be traced towards the north to the Inn Valley and towards the south to the Valsugana thrust belt, both of which show enhanced seismicity in the brittle upper crust. The seismic sections do not reveal any direct evidence for the presence of the Periadriatic Fault system, the presumed equivalent to the Insubric Line in the Western Alps. According to our new evolutionary model, the Sub-Tauern-Ramp is linked at depth with remnants of the subducted Penninic Ocean. The 'crocodile'-type model describes an upper/lower crustal decoupling and wedging of both the European and the Adriatic-African continents.

  17. High resolution seismic imaging of Rainier Mesa using surface reflection and surface to tunnel tomography

    SciTech Connect

    Majer, E.L.; Johnson, L.R.; Karageorgi, E.K.; Peterson, J.E.

    1994-06-01

    In the interpretation of seismic data to infer properties of an explosion source, it is necessary to account for wave propagation effects. In order to understand and remove these propagation effects, it is necessary to have a model. An open question concerning this matter is the detail and accuracy which must be present in the velocity model in order to produce reliable estimates in the estimated source properties. While it would appear that the reliability of the results would be directly related to the accuracy of the velocity and density models used in the interpretation, it may be that certain deficiencies in these models can be compensated by the and amount of seismic data which is used in the inversion. The NPE provided an opportunity to test questions of this sort. In August 1993, two high resolution seismic experiments were performed in N-Tunnel and on the surface of Rainier Mesa above it. The first involved a surface-to-tunnel imaging experiment with sources on the surface and receivers in tunnel U12n.23 about 88 meters west of the NPE. It was possible to estimate the apparent average velocity between the tunnel and the surface. In a separate experiment, a high resolution reflection experiment was performed in order to image the lithology in Rainier Mesa. Good quality, broad band, reflections were obtained from depths extending into the Paleozoic basement. A high velocity layer near the surface is underlain by a thick section of low velocity material, providing a nonuniform but low average velocity between the depth of the NPE and the surface.

  18. Processing and interpretation of seismic reflection data from Ogaden basin, Ethiopia

    SciTech Connect

    Tadesse, K.; Ebinger, C.J.; Clark, R.A.

    1996-12-31

    The Ogaden basin is believed to be an extensional basin created during the early rifting of Gondwana and the development of the western Indian Ocean. Preliminary studies conducted by various oil companies and national geoscientists suggest that the area is prospective for hydrocarbon accumulation. Prior to these studies, however, very little was known of the surface geology in this area and virtually nothing was known of the subsurface. The objectives of the study were to implement state-of-the-art seismic and gravity data processing and interpretation techniques in order to identify structural and/or stratigraphic trap sequences and indicate their significance in the hydrocarbon exploration of the basin. In this study, high resolution multi-channel reflection seismic data, acquired in 1993 from the Ogaden Basin, are used. The data were acquired for Hunt Oil Company using Vibroseis as an energy source. Various data enhancement techniques were applied to these data in order to produce an interpretable final seismic section for the identification of possible hydrocarbon habitats. These included discrimination and filtering of coherent noise from the signal, enhancing, focussing of the identified reflectors and static corrections. Statics solutions from shallow wells and automatic refraction statics were compared, with the best results obtained when automatic refraction solutions were applied. Our study has revealed various reflection horizons that can be potential stratigraphic traps at pinch outs and may be porous strata which are terminated by lateral transitions or interconnected lines of either elastic sediments or carbonates. We discuss these results in the light of gravity modelling designed to estimate maximum sediment thickness along the line.

  19. Processing and interpretation of seismic reflection data from Ogaden basin, Ethiopia

    SciTech Connect

    Tadesse, K.; Ebinger, C.J.; Clark, R.A. )

    1996-01-01

    The Ogaden basin is believed to be an extensional basin created during the early rifting of Gondwana and the development of the western Indian Ocean. Preliminary studies conducted by various oil companies and national geoscientists suggest that the area is prospective for hydrocarbon accumulation. Prior to these studies, however, very little was known of the surface geology in this area and virtually nothing was known of the subsurface. The objectives of the study were to implement state-of-the-art seismic and gravity data processing and interpretation techniques in order to identify structural and/or stratigraphic trap sequences and indicate their significance in the hydrocarbon exploration of the basin. In this study, high resolution multi-channel reflection seismic data, acquired in 1993 from the Ogaden Basin, are used. The data were acquired for Hunt Oil Company using Vibroseis as an energy source. Various data enhancement techniques were applied to these data in order to produce an interpretable final seismic section for the identification of possible hydrocarbon habitats. These included discrimination and filtering of coherent noise from the signal, enhancing, focussing of the identified reflectors and static corrections. Statics solutions from shallow wells and automatic refraction statics were compared, with the best results obtained when automatic refraction solutions were applied. Our study has revealed various reflection horizons that can be potential stratigraphic traps at pinch outs and may be porous strata which are terminated by lateral transitions or interconnected lines of either elastic sediments or carbonates. We discuss these results in the light of gravity modelling designed to estimate maximum sediment thickness along the line.

  20. Pressure-dependent seismic reflection amplitude changes in crystalline crust: lessons learned at the Continental Deep Drilling Site (KTB)

    NASA Astrophysics Data System (ADS)

    Beilecke, T.; Bram, K.; Buske, S.

    2010-01-01

    We conducted an active seismic experiment aimed at measuring changes in seismic reflection amplitudes as a consequence of fresh water injection and corresponding pressure changes at the German Continental Deep Drilling site (KTB). The injection took place at the bottom of the 4-km-deep pilot borehole in the SE2 fault zone in crystalline rock units between the springs of 2004 and 2005. Prior to the experiment, theoretical calculations indicated a possible increase in the compressional wave reflection coefficient as a result of an injection-induced reduction of the seismic velocities within the fault zone. Despite good repeatability of the emitted source signals, the experiment suffered from missing the clear reflection signals expected from the fault zone with regard to seismic data from past experiments. Applying various data-processing steps did not enhance the signals enough to obtain clear reflections or even pressure-dependent reflection amplitude changes. The signal-to-noise ratio remains smaller than the effects under observation. Provided that reflections are present in the data, the error bar of the recorded signals is of the order of 100 per cent. Therefore, we conclude that the experiment was not successful in seismically measuring pressure variations. However, important lessons for land seismic time-lapse measurements in crystalline environments have been learned: (i) The source should be capable of emitting frequencies below 30 Hz. (ii) The detector array setup proved to be partly questionable because in a scattering environment like the crystalline rocks at the KTB site, the incidence of a plane wave precondition might be violated for high-frequency signals. (iii) Near-surface variations of elastic properties likely influence seismic monitoring. (iv) Using a step function, that is a first-order pressure discontinuity, to model the subsurface pressure build-up, is very likely too simple an approach.

  1. Shear-wave reflection seismics as bridge between georadar and deeper subsurface surveying - a case study for quick-clay landslides in Sweden

    NASA Astrophysics Data System (ADS)

    Krawczyk, Charlotte M.; Polom, Ulrich; Malehmir, Alireza; Bastani, Mehrdad

    2013-04-01

    As part of a joint project studying clay-related landslides in Nordic countries, we successfully tested the use of shear-wave reflection seismics to survey shallow structures that are known to be related to quick-clay landslide processes. Co-sponsored via the Society of Exploration Geophysicists (SEG) program 'Geoscientists Without Borders (GWB)', several international groups apply a suite of applied geophysical and geotechnical methods to understand structural and physical conditions and the conditioning of this type of liquefaction. For this purpose, three 2D profiles were recorded in Frastad, southern Sweden, above the main slide plane area. Using a 120 m long streamer of 120 SH-geophones at 1 m spacing, and the ELVIS micro-vibrator as source, shear-wave data of very high quality were gathered, allowing a vertical resolution of 1 m and less. The longest profile along a paved road shows clear internal structuring of the up to 50 m thick marine sediments as well as strong undulations of top basement underneath. Different sedimentary sequences can be distinguished, and the quick clay sequence is interpreted in 15-20 m depth, which correlates well with the height of the most recent scarp. The sedimentary shear wave velocities suggest extremely low values of 100-120 m/s, which geotechnically prohibits building areas. In addition, test measurements on a stubble field showed the first time that the suppression of Love waves is not only restricted to paved surfaces and may also be achieved if reflection contrasts and low dispersion allow a suitable data processing. This opens new possibilities for a wide range of applications and specialized equipment adaptions with respect to reflection seismic surveying. In addition, the gap between structural data from georadar and P-wave seismic can be closed.

  2. Integrated Reflection Seismic Monitoring and Reservoir Modeling for Geologic CO2 Sequestration

    SciTech Connect

    John Rogers

    2011-12-31

    The US DOE/NETL CCS MVA program funded a project with Fusion Petroleum Technologies Inc. (now SIGMA) to model the proof of concept of using sparse seismic data in the monitoring of CO{sub 2} injected into saline aquifers. The goal of the project was to develop and demonstrate an active source reflection seismic imaging strategy based on deployment of spatially sparse surface seismic arrays. The primary objective was to test the feasibility of sparse seismic array systems to monitor the CO{sub 2} plume migration injected into deep saline aquifers. The USDOE/RMOTC Teapot Dome (Wyoming) 3D seismic and reservoir data targeting the Crow Mountain formation was used as a realistic proxy to evaluate the feasibility of the proposed methodology. Though the RMOTC field has been well studied, the Crow Mountain as a saline aquifer has not been studied previously as a CO{sub 2} sequestration (storage) candidate reservoir. A full reprocessing of the seismic data from field tapes that included prestack time migration (PSTM) followed by prestack depth migration (PSDM) was performed. A baseline reservoir model was generated from the new imaging results that characterized the faults and horizon surfaces of the Crow Mountain reservoir. The 3D interpretation was integrated with the petrophysical data from available wells and incorporated into a geocellular model. The reservoir structure used in the geocellular model was developed using advanced inversion technologies including Fusion's ThinMAN{trademark} broadband spectral inversion. Seal failure risk was assessed using Fusion's proprietary GEOPRESS{trademark} pore pressure and fracture pressure prediction technology. CO{sub 2} injection was simulated into the Crow Mountain with a commercial reservoir simulator. Approximately 1.2MM tons of CO{sub 2} was simulated to be injected into the Crow Mountain reservoir over 30 years and subsequently let 'soak' in the reservoir for 970 years. The relatively small plume developed from this

  3. AnisWave 2D

    2004-08-01

    AnisWave2D is a 2D finite-difference code for a simulating seismic wave propagation in fully anisotropic materials. The code is implemented to run in parallel over multiple processors and is fully portable. A mesh refinement algorithm has been utilized to allow the grid-spacing to be tailored to the velocity model, avoiding the over-sampling of high-velocity materials that usually occurs in fixed-grid schemes.

  4. Volcano-Tectonic History of the Island of Montserrat, West Indies, From Seismic Reflection Profiles

    NASA Astrophysics Data System (ADS)

    Kenedi, C. L.; Sparks, S. J.; Dean, S.; Hammond, J.; Malin, P. E.; Minshull, T.; Paulatto, M.; Peirce, C.; Ryan, G.; Shalev, E.; Voight, B.

    2008-12-01

    Seismic reflection profiles provide a cross-sectional view of crustal layers and thus details about local sedimentation rates, chronology, and depositional materials. Based on seismic profiles collected as part of the SEA-CALIPSO seismic experiment, we apply this method to interpreting the volcanic and local tectonic history of the island of Montserrat, in the Lesser Antilles arc. In December 2007, the vessel RRS James Cook towed a tuned, 2600 cubic inch, 8-airgun array along encircling and radial lines around Montserrat. The airguns fired every 60 sec (approx. every 140 m) at a pressure of 2000 psi. The ship also towed a 600 m streamer consisting of 48 hydrophone channels. Over a period of 77 hours, the hydrophones recorded a total of 4414 shots. Onboard the ship, data were stacked to produce 26 seismic profiles. The profiles vary in length up to 15 km and allow interpretation up to a depth of approx. 2.5 km. The profiles from east of Montserrat reveal fans of coarse-grained debris flows and submarine pyroclastic flows that derive from both the older volcanic centers and the active Soufriere Hills Volcano (SHV). The flows form tapering wedges that have been overlain by younger sea-floor sediments. Older ( > 1 Ma) sedimentary rocks, containing multiple reflective layers, deflect downwards towards and beneath Montserrat, forming a moat into which the debris and pyroclastic flows have deposited. A sub-sediment volcanic basement is present offshore at approximately 1.5 km depth. Offshore on the west side of the island the prominent Belham valley fault can be traced trending NW. The new data suggest that the fault line has been active in the recent geological past; the fault has offset submarine deposits offshore and tectonic blocks onshore (Garibaldi Hill, St. Georges Hill, Roches Bluff), has caused the down-warping of ocean sediments on the east side of the island, and likely influenced the location of domes and feeding conduits at and adjacent to the SHV. Montserrat

  5. Marvin Spur - Lomonosov Ridge Relationships Based on Reflection Seismic Profiling Near the North Pole

    NASA Astrophysics Data System (ADS)

    Lebedeva-Ivanova, N. N.; Gee, D. G.; Langinen, A. E.

    2006-12-01

    Reflection seismic profiles acquired from the drifting ice-station NP-28 in 1988-1989 and other neighboring profiles provide evidence of the character and origin of the Marvin Spur and Lomonosov Ridge. The NP-28 seismic images of the sedimentary successions capping the Ridge can be correlated with those of the AWI- 91090 profile, which was calibrated by the ACEX drilling at 88º N. Along the AWI line, the most prominent reflector package marks the base of the Cenozoic (Paleocene) section and its angular unconformity to underlying Mesozoic strata. The NP-28 ice-station crossed the Lomonosov Ridge three times, near the North Pole. In each profile, the Marvin Spur is also imaged, in one case below the floor of the Makarov Basin and in the two others as a narrow ridge parallel to the Lomonosov Ridge. A prominent composite reflector occurs at a few hundred meters depth in the sedimentary successions on both the Lomonosov Ridge and the Marvin Spur, underlain disconformably by less regular reflectors, dipping towards the Amerasian Basin. Correlation of both the seismic images and velocities (Vp) with the AWI-91090 profile suggests that this composite NP-28 reflector marks the base of the Cenozoic. The reflection profiles across the Lomonosov Ridge and Marvin Spur are similar; probably the Spur is a narrow sliver of thinned continental crust that was rifted off the Ridge. Towards the Greenland margin, the trough between the Lomonosov Ridge and the Marvin Spur narrows and the two appear to merge. Towards the Siberian margin, the trough widens and the crest of the Marvin Spur sinks beneath the Makarov Basin. It has been also imaged further along strike beneath this basin in the TRA(b)-90 profile (Langinen et al, ICAM-IV in press), where the composite reflector marks a clear unconformity capping the Spur and adjacent older successions. These lines of seismic evidence need to be tested by piston coring and drilling. They emphasize the importance of Cenozoic faulting for

  6. Wide-angle seismic reflection constraints on the lithosphere of the Variscan Belt on SW- Iberia.

    NASA Astrophysics Data System (ADS)

    Palomeras, I.; Ayarza, P.; Afonso, J.; Carbonell, R.; Martinez-Poyatos, D.; Simancas, F.; Gonzalez-Lodeiro, F.; Perez-Estaun, A.

    2008-12-01

    Two wide-angle seismic transects (A and B) were acquired across the Variscan Belt on SW-Iberia. They run across three major tectonic units in the area: South Portuguese Zone, Ossa-Morena Zone, and Central Iberian Zone. Transect A is approximately 300 km long and coincides with the course of the IBERSEIS deep seismic reflection profile. Transect B is 220 km long and is located to the SE of Transect A. The close station spacing along the transects (400 m on Transect A and 150 m on Transect B) allows to identify well defined arrivals within the upper, middle and lower crust as well as in the upper mantle. Resulting velocity models were obtained by forward modeling. The most remarkable features on these models are high velocity areas at mid crustal depths (15-20 km) with velocities in the range of 6.8-7.1 km/s. The Moho discontinuity is located at 31-33 km depth, characterized by a velocity jump from 7.1 km/s to 8.2 km/s. Shot gathers show also a sharp mantle reflection at offsets larger than 180 km which has been modeled as a fairly continuous feature with a velocity increase from 8.2 km/s to 8.4 km/s at 65-67 km depth. The nature of this boundary in still uncertain but it likely reflects a lithological change with subtle velocity/density contrasts, only visible at relatively high incidence angles. The velocity depth function for the crust in the area does not fit any of the standard average crustal velocity models due to the anomalous mid crustal velocities.

  7. Reflection seismic imaging of a hydraulically conductive fracture zone in a high noise area, Forsmark, Sweden

    NASA Astrophysics Data System (ADS)

    Juhlin, C.; Stephens, M. B.; Cosma, C.

    2007-05-01

    High resolution reflection seismic methods have proven to be useful tools for locating fracture zones in crystalline rock. Siting of potential high-level nuclear waste repositories is a particularly important application of these methods. By using small explosive sources (15-75 grams), high resolution images of the sub-surface have been obtained in the depth range 100 m to 2 km in Sweden, Canada and elsewhere. Although ambient noise conditions in areas such as the Fennoscandian and Canadian shields are generally low, industrial noise can be high in some areas, particularly at potential sites suitable for repositories, since these are often close to existing infrastructure. In addition, the presence of this infrastructure limits the choice of sources available to the geophysicist. Forsmark, located about 140 km north of Stockholm, is one such potential site where reflection seismics have been carried out. Existing infrastructure includes nuclear reactors for power generation and a low- level waste repository. In the vicinity of the reactors, it was not possible to use an explosive source due to permitting restrictions. Instead, a VIBSIST system consisting of a tractor mounted hydraulic hammer was used in the vicinity of the reactors. By repeatedly hitting the pavement, without breaking it, at predefined sweeps and then stacking the signals, shot records comparable to explosive data could be generated. These shot records were then processed using standard methods to produce stacked sections along 3 profiles within the reactor area. Clear reflections are seen in the uppermost 600 m along 3 of these profiles. Correlation of crossing profiles shows that the strongest reflection (B8) is generated by a gently east-southeast dipping interface. Prior to construction of the reactors, several boreholes were drilled to investigate the bedrock in the area. One of these boreholes was located close to where two of the profiles cross. Projection of the B8 reflection into the

  8. A Three-Dimensional Reflection Seismic Investigation of Seismogenic Zone, in the eastern Nankai accretionary prism

    NASA Astrophysics Data System (ADS)

    Ike, T.; Tokuyama, H.; Ashi, J.; Kuramoto, S.; Matsushima, J.; Yokota, T.; Pascal, G.; Lallemant, S.

    2001-12-01

    We carried out a 3-D reflection seismic survey [SFJ-KAIKO] in the eastern Nankai accretionary prism from June to July 2000. The crustal deformation of the eastern Nankai accretionary prism affected by a nearby collision between the Izu-Bonin arc and the central Japan. Several active fault systems were described by many high-resolution seismic data, and proposed that the Tokai and Kodaiba fault systems were derived from a decollement plane. The main objective of our experiment was to image the plate boundary and identify the up-dip limit of seismogenic zone. The 3-D survey covers 45km long and 5km wide area with 51 seismic lines, located about 50km southwest from Omaezaki. We applied the non-iterative Kirchhoff pre-stack time migration method (Matsushima et.,al 2001) with stacking velocity analysis to our 3-D data. The processed 3-D data gives us a significantly clear image of the thrust faults and the relationship between sediment deformation and thrust activity. A preliminary 3-D interpretation was conducted and leaded the following results.1) The Tokai and Kodaiba thrusts are clearly imaged as out-of-sequence thrusts. 2) Both thrusts are active fault that revealed by the structure of deformed sediments near seafloor. 3) A strong and low frequency reflector can be traced in the entire profile that should be a decollement plane. Tokai and Kodaiba fault systems merged to the decollement plane at same depth. The contact area of the thrust faults and the decollement may be suggesting the up-dip limit of seismogenic zone of the eastern Nankai accretionary prism .The 3-D image will contribute to reveal the mechanism of disastrous earthquakes in the Tokai area.

  9. 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.

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

    SciTech Connect

    Brocher, T.M.; Fuis, G.S.; Fisher, M.A.; Plafker, G.; Moses, M.J.; Taber, J.J. ); Christensen, N.I. . Dept. of Earth and Atmospheric Sciences)

    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 laboratory 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.

  11. A New Model for the Seismogenic Behavior of Subducted Seamounts Based on Multi-Channel Seismic Reflection and GPS Data Collected in Central Ecuador.

    NASA Astrophysics Data System (ADS)

    Collot, J. Y.; Sanclemente, E.; Ribodetti, A.; Chlieh, M.; Jarrin, P.; Nocquet, J. M.

    2014-12-01

    The relationship between subducted seamounts and earthquakes has remained controversial. Although seamounts are expected to subduct aseismically, they have also been considered to generate large earthquakes. Based on a remarkable case study in Central Ecuador, we show that a subducted seamount can lock the shallow megathrust along its trailing flank preparing for a possible shallow (<20 km), large magnitude (Mw ~7.0) tsunamogenic earthquake, while its leading flank keeps partially creeping along with frequent earthquake swarms and slow slip events (SSE). The erosive Ecuador convergent margin, which basement consists of high velocity (Vp=5 km/s) mafic rocks, is underthrust eastward at 4.7 cm/yr by the rugged Carnegie Ridge. As modeled by global positioning system (GPS) measurements acquired as close as 35 km from the trench axis at La Plata Island, the Central Ecuador margin figures a creeping subduction segment with the exception of a 50 km-diameter locked patch centered over the uplifted La Plata Island region. The 3D geometry of the plate-interface megathrust obtained from 2D-PreStack-Depth-Migration of a grid of multi-channel seismic reflection data collected near La Plata Island reveals a collection of closely spaced peaks that belong to a broad (55 X ~50 km) low-drag shape subducted seamount. The clear spatial correlation between the seamount and the highly coupled zone denotes the seamount as the main cause for both the locked patch and the island uplift. The absence of a seismically imaged subduction channel, the highly jagged seamount-trailing flank and the stiffness of the oceanic margin are found to be the principal long-term characteristics associated with shallow locking of the megathrust. Moreover, the combination of our structural interpretation and inter-seismic coupling map with 14-years of relocated seismicity, and the 2010 SSE and its associated microseismicity allow to propose a new model for the seismogenic behavior of subducting seamounts.

  12. Seismic reflection images beneath Puget Sound, western Washington State: The Puget Lowland thrust sheet hypothesis

    USGS Publications Warehouse

    Pratt, T.L.; Johnson, S.; Potter, C.; Stephenson, W.; Finn, C.

    1997-01-01

    Seismic reflection data show that the densely populated Puget Lowland of western Washington state is underlain by subhorizontal Paleogene and Neogene sedimentary rocks deformed by west and northwest trending faults and folds. From south to north beneath the Lowland, features seen on the seismic data include: the horizontally-stratified, 3.5 km thick Tacoma sedimentary basin; the Seattle uplift with south dipping (???20??) strata on its south flank and steeply (50?? to 90??) north dipping strata and the west-trending Seattle fault on its north flank; the 7.5 km thick, northward-thinning Seattle sedimentary basin; the antiformal Kingston arch; and the northwest trending, transpressional Southern Whidbey Island fault zone (SWIF). Interpreting the uplifts as fault-bend and fault-propagation folds leads to the hypothesis that the Puget Lowland lies on a north directed thrust sheet. The base of the thrust sheet may lie at 14 to 20 km depth within or at the base of a thick block of basaltic Crescent Formation; its edges may be right-lateral strike-slip faults along the base of the Cascade Range on the east and the Olympic Mountains on the west. Our model suggests that the Seattle fault has a long-term slip rate of about 0.25 mm/year and is large enough to generate a M7.6 to 7.7 earthquake.

  13. Tectonic evolution of the Salton Sea inferred from seismic reflection data

    USGS Publications Warehouse

    Brothers, D.S.; Driscoll, N.W.; Kent, G.M.; Harding, A.J.; Babcock, J.M.; Baskin, R.L.

    2009-01-01

    Oblique extension across strike-slip faults causes subsidence and leads to the formation of pull-apart basins such as the Salton Sea in southern California. The formation of these basins has generally been studied using laboratory experiments or numerical models. Here we combine seismic reflection data and geological observations from the Salton Sea to understand the evolution of this nascent pull-apart basin. Our data reveal the presence of a northeast-trending hinge zone that separates the sea into northern and southern sub-basins. Differential subsidence (10 mm yr 1) in the southern sub-basin suggests the existence of northwest-dipping basin-bounding faults near the southern shoreline, which may control the spatial distribution of young volcanism. Rotated and truncated strata north of the hinge zone suggest that the onset of extension associated with this pull-apart basin began after 0.5 million years ago. We suggest that slip is partitioned spatially and temporally into vertical and horizontal domains in the Salton Sea. In contrast to previous models based on historical seismicity patterns, the rapid subsidence and fault architecture that we document in the southern part of the sea are consistent with experimental models for pull-apart basins. ?? 2009 Macmillan Publishers Limited.

  14. Seismic reflection survey at Ayer Hangat site to investigate shallow subsurface structures

    NASA Astrophysics Data System (ADS)

    Khalil, Amin E.; Nawawi, Mohd; Kamel, Rami

    2016-01-01

    Ayer Hangat site is located in the island of Langkawi, northwest Malaysia. The site is characterized by the presence of hot spring. This hot spring is believed to be related to granitic intrusion nearby. Hence the present work is focusing on defining the shallow subsurface structures that control the migration of hot water to the surface. Seismic reflection method is used to achieve the goal of the present study. Forty three shot points were used with an offset of 5m of the nearest geophone. The shot-points interval is set to 1m. Seismograms were recorded on 24 channel TERRALOC instrument. The Geophone interval used was 1m. Conventional seismic data processing scheme was adopted. However, due to the fact that TERRALOC produce SEG2 data files, a script based on Obspy was written and used to convert to SEG-Y format. Afterwards, analyses were carried out using SU Package. The processed data is used to develop a model for the subsurface controlling structures. Such model will help in the understanding of the geothermal hot spring system in the area.

  15. Two dimensional restoration of seismic reflection profiles from Mozambique: technique for assessing rift extension histories

    SciTech Connect

    Iliffe, J.E.; Debuyl, M.; Kendall, C.G.St.C.; Lerche, I.

    1986-05-01

    Seismic reflection data from offshore Mozambique between longitudes 25/sup 0/ and 26/sup 0/ and latitudes 34/sup 0/ and 35/sup 0/ reveals a V-shaped rift, the apex of which points northward, toward the coast. This study retraces the rift's extensional history by geometric reconstruction of seismic profiles, selected perpendicular to tectonic strike. Depth conversions are performed, followed by bed length and volume balancing to test the interpretations and calculate a total extension value for the extension factor. The sediments are then backstripped in sedimentary sequences, restoring the increments of throw on faults accordingly. After each sequence is removed, the sediments are decompacted in an attempt to recover the original volume prior to the sequence deposition. The extension factor is again calculated. This process is repeated down the sequences until the result is the pre-rift state of the basin. This analysis results in an extension estimate for each sequence-time increment, as a percentage of the total extension. From this method, a detailed crustal extension history is deduced, which, when coupled to the thermal history from subsidence backstripping and paleoheatflow studies, could be used in the basin analysis assessment of the oil potential of this and other rifts.

  16. 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.

  17. Prestack reverse time migration for 3D marine reflection seismic data

    SciTech Connect

    Jang, Seonghyung; Kim, Taeyoun

    2015-03-10

    Prestack reverse time migration (RTM) is a method for imaging the subsurface using the inner product of wavefield extrapolation in shot domain and in receiver domain. It is well known that RTM is better for preserving amplitudes and phases than other prestack migrations. Since 3D seismic data is huge data volume and it needs heavy computing works, it requires parallel computing in order to have a meaningful depth image of the 3D subsurface. We implemented a parallelized version of 3D RTM for prestack depth migration. The results of numerical example for 3D SEG/EAGE salt model showed good agreement with the original geological model. We applied RTM to offshore 3D seismic reflection data. The study area is 12 × 25 km with 120 survey lines. Shot and receiver spacing is 25 m and 12.5 m. The line spacing is 100 m. Shot gathers were preprocessed to enhance signal to noise ratio and velocity model was calculated from conventional stack velocity. Both of them were used to obtain 3D image using RTM. The results show reasonable subsurface image.

  18. A low-frequency asymptotic model of seismic reflection from a high-permeability layer

    SciTech Connect

    Silin, Dmitriy; Goloshubin, Gennady

    2009-03-01

    Analysis of compression wave propagation through a high-permeability layer in a homogeneous poroelastic medium predicts a peak of reflection in the low-frequency end of the spectrum. An explicit formula expresses the resonant frequency through the elastic moduli of the solid skeleton, the permeability of the reservoir rock, the fluid viscosity and compressibility, and the reservoir thickness. This result is obtained through a low-frequency asymptotic analysis of the Biot's model of poroelasticity. A new physical interpretation of some coefficients of the classical poroelasticity is a result of the derivation of the main equations from the Hooke's law, momentum and mass balance equations, and the Darcy's law. The velocity of wave propagation, the attenuation factor, and the wave number, are expressed in the form of power series with respect to a small dimensionless parameter. The latter is equal to the product of the kinematic reservoir fluid mobility, an imaginary unit, and the frequency of the signal. Retaining only the leading terms of the series leads to explicit and relatively simple expressions for the reflection and transmission coefficients for a planar wave crossing an interface between two permeable media, as well as wave reflection from a thin highly-permeable layer (a lens). The practical implications of the theory developed here are seismic modeling, inversion, and attribute analysis.

  19. Seismic reflection data support episodic and simultaneous growth of the Tibetan Plateau since 25 Myr.

    PubMed

    Jiang, Xiao-Dian; Li, Zheng-Xiang

    2014-01-01

    The spectacular topography of the Tibetan Plateau is the result of collision between India and Eurasia over some 50 Myr, but how the plateau grew to its present size remains a topic of debate. Work along its eastern margin suggests a two-stage uplift (thus growth of the plateau) since 30-25 Myr. Here we report high-resolution seismic reflection and drill core results from the southern Tarim Basin that indicate a similar pattern for the northern margin of the plateau. The data suggest that uplift in northern Tibet started at ~23 Myr from near sea level, with the first episode finished by ~10 Myr, followed by a post-5-Myr episode of rapid uplift along the present plateau margin. The growth of the Tibetan Plateau after the Eocene thus appears to have been episodic in nature, and near-synchronous along both eastern and northern margins. PMID:25391269

  20. 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.

  1. 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.

  2. Seismic reflection data support episodic and simultaneous growth of the Tibetan Plateau since 25 Myr.

    PubMed

    Jiang, Xiao-Dian; Li, Zheng-Xiang

    2014-11-13

    The spectacular topography of the Tibetan Plateau is the result of collision between India and Eurasia over some 50 Myr, but how the plateau grew to its present size remains a topic of debate. Work along its eastern margin suggests a two-stage uplift (thus growth of the plateau) since 30-25 Myr. Here we report high-resolution seismic reflection and drill core results from the southern Tarim Basin that indicate a similar pattern for the northern margin of the plateau. The data suggest that uplift in northern Tibet started at ~23 Myr from near sea level, with the first episode finished by ~10 Myr, followed by a post-5-Myr episode of rapid uplift along the present plateau margin. The growth of the Tibetan Plateau after the Eocene thus appears to have been episodic in nature, and near-synchronous along both eastern and northern margins.

  3. High resolution, shallow seismic reflection survey of the Pen Branch fault

    SciTech Connect

    Stieve, A.

    1991-05-15

    The purpose of this project, at the Savannah River River Site (SRS) was to acquire, process, and interpret 28 km (17.4 miles) of high resolution seismic reflection data taken across the trace of the Pen Branch fault and other suspected, intersecting north-south trending faults. The survey was optimized for the upper 300 ft of geologic strata in order to demonstrate the existence of very shallow, flat lying horizons, and to determine the depth of the fault or to sediments deformed by the fault. Field acquisition and processing parameters were selected to define small scale spatial variability and structural features in the vicinity of the Pen Branch fault leading to the definition and the location of the Pen Branch fault, the shallowest extent of the fault, and the quantification of the sense and magnitude of motion. Associated geophysical, borehole, and geologic data were incorporated into the investigation to assist in the determination of optimal parameters and aid in the interpretation.

  4. Structural interpretation of seismic reflection data from eastern Salt Range and Potwar Plateau, Pakistan

    SciTech Connect

    Pennock, E.S.; Lillie, R.J.; Zaman, A.S.H.; Yousaf, M.

    1989-07-01

    Approximately 1600 km of seismic reflection profiles from the eastern Salt Range and Potwar Plateau (SR/PP) of Pakistan is integrated with available magnetostratigraphic, surface geologic, and well data to classify structural styles, determine the timing of deformation, and estimate the amount of telescoping of the sedimentary cover. The eastern SR/PP are similar to other fold-and-thrust belts underlain by evaporites in that (1) it is part of a zone of overthrusting that extends considerably farther over the Himalayan foreland than adjacent areas not underlain by evaporites, (2) the overall thrust wedge has a narrow cross-sectional taper, (3) structures verge toward the hinterland as well as toward the foreland, and (4) fold trends are long and continuous, consisting of tight salt-cored anticlines separated by broad synclines. 11 figures, 1 table.

  5. 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

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

    USGS Publications Warehouse

    Haines, S.S.; Pidlisecky, A.; 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.

  7. Characterization of the crust of Maine by seismic reflection and refraction

    SciTech Connect

    Stewart, D.B.; Luetgert, J.H.; Unger, J.D.; Phillips, J.D.

    1985-01-01

    Major structural features of the crust of Main and adjacent Quebec appear in both seismic reflection and refraction profiles gathered in 1983 and 1984 through US-Canada cooperative experiments and associated gravity, magnetic, and geologic studies. Excepting gabbroic plutons, the upper crust is sialic throughout Maine with velocity 5.7-6.3 km/sec; below approx.22 km, velocity increases to 6.8-7.2 km/sec. Crustal thinning, from 40 km in the NW to 35 km in the SE, accounts for all the increase in the regional gravity field to the SE. The crust-mantle transition is gradational but yields multiple strong Moho reflections and clear Pn arrivals. Seismic data permit five different kinds of continental crust (terranes) to be characterized. The terranes are separated by boundaries that penetrate most of the crust. No ancient oceanic crust was identified. In northwestern Maine, crust II with the Chain Lakes Massif and superposed ophiolite was obducted in the Taconian orogeny onto sialic (Grenville.) Crust I. Crust II is in steep contact with high grade sialic metamorphic rocks of crust III approx.10 km SE of the NW border of the Merrimack synclinorium. The contact is covered by approx.12 km of Silurian and Devonian metasedimentary rocks. Crust III contacts crust IV along the Norumbega fault zone; high grade Precambrian and lower Paleozoic metasedimentary rocks thrust southeastward make up the upper part of crust IV. Crust IV contacts crust V along the Turtle Head fault zone in Penobscot Bay. In Crust V approx.12 km of bimodal Lower Paleozoic volcanic rocks cover Precambrian rocks at medium grade. The irregular shapes of granitic plutons were determined to depths of 6-10 km.

  8. 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

  9. High-Resolution Multichannel Seismic-Reflection Data Acquired in the Northern Gulf of Mexico, 1998-99

    USGS Publications Warehouse

    Hart, Patrick E.; Cooper, Alan K.; Twichell, David C.; Lee, Myung; Agena, Warren

    2002-01-01

    During June 1998 and April 1999, the U.S. Geological Survey (USGS) conducted two research cruises in the northern Gulf of Mexico to acquire high-resolution seismic reflection data across the upper and middle continental slope as part of an investigation of the seismic character, distribution, and potential effects of naturally-occurring marine gas hydrates and related free gas within the gas hydrate stability zone. Over 1600 km of two-dimensional multichannel seismic reflection profiles were acquired during these two cruises. The specific objectives of this investigation are (a) to produce high-resolution images of the gas hydrate stability zone; (b) to study the distribution and character of potential seafloor failures and their relationship to known and inferred gas hydrate deposits; (c) to look at systematic variations in subsurface structure in gas hydrate and non-hydrate areas; and (d) to estimate, if possible, the amounts of hydrates present within the gas hydrate stability zone. The multichannel profiles provide high-quality images with approximately 5 meters of vertical resolution and up to 2 km of penetration. This report gives an overview of the acquisition and data processing of the multichannel seismic reflection profiles and provides references and links to reports with more detailed information. Geologic interpretations of these seismic profiles regarding gas hydrate occurrence and distribution within the study areas of this investigation are given in Cooper and Hart (2002).

  10. Structure and Tectonics of the Cheb Basin (NW-Bohemia) from a shallow reflection seismic survey

    NASA Astrophysics Data System (ADS)

    Halpaap, Felix; Paschke, Marco; Bleibinhaus, Florian

    2015-04-01

    In the seismically active region of Northwest Bohemia, we imaged structural characteristics of the Cenozoic Cheb Basin with a shallow 3.5 km reflection seismic survey to find proof of faulting along the Počatky-Plesná shear zone (PPZ). Previously, the shear zone's existence has been inferred from earthquakes that occur in swarms and concentrate in the focal zone of Nový Kostel, below the Cheb Basin, along a plane striking at 170°. The difference in strike between the planar focal zone and the 145° oriented, crustal-scale eastern border fault of the Cheb Basin, which forms the northern termination of the geomorphologically dominant Mariánské Lazně fault, was interpreted to hint to the existence of a second major crustal fault zone. With additional interpretations of river drainage patterns, a distinct 25 m terrain escarpment and the distribution of Quaternary sediments around the Plesná river, the surface outcrop of the PPZ was thought to be found. A P-velocity model which we obtained from tomographic inversion of the first arrivals revealed an uppermost layer of very slow seismic velocities (about 1 km/s) that varies strongly in thickness. We interpret this layer as unconsolidated Quaternary sediments, which impacted the quality of our recorded shot gathers negatively with increasing thickness of the layer. The result of our standard reflection seismic processing, challenged by strong ground roll, is an image of the eastern Cheb Basin's layers and several tectonic features along a cross-strike profile with varying resolution. Our seismic image shows undisturbed younger sediments of the upper neogene Vildštejn and Cypris Formation, overlying the early miocene Main Coal Seam Formation and a structured basement. The imaged maximum basin depth of 300 m and unconformities below and above the Vildštejn Formation correspond well with litostratigraphic borehole data and previous sedimentological and tectonic models. We observe reverse faults in the lower

  11. 4-D High-Resolution Seismic Reflection Monitoring of Miscible CO2 Injected into a Carbonate Reservoir

    SciTech Connect

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

    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 limestones 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.

  12. Deep Stucture of the Northwestern Atlantic Moroccan Margin Studied by OBS and Deep Multichannel Seismic Reflection.

    NASA Astrophysics Data System (ADS)

    MALOD, J. A.; Réhault, J.; Sahabi, M.; Géli, L.; Matias, L.; Diaz, J.; Zitellini, N.

    2001-12-01

    The Northwestern Atlantic Moroccan margin, a conjugate of the New Scotland margin, is one of the oldest passive margin of the world. Continental break up occurred at early Liassic time and the deep margin is characterized by a large salt basin. A good knowledge of this basin is of major interest to improve the initial reconstruction between Africa, North America and Iberia (Eurasia). It is also a good opportunity to study a mature passive margin and model its structure and evolution.Moreover, there is a need to assess the geological hazards linked to the neotectonic activity within the Africa-Eurasia plate boundary. These topics have been adressed during the SISMAR cruise carried out from April 9th to May 4th 2001.During this cruise, 3667 km of multichannel seismic reflection (360 channels, 4500 m long streamer, 4800 ci array of air guns) were recorded together with refraction records by means of 48 OBH/OBS drops. Simultaneously, some of the marine profiles have been extended onshore with 16 portable seismic land stations. We present the initial results of this study. Off El Jadida, the Moho and structures within the thinned continental crust are well imaged on both the reflection and refraction records. In the northern area, off Casablanca, we follow the deepening of the moroccan margin beneath the up to 9 sec (twtt) allochtonous series forming a prism at the front the Rif-Betic chain. Sismar cruise has been also the opportunity to record long seismic profiles making the junction between the Portuguese margin and the Moroccan one, and crossing the Iberian-African plate boundary. This allows to observe the continuity of the sedimentary sequence after the end of the large inter-plate motion in Early Cretaceous. In addition to the authors, SISMAR Group includes: AMRHAR Mostafa, BERMUDEZ VASQUEZ Antoni, CAMURRI Francesca, CONTRUCCI Isabelle, CORELA Carlos, DIAZ Jordi, DORVAL Philippe, EL ARCHI Abdelkrim, EL ATTARI Ahmed, GONZALEZ Raquel, HARMEGNIES Francois, JAFFAL

  13. Rhone glacier last deglaciation in western Lake Geneva from seismic reflection and sedimentary data

    NASA Astrophysics Data System (ADS)

    Girardclos, S.; Rachoud-Schneider, A.; Brutsch, N.

    2010-12-01

    Seismic reflection and geotechnical drilling were performed in spring 2009 in the western part of Lake Geneva within a public project to build a large bridge over the lake. Scientific analyse of this seismic and sediment record reveals new insights in the history of the Rhone glacier deglaciation and Lake Geneva formation. Seismic data, acquired with a 1 in3 airgun and a pinger source, images the bedrock lake basin as well as eight sismostratigraphic units of glacial, glacio-lacustrine and lacustrine facies. In the eastern part of studied area, gas reduces seismic data quality but nevertheless, the lateral asymmetry of the basin geometry and of the sediment infill appears. In the western part, the bedrock (i.e. Molasse) forms a 3° ramp bending toward east which is topped by only maximum 30 m of sediment. In the centre and eastern part of the lake basin, the bedrock lies deeper and is covered by 70 to 110 m of glacial to lacustrine units. The deepest unit (U1), which was detected on seismic lines but not drilled, is interpreted as glacial sediments left during an older glacial cycle. It is topped by the thick U6b and U7 units, interpreted as melt-out till of the Rhone glacier. Four 35 to 75 m-deep drillings confirm this interpretation and show that unit U6b was certainly compacted by a re-advance of the Rhone glacier. This data reveals a new glacial stage, older than stages of Coppet and Nyon, with a glacial front near ‘Le Reposoir’. The asymmetry of unit U7 also shows that the glacier melted first in the central and eastern part of the lake basin while it was still lying on the Molasse ‘ramp’ in the West. The next sequence, represented by units U8-U12, is interpreted as glacio-lacustrine deposits. They have variable sedimentary facies ranging from massive silt to laminated clayed silt with rare sand layers. Gravels of alpine origin and ‘galets mous’ in the silty matrix, interpreted as dropstones’, point to the recurrent presence of icebergs in the

  14. Lithospheric Structure Along the Wide-Angle Seismic Reflection Transect of the Central Iberian Massif

    NASA Astrophysics Data System (ADS)

    Ehsan, Siddique Akhtar; Carbonell, Ramon; Cembrowski, Marcel; Marti, David; Gil, Alba; Marzan, Ignacio; Ayarza, Puy; Martinez-Poyatos, David; Simancas, Jose Fernando; Azor, Antonio

    2014-05-01

    The Iberian Massif is the largest outcrop of the Late Paleozoic Variscan Orogen in western Europe. In May 2012, a spatially dense high resolution wide-angle seismic reflection profile ALCUDIA was acquired across the Central Iberian Massif. The ALCUDIA wide-angle profile investigates lithospheric structure of the Central Iberian Zone and a suture zone (the Central Unit). The experiment consisted in a main SW-NE line of receivers, c. 300 km long, and a supplementary transect, c. 35 km long, that sampled the crust beneath the Central Iberian System. The acoustic energy generated by 5 shots, c. 70 km apart, was recorded by over 900 TEXANS (single component, digital recording stations) from the IRIS-PASSCAL Instrument Center. Each shot consisted in 1 TM of explosives fired in a single 55-65 m deep borehole. Approximately, 100 stations were deployed across the Central Iberian System in an effort to map the topography of the crust mantle boundary beneath this mountain range. This design generated enough energy to be able to identify Pn and even mantle reflections. The preliminary analysis of the shot gathers reveals that the recorded events features relatively low frequencies (4-30 Hz). The processing of the shot gathers resulted into high amplitude reflective events within the upper crust and strong PmP phases. From the southwest to northeast, the interpreted PmP arrivals are located at c. 11 s and c. 12 s (normal incidence traveltime) respectively. The ALCUDIA wide-angle profile provided a detailed P-wave velocity structural model and complemented the previously acquired normal incidence deep seismic profile ALCUDIA. The velocity model obtained by forward modelling constraints the composition of the crust and upper mantle. The upper crust is located at c. 13 km and the Moho is in the 32-36 km range, equates to normal incidence reflection profile ALCUDIA. Existing knowledge indicates that the mid-lower crust along the southern part of the CIZ is characterized by

  15. Interpretation of a 3D Seismic-Reflection Volume in the Basin and Range, Hawthorne, Nevada

    NASA Astrophysics Data System (ADS)

    Louie, J. N.; Kell, A. M.; Pullammanappallil, S.; Oldow, J. S.; Sabin, A.; Lazaro, M.

    2009-12-01

    A collaborative effort by the Great Basin Center for Geothermal Energy at the University of Nevada, Reno, and Optim Inc. of Reno has interpreted a 3d seismic data set recorded by the U.S. Navy Geothermal Programs Office (GPO) at the Hawthorne Army Depot, Nevada. The 3d survey incorporated about 20 NNW-striking lines covering an area of approximately 3 by 10 km. The survey covered an alluvial area below the eastern flank of the Wassuk Range. In the reflection volume the most prominent events are interpreted to be the base of Quaternary alluvium, the Quaternary Wassuk Range-front normal fault zone, and sequences of intercalated Tertiary volcanic flows and sediments. Such a data set is rare in the Basin and Range. Our interpretation reveals structural and stratigraphic details that form a basis for rapid development of the geothermal-energy resources underlying the Depot. We interpret a map of the time-elevation of the Wassuk Range fault and its associated splays and basin-ward step faults. The range-front fault is the deepest, and its isochron map provides essentially a map of "economic basement" under the prospect area. There are three faults that are the most readily picked through vertical sections. The fault reflections show an uncertainty in the time-depth that we can interpret for them of 50 to 200 ms, due to the over-migrated appearance of the processing contractor’s prestack time-migrated data set. Proper assessment of velocities for mitigating the migration artifacts through prestack depth migration is not possible from this data set alone, as the offsets are not long enough for sufficiently deep velocity tomography. The three faults we interpreted appear as gradients in potential-field maps. In addition, the southern boundary of a major Tertiary graben may be seen within the volume as the northward termination of the strong reflections from older Tertiary volcanics. Using a transparent volume view across the survey gives a view of the volcanics in full

  16. 2-D High Resolution Seismic Imaging and Potential-Field Modeling of Small-Scale Intrabasin Faulting in Surprise Valley, California

    NASA Astrophysics Data System (ADS)

    Athens, N.; Fontiveros, V. C.; Klemperer, S. L.; Egger, A. E.; Glen, J. M.

    2010-12-01

    Surprise Valley, located in the northeast corner of California, constitutes the westernmost basin of the Basin and Range Province (BRP) and acts as a transition zone between the unextended Cenozoic volcanic rocks of the Modoc Plateau to the west and the extended BRP to the east. Previous seismic experiments undertaken in Surprise Valley to examine the structural setting of a developing extensional basin imaged the Surprise Valley Fault (SVF), the large-scale structure that controls the basin formation. In this study, we image small-scale structures associated with a prominent N-S-trending magnetic anomaly in the basin; these small-scale structures have no surface expression, yet they presumably play a role in the active geothermal system in the valley and may lend insight into the development of the basin. We recorded a total of 198 shots fired between geophones on a fixed linear array spanning ~ 1 km using a Betsy Seisgun source. The source yielded excellent penetration depths of up to 400 m, presumably due to the ideal conditions of fine-grained lake deposits saturated almost immediately below the surface. We used a standard seismic processing sequence to create an unmigrated time section, but lack of velocity control at depth led to the creation of a suite of different migrated images to explore the effects of strong lateral velocity variations in the subsurface. . Images obtained by applying Kirchhoff pre-stack depth migration to the seismic data reveal what we interpret to be an east-dipping (~56°) normal fault offsetting tilted strata of probable Oligocene age with ~250 meters of vertical throw. In addition to the 1 km seismic line, detailed gravity and magnetic surveys were undertaken to fully image the structure(s) north and south of the seismic line. The magnetic survey was performed with a cesium vapor total-field magnetometer installed on our newly developed all-terrain vehicle (ATV) magnetometer system, which was designed for efficient surveying in

  17. 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

  18. Accretion and Subduction of Oceanic Lithosphere: 2D and 3D Seismic Studies of Off-Axis Magma Lenses at East Pacific Rise 9°37-40'N Area and Downgoing Juan de Fuca Plate at Cascadia Subduction Zone

    NASA Astrophysics Data System (ADS)

    Han, Shuoshuo

    Two thirds of the Earth's lithosphere is covered by the ocean. The oceanic lithosphere is formed at mid-ocean ridges, evolves and interacts with the overlying ocean for millions of years, and is eventually consumed at subduction zones. In this thesis, I use 2D and 3D multichannel seismic (MCS) data to investigate the accretionary and hydrothermal process on the ridge flank of the fast-spreading East Pacific Rise (EPR) at 9°37-40'N and the structure of the downgoing Juan de Fuca plate at the Cascadia subduction zone offshore Oregon and Washington. Using 3D multichannel seismic (MCS) data, I image a series of off-axis magma lenses (OAML) in the middle or lower crust, 2-10 km from the ridge axis at EPR 9°37-40'N. The large OAMLs are associated with Moho travel time anomalies and local volcanic edifices above them, indicating off-axis magmatism contributes to crustal accretion though both intrusion and eruption (Chapter 1). To assess the effect of OAMLs on the upper crustal structure, I conduct 2-D travel time tomography on downward continued MCS data along two across-axis lines above a prominent OAML in our study area. I find higher upper crustal velocity in a region ~ 2 km wide above this OAML compared with the surrounding crust. I attribute these local anomalies to enhanced precipitation of alteration minerals in the pore space of upper crust associated with high-temperature off-axis hydrothermal circulation driven by the OAML (Chapter 2). At Cascadia, a young and hot end-member of the global subduction system, the state of hydration of the downgoing Juan de Fuca (JdF) plate is important to a number of subduction processes, yet is poorly known. As local zones of higher porosity and permeability, faults constitute primary conduits for seawater to enter the crust and potentially uppermost mantle. From pre-stack time migrated MCS images, I observe pervasive faulting in the sediment section up to 200 km from the deformation front. Yet faults with large throw and

  19. 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

    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.

  20. Comparison of Vibroseis and explosive source methods for deep crustal seismic reflection profiling in the Basin and Range province

    USGS Publications Warehouse

    Brocher, T.M.; Hart, P.E.

    1991-01-01

    Direct comparison of low-fold, high-energy explosive and high-fold, lower-energy Vibroseis methods for acquiring deep crustal seismic reflection data in the Basin and Range Province suggests that the high-fold common midpoint (CMP) method there does not provide the best possible image of lower crustal structure. -from Authors

  1. 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)

  2. Seismic reflection survey of the crustal structure beneath Unzen volcano, Kyushu, Japan

    NASA Astrophysics Data System (ADS)

    Matsumoto, Satoshi; Shimizu, Hiroshi; Onishi, Masazumi; Uehira, Kenji

    2012-05-01

    Unzen volcano is located in the western part of Kyushu, Japan. We carried out a seismic reflection survey at Unzen volcano in order to elucidate the structure of the volcano. Although the survey was conducted in a volcanic area under difficult conditions, such as artificial noises and a complex structure, we were able to resolve the structure beneath the profile using vibrator sources and a large number of stacking signals. The processed depth sections confirmed that Unzen volcano developed in a graben structure, as has been suggested in other geological studies. We imaged many subsurface normal faults shallower than 1 km. These faults, mostly covered with volcanic lava and deposits, were identified at the surface. Strong reflectors were found at a depth of approximately 3 km. They were located just above the pressure source of the latest eruption, as inferred from geodetic data. The geometric relationship between the reflection image, the pressure source location, and the lava dome suggests that the conduit from the lava dome could connect to the magma chamber located 4 km away from the lava dome.

  3. Crustal Structure across The Southwest Longmenshan Fault Zone from Seismic Wide Angle Reflection/Refraction Profile

    NASA Astrophysics Data System (ADS)

    Tian, Xiaofeng; Wang, Fuyun; Wang, Shuaijun; Duan, Yonghong

    2014-05-01

    The Lushan eathquake, which epicenter and focal depth were at 30.308° N, 102.888° E, and 14.0 km, is the latest intense earthquake occurring in the southwest section of the Longmenshan fault zone after the Ms 8.0 Wenchuan earthquake in 2008. According to the emergency field observations, the slip distribution of the Lushan earthquake was concentrated at the hypocenter, and did not rupture to the surface(Chen et al, 2013). The rupture history constrained by inverting waveforms showed that the causative fault plane of the Lushan event is apparently not a simple extension of either the Pengguan fault or the Beichuan fault that ruptured during the 2008 Mw 8.0 Wenchuan earthquake. The focal mechanism using the Cut and Paste algorithm showed this event occurred on a high dip-angle fault, but its dip angle is not steep enough to rupture the surface. All these research is not independent on the heterogeneous crust structure of the Longmenshan fault zone. A 450 km-long wide-angle reflection/refraction profile executed during September and October 2013. This experiment have provided the best opportunities to obtain better knowledge of seismic structure and properties of crust and uppermost mantle beneath the Southwest Longmenshan fault zone. This seismic profile extends from the west Sichuan Plain, through the Longmenshan Fault zone, and into the west Sichuan Plateau. We observed clear Pg, refraction Phase from the upper crust, Pi1/Pi2/Pi3, reflection/refraction Phase from intra-crust, PmP, reflection from the Moho boundary, and the Pn phase, refraction Phase from uppermost mantle. We present a hybrid tomographic and layered velocity model of the crust and uppermost mantle along the profile. The final velocity model reveals large variations both in structure and velocity, and is demonstrated that a particular model has minimum structure. The model shows the crustal thickness of the region is very variable. The Moho topography varies more than 10km in the southwest

  4. Crustal shortening followed by extensional collapse of the Cordilleran orogenic belt in northwestern Montana: Evidence from vintage seismic reflection profiles acquired in the Swan Range and Swan Valley

    NASA Astrophysics Data System (ADS)

    Rutherford, B. S.; Speece, M. A.; Stickney, M. C.; Mosolf, J. G.

    2013-12-01

    Reprocessing of one 24-fold (96 channel) and four 30-fold (120 channel) 2D seismic reflection profiles have revealed crustal scale reflections in the Swan Range and adjacent Swan River Valley of northwestern Montana. The five reprocessed profiles constitute 142.6 of the 303.3 linear km acquired in 1983-84 by Techo of Denver, Colorado. The four 30-fold profiles used helicopter-assisted dynamite shooting (Poulter method) and the 24-fold profile used the Vibroseis method. Acquisition parameters were state of the art for the time. The Swan Range lies east of the Rocky Mountain Trench and is part of the Cordilleran foreland thrust belt where the Lewis thrust system emplaced a thick slab of Proterozoic Belt Supergroup strata eastward and over Paleozoic and Mesozoic rocks during the Late Cretaceous to early Paleocene Laramide orogeny. Deeply drilled borehole data are absent within the study area; however, we generated a synthetic seismogram from the Arco-Marathon 1 Paul Gibbs well (total depth=5418 m), located approximately 70 km west of the reprocessed profiles, and correlated the well data to surface seismic profiles. Large impedance contrasts in the log data are interpreted to be tholeiitic Moyie sills within the Prichard Formation argillite (Lower Belt), which produce strong reflection events in regional seismic sections and result in highly reflective, east-dipping events in the reprocessed profiles. We estimate a depth of 10 km (3 to 3.5 seconds) to the basal detachment of the Lewis thrust sheet. The décollement lies within Belt Supergroup strata to the west of the Swan River Valley before contacting unreflective, west-dipping crystalline basement beneath the Swan Range--a geometry that results in a wedge of eastward-thinning, autochthonous Belt rocks. Distinct fault-plane signatures from the west-dipping, range-bounding Swan fault--produced by extensional collapse of the over-thickened Cordillera--are not successfully imaged. However, reflections from Cenozoic

  5. 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

  6. A High-resolution Seismic Reflection Survey at the Hanford Nuclear Site Using a Land Streamer

    NASA Astrophysics Data System (ADS)

    Hyde, E. R.; Speece, M. A.; Link, C. A.; Repasky, T.; Thompson, M.; Miller, S.; Cummins, G.

    2009-12-01

    From the 1940s through the mid 1990s, radioactively and chemically contaminated effluent waste was released into the ground at the Hanford Nuclear Site. Currently, Hanford is the site of a large-scale and ongoing environmental cleanup effort which includes the remediation of contaminated ground water. Identifying preferential pathways of groundwater contaminant flow is critical for the groundwater cleanup effort. During the summer of 2009, Montana Tech, in collaboration with the Confederated Tribes of the Umatilla Indian Reservation, collected a high resolution shallow seismic survey on the Hanford Central Plateau near the Gable Gap area of the Hanford Nuclear site. The goal of the survey was to demonstrate the feasibility of using a land streamer/gimbaled geophone acquisition approach to image the basalt bedrock topography. The survey objective is to improve the understanding of the subsurface water flow by identifying the topography of the basement basalt and possible erosional channels created during the Missoula flood events. Data was collected for a total of eight 2D lines with a combined length of about 11 km with a coverage area of approximately 6 sq.km. The profiles were aligned in north-south and east-west intersecting lines with a total of 5 profile intersections. The survey used a 227 kg accelerated weight drop and a 96-channel land streamer. The land streamer used gimbaled geophones with 2 m spacing. Source spacing was also 2 m for a nominal fold of 48. The rapid deployment land streamer, compared to conventional spiked geophones, significantly increased production in this off-road application. Typically, between 45 and 55 stations could be shot per hour in a pull and shoot approach. Deployment of the land streamer required about 45 minutes and about 30 minutes was required to shut down the survey. The survey successfully imaged the top of the basalt and demonstrated that a land streamer can produce quality seismic data in this area. The basalt bedrock

  7. The Nature of Co-seismic Rupture Zone of the 2010 Mentawai Tsunami Earthquake from Full Waveform Inversion of Long Offset Seismic Reflection Data

    NASA Astrophysics Data System (ADS)

    Singh, S. C.; Huot, G.

    2015-12-01

    The Sumatra subduction zone is one of the most seismically active zone on Earth. In the last one decade alone, it has hosted three Mw>8.4 great earthquakes (2004, 2005, 2007) along with 2010 tsunami earthquake. Although the 2007 Mentawai earthquake had Mw=8.4, it did not produce tsunami whereas the 2010 earthquake had Mw=7.8 only in the same region, it produced a large tsunami with a run up height of up to 8 m on Pagai Island, taking 800 lives. Therefore, understanding why an earthquake produce tsunami is fundamental for risk assessment as well for subduction zone processes. Prior to the 2010 earthquake we had acquired ultra-long offsets seismic reflection data in 2009 in the co-seismic slip zone using a 15 km long streamer, the longest streamer ever used, and found that the earth ruptured the frontal section of the subduction zone, which is normally believed to be aseismic, and possibly produced the tsunami. In order to quantify the nature of the co-seismic rupture zone and its link with the tsunami generation, we performed full waveform inversion of seismic reflection data. In order to obtain the high-resolution velocity model for the full waveform inversion, we first downward continue the data to the seafloor, picked first arrivals, and performed tomography. We used the tomographic velocity model as an input to the full waveform inversion. This process also reduced the computation cost significantly as the water depth in this area is 5.5 km. The resulting models shows the presence of thrust faults extending up to the subducting oceanic plate, suggesting that the frontal section of the subduction in this region was indeed locked, capable of hosting great earthquakes. Our inverted model provides the resolution of tens of meters, allowing to characterize the nature of the megathrust and other faults, and hence estimate the effective porosity, permeability and stress along these faults, subsequently the pore pressure.

  8. Integrated well log and 2-D seismic data interpretation to image the subsurface stratigraphy and structure in north-eastern Bornu (Chad) basin

    NASA Astrophysics Data System (ADS)

    Isyaku, Aminu A.; Rust, Derek; Teeuw, Richard; Whitworth, Malcolm

    2016-09-01

    Structural and stratigraphic mapping within the Bornu Basin in north east Nigeria was commonly carried out using traditional field geological methods. However, such traditional approaches remain inadequate in the semi-arid region characterised by topographically flat areas and lack of continuous bedrock outcrops that are mostly concealed beneath sand cover. Previous studies in the north-eastern part of the basin carried out using ditch cuttings from few wells and disconnected seismic data were largely inadequate and the resulting stratigraphic analyses were more often generalised. This paper presents an integrated structural and stratigraphic study of the basin using combined subsurface geophysical datasets. A Combined Log Pattern (CLP) method is a well log analysis, which utilises various well log data including gamma ray, resistivity, bulk density and sonic logs to identify lithology and stratigraphic boundaries of subsurface formations. This method is applied to constrain the subsurface stratigraphy of the north-eastern part of the Bornu Basin bordering the Lake Chad. In addition to qualitative combined well log analysis, the time-depth relationship of the sonic log and seismic data was quantitatively determined by tying a well with an intersecting seismic section to validate the stratigraphic facies horizons identified. Four well log facies and their environments of deposition were characterised from the combined well log analysis of the different log types. It is discovered that the Cretaceous basement structural features controlled the deposition of overlying formations in the basin. Without intact core data, the shallower wells were discovered to have bottomed over subsurface horst features while deeper wells penetrated into the basal facies contained mainly within the grabens. Main subsurface structural lineaments in the area include NW-SE, NE-SW and NNW-SSE trending faults, which mainly formed the horst and graben features. Some stratigraphic formations

  9. 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.

  10. Pronounced central uplift identified in the Bosumtwi impact structure, Ghana, using multichannel seismic reflection data

    NASA Astrophysics Data System (ADS)

    Scholz, Christopher A.; Karp, Tobias; Brooks, Keely M.; Milkereit, Bernd; Amoako, Philip Y. O.; Arko, Justice A.

    2002-10-01

    The Lake Bosumtwi impact structure is the youngest and best-preserved complex terrestrial impact crater and serves as an important reference site for the study of cratering processes. Because the impacting body struck continental crystalline target rocks and not a submerged sedimentary platform, no significant backwash processes have modified the crater morphology. Not only may Bosumtwi contain the best-preserved central uplift structure on Earth, but it is the most accessible relatively large, young crater in the solar system generated in a large gravity field. There is a well-established link between the Lake Bosumtwi impact structure and the Ivory Coast tektite field, and the lacustrine sediments within the crater contain a unique 1 m.y. record of paleoclimate in the continental tropics south of the Sahel. Eight profiles of marine-type multichannel seismic reflection (MCS) data were acquired from the 8-km-diameter, ˜75-m-deep lake that fills much of the crater. These were augmented by wide-angle seismic data acquired with ocean-bottom hydrophones. MCS data reveal a well-defined central uplift near the northwest-central part of the lake and a maximum postimpact lacustrine sediment thickness of ˜310 m. The central uplift structure has a diameter of 1.9 km and a maximum height of 130 m above the annular moat inside the crater. An intermediate velocity layer (3200 m/s) beneath the lacustrine sediment is interpreted as fallback breccia or a breccia-melt horizon. The measured apparent depth of the crater (da) is 500 m, implying a slightly higher aspect ratio for the structure than predicted from published empirical relationships. The Bosumtwi structure is a small complex crater that deviates slightly from trends predicted from classical scaling laws, perhaps because of the effects of a large gravity field.

  11. Structural and tectonic evolution of the eastern Cayman Trough (Caribbean Sea) from seismic reflection data

    SciTech Connect

    Leroy, S.; Mauffret, A.; Pubellier, M.

    1996-02-01

    The eastern Cayman Trough preserves a record of the Late Cretaceous to Paleogene Caribbean history that is largely affected by Neogene strike-slip tectonics of the current plate boundary. We conducted an analysis of seismic data within the eastern Cayman Trough, based upon single and multi-channel seismic reflection profiles collected during the Seacarib II cruise in 1987 and the Casis cruise in 1992. These data show that the basement of the eastern Cayman Trough can be divided into four domains from east to west, with distinct morphologic and sedimentary character and inferred older to younger ages: (1) a province of rifted Mesozoic continental crust exhibiting seven parallel horst blocks striking northeast-southwest; (2) a continent-ocean transition between provinces 1 and 3 that exhibits seamounts, small hills, and sedimentary basins; (3) an Eocene oceanic crust with rough basement but smoother relief than the rifted crust; basement trends are roughly north-south and oblique to the northwest trend in domain 1, and (4) the northern Jamaica slope, which forms an east-west-trending slope, with northward-dipping strata that flank the three deeper water domains of the Cayman Trough. The domains are interpreted to be the product of the Eocene east-west opening of the Cayman Trough as a pull-apart basin in a left-lateral strike-slip setting. Closure of the 1100 km of Eocene and younger oceanic crust of the Cayman Trough places the fault-block province adjacent to the Belize margin of Central America. A Neogene phase of transpression has reactivated structures in the four domains, along with on-land structures described by previous authors in Jamaica. The proximity of the eastern margin of the Cayman Trough to petroliferous, continental rocks in Central America suggests an improved possibility of hydrocarbon potential. Unfortunately, sediment thicknesses of less than 1 km probably are not conducive to hydrocarbon formation.

  12. Tectonics of the West Iberia continental margin from seismic reflection data

    NASA Astrophysics Data System (ADS)

    Henning, Alison Teagan

    Continental rifting is a fundamental component of the plate tectonic cycle. The West Iberia passive margin is a classic example of a nonvolcanic rifted margin. The West Iberia margin contains an enigmatic north-south ridge of serpentinized peridotite located within the ocean-continent transition. Interpretation of multichannel seismic data and tectonic subsidence analyses suggests that the ridge is located within a broad zone of exhumed mantle that has been serpentinized. This implies that seafloor spreading does not immediately follow continental breakup. Where the peridotite ridge is well-developed, it parallels a deeply-penetrating, west-dipping normal fault. Hydrodynamic circulation drove seawater down this fault close to the beginning of seafloor spreading and caused a concentration of serpentinization at its base. This water-driven process of formation accounts for the variability of the ridge along strike. Prestack depth migration of a 340 km long seismic reflection profile across the margin served as the basis for stratigraphic interpretation. The proximal margin displays horsts and grabens, with 1--2 km thick synrift deposits from Early Cretaceous (Valanginian) rifting. The deep water margin displays rotated blocks with distinct internal seismic patterns. These blocks formed during the final Cretaceous rifting event that led to continental breakup, and contain earlier Valanginian synrift deposits as part of the rotated blocks, thus providing evidence of two separate rifting stages along this profile. A large mantle-penetrating fault located seaward of the last rotated block of continental crust provides evidence for a third and final Cretaceous rifting event that may have been coeval with early seafloor spreading. Two independent estimates of crustal thickness along this line indicate stretching factors of 50% on the proximal margin (corresponding to a continental crustal thickness of ˜16 km), increasing to 100% in the deep water. Plate tectonics is one

  13. Reconciling deep seismic refraction and reflection data from the grenvillian-appalachian boundary in western New England

    USGS Publications Warehouse

    Hughes, S.; Luetgert, J.H.; Christensen, N.I.

    1993-01-01

    The Grenvillian-Appalachian boundary is characterized by pervasive mylonitic deformation and retrograde alteration of a suite of imbricated allochthonous and parautochthonous gneisses that were thrust upon the Grenvillian continental margin during the lower Paleozoic. Seismic reflection profiling across this structural boundary zone reveals prominent dipping reflectors interpreted as overthrust basement slices (parautochthons) of the Green Mountain Anticlinorium. In contrast, a seismic refraction study of the Grenvillian-Appalachian boundary reveals a sub-horizontally layered seismic velocity model that is difficult to reconcile with the pronounced sub-vertical structures observed in the Green mountains. A suite of rock samples was collected from the Green Mountain Anticlinorium and measured at high pressures in the laboratory to determine the seismic properties of these allochthonous and parautochthonous gneisses. The laboratory-measured seismic velocities agree favorably with the modelled velocity structure across the Grenvillian-Appalachian boundary suggesting that the rock samples are reliable indicators of the rock mass as whole. Samples of the parautochthonous Grenvillian basement exposed in the Green Mountains have lower velocities, by about 0.5 km/s, than lithologically equivalent units exposed in the eastern Adirondack Highlands. Velocity reduction in the Green Mountain parautochthons can be accounted for by retrograde metamorphic alteration (hydration) of the paragneisses. Seismic anisotropies, ranging from 2 to 12%, in the mylonitized Green Mountain paragneisses may also contribute to the observation of lower seismic velocities, where the direction of ray propagation is normal to the foliation. The velocity properties of the Green Mountain paragneisses are thus insufficiently different from the mantling Appalachian allochthons to permit their resolution by the Ontario-New York-New England seismic refraction profile. ?? 1993.

  14. Crustal structure at the Gulf of Guayaquil active margin (Ecuador), from multichannel seismic reflection data.

    NASA Astrophysics Data System (ADS)

    Calahorrano, A.; Collot, J.-Y.; Sage, F.; Ranero, C.

    2003-04-01

    During the SISTEUR cruise, multichannel seismic reflection lines were shot across the Ecuador trench-margin system, off the Gulf of Guayaquil. Line SIS-72, which cuts through the margin, immediately north of the Ecuador-Peru border, has been fully processed through pre-stack depth migration to reveal the inter-plate contact geometry, sediment subduction/underplating processes, and a thick fore-arc basin. Strong reflectors allow to identify the top of the Nazca plate oceanic crust (TOC), the inter-plate décollement (ID) and the top of the margin basement (TB). The TOC is imaged by a continuous, low frequency reflector, and shows a rough surface that dips ~4° landward for 24 km from the trench axis. Further to the East, the TOC reflector becomes discontinuous and shows a slope break from 4° to 10°, at a 10-km-depth. West of the trench, the TOC is overlain by a 200-m-thick, transparent unit of pelagic deposits, and 600 m of horizontally stratified trench turbidites. The ID reflector is relatively continuous and roughly reflects the TOC geometry. ID and TOC reflectors define a ~600-m-thick subduction channel, which terminates some 24 km landward from the trench, where the ID reflector steps down to join the TOC. Some reflections from the subduction channel appear to be shaped as the casing reflectors, while others have sigmoid shapes with landward dips associated with small oceanic highs of TOC. The ID crops out at the front of a 8-km-wide accretionary wedge, which encompasses ~4 trusts. The accretionary wedge has developed recently against a sharp-pointed buttress formed by the margin's rock framework as indicated by its reflection characteristics. The TB reflector is discontinuous and separates the basement from overlaying stratified sequences. The TB reflector extends from the toe of the margin to ~75 km landward, where it abruptly drops from a depth of 4 to 11 km, at the base of a 10-km-thick forearc basin. This basin, bounded by doming structures interpreted

  15. The efficiency of using a seismic base isolation system for a 2D concrete frame founded upon improved soft soil with rigid inclusions

    NASA Astrophysics Data System (ADS)

    Awwad, Talal; Donia, Modar

    2016-03-01

    2D finite element models were developed to analyze the effect of improved soft-soil foundation on the efficiency of a base-isolated concrete frame. Static and dynamic analyses were performed for a frame on raft foundation. Non-improved and improved soft-soil foundation using rigid inclusions were considered, as well as the use of high damping rubber bearing as base isolation. Results show that the use of rigid inclusions increases the efficiency of base isolation; base shear is reduced by 38% and maximum acceleration at the top of the frame by 30%.

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

    SciTech Connect

    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 was 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.

  17. 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.

  18. Urban Reflection Seismics: A High-resolution Shear-wave Survey in the Trondheim harbour area, Norway

    NASA Astrophysics Data System (ADS)

    Krawczyk, Charlotte; Polom, Ulrich; L'Heureux, Jean-Sebastien; Hansen, Louise; Lecomte, Isabelle; Longva, Oddva

    2010-05-01

    A shallow reflection shear-wave seismic survey was carried out in mid summer 2008 in the harbour area of Trondheim, Norway, that suffers from prominent landslide events in the last decades. The harbour has been built on man-made land fillings at the coast of the Trondheim Fjord in several expansions implicated in some submarine landslides, which are reported since about 100 years. Whereas high-resolution marine seismic methods mapped the fjord area in detail in the range of decimeters, the seismic investigation below the infilled and paved harbour area was a difficult challenge. Therefore, SH-polarized shear-wave reflection seismics was applied experimentally, and the field configuration was especially adapted for the application on paved surfaces with underlying soft soil of estimated more than 150 m thickness. A land streamer system of 120 channels (geophone interval of 1 m) was used in combination with LIAG's newly developed shear-wave vibrator buggy of 30 kN peak force. This mini truck is designed for full environment-friendly urban use and enables fast and sensitive operation within a seismic survey area. The sweep parameters were configured to 25-100 Hz range, 10 s duration, using 14 s recording time sampled by 1 ms interval. Shear wave frequencies above the used frequency range, which can also be generated by the seismic source, were avoided consciously to prevent disturbing air wave reflections during operation. For an advantageous solution for the seismic imaging of the subsoil down to the bedrock a grid of 4.2 profile-km was gathered. The data recorded experimentally in the initial seismic survey stage achieved finally a highly resolved image of the structure of the sediment body with ca. 1 m vertical resolution, clear detection of the bedrock, and probably deeper structures. The profiles were processed up to FD time migration, and indicate that slip planes, turbidity masses and other features relevant for geohazards are present within the top of the

  19. Urban Shear-wave Reflection Seismics: A High-resolution Survey in the Landslide-affected Trondheim Harbour Area, Norway

    NASA Astrophysics Data System (ADS)

    Krawczyk, C. M.; Polom, U.; Hansen, L.; L'Heureux, J.; Longva, O.; Lecomte, I.

    2009-12-01

    A shallow reflection shear-wave seismic survey was carried out in mid summer 2008 in the harbour area of Trondheim, Norway, that suffers from prominent landslide events in the last decades. The harbour has been built on man-made land fillings at the coast of the Trondheim Fjord in several expansions implicated in some submarine landslides. Whereas high-resolution marine seismic methods mapped the fjord area in detail, common seismic investigation of the infilled, paved harbour area was a difficult challenge. Therefore, SH-polarized shear-wave reflection seismics was applied experimentally, and the field configuration was especially adapted for the application on paved surfaces with underlying soft soil of more than 100 m thickness. A land streamer system of 120 channels (geophone interval of 1 m) was used in combination with LIAG's newly developed shear-wave vibrator buggy of 30 kN peak force. This mini truck is full environment-friendly for urban use and enables fast operation within a seismic survey area. The sweep parameters were configured to 25-100 Hz range, 10 s duration, using 14 s recording time sampled by 1 ms interval. Shear wave frequencies above the used frequency range, which can also be generated by the seismic source, were avoided consciously to prevent disturbing air wave reflections during operation. For an advantageous solution for the seismic imaging of the subsoil down to the bedrock ca. 4 km of 2.5-D profiles were gathered. The data recorded experimentally in the initial seismic survey stage achieved finally a highly resolved image of the structure of the sediment body with 1 m vertical resolution, clear detection of the bedrock, and probably deeper structures. These were processed up to FD time migration, and indicate that slip planes are present within the top of the bedrock. Due to the clear and continuous reflection events, also the shear-wave velocity could be calculated at least down to the bedrock to indicate the dynamic stiffness of the

  20. 3D Seismic Reflection Images of An Off-Axis Melt Lens And Its Associated Upper Crust Around 9°39'N, East Pacific Rise

    NASA Astrophysics Data System (ADS)

    Han, S.; Carton, H. D.; Carbotte, S. M.; Mutter, J. C.; Canales, J.; Nedimović, M. R.

    2011-12-01

    During the 3D multi-channel seismic (MCS) survey MGL0812 aboard the R/V Langseth, several mid-crust reflectors were discovered off axis on both flanks of the East Pacific Rise from 9°35.6-57.0'N. The reversed polarity of these off-axis reflections with respect to the seafloor and Moho reflections and the high attenuation of the crust detected beneath two of them in the north suggest that they arise from melts residing at the mid-crust level outside the axial low velocity zone (Canales et al. 2010). These off-axis melt lenses (OAML) are probable sites of off-axis volcanism and potential heat sources for localized hydrothermal circulation on the ridge flanks. We focus here on a prominent OAML discovered on the eastern flank around 9°39'N. Results from 1D travel time modeling and 2D streamer tomography of downward continued shot gathers show the presence of a thinner seismic layer 2A above the center of the OAML compared with its surrounding crust. We attribute this thinning to the effects of alteration associated with localized off-axis hydrothermal circulation driven by the OAML, where precipitation of secondary minerals infills pore space within the lower basalt section, leading to increased seismic velocities and thereby converting the lowermost seismic layer 2A into seismic layer 2B. To further constrain the respective 3D geometries of the OAML and the AMC, their spatial relations, and the spatial extent and shape of the region of altered upper crust associated with the OAML, we conduct 3D processing of a small MCS grid that encompasses most of this OAML, aimed at imaging both on- and off-axis melt lens events and the base of seismic layer 2A. This grid covers an ~4 km x 24 km area centered on the ridge crest between ˜9°37.5'-40'N and extending on both flanks, within which a third order ridge axis discontinuity and two high temperature hydrothermal vents identified during Alvin dives in 1991 and 1994 are present. The data were recorded by four 468-channel

  1. Lake Tanganyika Hydroclimate in the Pleistocene: Insights from New Seismic Reflection Data

    NASA Astrophysics Data System (ADS)

    Scholz, Christopher; Wood, Douglas

    2016-04-01

    Lake Tanganyika, in the western branch of the East African Rift, is one of the world's largest and oldest extant lakes, and undoubtedly holds a tropical paleoclimate record of unparalleled antiquity and fidelity. In anticipation of future scientific drilling in Lake Tanganyika, we present new analyses of basin-scale seismic reflection data from the central-southeastern parts of the lake. These analyses incorporate both newly reprocessed legacy multichannel data, as well as recently acquired commercial data sets from the region near Karema, Tanzania. The new analyses confirm the presence of thick sedimentary sections, in excess of 5 km in some localities, though the section in the immediate vicinity of Karema is thinner. Data from the southern part of the lake reveal a series of marked seismic-facies transitions, including the presence of older sediment packages that underlie previously identified "pre-rift" basement (the "Nyanja Event"). These older sediment packages may substantially predate the modern lake. The high-amplitude Nyanja Event is interpreted as the onset of late-Cenozoic rifting, and the changing character of the overlying depositional sequences reflects increasing relief in the rift valley, the variability of fluvial inputs, and the intermittent connectivity of upstream lake catchments. Earlier Tanganyika sequences are dominated by shallow lake and fluvial-lacustrine facies, whereas later sequences are characterized by extensive gravity flow deposition in deep water, and pronounced erosion and incision in shallow water depths and on littoral platforms. Extensive, well-defined progradational clinoform packages are observed in the Karema area, and are interpreted as paleodeltas of the Ifume River. These deposits are interpreted as Pleistocene in age due to their shallow position in the sedimentary section, and burial depths of less than 600 m. These deposits were laid down when the level of Lake Tanganyika was 250 m or more lower than present. The

  2. Enabling Technology for the Exploration of the Arctic Ocean - Multi Channel Seismic Reflection data acquisition

    NASA Astrophysics Data System (ADS)

    Coakley, B.; Anderson, R.; Chayes, D. N.; Goemmer, S.; Oursler, M.

    2009-12-01

    Great advances in mapping the Arctic Ocean have recently been made through the relatively routine acquisition of multibeam data from icebreakers operating on various cruise. The USCGC Healy, the German icebreaker Polarstern, the Canadian icebreaker Amundsen and the Swedish icebreaker Oden all routinely collect multibeam data, even while in heavy ice pack. This increase in data has substantially improved our knowledge of the form of the Arctic Ocean seafloor. Unfortunately, it is not possible to routinely collect Multi Channel Seismic Reflection (MCS) data while underway in the ice pack. Our inability to simply collect these data restricts how we understand many of the features that segment the basin by depriving us of the historical information that can be obtained by imaging the stratigraphy. Without these data, scientific ocean drilling, the ultimate ground truth for Marine Geology, cannot be done. The technology and expertise to collect MCS must be adapted for the particular circumstances of the Arctic Ocean. While MCS data have been collected in the Arctic Ocean, the procedures have relied on icebreakers towing equipment. Since icebreakers follow the path of least resistance through the pack, data are acquired in locations that are not scientifically optimal and rarely in the relatively straight lines necessary for optimal processing. Towing in the ice pack is also difficult, inefficient and puts this equipment at substantial risk of crushing or loss. While icebreakers are one means to collect these data, it is time to conduct a systematic evaluation of the costs and benefits of different platforms for MCS data acquisition. This evaluation should enable collection of high-quality data set at selected locations to solve scientific problems. Substantial uncertainties exist about the relative capabilities, costs and limitations for acquisition of MCS data from various platforms in the Arctic Ocean. For example; - Is it possible to collect multi-channel seismic

  3. University of Texas Institute for Geophysics Seismic Reflection Data Search Site

    NASA Astrophysics Data System (ADS)

    Shipley, T. H.; Gahagan, L. M.; Johnson, K. M.

    2001-12-01

    Since 1974 the University of Texas Institute for Geophysics (UTIG) has been acquiring digital seismic reflection data. UTIG's conventional archive contains the equivalent of approximately 16,000 field tapes and 3000 processed sections. There is no simple means to peruse data that are held in the archives resulting in gross under-utilization. This is a common problem for reflection data at other research institutions as well. Conversion of the archive to a modern online searchable data base and download facility is underway. As the first part of this development, UTIG data in the offshore regions of Southwest Japan and Costa Rica-Nicaragua are now available online. Our present efforts are aimed at (1) ensuring the integrity of the digital data, (2) creating descriptive metadata, and (3) providing rudimentary web access to a searchable database with links to downloadable seismic, navigation and image files. For field records, the bulk of the data, our goal is to provide metadata for independent reprocessing for educational or research needs. Older field data require supporting information about the geometry of the experiment, observer logs and other quality control information available in notebooks. More recent experiments are collecting these data in digital form for easier inclusion in the data base and for metadata construction. All shot data are in binary SEG-Y format. A valuable component of the database is the inclusion of stacks, migrations and single-channel sections produced during the course of project-related research. These processed data include the SEG-Y files, images and trace locations (stored in the SEG-Y headers and duplicated in linked ASCII files). Metadata include a simplified processing history. For specialists, the processed SEG-Y files may be used for additional post-stack processing, display or loading into interpretation systems. For non-specialists and students the images provide instant access to geologic cross sections around the world

  4. 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.

  5. Seismic Reflection Project Near the Southern Terminations of the Lost River and Lemhi Faults, Eastern Snake River Plain, Idaho

    SciTech Connect

    S. M. Jackson; G. S. Carpenter; R. P. Smith; J. L. Casper

    2006-10-01

    Thirteen seismic reflection lines were processed and interpreted to determine the southern terminations of the Lost River and Lemhi faults along the northwest boundary of the eastern Snake River Plain (ESRP). The southernmost terminations of the Arco and Howe segments were determined to support characterization of the Lost River and Lemhi fault sources, respectively, for the INL probabilistic seismic hazard analysis. Keywords:Keywords are required forExternal Release Review*Keywords  Keywords *Contacts (Type and Name are required for each row) Type ofContactContact Name  POC Editor RecordFour commercial seismic reflection lines (Arco lines 81-1 and 81-2; Howe lines 81-3 and 82-2) were obtained from the Montana Power Company. The seismic data were collected in the early 1980’s using a Vibroseis source with station and shot point locations that resulted in 12-fold data. Arco lines 81?1 and 81?2 and Howe lines 81?3 and 82?2 are located within the basins adjacent to the Arco and Howe segments, respectively. Seven seismic lines (Arco lines A1, A2, A3, and A4 and Howe lines H1, H2, and H3) were acquired by EG&G Idaho, Inc. Geosciences for this study using multiple impacts with an accelerated weight drop source. Station and shot point locations yielded 12-fold data. The seismic reflection lines are oriented perpendicular to and at locations along the projected extensions of the Arco and Howe fault segments within the ESRP. Two seismic lines (Arco line S2 and Howe line S4) were obtained from Sierra Geophysics. In 1984, they acquired seismic reflection data using an accelerated weight drop source with station and shot point locations that yielded 6-fold data. The two seismic reflection lines are oriented perpendicular to and at locations along the projected extensions of the Arco and Howe fault segments within the ESRP. In 1992 for this study, Geotrace Technologies Inc. processed all of the seismic reflection data using industry standard processing techniques. The

  6. Late-stage stretching and subsidence rates in the Danakil Depression, evidenced from borehole records and seismic reflection data

    NASA Astrophysics Data System (ADS)

    Booth, Adam; Bastow, Ian; Magee, Craig; Keir, Derek; Corti, Giacomo; Jackson, Chris; Wilkinson, Jason

    2016-04-01

    The Ethiopian and Afar Rift systems provide a globally unique opportunity to study the incipient transition from continental rifting to sea-floor spreading. A consensus has emerged that a considerable proportion of plate extension in Ethiopia is accommodated by dyke intrusion, with smaller contributions from crustal thinning. However, observations of thinned crust and a pulse in Quaternary-Recent basaltic volcanism within Ethiopia's Danakil Depression have been cited (Bastow and Keir, 2011) as evidence that localised plate stretching may mark the final stages of continent-ocean transition. We explore this hypothesis using an archive of five 2-D seismic reflection profiles, each between 7-10 km in length, and ˜120 borehole records distributed over an area of 225 km2. From depth and age relationships of key marker horizons, we also suggest local subsidence and extension rates. The borehole archive reveals extensive evaporite sequences deposited in and around an asymmetric basin, bounded to the west by a network of east-dipping normal faults. West of the basin, the maximum observed thickness of evaporites is 150 m, beneath which are deposits of clastic sediment, but a sequence of evaporites at least 900 m thick is observed at the basin centre. The sedimentary architecture of these sequences suggests deposition in a shallow salt-pan environment, with seasonal - potentially diurnal - freshening of the brine supply (Warren, 2012). Isotopic analysis of reef carbonates in the basin flank dates the last marine incursion into the Danakil Depression at 24-230ka (Lalou et al., 1970; Bonatti et al., 1971; Bannert et al., 1971), therefore the evaporite sequence must be younger than this. A key marker horizon within the evaporites is the potash-bearing Houston Formation, also distinct in borehole records given its high porosity (25-40%) and radioactivity (50-250 API units). The elevation of the Houston Formation is ˜500 m deeper in the centre of the basin than on the flank

  7. Late-stage stretching and subsidence rates in the Danakil Depression, evidenced from borehole records and seismic reflection data

    NASA Astrophysics Data System (ADS)

    Booth, Adam; Bastow, Ian; Magee, Craig; Keir, Derek; Corti, Giacomo; Jackson, Chris; Wilkinson, Jason

    2016-04-01

    The Ethiopian and Afar Rift systems provide a globally unique opportunity to study the incipient transition from continental rifting to sea-floor spreading. A consensus has emerged that a considerable proportion of plate extension in Ethiopia is accommodated by dyke intrusion, with smaller contributions from crustal thinning. However, observations of thinned crust and a pulse in Quaternary-Recent basaltic volcanism within Ethiopia's Danakil Depression have been cited (Bastow and Keir, 2011) as evidence that localised plate stretching may mark the final stages of continent-ocean transition. We explore this hypothesis using an archive of five 2-D seismic reflection profiles, each between 7-10 km in length, and ˜120 borehole records distributed over an area of 225 km2. From depth and age relationships of key marker horizons, we also suggest local subsidence and extension rates. The borehole archive reveals extensive evaporite sequences deposited in and around an asymmetric basin, bounded to the west by a network of east-dipping normal faults. West of the basin, the maximum observed thickness of evaporites is 150 m, beneath which are deposits of clastic sediment, but a sequence of evaporites at least 900 m thick is observed at the basin centre. The sedimentary architecture of these sequences suggests deposition in a shallow salt-pan environment, with seasonal - potentially diurnal - freshening of the brine supply (Warren, 2012). Isotopic analysis of reef carbonates in the basin flank dates the last marine incursion into the Danakil Depression at 24-230ka (Lalou et al., 1970; Bonatti et al., 1971; Bannert et al., 1971), therefore the evaporite sequence must be younger than this. A key marker horizon within the evaporites is the potash-bearing Houston Formation, also distinct in borehole records given its high porosity (25-40%) and radioactivity (50-250 API units). The elevation of the Houston Formation is ˜500 m deeper in the centre of the basin than on the flank

  8. Thick- and thin-skinned tectonics of the eastern border of the Leinetal Graben, Lower Saxony, Germany, as deduced from reflection seismics

    NASA Astrophysics Data System (ADS)

    Tanner, David C.; Musmann, Patrick; Wawerzinek, Britta; Krawczyk, Charlotte M.; Buness, Hermann; Thomas, Rüdiger

    2014-05-01

    The Leinetal Graben in northern Germany is a N-S striking, intra-plate tectonic graben that, according to the youngest sediments within the graben, occurred post-Jurassic, probably late Cretaceous. We show, by interpreting two (1.8 and 3.2 km long), 2D, P-wave, reflection-seismic profiles which cross the eastern border faults of the Leinetal Graben, that the tectonic evolution began much earlier, probably in the Early Triassic. The profiles show information to a depth of approx. 1 km. Using two deep boreholes to calibrate the seismic, we interpreted the Mesozoic sedimentary layers down to Triassic Zechstein salt and the faults that affect these strata. We recognize two sets of faults: firstly steep, planar faults, that are closely clustered and terminate in the Zechstein salt, and secondly shallow faults that connect between two of the first set of faults and have very variable dip, depending on the lithology they cut at that point. These two systems represent thick- and thin-skinned tectonics, respectively. We envisage the late Triassic pro-Leinetal Graben structure as a salt down-building area or as the result of rafting of sandstone units on the salt layer. The system was later reactivated in the Late Cretaceous during intra-plate N-S compression and E-W extension. By restoring the deformation caused by the thin-skinned fault, we are able to determine the amount of area change in the hanging-wall caused by the fault, due to its undulating geometry. Area change is heterogeneous, but reaches 3-4% locally. This may well be sufficient to allow fluids to flow in the fault damage zone in these areas. It would also account for the different seismic appearance of the fault in the two profiles if fluids were heterogeneously distributed along it. This method of retro-deformation is entirely appropriate to determine the suitability of a brittle fault for, for instance, geothermal applications.

  9. Reflection seismic survey across a fault zone in the Leinetal Graben, Germany, using P- and SH-waves

    NASA Astrophysics Data System (ADS)

    Musmann, P.; Polom, U.; Buness, H.; Thomas, R.

    2012-04-01

    Fault systems are considered as a valuable hydro-geothermal reservoir for heat and energy extraction, as permeability may be enhanced compared to the surrounding host rock. Seismic measurements are a well established tool to reveal their structure at depth. Apart from structural parameters like dip, extent and throw, they allow us to derive lithologic parameters, e.g. seismic velocities and impedance. Usually, only compressional waves have been used so far. In the context of the "gebo" Collaborative Research Program, seismic methods are revised to image and characterize geological fault zones in order to minimize the geological and technical risk for geothermal projects. In doing so, we evaluate and develop seismic acquisition, processing and interpretation techniques both for compressional and shear wave surveys to estimate the geothermal potential of fault zones. Here, we present results from high-resolution P- and SH-wave reflection seismic surveys along one and the same profile. They were carried out across the eastern border of the Leinetal Graben, Lower Saxony, Germany. At this survey site, primarily Triassic units crop out that are disrupted by major fault system probably extending down into Permian Zechstein. The seismic P-wave measurements (2.5 m CDP spacing, 20 - 180 Hz sweep sent out by a small vibrator) imaged the structure of the subsurface and its fault inventory with high resolution. Imaging ranges from approximately 50 m (base Keuper) to approximately 1.8 km (within Zechstein) depth. The profiles reveal that the area has undergone multiphase tectonics. This becomes manifest in a complex seismic reflection pattern. In addition the P-wave velocity model shows several features that can be related to folding and faulting. Preliminary results of the SH-wave measurements (0.5 m CDP spacing, 10 - 100 Hz sweep) show that the complex structural geological settings in the subsurface, as imaged by the P-wave survey, can also be imaged by a reflection shear

  10. High-resolution marine seismic reflection data from the San Francisco Bay area

    USGS Publications Warehouse

    Childs, Jonathan R.; Hart, Patrick; Bruns, Terry R.; Marlow, Michael S.; Sliter, Ray

    2000-01-01

    Between 1993 and 1997, the U.S. Geological Survey acquired high-resolution, marine seismic-reflection profile data across submerged portions of known and inferred upper crustal fault zones throughout the greater San Francisco Bay area. Surveys were conducted oversouth San Francisco Bay in the vicinity of the San Bruno shoal (roughly between the San Francisco and Oakland airports), over the offshore extension of the San Andreas fault system west of the Golden Gate, over the Hayward fault to Rodgers Creek fault step-over in San Pablo Bay, and over the Kirby Hills fault where it crosses the western Sacramento Delta. Reconnaissance profiles were acquired elsewhere throughout the San Francisco and San Pablo Bays. These data were acquired by the U.S. Geological Survey, Western Coastal and Marine Geology Team, under the auspices of the Central California/San Francisco Bay Earthquake Hazards Project. Analysis and interpretation of some of these profiles has been published by Marlow and others (1996, 1999). Further analysis and interpretation of these data are available in a USGS. Professional Paper Crustal Structure of the Coastal and Marine San Francisco Bay Region, T. Parsons, editor, http://geopubs.wr.usgs.gov/prof-paper/pp1658/ [link added 2012 mfd].

  11. 3D Seismic Reflection Data: Has the Geological Hubble Retained Its Focus?

    NASA Astrophysics Data System (ADS)

    Jackson, Christopher

    2016-04-01

    In their seminal paper in 2002, Joe Cartwright and Mads Huuse referred to 3D seismic reflection data as the 'Geological Hubble', illustrating how these data had the potential to revolutionise our understanding of the genesis and evolution of sedimentary basins. 14 years on, I will here outline just some of the key recent advances made in our understanding of basin structure and stratigraphy, focusing on: (i) the intrusion and extrusion of igneous rocks; (ii) salt tectonics, with particular emphasis on intrasalt structure and the kinematics and mechanics of diapirism; (iii) the geometry and growth of normal faults; and (iv) the structure and emplacement of mass-transport complexes (MTCs). I will stress that future advances at least partly relies on hydrocarbon exploration companies and government agencies continuing to make their data freely available via easy-to-access data portals. I will issue a clarion call to academics, stressing that 'geodynamicists', sedimentologists, structural geologists and geomorphologists, amongst others, can benefit from utilising what I believe are currently an underused data type.

  12. Seismic reflection study of recessional moraines beneath Lake Superior and their relationship to regional deglaciation

    USGS Publications Warehouse

    Landmesser, C.W.; Johnson, T.C.; Wold, R.J.

    1982-01-01

    Approximately 8000 km of continuous seismic reflection profiles throughout Lake Superior were examined for evidence of recessional moraines and other ice-margin deposits associated with the retreat of late Wisconsin ice. These features are correlated with the record of glacial-lake evolution in western Lake Superior. An offlapping sequence of glacial and glacial-lacustrine dediments overlying bedrock is recognized in west-central Lake Superior that is progressively younger to the northeast. The sequence underlies more recent glaical-lacustrine and postglacial sediments. Four facies are recognized on the basis of geomorphologic and acoustic properties and are interpreted to represent a southwest-to-northeast assemblage of: proglacial stratified drift (facies A), drift in major end moraines (facies B), till deposited as glacial retreat resumed, or possibly late-stage ablation till (facies C), and basal till (facies D). The prominent moraines of facies B are unusually thick and are believed to mark the ice-margin shorelines of successive major proglacial lakes that formerly occupied parts of western Lake Superior. The moraines are tentatively correlated with Glacial Lake Duluth (unit 1), Glacial Lake Washburn (unit 2), and Glacial Lake Beaver Bay (unit 3), the most prominent of lakes drained via the progressively lower outlets via the Moose Lake/ Brule-St. Croix Rivers, the Huron Mountains, and the Au Train-Whitefish regions, respectively. ?? 1982.

  13. Structure of the eastern Seattle fault zone, Washington state: New insights from seismic reflection data

    USGS Publications Warehouse

    Liberty, L.M.; Pratt, T.L.

    2008-01-01

    We identify and characterize the active Seattle fault zone (SFZ) east of Lake Washington with newly acquired seismic reflection data. Our results focus on structures observed in the upper 1 km below the cities of Bellevue, Sammamish, Newcastle, and Fall City, Washington. The SFZ appears as a broad zone of faulting and folding at the southern boundary of the Seattle basin and north edge of the Seattle uplift. We interpret the Seattle fault as a thrust fault that accommodates north-south shortening by forming a fault-propagation fold with a forelimb breakthrough. The blind tip of the main fault forms a synclinal growth fold (deformation front) that extends at least 8 km east of Vasa Park (west side of Lake Sammamish) and defines the south edge of the Seattle basin. South of the deformation front is the forelimb break-through fault, which was exposed in a trench at Vasa Park. The Newcastle Hills anticline, a broad anticline forming the north part of the Seattle uplift east of Lake Washington, is interpreted to lie between the main blind strand of the Seattle fault and a backthrust. Our profiles, on the northern limb of this anticline, consistently image north-dipping strata. A structural model for the SFZ east of Lake Washington is consistent with about 8 km of slip on the upper part of the Seattle fault, but the amount of motion is only loosely constrained.

  14. The MIRROR cruise (2011): Deep crustal structure of the Moroccan Atlantic Margin from wide-angle and reflection seismic data

    NASA Astrophysics Data System (ADS)

    Klingelhoefer, F.; Aslanian, D.; Sahabi, M.; Moulin, M.; Schnurle, P.; Berglar, K.; Biari, Y.; Feld, A.; Graindorge, D.; Corela, C.; Mehdi, K.; Zourarah, B.; Perrot, J.; Alves Ribeiro, J.; Reichert, C. J.

    2011-12-01

    The study of conjugate margins is important to test different hypotheses of rifting and initial opening of an ocean. In this scope, seven wide-angle seismic profiles were acquired on the Moroccan Atlantic margin (at the latitudes between 32° and 33° N) together with coincident deep frequency reflection seismic data during the MIRROR cruise in May and June 2011. The main seismic profile is conjugate to an existing wide-angle seismic profile off Nova Scotia (SMART 2). Further objectives of the cruise were to image ocean-continent transition zone, to detect and eventually quantify exhumed upper mantle material present in this zone and to determine the origin of the high amplitude West African Magnetic Anomaly, which is conjugate to the north American East Coast Magnetic Anomaly and can be linked to the opening of the Atlantic. Two of the newly acquired profiles are located perpendicular and five parallel to the Moroccan margin. The seismic profiles are between 130 and 260 km in length and between 28 and 13 ocean-bottom seismometers were deployed on each one. One profile was extended on land by 15 landstations in order to better image the zone of continental thinning. A 4.5 km digital streamer and a 7200 cu inch tuned airgun array were used for the acquisition of the seismic data. Additionally magnetic, bathymetric and high resolution seismic data were acquired in the study region. Preliminary results from tomographic inversion of the first arrivals from the ocean-bottom seismometer data image the zone of crustal thinning from about 25 km to 6 km in the basin along about 70 kilometers of the profiles which are located perpendicular to the margin. The oceanic crust can be divided into 2 regions, based on the lower crustal velocities. Upper mantle velocities are about 8.0 km/s. The coincident reflection seismic data show the fine basement and sedimentary structures including salt tectonics in the basin. The comparative study of the two conjugate profiles on the

  15. Evidence for the use of reflected self-generated seismic waves for spatial orientation in a blind subterranean mammal.

    PubMed

    Kimchi, Tali; Reshef, Moshe; Terkel, Joseph

    2005-02-01

    Subterranean mammals like the blind mole-rat (Rodentia: Spalax ehrenbergi) are functionally blind and possess poor auditory sensitivity, limited to low-frequency sounds. Nevertheless, the mole-rat demonstrates extremely efficient ability to orient spatially. A previous field study has revealed that the mole-rat can assess the location, size and density of an underground obstacle, and accordingly excavates the most efficient bypass tunnel to detour around the obstacles. In the present study we used a multidisciplinary approach to examine the possibility that the mole-rat estimates the location and physical properties of underground obstacles using reflected self-generated seismic waves (seismic 'echolocation'). Our field observations revealed that all the monitored mole-rats produced low-frequency seismic waves (250-300 Hz) at intervals of 8+/-5 s (range: 1-13 s) between head drums while digging a bypass to detour an obstacle. Using a computerized simulation model we demonstrated that it is possible for the mole-rat to determine its distance from an obstacle boundary (open ditch or stone) by evaluating the amplitude (intensity) of the seismic wave reflected back to it from the obstacle interface. By evaluating the polarity of the reflected wave the mole-rat could distinguish between air space and solid obstacles. Further, the model showed that the diffracted waves from the obstacle's corners could give the mole-rat precise information on the obstacle size and its relative spatial position. In a behavioural experiment using a special T-maze setup, we tested whether the mole-rat can perceive seismic waves through the somatosensory system and localize the source. The results revealed that the mole-rat is able to detect low frequency seismic waves using only its paws, and in most cases the mole-rats determined accurately the direction of the vibratory source. In a histological examination of the glabrous skin of the mole-rat's paws we identified lamellate corpuscle

  16. Comparison of P- and S-wave velocity profiles obtained from surface seismic refraction/reflection and downhole data

    USGS Publications Warehouse

    Williams, R.A.; Stephenson, W.J.; Odum, J.K.

    2003-01-01

    High-resolution seismic-reflection/refraction data were acquired on the ground surface at six locations to compare with near-surface seismic-velocity downhole measurements. Measurement sites were in Seattle, WA, the San Francisco Bay Area, CA, and the San Fernando Valley, CA. We quantitatively compared the data in terms of the average shear-wave velocity to 30-m depth (Vs30), and by the ratio of the relative site amplification produced by the velocity profiles of each data type over a specified set of quarter-wavelength frequencies. In terms of Vs30, similar values were determined from the two methods. There is <15% difference at four of the six sites. The Vs30 values at the other two sites differ by 21% and 48%. The relative site amplification factors differ generally by less than 10% for both P- and S-wave velocities. We also found that S-wave reflections and first-arrival phase delays are essential for identifying velocity inversions. The results suggest that seismic reflection/refraction data are a fast, non-invasive, and less expensive alternative to downhole data for determining Vs30. In addition, we emphasize that some P- and S-wave reflection travel times can directly indicate the frequencies of potentially damaging earthquake site resonances. A strong correlation between the simple S-wave first-arrival travel time/apparent velocity on the ground surface at 100 m offset from the seismic source and the Vs30 value for that site is an additional unique feature of the reflection/refraction data that could greatly simplify Vs30 determinations. ?? 2003 Elsevier Science B.V. All rights reserved.

  17. Seismic-reflection profiles of the central part of the Clarendon-Linden fault system of western New York in relation to regional seismicity

    USGS Publications Warehouse

    Fakundiny, R.H.; Pomeroy, P.W.

    2002-01-01

    Geological and geophysical research in upstate New York, with few exceptions, has not definitively associated seismicity with specific Proterozoic basement or Paleozoic bedrock structures. The central part of the Clarendon-Linden fault system (CLFS) between Batavia and Dale, NY is one of those exceptions where seismicity has been studied and has been spatially associated with structure. The CLFS is either a complex system of long faults with associated shorter branches and parallel segments, or a region of many short faults aligned north-south from the Lake Ontario shore southward to Allegany County, NY. Interpretation of 38 km of Vibroseis and approximately 56 km of conventional seismic-reflection data along 13 lines suggests that the CLFS is a broad zone of small faults with small displacements in the lower Paleozoic bedrock section that is at least 77 km long and 7-17 km wide and spatially coincident with a northtrending geophysical (combined aeromagnetic and gravity) lineament within the basement. The relative offset across the faults of the system is more than 91 m near Attica, NY. The CLFS is the expression of tectonic crustal adjustments within the Paleozoic rock above the boundary of two basement megablocks of differing petrologic provinces and differing earthquake characteristics that forms the eastern side of the Elzevir-Frontenac boundary zone. Deep seismic-reflection profiles display concave-eastward listric faults that probably merge at depth near the mid-crustal boundary layer. An interpretive vertical section provides the setting for refined definitions of the CLFS, its extensions at depth and its relation to seismicity. Most modern seismicity in western New York and the Niagara Peninsula of Ontario occurs in apparent patterns of randomly dispersed activity. The sole exception is a line of seven epicenters of small earthquakes that trend east from Attica, NY into the Rochester basement megablock. Earthquakes may be triggered at the intersections of

  18. A Seismic Reflection Profiling Survey of Lake Toba, Sumatra, Indonesia: Preliminary Findings from the Field

    NASA Astrophysics Data System (ADS)

    Chesner, C. A.; Dolan, M. T.; Halsor, S. P.; Bohnenstiehl, D. R.; Liu, J.; Nasution, A.

    2012-12-01

    Lake Toba lies within the giant Toba Caldera that last erupted 74,000 years ago. In its early history, Lake Toba may have covered about 1800 km2, possibly reaching depths of 750 m. The central portion of the 100 x 30 km caldera has since been uplifted to form the asymmetrical Samosir Island resurgent dome (60 x 20 km). Its upper surface dips gently to the west while its eastern margin consists of a series of parallel normal faults with total displacement of at least 1100 m. Several lava domes have been emplaced along these faults as well as the southwestern caldera ring fracture. At least 30 m of laminated tuffaceous sand and silt, diatomaceous clay, diatomites, and volcanic ash cover Samosir Island and sediments up to 100 m have been reported. In an effort to understand the post-collapse sedimentation, structural, volcanic, and resurgent histories of the caldera, we conducted a 14 day seismic reflection profiling survey of Lake Toba in July/August 2012. An EdgeTech SB-512i "chirp" sonar unit was towed across about 900 km of transect lines. Signal penetration was not affected by water depth, which sometimes exceeded 500 m, but was often reduced by adverse tow conditions or strong stratigraphic reflectors, and occasionally lost altogether possibly due to gas pockets in the sediments. In areas of flat-lying or gently sloping lake bottom, about 10-30 m of lake sediments was typically detected. Along the steep caldera bounding faults and the faulted eastern margin of the Samosir resurgent dome virtually no sediments were detected. However, up to 90 m of laminated sediments were apparent on the crest and gently sloping submerged portions of Samosir. These thick sedimentary sequences showed distinct marker horizons with evidence of faulting, folding, sliding, and slumping. Local unconformities or onlapping sequences demonstrated discrete sedimentary episodes. Several subaqueous lava domes were discovered that uplifted, folded, and sometimes truncated the sedimentary

  19. Structure of the Gabon Margin from integrated seismic reflection and gravity data

    NASA Astrophysics Data System (ADS)

    Dupré, Stéphanie; Cloetingh, Sierd; Bertotti, Giovanni

    2011-06-01

    In the South Gabon Basin, deep multi-channel seismic reflection and gravity modeling analysis have shed light on key features of the structure of the margin. The thinned continental crust beneath the Gabon Margin appears to be composed of two distinct layers, separated by a clear, strong and more or less continuous reflector running in the 7-10 s TWT window. The lower crust is characterized by a higher density, intermediate between the lower values of the upper crust and the denser values of the mantle. The lower crust is irregularly shaped and presents lateral thickness variations along the direction of thinning and along the coast. In the offshore thinned continental domain, the lower and upper crust form a 20-25 km thick body. Crustal thicknesses point to a relatively sharp and narrow transition, along a few tens of kilometers, between the unthinned and the thinned continental crust. The high density layer identified offshore Gabon presents similar characteristics in density, geometry and spatial distribution, as the underplated magmatic bodies observed along volcanic margins, e.g. along the South Atlantic Namibia Margin or the North Atlantic Vøring Margin. Although this lower crustal body could possibly represent ultra mafic serpentinized rocks or high grade metamorphic crustal rocks, we suggest that it could be composed of mafic rocks. Magmas resulting from partial melting during rifting may underplate the crust and/or be intruded in the lower crust through a system of dykes and sills. In this view, the present-day crustal thicknesses along rifted margins, characterized by magmatic underplating and/or intrusion, are not representative of the thinning that the crust experienced during rifting. Results of this study point to relatively shallow sedimentary basins along the South Gabon Margin. The deepest offshore depocenters located under the westernmost side of the continental platform appear to be associated with the deepest syn-rift basins These basins seem

  20. Subsurface structure along the eastern marginal fault zone of Yokote Basin by Seismic reflection profiling studies, Northeast Japan

    NASA Astrophysics Data System (ADS)

    Kagohara, K.; Imaizumi, T.; Echigo, T.; Miyauchi, T.; Sato, H.

    2005-12-01

    Typical reverse faults, which are known as Senya earthquake faults appeared along the western foot of the Mahiru Mountains, associated with The Rikuu Earthquake (Mj7.2) of 1896 in Northeast Japan. Eastern marginal fault zone of the Yokote Basin consist of four main surface ruptures, about 35 km long, Obonai fault, Shiraiwa fault, Ota fault and Senya fault, depending on their continuity and strike (Matsuda et al., 1980). We carried out the seismic reflection profiling across these faults (Kawaguchi03 Seismic line, Unjono04 Seismic line and Kotaki05 Seismic line) to clarify the subsurface structure of these reverse fault system based on the data of tectonic geomorphology and structural geology and furthermore, to discuss the timing of migration of the thrusting from the range front to the basin margin. The seismic source was mini-vibrator trucks, with 20seconds of 10-100Hz signals at 10m or 5m intervals. The sweep signals were recorded by a digital telemetry system (GDAPS-4a) with 10 Hz geophones. The obtained seismic reflection data were processed by conventional Common mid-point (CMP) methods, including post-stack migration and depth conversion. The resulting seismic reflection profile reveals a thrust structure beneath these areas. At the Center of Senya hills there are two thrusts and one high angle reverse fault (1997 Seismic Line). Senya fault is an active frontal emergent thrust with flat and ramp structure. Although, the high angle reverse fault, located along the foot of the range is a short-cut branching fault from the Senya fault in the central part of the Senya hill (Sato et al., 1998), in the Unjono04 seismic line, the depth of the flat and ramp structure gradually shallow in the north part of the Senya hill, where the flexure scarp accompanied with antithetic faults formed on the fluvial terraces. In the Kawaguchi03 seismic line, the concealed fault, 0.5km below the surface, branched from the master Ota fault, form a flexure scarplet on the alluvial fan

  1. USING RECENT ADVANCES IN 2D SEISMIC TECHNOLOGY AND SURFACE GEOCHEMISTRY TO ECONOMICALLY REDEVELOP A SHALLOW SHELF CARBONATE RESERVOIR: VERNON FIELD, ISABELLA COUNTY, MI.

    SciTech Connect

    James R. Wood; W. Quinlan

    2003-07-01

    The principal objective of this demonstration project is to test surface geochemical techniques for detecting trace amounts of light hydrocarbons in pore gases as a means of reducing risk in hydrocarbon exploration and production. As part of the project, a field demonstration was undertaken to assess the validity and usefulness of the microbial surface geochemical technique. The surface geochemistry data showed a strong anomaly in the Myrtle Beach area that would justify drilling by itself and even more so in conjunction with the structural interpretation from the 3D seismic data. The Myrtle Beach geochemical survey indicated a good to excellent prospect which was confirmed by drilling. Presented in this quarterly report is the Case History and Well Summary for the Myrtle Beach area in Burke County, North Dakota. This case history presents the important technical details regarding the geochemistry and the two vertical wells that are part of this field demonstration, and the applicability of these results to other demonstration projects. This format could be duplicated for other demonstration projects and is being used on all subsequent field demonstrations as they near completion.

  2. Simulation of seismic wave propagation in 2D poroelastic media using weighted-averaging finite difference stencils in the frequency-space domain

    NASA Astrophysics Data System (ADS)

    Yang, Qingjie; Mao, Weijian

    2016-10-01

    The poroelastodynamic equations are used to describe the dynamic solid-fluid interaction in the reservoir. To obtain the intrinsic properties of reservoir rocks from geophysical data measured in both laboratory and field, we need an accurate solution of the wave propagation in porous media. At present, the poroelastic wave equations are mostly solved in the time domain, which involves a difficult and complicated time convolution. In order to avoid the issues caused by the time convolution, we propose a frequency-space domain method. The poroelastic wave equations are composed of a linear system in the frequency domain, which easily takes into account the effects of all frequencies on the dispersion and attenuation of seismic wave. A 25-point weighted-averaging finite different scheme is proposed to discretize the equations. For the finite model, the perfectly matched layer technique is applied at the model boundaries. We validated the proposed algorithm by testing three numerical examples of poroelastic models, which are homogenous, two-layered and heterogeneous with different fluids, respectively. The testing results are encouraging in the aspects of both computational accuracy and efficiency.

  3. A high resolution seismic reflection image for the oceanic LAB (Lithosphere-Asthenosphere Boundary), beneath southern North Island, New Zealand

    NASA Astrophysics Data System (ADS)

    Stern, T. A.; Henrys, S. A.; Okaya, D. A.; Savage, M. K.; Sato, H.; Iwasaki, T.; Louie, J. N.; Lamb, S. H.

    2014-12-01

    We present the first high-resolution, multichannel, seismic-reflection image for the base of an oceanic plate. Our image is based on an 85 km-long, ~ 900 station deployment across the lower North Island of New Zealand. 12 x 500 kg dynamite shots were used as seismic sources. Strong reflections at a two way travel time of 9-12 s define the top of the plate that dips to the NW at ~ 12-15 degrees. Between 27-32 s we identify a pair of reflections on some shot gathers that are interpreted to come from a reflection 90-100 km deep, that dips to the NW at 15 degrees. We interpret the reflection pair as marking a Lithosphere-Asthenosphere Boundary (LAB) zone at the base of the Pacific plate. Using all 12 shots we made a CDP-stacked image (maximum fold = 15) that shows the LAB as a double event (2-3 s apart) dipping roughly parallel to the top of the plate and Benioff zone. Shot quality varies but the highest frequencies we record from the base of the plate are ~ 18 Hz, suggesting a boundary zone < 1 km thick. Seismic amplitude attributes, calibrated to the reflection from the top of the plate, indicate P-wave speed drops off at least 8% across the LAB boundary. The double reflection at the LAB is interpreted to be a 10 km-thick layer of low seismic wave speed. Because it is so sharp it cannot be a thermal boundary and must represent some form of mechanical change. Previous attempts to explain the abruptness of seismic wave speed changes at the LAB have appealed to layered zones of ponded melt, or anelastic relaxation due to water accumulating beneath the LAB. Both mechanisms may explain our observations and both would point to low viscosity below the LAB. However, the fact we see a ~ 10 km thick channel, with strong acoustic impedances each side of the channel, suggests a shear zone where plate motion ( ~ 9 cm/y in hotspot reference frame) is taken up and strain rates of ~3 x 10-13 s-1 are generated. This interpreted, low wave-speed, low-viscosity, shear zone appears to be

  4. Seismic Reflection Images of the 1946 Nankai Megasplay Fault off Kii Peninsula, southwest Japan (Invited)

    NASA Astrophysics Data System (ADS)

    Park, J.; Kodaira, S.

    2010-12-01

    The Nankai Trough subduction zone, where the Philippine Sea Plate subducts beneath the Eurasian Plate to the NNW, is known as one of the best-suited convergent plate margins for studying subduction zone earthquakes. Historically, large earthquakes along the subduction zone have occurred with a recurrence interval of 100-200 years. The Nankai subduction zone has been of interest from the viewpoints of seismic hazards and earthquake potential since the last two large megathrust earthquakes, i.e., the 1944 Tonankai (M = 8.1) and 1946 Nankaido (M = 8.3) events, which occurred off the Kii peninsula, southwest Japan. The Nankai subduction zone may be divided into four discrete domains (A through D) marked by the megathrust earthquake rupture, each of which roughly corresponds to a geologically well-defined forearc basin. The boundary between domains A-B (western Nankai) and C-D (eastern Nankai) has almost persisted over the historic earthquake cycles, except for Hoei earthquake (M = 8.7) in 1707. Even though a numerical experiment has succeeded in simulating the 1707 Hoei event simultaneously rupturing the domains A, B, and C, there has been no direct geologic and geophysical observations to discuss the existence of boundary between domains A-B and C-D. In order to obtain detailed crustal structure images of the 1946 Nankai earthquake rupture zone, we conducted a multi-channel seismic (MCS) reflection survey in the Nankai Trough subduction zone off Kii Peninsula, using R/V Kairei of the Japan Marine Science and Technology Center in 2001. For deep-penetration seismic imaging, a large volume (~200 liters) air gun array was used as the controlled sound source. The MCS data recording was done with a 4 km, 160-channel streamer with 25 m group spacing. Data processing included trace editing, pre-filtering, spherical divergence correction, signature deconvolution, CMP (Common Mid Point) sort, NMO correction, multiple suppression by parabolic radon transform, CMP stack, and time

  5. Seismic Reflection Imaging of Along-Strike Changes in the Hikurangi Margin Subduction Interface, North Island, New Zealand

    NASA Astrophysics Data System (ADS)

    Barker, D.; Sutherland, R.; Bannister, S.; Toulmin, S.; Henrys, S.; Reyners, M.; Pecher, I.; Uruski, C.; Maslen, G.

    2006-12-01

    Seismic reflection data from the subduction margin off the east coast of the North Island, New Zealand, show first-order structural features in the upper plate and subducting slab geometry that we relate to plate coupling at the subduction interface. Beneath the eastern coastline of North Island, New Zealand, the subducted Pacific plate dips at less than 3 degrees to the northwest and is at a depth of less than 15 km. This shallow geometry is optimum for detailed geophysical studies of the subduction decollement using both active-source and passive-source experiments. In March-May 2005 a new industry seismic reflection survey, 05CM, was undertaken offshore of the east coast. Although primarily intended to identify hydrocarbon plays, the survey was also designed to be capable of seismically imaging the subducted plate, using a 12-km-long streamer and 12 s record lengths. In total, over 2800 km of data were recorded along the margin. Repeated damage to the seismic streamer from shark bites meant only some profiles were collected to the original full survey specifications. Remaining data were acquired with a shorter streamer (4-6 km) and record length (8 s), still sufficient to provide a grid of high quality reflection data revealing first-order structural features of the upper plate and along-strike changes in subducting slab geometry. We suggest that these along-strike changes reflect the transition from a coupled plate interface in the south to decoupled in the north, a feature of the Hikurangi subduction system previously inferred from other geological and geophysical observations.

  6. USING RECENT ADVANCES IN 2D SEISMIC TECHNOLOGY AND SURFACE GEOCHEMISTRY TO ECONOMICALLY REDEVELOP A SHALLOW SHELF CARBONATE RESERVOIR: VERNON FIELD, ISABELLA COUNTY, MI.

    SciTech Connect

    James R. Wood; T.J. Bornhorst; S.D. Chittichk; William B. Harrison; W. Quinlan

    2001-01-01

    The geochemical sampling team collected additional 148 samples at Vernon Field along 5 new traverses. Most of the locations were sampled for three types of analyses: microbial, iodine and enzyme leach; no results from the second batch of samples were available in time for this report. In addition to the sampling, a study was begun on the feasibility of collecting and analyzing hydrocarbon gases (C1-C8) directly. Although several companies offer these services, the cost ($200-300/sample w/o sampling fee) is high, on par with the cost of a 3D seismic survey, and may not include the raw data. However direct sampling of reservoir gases collecting in the soil appear to offer the best approach and should be included in this study. It would probably work well at Vernon Field. It may be possible to lower costs considerably; initial estimates of $20/sample for GCMS (Gas Chromatography--mass spectrometry) analysis are attractive and might induce to Michigan producers to include soil surveys in their routine field work-ups. A complete set of digital data was assembled for Vernon Field and nearby locations. The set consists of well locations, formation top picks, lithologies and scanned images of driller's reports and scout tickets. Well logs are still being located. The annual meeting for the Class Revisit work group is tentatively scheduled for the week of March 1-7 in Tampa, Fl. By that time all of the geochemical data will be available and final decisions regarding drilling can be made.

  7. Deep crustal structure of the North-West African margin from combined wide-angle and reflection seismic data (MIRROR seismic survey)

    NASA Astrophysics Data System (ADS)

    Biari, Y.; Klingelhoefer, F.; Sahabi, M.; Aslanian, D.; Schnurle, P.; Berglar, K.; Moulin, M.; Mehdi, K.; Graindorge, D.; Evain, M.; Benabdellouahed, M.; Reichert, C.

    2015-08-01

    The structure of the Moroccan and Nova Scotia conjugate rifted margins is of key importance for understanding the Mesozoic break-up and evolution of the northern central Atlantic Ocean basin. Seven combined multichannel reflection (MCS) and wide-angle seismic (OBS) data profiles were acquired along the Atlantic Moroccan margin between the latitudes of 31.5° and 33° N during the MIRROR seismic survey in 2011, in order to image the transition from continental to oceanic crust, to study the variation in crustal structure, and to characterize the crust under the West African Coast Magnetic Anomaly (WACMA). The data were modeled using a forward modeling approach. The final models image crustal thinning from 36 km thickness below the continent to approximately 8 km in the oceanic domain. A 100 km wide zone characterized by rough basement topography and high seismic velocities up to 7.4 km/s in the lower crust is observed westward of the West African Coast Magnetic Anomaly. No basin underlain by continental crust has been imaged in this region, as has been identified north of our study area. Comparison to the conjugate Nova Scotian margin shows a similar continental crustal thickness and layer geometry, and the existence of exhumed and serpentinized upper mantle material on the Canadian side only. The oceanic crustal thickness is lower on the Canadian margin.

  8. tomo3d: a new 3-D joint refraction and reflection travel-time tomography code for active-source seismic data

    NASA Astrophysics Data System (ADS)

    Meléndez, A.; Korenaga, J.; Sallares, V.; Ranero, C. R.

    2012-12-01

    We present the development state of tomo3d, a code for three-dimensional refraction and reflection travel-time tomography of wide-angle seismic data based on the previous two-dimensional version of the code, tomo2d. The core of both forward and inverse problems is inherited from the 2-D version. The ray tracing is performed by a hybrid method combining the graph and bending methods. The graph method finds an ordered array of discrete model nodes, which satisfies Fermat's principle, that is, whose corresponding travel time is a global minimum within the space of discrete nodal connections. The bending method is then applied to produce a more accurate ray path by using the nodes as support points for an interpolation with beta-splines. Travel time tomography is formulated as an iterative linearized inversion, and each step is solved using an LSQR algorithm. In order to avoid the singularity of the sensitivity kernel and to reduce the instability of inversion, regularization parameters are introduced in the inversion in the form of smoothing and damping constraints. Velocity models are built as 3-D meshes, and velocity values at intermediate locations are obtained by trilinear interpolation within the corresponding pseudo-cubic cell. Meshes are sheared to account for topographic relief. A floating reflector is represented by a 2-D grid, and depths at intermediate locations are calculated by bilinear interpolation within the corresponding square cell. The trade-off between the resolution of the final model and the associated computational cost is controlled by the relation between the selected forward star for the graph method (i.e. the number of nodes that each node considers as its neighbors) and the refinement of the velocity mesh. Including reflected phases is advantageous because it provides a better coverage and allows us to define the geometry of those geological interfaces with velocity contrasts sharp enough to be observed on record sections. The code also

  9. tomo3d: a new 3-D joint refraction and reflection travel-time tomography code for active-source seismic data

    NASA Astrophysics Data System (ADS)

    Meléndez, A.; Korenaga, J.; Sallarès, V.; Ranero, C. R.

    2012-04-01

    We present the development state of tomo3d, a code for three-dimensional refraction and reflection travel-time tomography of wide-angle seismic data based on the previous two-dimensional version of the code, tomo2d. The core of both forward and inverse problems is inherited from the 2-D version. The ray tracing is performed by a hybrid method combining the graph and bending methods. The graph method finds an ordered array of discrete model nodes, which satisfies Fermat's principle, that is, whose corresponding travel time is a global minimum within the space of discrete nodal connections. The bending method is then applied to produce a more accurate ray path by using the nodes as support points for an interpolation with beta-splines. Travel time tomography is formulated as an iterative linearized inversion, and each step is solved using an LSQR algorithm. In order to avoid the singularity of the sensitivity kernel and to reduce the instability of inversion, regularization parameters are introduced in the inversion in the form of smoothing and damping constraints. Velocity models are built as 3-D meshes, and velocity values at intermediate locations are obtained by trilinear interpolation within the corresponding pseudo-cubic cell. Meshes are sheared to account for topographic relief. A floating reflector is represented by a 2-D grid, and depths at intermediate locations are calculated by bilinear interpolation within the corresponding square cell. The trade-off between the resolution of the final model and the associated computational cost is controlled by the relation between the selected forward star for the graph method (i.e. the number of nodes that each node considers as its neighbors) and the refinement of the velocity mesh. Including reflected phases is advantageous because it provides a better coverage and allows us to define the geometry of those geological interfaces with velocity contrasts sharp enough to be observed on record sections. The code also

  10. 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.

  11. Crustal deformation styles along the reprocessed deep seismic reflection transect of the Central Iberian Zone (Iberian Peninsula)

    NASA Astrophysics Data System (ADS)

    Ehsan, Siddique Akhtar; Carbonell, Ramon; Ayarza, Puy; Martí, David; Pérez-Estaún, Andrés; Martínez-Poyatos, David Jesús; Simancas, Jose Fernando; Azor, Antonio; Mansilla, Luis

    2014-05-01

    The multichannel normal incidence (230 km long) deep seismic reflection profile ALCUDIA was acquired in summer 2007. This transect samples an intracontinental Variscan orogenic crust going across, from north to south, the major crustal domain (the Central Iberian Zone) and its suture zone with the Ossa-Morena Zone (the Central Unit) both build up most of the southwestern part of the Iberian Peninsula basement. This high resolution (60-90 fold) profile images about 70 km depth (20 s TWTT) of the continental lithosphere. A new data processing flow provides better structural constraints on the shallow and deep structures resulting in an image that reveals indentation features which strongly suggest horizontal tectonics. The ALCUDIA seismic image shows an upper crust c. 13 km thick decoupled from the comparatively reflective lower crust. The shallow reflectivity of the upper crust can be correlated with surface geological features mapped in the field whereas the deep reflectivity represents inferred imbricate thrust systems and listric extensional faults. The reflectivity of the mid-lower crust is continuous, high amplitude, and horizontal to arcuate though evidences of deformation are present as ductile boudinage structures, thrusting and an upper mantle wedge, suggesting a transpressional flower structure. The image reveals a laminated c. 1.5 km thick, subhorizontal to flat Moho indicating an average crustal thickness of 31-33 km. The Moho shows laterally variable signature, being highly reflective beneath the Central Iberian Zone, but discontinuous and diffuse below the Ossa-Morena Zone. The gravity response suggests relatively high density bodies in the mid-lower crust of the southern half of the transect. The seismic results suggest two major horizontal limits, a horizontal discontinuity at c. 13-15 km (corresponding to the brittle-ductile transition) and the Moho boundary both suggested to act as decoupling surfaces.

  12. Ground magnetic studies along a regional seismic-reflection profile across Bare Mountain, Crater Flat and Yucca Mountain, Nevada

    SciTech Connect

    Langenheim, V.E.; Ponce, D.A.

    1995-12-31

    Ground magnetic data were collected along a 26-km-long regional seismic-reflection profile in southwest Nevada that starts in the Amargosa Desert, crosses Bare Mountain, Crater Flat and Yucca Mountain, and ends in Midway Valley. Parallel ground magnetic profiles were also collected about 100 m to either side of the western half of the seismic-reflection line. The magnetic data indicate that the eastern half of Crater Flat is characterized by closely-spaced faulting (1--2 km) in contrast to the western half of Crater Flat. Modeling of the data indicates that the Topopah Spring Tuff is offset about 250 m on the Solitario Canyon fault and about 50 m on the Ghost Dance fault. These estimates of fault offset are consistent with seismic-reflection data and geologic mapping. A broad magnetic high of about 500--600 nT is centered over Crater Flat. Modeling of the magnetic data indicates that the source of this high is not thickening and doming of the Bullfrog Tuff, but more likely lies below the Bullfrog Tuff. Possible source lithologies for this magnetic high include altered argillite of the Eleana Formation, Cretaceous or Tertiary intrusions, and mafic sills.

  13. Precambrian crust beneath the Mesozoic northern Canadian Cordillera discovered by Lithoprobe seismic reflection profiling

    NASA Astrophysics Data System (ADS)

    Cook, Frederick A.; Clowes, Ronald M.; Snyder, David B.; van der Velden, Arie J.; Hall, Kevin W.; Erdmer, Philippe; Evenchick, Carol A.

    2004-04-01

    The Cordillera in northern Canada is underlain by westward tapering layers that can be followed from outcrops of Proterozoic strata in the Foreland belt to the lowermost crust of the orogenic interior, a distance of as much as 500 km across strike. They are interpreted as stratified Proterozoic rocks, including ˜1.8-0.7 Ga supracrustal rocks and their basement. The layering was discovered on two new deep seismic reflection profiles in the Yukon (Line 3; ˜650 km) and northern British Columbia (Line 2; ˜1245 km in two segments) that were acquired as part of the Lithoprobe Slave-Northern Cordillera Lithospheric Evolution (SNORCLE) transect. In the Mackenzie Mountains of the eastern Yukon, the layering in Line 3 is visible between 5.0 and 12.0 s (˜15 to 36 km depth). It is followed southwestward for nearly 650 km (˜500 km across strike) and thins to less than 1.0 s (˜3.0-3.5 km thickness) near the Moho at the Yukon-Alaska international boundary. In the northern Rocky Mountains of British Columbia, the upper part of the layering on Line 2 correlates with outcrops of Proterozoic (1.76-1.0 Ga) strata in the Muskwa anticlinorium. At this location, the layering is at least 15 km thick and is followed westward then southward into the middle and lower crust for ˜700 km (˜300 km across strike). It disappears as a thin taper at the base of the crust ˜150 km east of the coast of the Alaskan panhandle. The only significant disruption in the layering occurs at the Tintina fault zone, a late to postorogenic strike-slip fault with up to 800 km of displacement, which appears as a vertical zone of little reflectivity that disrupts the continuity of the deep layering on both profiles (˜300 km apart). The base of the layered reflection zone coincides with the Moho, which exhibits variable character and undulates in a series of broad arches with widths of ˜150 km. In general, the mantle appears to have few reflections. However, at the southwest end of Line 3 near the Alaska

  14. 4-D High-Resolution Seismic Reflection Monitoring of Miscible CO2 Injected into a Carbonate Reservoir

    SciTech Connect

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

    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-Kansas 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.

  15. 4-D High-Resolution Seismic Reflection Monitoring of Miscible CO2 Injected into a Carbonate Reservoir

    SciTech Connect

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

    2006-08-31

    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 in an attempt 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-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.

  16. Site Characterization of the Source Physics Experiment Phase II Location Using Seismic Reflection Data

    NASA Astrophysics Data System (ADS)

    Sexton, E. A.; Snelson, C. M.; Chipman, V.; Emer, D. F.; White, R. L.; Emmitt, R.; Wright, A. A.; Drellack, S.; Huckins-Gang, H.; Mercadante, J.; Floyd, M.; McGowin, C.; Cothrun, C.; Bonal, N.

    2013-12-01

    An objective of the Source Physics Experiment (SPE) is to identify low-yield nuclear explosions from a regional distance. Low-yield nuclear explosions can often be difficult to discriminate among the clutter of natural and man-made explosive events (e.g., earthquakes and mine blasts). The SPE is broken into three phases. Phase I has provided the first of the physics-based data to test the empirical models that have been used to discriminate nuclear events. The Phase I series of tests were placed within a highly fractured granite body. The evolution of the project has led to development of Phase II, to be placed within the opposite end member of geology, an alluvium environment, thereby increasing the database of waveforms to build upon in the discrimination models. Both the granite and alluvium sites have hosted nearby nuclear tests, which provide comparisons for the chemical test data. Phase III of the SPE is yet to be determined. For Phase II of the experiment, characterization of the location is required to develop the geologic/geophysical models for the execution of the experiment. Criteria for the location are alluvium thickness of approximately 170 m and a water table below 170 m; minimal fracturing would be ideal. A P-wave mini-vibroseis survey was conducted at a potential site in alluvium to map out the subsurface geology. The seismic reflection profile consisted of 168 geophone stations, spaced 5 m apart. The mini-vibe was a 7,000-lb peak-force source, starting 57.5 m off the north end of the profile and ending 57.5 m past the southern-most geophone. The length of the profile was 835 m. The source points were placed every 5 m, equally spaced between geophones to reduce clipping. The vibroseis sweep was from 20 Hz down to 180 Hz over 8 seconds, and four sweeps were stacked at each shot location. The shot gathers show high signal-to-noise ratios with clear first arrivals across the entire spread and the suggestion of some shallow reflectors. The data were

  17. Palaeoceanographic significance of sedimentary features at the Argentine continental margin revealed by multichannel seismic reflection data

    NASA Astrophysics Data System (ADS)

    Gruetzner, Jens; Uenzelmann-Neben, Gabriele; Franke, Dieter

    2010-05-01

    The thermohaline circulation in the Argentine Basin today is characterized by the interaction of northward flowing Antarctic water masses (Antarctic Intermediate Water, AAIW; Circumpolar Deep Water, CDW; Antarctic Bottom Water, AABW) and southward flowing North Atlantic Deep Water (NADW). The transfer of heat and energy via both AABW and NADW constitutes an important component in maintaining the global conveyor belt. We aim at a better understanding of both paths and intensity of this current system in the past by investigating an extensive (> 11000 km) set of high quality seismic reflection profiles from the Argentine continental margin. The profiles show a significant contourite system containing both erosive and depositional features that formed through the evolution of water masses and their modifications (path, physical and chemical properties) due to plate tectonic events such as the opening of the Drake Passage or the extensive emplacement of volcanic flows at the Rio Grande Rise. Overall the depositional features indicate that along slope (contour current) transport dominates over down slope (turbiditic) processes at the southern Argentine margin south of 45° S. Further to the North down slope transport was more extensive as indicated by the presence of submarine canyons crossing the slope down to a depth of ~3500 m. Here we present preliminary results from the southern part of the continental margin (42°-50° S) where we focus on a set of ~50 km wide terraces on the slope and rise separated by contouritic channels. The terraces developed over time in alternating constructional (depositional) and erosive phases. An initial age frame was developed by mapping regional reflectors and seismic units known from previous studies. The sedimentary layer between regional reflectors AR 4 and AR 5 spanning roughly the time interval from the Eocene/Oligocene boundary to the early middle Miocene is thin (0.1 - 0.4 s TWT) below the Valentine Feilberg Terrace but

  18. Geophysical Investigation of Avon Valley, West-Central Montana, using Gravity and Seismic Reflection Profiling

    NASA Astrophysics Data System (ADS)

    Knatterud, L.; Mosolf, J.; Speece, M. A.; Zhou, X.

    2014-12-01

    The Avon Valley and adjacent mountains in west-central Montana lie within the Lewis and Clark Line, a major system of WNW-striking faults and folds that transect the more northerly structural grain of the northern Rockies and represent alternating episodes of transtensional and transpressional deformation. The northwest-trending valley has been previously interpreted as an extensional half graben filled with Tertiary sedimentary and volcanic deposits; however, little-to-no geophysical constraints on basin architecture or the thickness of Tertiary fill have been reported. A major northwest-striking fault with significant normal displacement clearly bounds the valley to the northeast, juxtaposing Tertiary sedimentary deposits against Proterozoic-Mesozoic units deformed by shortening structures and crosscut by Cretaceous granitic intrusions. Tertiary volcanic deposits unconformably overlying faulted and folded Phanerozoic-Proterozoic sequences in the eastern Garnet Range bound the valley to the southwest, but in the past no faults had been mapped along this margin. New mapping by the Montana Bureau of Mines and Geology (MBMG) has identified a system of high-angle, northwest- and northeast-striking, oblique-slip faults along the southwest border of the Avon calling into question if the valley is a half, full, or asymmetrical graben. Geophysical data has recently been acquired by Montana Tech to help define the structural architecture of the Avon Valley and the thickness of its Tertiary fill. Gravity data and a short seismic reflection profile have been collected and a preliminary interpretation of these data indicates a half graben with a series of normal faults bounding the western side of the valley. Ongoing gravity data collection throughout 2014 should refine this interpretation by better defining the bedrock-Tertiary interface at depth.

  19. High-resolution seismic reflection profiling of the Santa Monica Fault Zone, West Los Angeles, California

    USGS Publications Warehouse

    Dolan, J.F.; Pratt, T.L.

    1997-01-01

    High-resolution seismic reflection data obtained across the Santa Monica fault in west Los Angeles reveal the near-surface geometry of this active, oblique-reverse-left-lateral fault. Although near-surface fault dips as great as 55?? cannot be ruled out, we interpret the fault to dip northward at 30?? to 35?? in the upper few hundred meters, steepening to ???65?? at 1 to 2 km depth. A total of ???180 m of near-field thrust separation (fault slip plus drag folding) has occurred on the fault since the development of a prominent erosional surface atop ???1.2 Ma strata. In the upper 20 to 40 m strain is partitioned between the north-dipping main thrust strand and several closely spaced, near-vertical strike-slip faults observed in paleoseismologic trenches. The main thrust strand can be traced to within 20 m of the ground surface, suggesting that it breaks through to the surface in large earthquakes. Uplift of a ???50,000-year-old alluvial fan surface indicates a short-term, dip-slip rate of ???0.5 mm/yr, similar to the ???0.6 mm/yr dip-slip rate derived from vertical separation of the oxygen isotope stage 5e marine terrace 3 km west of the study site. If the 0.6 mm/yr minimum, dip-slip-only rate characterizes the entire history of the fault, then the currently active strand of the Santa Monica fault probably began moving within the past ???300,000 years. Copyright 1997 by the American Geophysical Union.

  20. Classification of earthquake site effects by shallow reflection seismics using a shear-wave land-streamer system

    NASA Astrophysics Data System (ADS)

    Polom, U.; Arsyad, I.; Wiyono, S.; Krawczyk, C. M.

    2007-12-01

    Touched in the SW by the Great Sumatra Fault, the densely populated delta of the Krueng Aceh River consists mainly of young alluvial sediments of clay, sand and gravel with partially high organic content. The depth of this sediment body and its internal structure are widely unknown. Whereas traditional timber constructed buildings are mostly unaffected by strong earthquakes, the change to concrete building techniques added a significant new and locally unknown seismic risk in this region. The classification of earthquake site effects in the city of Banda Aceh and the surrounding region of Aceh Besar was the aim of a high-resolution shear-wave reflection seismic survey in the Indonesian province Nanggroe Aceh Darussalam. In cooperation with the Government of Indonesia and local counterparts, this was part of the Project "Management of Georisk" of the Federal Institute for Geosciences and Natural Resources. Using shear-wave reflection seismics in combination with a land streamer has proven to be an enormously useful method in the sedimentary regions of the Aceh province with an easy and fast recording operation. In addition, the specialized seismic system accounts for compacted soil surfaces which allows a wide range of applications within cities, industrial sites, paved roads and also on small dirt roads. Using a vibrator seismic source, this technique was applied successfully also in areas of high building density in the city of Banda Aceh or in the surrounding mostly agricultural environment. Combined with standard geoengineering investigations like cone penetrometer tests, it was possible to evaluate the soil stiffness in populated urban areas down to 100 m depth in terms of the IBC2003. This is important for the exploration of new areas for save building foundation and groundwater aquifer detection in the tsunami-flooded region.

  1. Application of advanced seismic reflection imaging techniques to mapping permeable zones at Dixie Valley, Nevada. Final technical report

    SciTech Connect

    1998-02-18

    Multifold seismic reflection data from the Dixie Valley geothermal field in Nevada were reprocessed using a nonlinear optimization scheme called simulated annealing to model subsurface acoustic velocities, followed by a pre-stack Kirchhoff migration to produce accurate and detailed depth-migrated images of subsurface structure. In contrast to conventional processing techniques, these methods account for significant lateral variations in velocity and thus have the potential ability to image steeply-dipping faults and fractures that may affect permeability within geothermal fields. The optimization scheme develops two-dimensional velocity models to within 6% of velocities obtained from well and surface geologic data. Only the seismic data (i.e., first arrival times of P waves) are used to construct the velocity models and pre-stack migration images, and no other a priori assumptions are invoked. Velocities obtained by processing individual seismic tracks were integrated to develop a block diagram of velocities to 2.3 km depth within the Dixie Valley geothermal field. Details of the tectonic and stratigraphic structure allowed three dimensional extension of the interpretations of two dimensional data. Interpretations of the processed seismic data are compared with well data, surface mapping, and other geophysical data. The Dixie Valley fault along the southeastern Stillwater Range Piedmont is associated with a pronounced lateral velocity gradient that is interpreted to represent the juxtaposition of relatively low velocity basin-fill strata in the hanging wall against higher velocity crystalline rocks in the footwall. The down-dip geometry of the fault was evaluated by inverting arrival times from a negative move-out event, which we associate with the dipping fault plane, on individual shot gathers for seismic line SRC-3 for the location and depth of the associated reflection points on the fault.

  2. Thrust fault segmentation and downward fault propagation in accretionary wedges: New Insights from 3D seismic reflection data

    NASA Astrophysics Data System (ADS)

    Orme, Haydn; Bell, Rebecca; Jackson, Christopher

    2016-04-01

    The shallow parts of subduction megathrust faults are typically thought to be aseismic and incapable of propagating seismic rupture. The 2011 Tohoku-Oki earthquake, however, ruptured all the way to the trench, proving that in some locations rupture can propagate through the accretionary wedge. An improved understanding of the structural character and physical properties of accretionary wedges is therefore crucial to begin to assess why such anomalously shallow seismic rupture occurs. Despite its importance, we know surprisingly little regarding the 3D geometry and kinematics of thrust network development in accretionary prisms, largely due to a lack of 3D seismic reflection data providing high-resolution, 3D images of entire networks. Thus our current understanding is largely underpinned by observations from analogue and numerical modelling, with limited observational data from natural examples. In this contribution we use PSDM, 3D seismic reflection data from the Nankai margin (3D Muroto dataset, available from the UTIG Academic Seismic Portal, Marine Geoscience Data System) to examine how imbricate thrust fault networks evolve during accretionary wedge growth. We unravel the evolution of faults within the protothrust and imbricate thrust zones by interpreting multiple horizons across faults and measuring fault displacement and fold amplitude along-strike; by doing this, we are able to investigate the three dimensional accrual of strain. We document a number of local displacement minima along-strike of faults, suggesting that, the protothrust and imbricate thrusts developed from the linkage of smaller, previously isolated fault segments. Although we often assume imbricate faults are likely to have propagated upwards from the décollement we show strong evidence for fault nucleation at shallow depths and downward propagation to intersect the décollement. The complex fault interactions documented here have implications for hydraulic compartmentalisation and pore

  3. Constraining the role of magma before, during and after the break-up of continents using seismic reflection data

    NASA Astrophysics Data System (ADS)

    Magee, C.; Jackson, C. A. L.; Schofield, N.; Holford, S. P.

    2014-12-01

    The ability to visualize networks of igneous intrusions in 3D using seismic reflection data has revolutionized our understanding of how magma migrates and is emplaced during continental breakup. Numerous seismic-based studies have shown that: (i) sub-horizontal or saucer-shaped sill intrusions represent a major component of magmatic systems within sedimentary basins; (ii) these sills may be interconnected to form laterally extensive (>100's km2) sill-complexes; (iii) magma flow indicators can be mapped within the sills to reconstruct magma migration routes and source positions; (iv) space-making mechanisms (e.g., forced folds) can be identified, which provide constraints on intrusive style (e.g., brittle or non-brittle); and (v) cross-cutting and seismic-stratigraphic relationships between the sills and host rock can be used to constrain the age of igneous activity. We use a series of seismic data, primarily from the Rockall Basin, NE Atlantic and offshore Australia, to demonstrate how the observations described above can be synthesized to reconstruct the evolution of ancient magmatic systems located along continental volcanic rifted margins. Our results demonstrate that the architecture of such intrusive networks is significantly influenced by the pre-existing structure and lithology of the host rock. Importantly, relatively dating the intrusive and extrusive components of magmatic systems suggests igneous activity may occur more intermittently and over longer time periods than previously thought, potentially spanning entire break-up histories. Overall, seismic reflection data provide important insights into: (i) the role of magma before, during and after continental break-up; and (ii) the influence of crystallised intrusion networks on subsequent basin evolution and fluid flow processes.

  4. New insights on the subsidence of the Ganges-Brahmaputra Delta Plain by using 2D multichannel seismic data, gravity and flexural modeling, BanglaPIRE Project

    NASA Astrophysics Data System (ADS)

    Grall, C.; Pickering, J.; Steckler, M. S.; Spiess, V.; Seeber, L.; Paola, C.; Goodbred, S. L., Jr.; Palamenghi, L.; Schwenk, T.

    2015-12-01

    Deltas can subside very fast, yet many deltas remain emergent over geologic time. A large sediment input is often enough to compensate for subsidence and rising sea level to keep many deltas at sea level. This implies a balance between subsidence and sedimentation, both of which may, however, be controlled by independent factors such as sediment supply, tectonic loads and sea-level change. We here examine the subsidence of the Ganges-Brahmaputra Delta (GBD). Located in the NE boundary of the Indian-Eurasian collision zone, the GBD is surrounded by active uplifts (Indo-Burma Fold Belt and the Shillong Massif). The pattern of subsidence from these tectonic loads can strongly vary depending on both loads and lithospheric flexural rigidity, both of which can vary in space and time. Sediment cover changes both the lithostatic pressure and the thermal properties and thus the rigidity of the lithosphere. While sediments are deposited cold, they also insulate the lithosphere, acting as a thermal blanket to increase lower crustal temperatures. These effects are a function of sedimentation rates and may be more important where the lithosphere is thin. At the massive GBD the impact of sedimentation should be considered for properly constraining flexural subsidence. The flexural rigidity of the lithosphere is here modeled by using a yield-stress envelope based on a thermomechanic model that includes geothermal changes associated with sedimentation. Models are constrained by using two different data sets, multichannel seismic data correlated to borehole stratigraphy, and gravity data. This approach allows us to determine the Holocene regional distribution of subsidence from the Hinge Zone to the Bengal Fan and the mass-anomalies associated with the flexural loading. Different end-member scenarios are explored for reproducing the observed land tilting and gravity anomalies. For all scenarios considered, data can be reproduced only if we consider an extremely weak lithosphere and

  5. The Moho Structure of Shatsky Rise Oceanic Plateau, Northwest Pacific, from Multichannel Seismic Reflection and Wide-angle Refraction Data

    NASA Astrophysics Data System (ADS)

    Zhang, J.; Sager, W. W.; Korenaga, J.

    2013-12-01

    Moho structure is important for understanding crustal structure, isostatic compensation, and magmatic emplacement in the crust. This structure is often poorly known because the discontinuity is deep within the Earth. Oceanic plateaus are large igneous constructs with anomalously thick crust whose thickness is important evidence about the formation of these features. Multichannel seismic (MCS) reflection and wide-angle refraction data were collected over the southern half of the Shatsky Rise oceanic plateau, and these data allow us to image the lower crustal structure of the plateau. MCS reflection data were reprocessed by constant velocity stack, instead of common-depth-point stack, producing better seismic reflection images of the Moho. MCS reflection sections show that the Moho discontinuity is characterized by a single reflection event composed of a number of individual, subparallel reflectors with variable length, shape, and strength. The Moho starts shallow (with a normal crustal thickness of ~6-7 km) at the edges of the rise, and it can be seen in MCS profiles up to a thickness of ~15 km. The tomographic Moho reflector based on wide-angle data can be matched with MCS results, showing that the dip continues toward the middle, reaching maximum thickness of ~30 km at the plateau center. Shatsky Rise Moho structure is consistent with nearly complete isostatic balance, which is why the plateau exhibits a small free-air gravity signature. Shatsky Rise was built on young oceanic lithosphere with little rigidity, so the plateau formed in isostatic equilibrium with a deep crustal root.

  6. Shear Wave Reflection Seismics Image Internal Structure of Quick-Clay Landslides in Sweden

    NASA Astrophysics Data System (ADS)

    Polom, U.; Krawczyk, C. M.; Malehmir, A.

    2014-12-01

    Covering many different sizes of scale, landslides are widespread and pose a severe hazard in many areas as soon as humans or infrastructure are affected. In order to provide geophysical tools and techniques to better characterize sites prone to sliding, a geophysical assessment working towards a geotechnical understanding of landslides is necessary. As part of a joint project studying clay-related landslides in Nordic countries by a suite of geophysical methods, we therefore tested the use of shear wave reflection seismics to survey shallow structures that are known to be related to quick-clay landslide processes in southern Sweden. On two crossing profiles, a land streamer consisting of 120 SH-geophones with 1 m spacing was deployed, and an ELVIS micro-vibrator was shaking every 4 m to generate the shear wave signal. SH-wave data of high quality were thereby acquired to resolve the gaps between P-wave data and electrical and surface wave based methods of lower resolution. After quality control, correlation, subtractive stack, and geometry setup, single shot gathers already demonstrate the high data quality gained in the region, especially on a gravel road. The migrated depth sections image the structural inventory down to ca. 50 m depth with vertical resolution of less than 1 m. Horizontally layered sediments are visible in the upper 40 m of soft (marine) sediments, followed by top basement with a rough topography varying between ca. 20-40 m depth. The imaged, bowl-shaped basement morphology centres near the profile crossing, and basement is exposed at three sides of the profiles. Three distinct sediment sequences are separated by high-amplitude unconformities. The quick-clay layer may be located above the marked reflection set that lies on top of the more transparent sequence that levels out the basement. Located between 15-20 m depth, this correlates with the height of the last scarp that occurred in the area. In addition, shear wave velocities are determined

  7. Two-dimensional Quantitative Imaging of A Gas Hydrate Bottom-simulating Reflector On The Colombia-ecuador Convergent Margin From Multichannel Seismic Reflection Data By Asymptotic Waveform Inversion

    NASA Astrophysics Data System (ADS)

    Ribodetti, A.; Operto, S.; Collot, J. Y.

    Many studies have been performed to analyse the presence of hydrate through the ob- servation of bottom-simulating reflectors (BSR), thought to represent the base of the hydrate stability field. Much of the available information has come from seismic re- flection data calibrated by limited in situ (drilling, borehole) data. Numerous studies involving forward modeling and inversion of multichannel seismic reflection and OBS refraction data have been carried out to constrain seismic velocity enhancement due to hydrate above the BSR and the presence of low velocity associated with free gas in the sediment beneath it. In this work, asymptotic waveform inversion is applied to 2-D multichannel seismic reflection (MCS) data acquired on the Colombia-Ecuador margin during the SISTEUR cruise to develop a 2-D model of a gas hydrate bottom-simulating reflector. The output of inversion is a 2-D quantitive depth model for velocity and attenuation. Resolution of tomographic models is controlled both by the source bandwith and the source-receiver acquisition aperture range. Due to the limited source bandwith and source-receiver aperture range, geological interpretation of the inversion results can be difficult. In order to remove the source signature from the tomographic images and estimate the absolute values of the physical parameters (velocity, attenuation) along the BSR we designed a specific post-processing procedure. The post-processing is formulated as an inverse problem. The tomographic models constitute the data space processed as a serie of one-dimensional velocity/attenuation logs located at different horizontal po- sitions along the 2-D profile. The model space is composed of a family of realistic impulse BSR models parameterized by a limited number of parameters. The predicted dataset are computed by convolution of the depth-to-time converted impulse mod- els with the source wavelet and compared with the tomographic models. The inverse problem is solved by a

  8. A high-resolution seismic reflection/refraction study of the Chugach- Peninsular terrane boundary, southern Alaska

    USGS Publications Warehouse

    Brocher, T.M.; Fisher, M.A.; Geist, E.L.; Christensen, N.I.

    1989-01-01

    We present results from a high-resolution seismic refraction analysis of the shallow (approximately 2 km) crustal structure along the 107-km-long Trans-Alaska Crustal Transect Chugach reflection line in southern Alaska and a comparison with laboratory measurements of field samples. The refraction analysis includes the two-dimensional interpretation of several thousand first- and secondary-arrival travel times digitized from 1024-channel split-spread common shot gathers. The velocity model derived from this analysis better defines the location and geometry of terrane boundaries than does the normal incidence reflection section and agrees well with surface mapping of lithologies. Furthermore, the model predicts travel times within 100 ms of the reflection times recorded from the base of the Quaternary on the Chugach reflection section. -from Authors

  9. 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

    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.

  10. 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

    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.

  11. 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.W.; 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.

  12. High-Resolution Seismic Reflection and Refraction Imaging of the Hayward Fault in Fremont, Alameda County, California

    NASA Astrophysics Data System (ADS)

    Everson, E. D.; Rymer, M. J.; Goldman, M. R.; Catchings, R. D.

    2007-12-01

    In July 2007, the U.S. Geological Survey acquired a 60-m-long seismic reflection and refraction profile across the main trace of the Hayward fault in Fremont Central Park, Fremont, California. The profile was designed to determine the geometry, seismic velocities, and possible structural complexities of the fault. The study was along a part of the surface rupture of the 1868 M 7.0 Hayward earthquake. We used single-element, 40-Hz vertical geophones placed at 1-m intervals along the profile with 0.5-m lateral offset from the shot points, also with 1-m intervals. Seismic sources were generated by multiple sledgehammer blows at each shot point. Data were recorded unfiltered in the field on a Geometrics Strataview RX-60 seismograph at a sampling rate of 0.5 ms for 2 s. Geophone locations were measured in 3D using differential GPS. We developed a velocity model using the Hole (1992) code to invert P-wave first arrivals of the refraction data. Seismic P-wave velocities range from about 200 m/s near the surface to approximately 800 m/s at a depth of 13 to 16 m. The velocity model was then applied to the reflection data to develop an unmigrated common depth point (CDP) stack. The reflection data indicate the presence of at least three fault strands in an approximately 20-m-wide zone. We believe the three strands define an upwardly flaring 'flower structure', with the central strand being the main strand of the Hayward fault. The three strands project to merge at a depth of about 150 m; the overall dip of the fault zone in the upper 100 m is to the northeast, at about 88 degrees.

  13. 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.

  14. 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

  15. Improved Dead Sea sinkhole site characterization at Ghor Al Haditha, Jordan, based on repeated shear wave reflection seismic profiling

    NASA Astrophysics Data System (ADS)

    Polom, Ulrich; Alrshdan, Hussam; Al-Halbouni, Djamil; Sawarieh, Ali; Dahm, Torsten; Krawczyk, CharLotte M.

    2016-04-01

    In October 2014 a high-resolution shallow shear wave reflection seismic survey was carried out at the Dead Sea sinkhole site Ghor Al Haditha, Jordan. It extended a survey undertaken in 2013, also in order to gather time-lapse profiles. In the framework of the DEad SEa Research Venue (DESERVE), a virtual institute of the Helmholtz Association and international partners, this investigation is part of a cross-disciplinary and cooperative international project of the Helmholtz Centers KIT, GFZ, and UFZ. At the investigation site, characterized by alluvial fan deposits, ongoing subsidence and sinkhole processes in the subsurface create massive reshaping of farming areas, including the destruction of housings, industrial sites, and infrastructure. The sinkhole hazard at the Dead Sea is significant, since similar processes are observed at several coastal segments of the Dead Sea. The new survey (in total 2.1 profile km) was targeted to improve the knowledge about the subsurface structures and to confine the results of the initial survey (1.8 km profile km), with respect to the presence or non-presence of a massive salt layer proposed at nearly 40 m depth. This salt layer is the central part of a widely established process hypothesis to generate shallow cavities by salt subrosion, which subsequently collapse to sinkholes at the surface. Results of the initial survey carried out in 2013 highlighted a new process hypothesis of subsurface mass transport by Dead Sea mud mobilization enclosed in the alluvial fan, so that an extended survey was undertaken in 2014. This, indeed, confirmed that there are no reflection seismic signal responses that would be expected to occur in the presence of a massive salt layer. Since evaluation of both hypothesis by new drilling could not be carried out due to safety reasons and permissions, it remained unclear which hypothesis is valid for the investigation site. However, we combined the 2013 and 2014 reflection seismic profiles and the

  16. USING RECENT ADVANCES IN 2D SEISMIC TECHNOLOGY AND SURFACE GEOCHEMISTRY TO ECONOMICALLY REDEVELOP A SHALLOW SHELF CARBONATE RESERVOIR: VERNON FIELD, ISABELLA COUNTY, MI

    SciTech Connect

    James R. Wood; A. Wylie; W. Quinlan

    2004-04-01

    One of the main objectives of this demonstration project is to test surface geochemical techniques for detecting trace amounts of light hydrocarbons in pore gases as a means of reducing risk in hydrocarbon exploration and production. As part of the project, several field demonstrations were undertaken to assess the validity and usefulness of the microbial surface geochemical technique. The important observations from each of these field demonstrations are briefly reviewed in this annual report. These demonstrations have been successful in identifying the presence or lack of hydrocarbons in the subsurface and can be summarized as follows: (1) The surface geochemistry data showed a fair-to-good microbial anomaly that may indicate the presence of a fault or stratigraphic facies change across the drilling path of the State Springdale & O'Driscoll No.16-16 horizontal demonstration well in Manistee County, Michigan. The well was put on production in December 2003. To date, the well is flowing nearly 100 barrels of liquid hydrocarbons per day plus gas, which is a good well in Michigan. Reserves have not been established yet. Two successful follow-up horizontal wells have also been drilled in the Springdale area. Additional geochemistry data will be collected in the Springdale area in 2004. (2) The surface geochemistry sampling in the Bear Lake demonstration site in Manistee County, Michigan was updated after the prospect was confirmed and production begun; the original subsurface and seismic interpretation used to guide the location of the geochemical survey for the Charlich Fauble re-entry was different than the interpretation used by the operator who ultimately drilled the well. As expected, the anomaly appears to be diminishing as the positive (apical) microbial anomaly is replaced by a negative (edge) anomaly, probably due to the pressure draw-down in the reservoir. (3) The geochemical sampling program over the Vernon Field, Isabella County, Michigan is now

  17. The Hosgri Fault Zone, Central California: Collection and Preliminary Analysis of Marine Magnetic and Seismic Reflection Data

    NASA Astrophysics Data System (ADS)

    Watt, J. T.; Fisher, M. A.; Scheirer, D. S.; Johnson, S. Y.; Sliter, R. W.; Hart, P. E.

    2008-12-01

    Newly acquired high-resolution marine magnetic and seismic-reflection data collected offshore Point Buchon, California, are being combined with existing regional magnetic, oil industry multichannel seismic (MCS), onshore geology, and seismicity data to investigate the tectonics and earthquake hazards associated with the Hosgri and other nearshore fault zones. This research is part of a broader study of earthquake hazards in the central coastal California region that was most recently illustrated by the 2003 M6.6 San Simeon earthquake. High-resolution marine magnetic and single-channel mini-sparker seismic reflection data were collected in June 2008 aboard the USGS R/V Parke Snavely. These data were collected in the offshore areas between Cayucos and Pismo Beach from the nearshore (6 m depth) to just west of the Hosgri Fault Zone. The seismic reflection data were collected using a mini-sparker source and a 15-meter single-channel hydrophone streamer at a 500 joule power level and shot interval of 1/2 second, generating a signal between 200 and 1500 Hz. The G-882 cesium marine magnetometer was mounted on the opposite side of the stern as the seismic source and streamer and was towed approximately 30 meters behind the vessel. Mini-sparker and marine magnetic data were collected simultaneously along shore-perpendicular tracklines spaced 800 meters apart. Along the Hosgri Fault Zone, marine magnetic data were collected with 400 meter trackline spacing. Marine magnetic data reveal two distinctive magnetic anomaly patterns north and south of Point Buchon. The transition between these anomaly patterns corresponds to the boundary between the Los Osos Valley and the San Luis/Pismo structural block to the south. Within the northern offshore Los Osos Valley block a series of broad magnetic highs extends northwestward from Morro Rock. These anomalies may signify the offshore extension of the Oligocene Morro Rock-Islay Hill igneous complex that appears to have been displaced

  18. Seismic reflection mapping of discontinuous sandstone bodies. Part I: synthetic modeling studying

    SciTech Connect

    Dobecki, T.L.

    1980-06-01

    Utilizing depth models consistent with the size, velocity, and density of observed sandstone channels in the upper Cretaceous Mesa Verde and Tertiary Wasatch formations, the synthetic seismic response of such channel lenses has been computed. By varying the lens thickness, depth, number, and separation, it was possible to observe the net effect on the seismic response and, in turn, how these affects might influence interpretation of field data.

  19. Phase-Shifted Based Numerical Method for Modeling Frequency-Dependent Effects on Seismic Reflections

    NASA Astrophysics Data System (ADS)

    Chen, Xuehua; Qi, Yingkai; He, Xilei; He, Zhenhua; Chen, Hui

    2016-08-01

    The significant velocity dispersion and attenuation has often been observed when seismic waves propagate in fluid-saturated porous rocks. Both the magnitude and variation features of the velocity dispersion and attenuation are frequency-dependent and related closely to the physical properties of the fluid-saturated porous rocks. To explore the effects of frequency-dependent dispersion and attenuation on the seismic responses, in this work, we present a numerical method for seismic data modeling based on the diffusive and viscous wave equation (DVWE), which introduces the poroelastic theory and takes into account diffusive and viscous attenuation in diffusive-viscous-theory. We derive a phase-shift wave extrapolation algorithm in frequencywavenumber domain for implementing the DVWE-based simulation method that can handle the simultaneous lateral variations in velocity, diffusive coefficient and viscosity. Then, we design a distributary channels model in which a hydrocarbon-saturated sand reservoir is embedded in one of the channels. Next, we calculated the synthetic seismic data to analytically and comparatively illustrate the seismic frequency-dependent behaviors related to the hydrocarbon-saturated reservoir, by employing DVWE-based and conventional acoustic wave equation (AWE) based method, respectively. The results of the synthetic seismic data delineate the intrinsic energy loss, phase delay, lower instantaneous dominant frequency and narrower bandwidth due to the frequency-dependent dispersion and attenuation when seismic wave travels through the hydrocarbon-saturated reservoir. The numerical modeling method is expected to contribute to improve the understanding of the features and mechanism of the seismic frequency-dependent effects resulted from the hydrocarbon-saturated porous rocks.

  20. 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.

  1. 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

  2. Hydrothermal fluid flow system around the Iheya North Knoll in the mid-Okinawa trough based on seismic reflection data

    NASA Astrophysics Data System (ADS)

    Tsuji, Takeshi; Takai, Ken; Oiwane, Hisashi; Nakamura, Yasuyuki; Masaki, Yuka; Kumagai, Hidenori; Kinoshita, Masataka; Yamamoto, Fujio; Okano, Tadashi; Kuramoto, Shin'ichi

    2012-02-01

    Seismic reflection data around the Iheya North Knoll hydrothermal field provide insights into geological structures that control subseafloor hydrothermal fluid flow in the sediment-covered continental backarc basin of the mid-Okinawa Trough. We identified the seismic expression of widespread porous volcaniclastic pumiceous deposits and intrusions as a result of silicic arc volcanism. The porous and permeable volcanic deposits are distributed in an area extending updip from the thick succession of the deep trough to the seafloor at the hydrothermal field. Their regional structure focuses the flow of hydrothermal fluids derived from the surrounding trough-fill sediments and directs them to the vents of the hydrothermal field. The high concentrations of CH4 and NH4 in the fluids of the hydrothermal field are likely derived from the interaction of migrating fluids with trough-fill sediments.

  3. Reflected and mode-converted seismic waves within the shallow aleutian subduction zone, southern Kenai Peninsula, Alaska

    USGS Publications Warehouse

    Stephens, C.D.; Page, R.A.; Lahr, J.C.

    1990-01-01

    Pronounced secondary phases observed in local recordings of quarry shots and earthquakes on the southern Kenai Peninsula are identified as reflected P and S and converted S-to-P phases originating within four depth ranges: in the upper few kilometers of the Cook Inlet Tertiary basin, at midcrustal depths within the overthrust North American plate, at about 35 km depth near the top of the Wadati-Benioff seismic zone in proximity to the inferred interplate megathrust, and at about 5-10 km below the megathrust in the subducted Pacific plate. The positions and origins of the mid-upper plate (MUP) discontinuity and similar reflectors are discussed. It appears the the MUP discontinuity is seismically inactive and does not represent a brittle-ductile transition zone within the upper plate. The two converted S-to-P phases generated near the top of the subducted plate could indicate a low velocity zone associated with subducted oceanic crust. -after Authors

  4. Geology of the continental margin beneath Santa Monica Bay, Southern California, from seismic-reflection data

    USGS Publications Warehouse

    Fisher, M.A.; Normark, W.R.; Bohannon, R.G.; Sliter, R.W.; Calvert, A.J.

    2003-01-01

    We interpret seismic-reflection data, which were collected in Santa Monica Bay using a 70-in3 generator-injector air gun, to show the geologic structure of the continental shelf and slope and of the deep-water, Santa Monica and San Pedro Basins. The goal of this research is to investigate the earthquake hazard posed to urban areas by offshore faults. These data reveal that northwest of the Palos Verdes Peninsula, the Palos Verdes Fault neither offsets the seafloor nor cuts through an undeformed sediment apron that postdates the last sea level rise. Other evidence indicates that this fault extends northwest beneath the shelf in the deep subsurface. However, other major faults in the study area, such as the Dume and San Pedro Basin Faults, were active recently, as indicated by an arched seafloor and offset shallow sediment. Rocks under the lower continental slope are deformed to differing degrees on opposite sides of Santa Monica Canyon. Northwest of this canyon, the continental slope is underlain by a little-deformed sediment apron; the main structures that deform this apron are two lower-slope anticlines that extend toward Point Dume and are cored by faults showing reverse or thrust separation. Southeast of Santa Monica Canyon, lower-slope rocks are deformed by a complex arrangement of strike-slip, normal, and reverse faults. The San Pedro Escarpment rises abruptly along the southeast side of Santa Monica Canyon. Reverse faults and folds underpinning this escarpment steepen progressively southeastward. Locally they form flower structures and cut downward into basement rocks. These faults merge downward with the San Pedro Basin fault zone, which is nearly vertical and strike slip. The escarpment and its attendant structures diverge from this strike-slip fault zone and extend for 60 km along the margin, separating the continental shelf from the deep-water basins. The deep-water Santa Monica Basin has large extent but is filled with only a thin (less than 1.5-km

  5. Structure and evolution of the eastern Gulf of Aden conjugate margins from seismic reflection data

    NASA Astrophysics Data System (ADS)

    d'Acremont, Elia; Leroy, Sylvie; Beslier, Marie-Odile; Bellahsen, Nicolas; Fournier, Marc; Robin, Cécile; Maia, Marcia; Gente, Pascal

    2005-03-01

    The Gulf of Aden is a young and narrow oceanic basin formed in Oligo-Miocene time between the rifted margins of the Arabian and Somalian plates. Its mean orientation, N75°E, strikes obliquely (50°) to the N25°E opening direction. The western conjugate margins are masked by Oligo-Miocene lavas from the Afar Plume. This paper concerns the eastern margins, where the 19-35 Ma breakup structures are well exposed onshore and within the sediment-starved marine shelf. Those passive margins, about 200 km distant, are non-volcanic. Offshore, during the Encens-Sheba cruise we gathered swath bathymetry, single-channel seismic reflection, gravity and magnetism data, in order to compare the structure of the two conjugate margins and to reconstruct the evolution of the thinned continental crust from rifting to the onset of oceanic spreading. Between the Alula-Fartak and Socotra major fracture zones, two accommodation zones trending N25°E separate the margins into three N110°E-trending segments. The margins are asymmetric: offshore, the northern margin is narrower and steeper than the southern one. Including the onshore domain, the southern rifted margin is about twice the breadth of the northern one. We relate this asymmetry to inherited Jurassic/Cretaceous rifts. The rifting obliquity also influenced the syn-rift structural pattern responsible for the normal faults trending from N70°E to N110°E. The N110°E fault pattern could be explained by the decrease of the influence of rift obliquity towards the central rift, and/or by structural inheritance. The transition between the thinned continental crust and the oceanic crust is characterized by a 40 km wide zone. Our data suggest that its basement is made up of thinned continental crust along the southern margin and of thinned continental crust or exhumed mantle, more or less intruded by magmatic rocks, along the northern margin.

  6. Lithospheric velocity model across the Southern Central Iberian Zone (Variscan Iberian Massif): The ALCUDIA wide-angle seismic reflection transect

    NASA Astrophysics Data System (ADS)

    Ehsan, Siddique Akhtar; Carbonell, Ramon; Ayarza, Puy; Martí, David; Martínez Poyatos, David; Simancas, José Fernando; Azor, Antonio; Ayala, Concepción; Torné, Montserrat; Pérez-Estaún, Andrés.

    2015-03-01

    A P wave seismic velocity model has been obtained for the Central Iberian Zone, the largest continental fragment of the Iberian Variscan Belt. The spatially dense, high-resolution, wide-angle seismic reflection experiment, ALCUDIA-WA, was acquired in 2012 across central Iberia, aiming to constrain the lithospheric structure and resolve the physical properties of the crust and upper mantle. The seismic transect, ~310 km long, crossed the Central Iberian Zone from its suture with the Ossa-Morena Zone to the southern limit of the Central System mountain range. The energy generated by five shots was recorded by ~900 seismic stations. High-amplitude phases were identified in every shot gather for the upper crust (Pg and PiP) and Moho (PmP and Pn). In the upper crust, the P wave velocities increase beneath the Cenozoic Tajo Basin. The base of the upper crust varies from ~13 km to ~20 km between the southernmost Central Iberian Zone and the Tajo Basin. Lower crustal velocities are more homogeneous. From SW-NE, the traveltime of PmP arrivals varies from ~10.5 s to ~11.8 s, indicating lateral variations in the P wave velocity and the crustal thickness, reflecting an increase toward the north related with alpine tectonics and the isostatic response of the crust to the orogenic load. The results suggest that the high velocities of the upper crust near the Central System might correspond to igneous rocks and/or high-grade metamorphic rocks. The contrasting lithologies and the increase in the Moho depth to the north evidence differences in the Variscan evolution.

  7. Seismic-reflection imaging of Tertiary faulting and related post-Eocene deformation 20 km North of Memphis, Tennessee

    USGS Publications Warehouse

    Williams, R.A.; Stephenson, W.J.; Odum, J.K.; Worley, D.M.

    2001-01-01

    Other than the Crittenden County fault zone (CCFZ), little is known about the seismic hazard from earthquake faults within 50 km of Memphis, Tennessee, a city that contains a large inventory of older buildings that are vulnerable to moderate and strong earthquake ground shaking. To address this lack of knowledge about faulting near Memphis, we acquired a 4.5 km long Mini-Sosie seismic-reflection profile across the boundary between the loess-covered bluffs and modern Mississippi River flood plain in Meeman-Shelby Forest State Park north of Memphis. We imaged a previously unknown reverse/thrust fault that displaces Paleozoic and Cretaceous rocks and upwarps Tertiary deposits on the floodplain portion of the profile about 25 km north of downtown Memphis. The Paleozoic and Cretaceous rocks are vertically faulted about 70 and 40 m, respectively, in an up-to-the-west sense of displacement. The fault displacement apparently terminates in the basal portion of the Paleocene section and causes only an upwarping of the overlying deposits. The overlying Paleocene and Eocene deposits, which are probably the youngest deposits imaged, are upwarped about 50-60 m with the same sense of displacement as the underlying older units. The sense of displacement, amplitude, and appearance of the fault in the seismic data are very similar to that observed in the seismic reflection images of the CCFZ 15 km west of this profile. Although we have imaged this new fault in only one location, its proximity to Memphis and similarities to the CCFZ, leads us to speculate that it may be a parallel structure to the CCFZ and thus warrants further study. ?? 2001 Elsevier Science B.V. All rights reserved.

  8. Characterization of the Vajont landslide (North-Eastern Italy) by means of reflection and surface wave seismics

    NASA Astrophysics Data System (ADS)

    Petronio, Lorenzo; Boaga, Jacopo; Cassiani, Giorgio

    2016-05-01

    The mechanisms of the disastrous Vajont rockslide (North-Eastern Italy, October 9, 1963) have been studied in great detail over the past five decades. Nevertheless, the reconstruction of the rockslide dynamics still presents several uncertainties, including those related to the accurate estimation of the actual landslide mass. This work presents the results of a geophysical characterization of the Vajont landslide body in terms of material properties and buried geometry. Both aspects add new information to the existing dataset and will help a better understanding of the rockslide failure mechanisms and dynamics. In addition, some general considerations concerning the intricacies of landslide characterization can be drawn, with due attention to potential pitfalls. The employed techniques are: (i) high resolution P-wave reflection, (ii) high resolution SH-wave reflection, (iii) controlled source surface wave analysis. We adopted as a seismic source a vibrator both for P waves and SH waves, using vertical and horizontal geophones respectively. For the surface wave seismic survey we used a heavy drop-weight source and low frequency receivers. Despite the high noise level caused by the fractured conditions of the large rock body, a common situation in landslide studies, we managed to achieve a satisfying imaging quality of the landslide structure thanks to the large number of active channels, the short receiver interval and the test of appropriate seismic sources. The joint use of different seismic techniques help focus the investigation on the rock mass mechanical properties. Results are in good agreement with the available borehole data, the geological sections and the mechanical properties of the rockmass estimated by other studies. In general the proposed approach is likely to be applicable successfully to similar situations where scattering and other noise sources are a typical bottleneck to geophysical data acquisition on landslide bodies.

  9. Location, structure, and seismicity of the Seattle fault zone, Washington: Evidence from aeromagnetic anomalies, geologic mapping, and seismic-reflection data

    USGS Publications Warehouse

    Blakely, R.J.; Wells, R.E.; Weaver, C.S.; Johnson, S.Y.

    2002-01-01

    A high-resolution aeromagnetic survey of the Puget Lowland shows details of the Seattle fault zone, an active but largely concealed east-trending zone of reverse faulting at the southern margin of the Seattle basin. Three elongate, east-trending magnetic anomalies are associated with north-dipping Tertiary strata exposed in the hanging wall; the magnetic anomalies indicate where these strata continue beneath glacial deposits. The northernmost anomaly, a narrow, elongate magnetic high, precisely correlates with magnetic Miocene volcanic conglomerate. The middle anomaly, a broad magnetic low, correlates with thick, nonmagnetic Eocene and Oligocene marine and fluvial strata. The southern anomaly, a broad, complex magnetic high, correlates with Eocene volcanic and sedimentary rocks. This tripartite package of anomalies is especially clear over Bainbridge Island west of Seattle and over the region east of Lake Washington. Although attenuated in the intervening region, the pattern can be correlated with the mapped strike of beds following a northwest-striking anticline beneath Seattle. The aeromagnetic and geologic data define three main strands of the Seattle fault zone identified in marine seismic-reflection profiles to be subparallel to mapped bedrock trends over a distance of >50 km. The locus of faulting coincides with a diffuse zone of shallow crustal seismicity and the region of uplift produced by the M 7 Seattle earthquake of A.D. 900-930.

  10. Continuous seismic-reflection survey of the Great Salt Lake, Utah- east of Antelope and Fremont Islands

    USGS Publications Warehouse

    Lambert, P.M.; West, J.C.

    1989-01-01

    A continuous seismic-reflection survey of the Great Salt Lake, Utah, was conducted east of Fremont and Antelope Islands in 1984 by the U.S. Geological Survey in cooperation with the Utah Department of Natural Resources and produced data along approximately 80 miles of seismic lines. The survey was conducted to determine depth to consolidated rock, and definition and continuity of overlying basin fill under the lake. Interpretation of the data indicates the presence of faulted rock dipping away from Fremont and Antelope Islands. A north-south-trending consolidated-rock ridge is identified 200 ft below lake bottom, 275 miles east of Fremont Island. Shallow rock is also inferred 380 ft below lake bottom, near Hooper Hot Springs, and 520 ft below lake bottom approximately 4 miles east of the south end of Antelope Island. Interpretation of reflections from overlying basin fill indicates fine-grained, thinly-bedded deposits that become coarser with depth. Strong reflectors in the basin fill can be correlated with water-bearing strata penetrated by wells near the north end of Antelope Island and along the east shore of the lake. Many continuous, high-amplitude reflections can be identified in data from basin fill and may represent sedimentary sections or aquifer boundaries but cannot be defined because of a lack of subsurface control in the area. (USGS)

  11. Lateral continuity of basement seismic reflections in 15 Ma ultrafast-spreading crust at ODP Site 1256

    NASA Astrophysics Data System (ADS)

    Nag, Sreeja; Swift, Stephen A.

    2011-09-01

    The Ocean Drilling Program (ODP) initiated drilling at Site 1256D in the Guatemala Basin, about 1,000 km off the East Pacific Rise to penetrate plutonic rocks, anticipated to be relatively shallow in this region, formed at an ultra-fast spreading rate. IODP Expedition E312 successfully drilled into gabbros at ~1,150 m in basement. Multi-channel seismic traces show weak laterally coherent sub-basement reflections at borehole depths. Synthetic reflectivity seismograms were computed using a Ricker wavelet and impedance profiles from borehole sonic logs. These seismograms show significant sub-basement amplitude peaks. A zero-offset vertical seismic profile, shot on E312, was processed to investigate the authenticity of these reflections and their relationship to borehole geology. A dual scheme of the median filtering and F-K dip filtering was used. Tests with synthetic seismograms indicate the approach is effective at reasonable SNR levels. Downgoing energy is clearly identified but negligible upgoing energy is visible over random noise. These results indicate that lava flows and igneous contacts in upper ocean crust have significant topography on lateral scales less than the Fresnel Zone (~300 m) due to igneous and tectonic processes.

  12. Mapping of crustal scale tectonic boundaries in the Ossa-Morena Zone using reprocessed IBERSEIS reflection seismic data

    NASA Astrophysics Data System (ADS)

    Kashubin, A. S.; Juhlin, C.

    2010-06-01

    The IBERSEIS deep seismic reflection profile imaged crustal scale structures in the SW Iberian Variscan belt, crossing the South Portuguese Zone, the Ossa-Morena Zone and the Central Iberian Zone in Spain. Two subsets of the profile, corresponding to the South Portuguese Zone-Ossa-Morena Zone and the Ossa-Morena Zone-Central Iberian Zone tectonic contacts, have been reprocessed with the aim of investigating the influence of cross-dip and to better image steeply dipping features. Alternative strategies for binning midpoints into common depth point (CDP) bins using different azimuths were examined for synthetic data. We show that the choice of the CDP-processing line and the bin azimuth orientation has a significant impact on the normal moveout and dip-moveout velocities and is crucial to optimizing the quality of the stacked seismic image along the crooked profile. Multi-azimuth binning, normal moveout/dip-moveout, and migration velocity analysis on synthetic and real data show the presence of clear sub-vertical upper crustal structures near the South Portuguese Zone-Ossa-Morena Zone suture, the Aroche fault. This sub-vertical reflectivity that was not imaged earlier, projects into a location in the lower crust with low reflectivity.

  13. 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.

  14. High-resolution seismic reflection imaging of growth folding and shallow faults beneath the Southern Puget Lowland, Washington State

    USGS Publications Warehouse

    Clement, C.R.; Pratt, T.L.; Holmes, M.L.; Sherrod, B.L.

    2010-01-01

    Marine seismic reflection data from southern Puget Sound, Washington, were collected to investigate the nature of shallow structures associated with the Tacoma fault zone and the Olympia structure. Growth folding and probable Holocene surface deformation were imaged within the Tacoma fault zone beneath Case and Carr Inlets. Shallow faults near potential field anomalies associated with the Olympia structure were imaged beneath Budd and Eld Inlets. Beneath Case Inlet, the Tacoma fault zone includes an ???350-m wide section of south-dipping strata forming the upper part of a fold (kink band) coincident with the southern edge of an uplifted shoreline terrace. An ???2 m change in the depth of the water bottom, onlapping postglacial sediments, and increasing stratal dips with increasing depth are consistent with late Pleistocene to Holocene postglacial growth folding above a blind fault. Geologic data across a topographic lineament on nearby land indicate recent uplift of late Holocene age. Profiles acquired in Carr Inlet 10 km to the east of Case Inlet showed late Pleistocene or Holocene faulting at one location with ???3 to 4 m of vertical displacement, south side up. North of this fault the data show several other disruptions and reflector terminations that could mark faults within the broad Tacoma fault zone. Seismic reflection profiles across part of the Olympia structure beneath southern Puget Sound show two apparent faults about 160 m apart having 1 to 2 m of displacement of subhorizontal bedding. Directly beneath one of these faults, a dipping reflector that may mark the base of a glacial channel shows the opposite sense of throw, suggesting strike-slip motion. Deeper seismic reflection profiles show disrupted strata beneath these faults but little apparent vertical offset, consistent with strike-slip faulting. These faults and folds indicate that the Tacoma fault and Olympia structure include active structures with probable postglacial motion.

  15. High-resolution seismic reflection imaging of growth folding and shallow faults beneath the Southern Puget Lowland, Washington State

    USGS Publications Warehouse

    Odum, Jackson K.; Stephenson, William J.; Pratt, Thomas L.; Blakely, Richard J.

    2016-01-01

    Marine seismic reflection data from southern Puget Sound, Washington, were collected to investigate the nature of shallow structures associated with the Tacoma fault zone and the Olympia structure. Growth folding and probable Holocene surface deformation were imaged within the Tacoma fault zone beneath Case and Carr Inlets. Shallow faults near potential field anomalies associated with the Olympia structure were imaged beneath Budd and Eld Inlets. Beneath Case Inlet, the Tacoma fault zone includes an ∼350-m wide section of south-dipping strata forming the upper part of a fold (kink band) coincident with the southern edge of an uplifted shoreline terrace. An ∼2 m change in the depth of the water bottom, onlapping postglacial sediments, and increasing stratal dips with increasing depth are consistent with late Pleistocene to Holocene postglacial growth folding above a blind fault. Geologic data across a topographic lineament on nearby land indicate recent uplift of late Holocene age. Profiles acquired in Carr Inlet 10 km to the east of Case Inlet showed late Pleistocene or Holocene faulting at one location with ∼3 to 4 m of vertical displacement, south side up. North of this fault the data show several other disruptions and reflector terminations that could mark faults within the broad Tacoma fault zone. Seismic reflection profiles across part of the Olympia structure beneath southern Puget Sound show two apparent faults about 160 m apart having 1 to 2 m of displacement of subhorizontal bedding. Directly beneath one of these faults, a dipping reflector that may mark the base of a glacial channel shows the opposite sense of throw, suggesting strike-slip motion. Deeper seismic reflection profiles show disrupted strata beneath these faults but little apparent vertical offset, consistent with strike-slip faulting. These faults and folds indicate that the Tacoma fault and Olympia structure include active structures with probable postglacial motion.

  16. Proterozoic structure, cambrian rifting, and younger faulting as revealed by a regional seismic reflection network in the Southern Illinois Basin

    USGS Publications Warehouse

    Potter, C.J.; Drahovzal, J.A.; Sargent, M.L.; McBride, J.H.

    1997-01-01

    Four high-quality seismic reflection profiles through the southern Illinois Basin, totaling 245 km in length, provide an excellent regional subsurface stratigraphic and structural framework for evaluation of seismic risk, hydrocarbon occurrence, and other regional geologic studies. These data provide extensive subsurface information on the geometry of the intersection of the Cambrian Reelfoot and Rough Creek rifts, on extensive Proterozoic reflection sequences, and on structures (including the Fluorspar Area Fault Complex and Hicks Dome) that underlie a transitional area between the well-defined New Madrid seismic zone (to the southwest) and a more diffuse area of seismicity in the southern Illinois Basin. Our principal interpretations from these data are listed here in order of geologic age, from oldest to youngest: 1. Prominent Proterozoic layering, possibly equivalent to Proterozoic (???1 Ga) Middle Run Formation clastic strata and underlying (1.3-1.5 Ga) volcanic rocks of the East Continent rift basin, has been strongly deformed, probably as part of the Grenville foreland fold and thrust belt. 2. A well-defined angular unconformity is seen in many places between Proterozoic and Cambrian strata; a post-Grenville Proterozoic sequence is also apparent locally, directly beneath the base of the Cambrian. 3. We infer a major reversal in Cambrian rift polarity (accommodation zone) in the Rough Creek Graben in western Kentucky. 4. Seismic facies analysis suggests the presence of basin-floor fan complexes at and near the base of the Cambrian interval and within parts of a Proterozoic post-Grenville sequence in several parts of the Rough Creek Graben. 5. There is an abrupt pinchout of the Mount Simon Sandstone against crystalline basement beneath the Dale Dome (near the Texaco no. 1 Cuppy well, Hamilton County) in southeastern Illinois, and a more gradual Mount Simon pinchout to the southeast. 6. Where crossed by the seismic reflection line in southeast Illinois, some

  17. A simple method for migrating narrow aperture, noisy seismic reflection data and application to Project INDEPTH (International Deep Profiling of Tibet and the Himalaya) deep seismic profiles

    NASA Astrophysics Data System (ADS)

    Alsdorf, Doug

    1997-08-01

    Migration of deep seismic data is often hindered by a narrow recording aperture (line length by record length) and a low signal-to-noise ratio. The severity of typical migration artifacts (e.g., lateral smearing of discontinuous reflections into synforms, "smiles") increases with travel time such that interpreters of deep seismic data have often substituted migrated line drawings for the actual sections. As part of Project INDEPTH (International Deep Profiling of Tibet and the Himalaya), a new migration method was developed to address both the noise and migration issues. The method works in the time-space domain and uses the simple, constant velocity, straight ray path to perform the migration. First, only amplitudes within a given range are retained for migration, thus avoiding high-amplitude noise bursts and low-amplitude background noise. Then, the local dip of a reflection is found by automatically fitting a straight line to the highest amplitudes within a small window (several time samples by several traces) and calculating the dip of the line using a constant velocity. Finally, using this dip, the method migrates a selected amplitude value. The dips, lateral positions, and depths of the migrated events compare very well with output from more conventional algorithms (e.g.,fk-Stolt, finite difference, etc.). The advantages of the new method include fewer artifacts, fast computer run times, low memory use and the ability to migrate long profiles and travel times (e.g., 50 s). The output of the method is a grid of migrated amplitudes (not wavelets) or dip values which is particularly effective for making small figures, such as those needed for publication. The principal disadvantage is the use of a constant migration velocity.

  18. 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.

  19. Seismic-reflection and sidescan-sonar data collected on the Potomac River, Maryland and Virginia, during May 1979

    USGS Publications Warehouse

    Knebel, Harley J.

    1981-01-01

    The U.S. Geological Survey collected 2,170 line kilometers of single-channel seismic-reflection profiles and sidescan sonar records on the Potomac River during R/V NEECHO cruise NE-3-79 in May 1979 (Fig. 1, maps 1-4). The purposes of the survey were to define: (1) areas of sediment accumulation and erosion; (2) the thickness of Holocene sediments; (3) the internal structure of the near-surface sediments; (4) the types of bottom topography; and (5) the general geologic framework of the tidal river and estuary.

  20. Modeling of time-lapse seismic reflection data from CO2 sequestration at West Pearl Queen Field

    NASA Astrophysics Data System (ADS)

    Bartel, L. C.; Haney, M. M.; Aldridge, D. F.; Symons, N. P.; Elbring, G. J.

    2006-12-01

    Sequestration of CO2 in depleted oil reservoirs, saline aquifers, or unminable coal sequences may prove to be an economical and environmentally safe means for long-term removal of carbon from the atmosphere. Requirements for storage of CO2 in subsurface geologic repositories (e.g., less than 0.1% per year leakage) pose significant challenges for geophysical remote sensing techniques. The many issues relevant to successful CO2 sequestration (volume in place, migration, leakage rate) require improved understanding of the advantages and pitfalls of potential monitoring methods. Advanced numerical modeling of time-lapse seismic reflection responses offers a controlled environment for testing hypotheses and exploring alternatives. The U.S. Department of Energy has conducted CO2 sequestration and monitoring tests at West Pearl Queen (WPQ) field in southeastern New Mexico. High-quality 9C/3D seismic reflection data were acquired before and after injection of ~2 kt of CO2 into a depleted sandstone unit at ~4200 ft depth. Images developed from time- lapse seismic data appear to reveal strong reflectivity changes attributed to displacement of brine by CO2. We are pursuing seismic numerical modeling studies with the goal of understanding and assessing the reliability and robustness of the time-lapse reflection responses. A 3D time-domain finite-difference isotropic elastic wave propagation algorithm generates realistic synthetic data. With this capability, we examine how various types of errors and noise in the 4D data degrade the ability to image a deep CO2 plume. Source/receiver sampling, subsurface illumination, correlated geologic heterogeneity, and static shifts are considered. As a result, we are able to make quantitative estimates of the tolerable errors for monitoring CO2 injection at WPQ field. Future plans include incorporating 3D poroelastic wave propagation modeling into the analysis. Sandia National Laboratories is a multiprogram science and engineering facility

  1. New seismic reflection techniques applied to gas recognition in the Rharb Basin, Morocco

    SciTech Connect

    Jabour, H.; Dakki, M. )

    1994-07-01

    The Rharb basin in Morocco is a Tertiary foreland filled by clastic series during the Miocene and Pliocene. This terrigenous influx, derived from the prerif to the northeast and the Meseta to the south, is characterized by a sandy episode during much of the Messinian and the Tortonian. The sand deposits were probably related to the uplift and major erosion of a part of the prerif during the sliding of an olistostrome (prerif nappe). Although most of the wells drilled in the basin have encountered biogenic gas accumulations, the problem still facing exploration in the area is seismic resolution and thin-bed tuning analysis. Recent studies using high seismic resolution techniques have permitted the authors to gain a deep insight into the stratigraphy and depositional environment of the thin sand reservoirs and their fluid content. AVO stratigraphy, inversion of seismic traces into acoustic impedance traces and seismic attributes calculation, and computing provide a remarkable example of the possibilities of depicting the lateral and vertical evolution of reservoir facies and localizing biogenic gas accumulations. Out of five recent exploratory wells drilled based on this new technique, three encountered gas-bearing sands with economic potential. Fifty-three amplitude anomalies have been identified and await processing.

  2. Using the IODP Expedition 312 Vertical Seismic Profile to Investigate Sub-basement Reflections in Multi-Channel Profiles

    NASA Astrophysics Data System (ADS)

    Nag, S.; Swift, S. A.; Stephen, R. A.

    2008-05-01

    The Ocean Drilling Program (ODP) initiated drilling at Site 1256D in the Guatemala Basin, about 1000km off the East Pacific Rise to penetrate plutonic rocks, anticipated to be relatively shallow in this region formed at an ultra- fast spreading rate. IODP Expedition E312 successfully drilled into gabbros at ~ 1150m in basement. Multi- channel seismic traces, although not processed for the purpose, show weak laterally-coherent sub-basement reflections at borehole depths (Hallenborg et. al., Journal of Geophysical Research, Vol 108 No. B11, 2532, 2003). Synthetic reflectivity seismograms were computed using a Ricker wavelet and impedance profiles from borehole sonic logs. They strongly suggest the presence of significant sub-basement amplitude peaks - although attenuation has not been modeled. Zero-offset vertical seismic profiles were processed to investigate the authenticity of these reflections and interpret the geological features that caused them. A dual scheme of the median filtering and F-K dip filtering was used. Down-going energy is clearly identified but negligible up-going energy is visible over random noise. The absence of geophones above the basement prevents comparison of basement reflections with sub-basement ones, so that a critical energy level above the noise could be established to identify up-going energy. The negative results are consistent with the topography of geological horizons on horizontal scales less than the Fresnel Zone (~ 300m). This expedition is the first penetration through volcanic extrusives and dikes into plutonic basement. In such a setting, sub-basement reflections, if present, would have been accurately measured. Absence of such clear and comprehensible observations in this area strongly suggests that lava flows and igneous contacts in upper ocean crust have significant topography on lateral scales < 300 m due to igneous and tectonic processes.

  3. 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.

  4. Computed tomography imaging spectrometer (CTIS) with 2D reflective grating for ultraviolet to long-wave infrared detection especially useful for surveying transient events

    NASA Technical Reports Server (NTRS)

    Wilson, Daniel W. (Inventor); Maker, Paul D. (Inventor); Muller, Richard E. (Inventor); Mouroulis, Pantazis Z. (Inventor)

    2003-01-01

    The optical system of this invention is an unique type of imaging spectrometer, i.e. an instrument that can determine the spectra of all points in a two-dimensional scene. The general type of imaging spectrometer under which this invention falls has been termed a computed-tomography imaging spectrometer (CTIS). CTIS's have the ability to perform spectral imaging of scenes containing rapidly moving objects or evolving features, hereafter referred to as transient scenes. This invention, a reflective CTIS with an unique two-dimensional reflective grating, can operate in any wavelength band from the ultraviolet through long-wave infrared. Although this spectrometer is especially useful for rapidly occurring events it is also useful for investigation of some slow moving phenomena as in the life sciences.

  5. Computed Tomography Imaging Spectrometer (CTIS) with 2D Reflective Grating for Ultraviolet to Long-Wave Infrared Detection Especially Useful for Surveying Transient Events

    NASA Technical Reports Server (NTRS)

    Wilson, Daniel W. (Inventor); Maker, Paul D. (Inventor); Muller, Richard E. (Inventor); Mouroulis, Pantazis Z. (Inventor)

    2003-01-01

    The optical system of this invention is an unique type of imaging spectrometer, i.e. an instrument that can determine the spectra of all points in a two-dimensional scene. The general type of imaging spectrometer under which this invention falls has been termed a computed-tomography imaging spectrometer (CTIS). CTIS's have the ability to perform spectral imaging of scenes containing rapidly moving objects or evolving features, hereafter referred to as transient scenes. This invention, a reflective CTIS with an unique two-dimensional reflective grating, can operate in any wavelength band from the ultraviolet through long-wave infrared. Although this spectrometer is especially useful for events it is also for investigation of some slow moving phenomena as in the life sciences.

  6. S-waves velocity model for the SW-Iberia derived from the IBERSEIS wide-angle seismic reflection transects

    NASA Astrophysics Data System (ADS)

    Palomeras, I.; Marti, D.; Carbonell, R.; Ayarza, P.; Simancas, F.; Martinez-Poyatos, D.; Azor, A.; Gonzalez-Lodeiro, F.; Perez-Estaun, A.

    2009-04-01

    The IBERSEIS wide-angle seismic reflection transects acquired in 2003 in SW-Iberia Peninsula provided constraints on the P-wave seismic velocity structure across the three tectonic provinces in the area: the South Portuguesse Zone (SPZ), the Ossa-Morena Zone (OMZ) and the Central Iberia Zone (CIZ). These data were acquired by 650 vertical component seismographs (TEXAN seismic recorders) from the IRIS-PASSCAL Instrument center, using explosive sources with charge sizes ranging from 500 to 1000 kg. Both transects A and B are, approximately, 300 km long with a station spacing of 400 m and of 150 m respectively. The relatively small station spacing favored the lateral correlation of the seismic events and provided enough resolution for the identification of shear-wave arrivals. The most prominent S-wave phase recorded by the vertical component sensors corresponds to the SmS which is nearly horizontal for a velocity reduction of 4600 m/s. This phase can even be followed up to near vertical incidence at 18 s(twtt). A few S-wave crustal arrivals can be also identified, although at small offsets they interfere with the previous P-wave arrivals. The Sn phase can be observed at very far offsets providing additional constraints on the nature of the shallow subcrustal mantle. Furthermore, slant stacks of the shot gathers (tau-p sections) reveal the existing of PS energy. PS phases are more difficult to identify in the shot gathers. Finally, a preliminary S-wave velocity model has been derived by iterative forward modeling to provide additional constraints on the nature of the deep crust and upper mantle beneath the Variscan of SW-Iberia.

  7. Seismic Reflection Imaging of the Heat Source of an Ultramafic-Hosted Hydrothermal System (Rainbow, Mid-Atlantic Ridge 36° 10-17'N)

    NASA Astrophysics Data System (ADS)

    Canales, J. P.; Dunn, R. A.; Sohn, R. A.; Horning, G.; Arai, R.; Paulatto, M.

    2015-12-01

    Most of our understanding of hydrothermal systems and the nature of their heat sources comes from models and observations at fast and intermediate spreading ridges. In these settings, hydrothermal systems are mainly located within the axial zone of a spreading segment, hosted in basaltic rock, and primarily driven by heat extracted from crystallization of crustal melt sills. In contrast, hydrothermal systems at slow-spreading ridges like the Mid-Atlantic Ridge (MAR) show a great variety of venting styles and host-rock lithology, and are located in diverse tectonic settings like axial volcanic ridges, non-transform discontinuities (NTDs), the foot of ridge valley walls, and off-axis inside corner highs. Among MAR systems, the Rainbow hydrothermal field (RHF) stands out as an end-member of this diversity: an ultramafic-hosted system emitting H2 and CH4-rich fluids at high temperatures and high flow rates, which suggests a magmatic heat source despite the lack of evidence for recent volcanism and its location within an NTD with presumably low magma budget. We present 2D multichannel seismic reflection images across the Rainbow massif from the NSF-funded MARINER multidisciplinary geophysical study that reveal, for the first time, the magmatic system driving hydrothermal circulation in an ultramafic setting. Data were acquired in 2013 onboard the RV M. Langseth with an 8-km-long hydrophone streamer. The images have been obtained from pre-stack depth migrations using a regional 3D P-wave velocity model from a coincident controlled-source seismic tomography experiment using ocean bottom seismometers. Our images show a complex magmatic system centered beneath the RHF occupying an areal extent of ~3.7x6 km2, with partially molten sills ranging in depth between ~3.4 km and ~6.9 km below the seafloor. Our data also image high-amplitude dipping reflections within the massif coincident with strong lateral velocity gradients that may arise from detachment fault planes

  8. Evidence of a possible NNE-trending fault zone in the Summerville, South Carolina, area from shallow seismic reflection surveys

    SciTech Connect

    Marple, R.T.; Talwani, P. . Geology Dept.)

    1994-03-01

    Five high-resolution seismic-reflection surveys trending approximately WNW-ESE and totaling about 31 km were acquired in the Summerville, South Carolina, area. The surveys trend across the postulated Woodstock fault zone. These newly acquired data together with earlier data revealed the existence of an [approximately]50-km-long feature associated with gentle warping of the shallow sediments that lies along a recently described zone of river anomalies (ZRA). The first ([approximately]5.9-km-long) seismic reflection profile located about 14 km NNE of Summerville revealed that the J reflector (basalt) at about 670 m depth is offset about 30--40 m with the west side up. The overlying sediments displayed upwarping rather than brittle offset. A second ([approximately]6.7-km-long) survey located along interstate Highway 26 revealed as much as 30--40 m of upwarping of the sediments above about 450 m depth. A third ([approximately]7.3-km-long) profile acquired through the town of Summerville revealed four, [approximately]200--300 m wide, nearly vertical zones in which the reflectors are noncoherent. Away from these zones the reflectors are relatively flat and are slightly higher on the west side of each zone. The fourth (3-km-long) survey was located about 5 km SW of Middleton Gardens and indicated minor faulting at about 500 m depth. The fifth ([approximately]6.4-km-long) seismic survey acquired just north of Ravenel revealed an [approximately]0.5-km-wide zone in which the reflectors in the top 350 m displayed as much as 20 m of upwarping. On all the surveys, except for the first, the basalt was at too great a depth to be resolved.

  9. Seismic reflection images of a near-axis melt sill within the lower crust at the Juan de Fuca ridge.

    PubMed

    Canales, J Pablo; Nedimović, Mladen R; Kent, Graham M; Carbotte, Suzanne M; Detrick, Robert S

    2009-07-01

    The oceanic crust extends over two-thirds of the Earth's solid surface, and is generated along mid-ocean ridges from melts derived from the upwelling mantle. The upper and middle crust are constructed by dyking and sea-floor eruptions originating from magma accumulated in mid-crustal lenses at the spreading axis, but the style of accretion of the lower oceanic crust is actively debated. Models based on geological and petrological data from ophiolites propose that the lower oceanic crust is accreted from melt sills intruded at multiple levels between the Moho transition zone (MTZ) and the mid-crustal lens, consistent with geophysical studies that suggest the presence of melt within the lower crust. However, seismic images of molten sills within the lower crust have been elusive. Until now, only seismic reflections from mid-crustal melt lenses and sills within the MTZ have been described, suggesting that melt is efficiently transported through the lower crust. Here we report deep crustal seismic reflections off the southern Juan de Fuca ridge that we interpret as originating from a molten sill at present accreting the lower oceanic crust. The sill sits 5-6 km beneath the sea floor and 850-900 m above the MTZ, and is located 1.4-3.2 km off the spreading axis. Our results provide evidence for the existence of low-permeability barriers to melt migration within the lower section of modern oceanic crust forming at intermediate-to-fast spreading rates, as inferred from ophiolite studies.

  10. Identifying the Structure of a Brine Cavern Using Two-Dimensional Seismic Reflection Imagery, Carlsbad, New Mexico

    NASA Astrophysics Data System (ADS)

    Schneider, J. M.; Goodman, W. M.

    2011-12-01

    Shallow depths to the salt-bearing formations of the Permian Basin provide for cost-effective solution-mining operations in southeastern New Mexico and northwestern Texas. Over extraction of salt, coupled with limited overburden thickness and competency, led to the collapse of two solution-mined caverns near Carlsbad, New Mexico, in 2008. These collapses prompted the New Mexico Oil Conservation Division (OCD) to conduct an investigation focusing on brine extraction wells with geologic conditions and dimensions comparable to the collapsed wells. OCD concluded that the operations and geologic setting of the I&W, Inc. well site, located at the intersection of U.S. Highway 285 and 62 in the city of Carlsbad, shared similarities to sites where caverns failed. In 2009, a high-resolution, two-dimensional, P-wave seismic reflection analysis assisted in defining the lateral extent of the cavern and deformation of the overlying bridging strata at the I&W site. Cavern effects include downwarping and loss of amplitude of reflectors interpreted to represent upper Salado and overlying Rustler Formation strata. The snapshot of subsurface conditions provided by the seismic reflection data is being augmented with routine surface subsidence measure measurements as well as additional surface geophysical programs.

  11. 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.

  12. Thickness and geometry of Cenozoic deposits in California Wash area, Nevada, based on gravity and seismic-reflection data

    USGS Publications Warehouse

    Langenheim, V.E.; Miller, J.J.; Page, W.R.; Grow, J.A.

    2001-01-01

    Gravity and seismic-reflection data provide insights into the subsurface stratigraphy and structure of the California Wash area of southern Nevada. This area is part of the Lower Colorado flow system and stratigraphic and structural data are important inputs into developing the hydrogeologic framework. These data indicate that the basin beneath California Wash reaches depths of 2-3 km. The eastern margin of the basin coincides with a system of young (Quaternary and late Tertiary) faults, although both seismic and gravity data indicate that the major basin-bounding fault is 2-3 km west of the mapped young faults. Dry Lake Valley, the adjacent valley to the west, is characterized by thinner basin fill. The basin configuration beneath both California Wash and Dry Lake Valleys based on the inversion of gravity data is unconstrained because of the lack of gravity stations north of 36030?. Broad aeromagnetic anomalies beneath pre-Cenozoic basement in the Muddy Mountains and Arrow Canyon Range reflect Precambrian basement at depths of ~ 5 km. These rocks are probably barriers to ground-water flow,except where fractured.

  13. High-resolution seismic-reflection imaging 25 years of change in I-70 sinkhole, Russell County, Kansas

    USGS Publications Warehouse

    Miller, R.D.; Steeples, D.W.; Lambrecht, J.L.; Croxton, N.

    2006-01-01

    Time-lapse seismic reflection imaging improved our understanding of the consistent, gradual surface subsidence ongoing at two sinkholes in the Gorham Oilfield discovered beneath a stretch of Interstate Highway 70 through Russell and Ellis Counties in Kansas in 1966. With subsidence occurring at a rate of around 10 cm per year since discovery, monitoring has been beneficial to ensure public safety and optimize maintenance. A miniSOSIE reflection survey conducted in 1980 delineated the affected subsurface and successfully predicted development of a third sinkhole at this site. In 2004 and 2005 a high-resolution vibroseis survey was completed to ascertain current conditions of the subsurface, rate and pattern of growth since 1980, and potential for continued growth. With time and improved understanding of the salt dissolution affected subsurface in this area it appears that these features represent little risk to the public from catastrophic failure. However, from an operational perspective the Kansas Department of Transportation should expect continued subsidence, with future increases in surface area likely at a slightly reduced vertical rate. Seismic characteristics appear empirically consistent with gradual earth material compaction/settling. ?? 2005 Society of Exploration Geophysicists.

  14. Feasibility of High Resolution P- and S-Wave Seismic Reflection to Detect Methane Hydrate

    SciTech Connect

    Hunter, J.A.

    2000-08-02

    In March, 1999, a combined geophysical field team from the Kansas Geological Survey, Oak Ridge National Laboratory, and the Geological Survey of Canada, performed some experimental high resolution seismic testing at the Mallik drill site in the Mackenzie Delta, Northwest Territories, where drilling and sampling had previously identified gas hydrates at depth beneath a thick permafrost zone. In this information document, we show data from this seismic test, along with comparisons and observations significant to the effective use of high resolution imaging and important considerations about high resolution operations in this environment. Included are discussions and examples based on previous studies at this site, data acquisition, processing, correlation of results with other data sets and some recommendations for future surveying.

  15. Examples of deep-water-bottom multiple dereverberation techniques applied to seismic-reflection data from the Atlantic Outer Continental Shelf

    USGS Publications Warehouse

    Peterson, Steven D.; Balch, A.H.; Patterson, W.C.; Taylor, D.J.

    1979-01-01

    Seismic-reflection data recorded in deep water over the Atlantic Outer Continental Shelf are often dominated by multiply-reflected seismic energy. This energy reverberates between the surface of the water and the seafloor (or other strong reflectors), and makes portions of the seismic data completely useless. Several different data-processing techniques can be applied to partially suppress these multiples and enhance the interpretability of the data. These techniques include (1) the three-point operator, (2) predictive deconvolution, (3) near-trace muting, (4) spatially variant bandpass filters, (5) Nth root stack, and (6) trace distance weighting. Application of these methods to several seismic lines indicates that trace distance weighting is the most useful method studied for suppressing deep-water-bottom multiples for data from the Atlantic Outer Continental Shelf.

  16. SinoProbe-02: Deep Seismic Reflection Profiling of the Bangong Suture and Qiangtang terrane in central Tibet

    NASA Astrophysics Data System (ADS)

    Lu, Z.; Chen, C.; Gao, R.; Brown, L.; Xiong, X.; Li, W.; Deng, G.

    2010-12-01

    The Bangong Suture represents the tectonic junction between the two primary terranes of the Tibetan Plateau- the Lhasa block and the Qiangtang terrane.This suture was originally formed during a Jurassic collision of these two terranes,but has retained considerably significance as the suspect surface position of the buried mantle suture between Indian and Asian lithosphere that formed during Himalayan collision.As a corollary,these terranes have been associated with very different styles of mantle tectonics,perhaps as a result of mantle delamination beneath the Qiangtang.There have been a number of attempts to probe the deep structure of both the suture and its flanking terranes with refraction and teleseismic methods.Here we report the results of the first multichannel seismic reflection profile across this critical region.Deep seismic reflection method is internationally recognized as a pioneering technology for imaging crustal details,and it has been successfully applied in Southern Tibetan plateau in early 1990s.From October 2009 to May 2010,SinoProbe collected 310 km of a deep seismic reflection profile crossing BNS,successfully revealing structural details down to the Moho and possible deeper.The profile starts west of Silin Co in the northern Lhasa block,crosses the Bangong-Nujiang suture west of Lunpola,skirts the eastern extension of the central Qiantang anticline and ends at Dogai Coring just of south of Jinsha suture.The survey used explosive sources with variable shot size to insure adequate imaging of both the upper and lower crust.In the southern part of the profile,small shots of 50kg explosive were placed at 30m depth at 250m spacing,augmented by larger shots of 200kg t 50m depth spaced every 1km.In addition,large shots of 1000kg were placed every 50km.In the middle and north part,only 200 kg shots at 500m spacing along with the big shots.A linear array of receivers was used with a group interval of 50 m.The data was acquired by Sercel 408 XL using

  17. Nature of the lithosphere across the Variscan orogen of SW Iberia: Dense wide-angle seismic reflection data

    NASA Astrophysics Data System (ADS)

    Palomeras, I.; Carbonell, R.; Flecha, I.; Simancas, F.; Ayarza, P.; Matas, J.; MartíNez Poyatos, D.; Azor, A.; GonzáLez Lodeiro, F.; PéRez-Estaún, A.

    2009-02-01

    Two wide-angle seismic transects have been acquired across the SW Iberian Massif. They crossed three major geological zones (South Portuguese Zone, Ossa-Morena Zone, and Central Iberian Zone), with their tectonic contacts and the Pyrite Belt being of greatest interest. A total of 690 digital seismic recording instruments (650 Texans and 40 Reftek 3 component units) from the IRIS-PASSCAL Instrument Pool were used. The transects (A and B) are each approximately 300 km long and consist of 3 and 6 shot points, respectively, with an approximately 60-km shot point interval. The charge sizes range from 1000 kg at the edges to 500 kg at the center. These recently acquired experiments were designed to provide velocity constraints on the lithosphere and to complement the previously acquired normal incidence seismic profile IBERSEIS. Both data sets are part of the SW Iberia project, which was developed within the EUROPROBE program and designed to address fundamental questions about the nature and dynamics of the Variscan lithosphere. The acquisition parameters provide closely spaced wide-angle seismic images of the lithosphere beneath SW Iberia. In transect A, the station spacing was on average 400 m, while along transect B, the receiver spacing was approximately 150 m. Because of this close trace spacing, the lateral continuity of the seismic arrivals is greatly improved. Frequency analysis revealed that the recorded events feature relatively low frequencies (6-25 Hz). After processing, the shot records show high-amplitude and well-defined arrivals. The interpreted PmP arrival, located at approximately 11 s (normal incidence traveltime), is characterized by high amplitude and relatively low frequency (6-12 Hz). A well-defined Pn arrival appears at offsets beyond 120 km. At far offsets greater than 180 km, an upper mantle reflection is observed. Furthermore, within the upper crust, the shots records feature a relatively high-velocity arrival, located at 4-5-s normal incidence

  18. First results of a high resolution reflection seismic survey of the Central Northern Venezuelan Shelf

    NASA Astrophysics Data System (ADS)

    Avila, J.; van Welden, A.; Audemard, F.; de Batist, M.; Beck, C.; Scientific Party, G.

    2008-05-01

    In September - November 2007 the first high resolution marine seismic campaign on the North-Central coast of Venezuela was carried out between Cabo Codera and Golfo Triste. The principal aim of this work was to characterize the active San Sebastian Fault (SSF) and to analyze Cenozoic sedimentation on the Venezuela shelf focusing on: i) effects of active tectonics and ii) coastal landslides/flashflood deposits related to 1999 Vargas catastrophic event or to similar phenomena. Data were acquired onboard R/V GUAIQUERI II from the Oceanographic Institute of the Oriente University. The seismic source was a "CENTIPEDE" sparker (RCGM) operated between 300 and 600 J, 1.3 kHz main frequency. We used a single-channel streamer with 10 hydrophones. In total, 49 seismic profiles were collected, with a cumulative length of 1000 km approximately. In these seismic profiles we identified and separated the deposits into three main units. Unit (U1) comprises low energy reflectors mainly dipping in southward direction (i.e. toward the coast bounded by the San Sebastian Fault). This unit also includes a number of isolated acoustic anomalies, which we tentatively interpret as coral reefs. Its top is defined as Basal Erosional Discontinuity (BED) onto which Unit 2 (U2) deposits are onlapping. U2 is acoustically well-stratified, with strong reflectors. Gradual variations in thickness and a wavy configuration allow us to interpret U2 as probably Quaternary current-related deposits. Last Unit (U3) was defined on the Venezuela shelf and corresponds to prograding sequences probably related to the terrigenous input of the Tuy River. Impact of eustatic fluctuations on these deposits are discussed. The data were also used to construct a simplified bathymetry of the studied area. The lateral transition from the western Cariaco-Tuy pull-apart basin to the (single) SSF was clearly imaged (mostly folds and gravity faults). The survey also displayed prograding sediments bodies in La Tortuga Shelf

  19. Anatomy of a Complex Fault Zone: Land Seismic Reflection Imaging of the Tacoma Fault Zone, Washington State

    NASA Astrophysics Data System (ADS)

    Pape, K.; Liberty, L. M.; Pratt, T. L.

    2005-12-01

    Preliminary interpretations of new land-based seismic reflection images across the Tacoma fault zone in western Washington State document a complex pattern of faulting and folding. The Tacoma fault zone bounds gravity and aeromagnetic anomalies for 50 km across the central Puget Lowland west of the city of Tacoma, and tomography data suggest there is as much as 6 km of post-Eocene uplift of the hanging wall relative to Tacoma basin sediments to the south. We acquired four north-south seismic reflection profiles to define the character and tectonic history of the Tacoma fault zone. The 6-km long Powerline Road profile, located west of Case Inlet, perpendicularly crosses the 4-km-long Catfish Lake scarp discerned from Lidar data and trenching. The profile shows flat-lying strata on the south, but the north part of the profile is dominated by south-dipping Tertiary and older strata that appear to form the limb of an anticline. There appears to be at least one, and likely two faults in the Tertiary and older strata, although it is not clear these faults penetrate the shallowest Pleistocene strata. The 8.5-km long Carney Lake profile is located east of Case Inlet and spans two scarps imaged on Lidar data. This profile shows a similar geometry to the Powerline Road profile, folded and faulted Tertiary and older strata adjacent to flat-lying marine sediments of the Tacoma Basin. The 9-km long Bethel-Burley profile across the east portion of the Tacoma fault near Gig Harbor shows a significantly different reflector geometry than the profiles to the west. The Bethel-Burley profile is dominated by a strong, south-dipping reflection that becomes a prominent arch near the north end of the section. The strength of the reflector suggests that it marks the top of the Eocene basement rocks. South-dipping strata on this profile match those imaged on marine profiles from Carr Inlet. The new seismic reflection data support an interpretation in which the north edge of the Tacoma basin

  20. Active seismic and microseismic reflection imaging of the Precordilleran crust, fore-arc of the North-Chilean subduction zone (Central Andes)

    NASA Astrophysics Data System (ADS)

    Wenske, Ina; Hellwig, Olaf; Schmelzbach, Cedric; Buske, Stefan; Kummerow, Jörn; Wigger, Peter; Shapiro, Serge A.

    2013-04-01

    In the fore-arc of the Chilean subduction zone, prominent trench-parallel fault systems can be traced for more than thousand kilometers in north-south direction. These fault systems possibly crosscut parts or the entire crust and are expected to have a close relationship to transient processes of the subduction earthquake cycle. With the motivation to image and characterize the structural inventory and the processes that occur in the vicinity of these large-scale fault zones, we are currently performing a combined analysis of active and passive seismic data sets. The active-seismic data analysis is intended to provide images of the faults at depth and allow linking surface information to subsurface structures. The correlation of the active seismic data with the observed seismicity around these fault systems complements the imaging and potentially reveals the origin and the nature of the seismicity (incl. tremors) bound to these fault systems. Furthermore, reflection information extracted from passive-seismic waveform data has the potential to complement the active seismic imaging. In 1996, an approximately 350 km long west-east running reflection seismic profile was acquired to image the entire crust of the Central Andean fore-arc system (North Chile; ANCORP96 seismic line). Several features such as the downgoing plate (Nazca reflector) and the Quebrada Blanca Bright Spot at mid-crustal level were clearly imaged using both standard CMP processing and Kirchhoff prestack depth migration. The latter proved to be more successful in coping with the low data coverage and varying data quality. However, the original images were not providing conclusive information on the upper crust (< 10 km depth) due to the sparse acquisition geometry and the partly insufficient removal of source-generated noise. The major goal of our current re-processing of the ANCORP96 reflection seismic data set using adapted noise-suppression schemes and a novel prestack depth migration technique

  1. Oceanic Character of Sub-Salt Crust in the NW Gulf of Mexico (GOM) Using Seismic Refraction and Reflection Data

    NASA Astrophysics Data System (ADS)

    Karner, G. D.; Johnson, C. A.

    2015-12-01

    Significant renewed interest in the geological development of the NW GOM is exemplified by the acquisition of academic seismic refraction and oil industry seismic reflection data. There is agreement that the GOM formed by Jurassic separation of North America and Yucatan, but disagreements remain on the distribution and timing of extended continental versus oceanic crust. Van Avendonk et al. (Geology, v43, 2015) interpreted seismic refraction data from the 2010 "GUMBO" expedition as rifted continental crust thinned by large-scale extensional faulting and syn-rift magmatism beneath the NW GOM. However, seismic reflection evidence for this extension is non-existent, and diagnostic fault-controlled syn-rift packages are not resolved. A very different interpretation of basement type and basin evolution is possible by applying geological process linked to hyper-extended margin formation to the same data. We note: 1) Base salt and Moho interfaces are well imaged; top basement is not resolved. We interpret a pre-salt sedimentary sequence 5-10 km thick, with velocities up to 6 km/s; high velocities in this sequence likely relate to greenschist-facies metamorphism associated with early high heat flow and deep burial. 2) Velocities of 6-8 km/s characterize crystalline basement but do not uniquely determine crustal type (i.e., velocity does not equate to rock type). Lateral variations (0-8 km) in crustal thickness are consistent with slow/ultra-slow seafloor spreading. 3) The undeformed base salt reflector and pre-salt sediment sequence imply a post-kinematic setting and a substantial delay between breakup and Callovian salt deposition. 4) Liassic Central Atlantic breakup is kinematically linked to the GOM and related SDR magmatism. Inboard SDRs, observed on both conjugate margins of the GOM, imply outboard oceanic crust. Together, these observations are consistent with regional sub-salt basement of early-mid Jurassic slow/ultra-slow spreading oceanic crust, associated with

  2. Basement depth and sedimentary infill from deep seismic reflection data at the western tip of the offshore Corinth Rift

    NASA Astrophysics Data System (ADS)

    Beckers, Arnaud; Tripsanas, Efthymios; Hubert-Ferrari, Aurélia; Beck, Christian; Sakellariou, Dimitris

    2015-04-01

    The Corinth rift is a young continental rift located in central Greece. The active part of the rift forms an E-W striking depression - the Gulf of Corinth - that is the deepest in its central part. Extensive seismic surveys have imaged the basin's basement and allowed to estimate the total extension across most of the Gulf except its western tip. Extension is high in the central part and decreases westward and eastward, as reflected in the present-day bathymetry. Two decades of GPS measurements have shown that the extension rate increases westwards from ~5 to 10-15 mm yr-1, but this is not consistent with the long term pattern. However, no data allowed so far to estimate the basement depth at the western tip of the Gulf, where the geodetic extension rate is the largest. Such data would allow to check the apparent inconsistency between the present rate and the long-term estimates of crustal extension. We present here an unpublished multichannel seismic line dating from 1979 and crossing the western tip of the Gulf of Corinth. The line is 22 km long and strikes WNW-ESE, from the Mornos delta to the West-Channel fault. A Maxipulse source has been used, allowing to image the basement below the synrift sedimentary infill. To the east, a ~1.6 km deep basin is imaged between the southern margin of the Gulf and an inactive south-dipping fault located between the Aigion and the Trizonia faults. The sedimentary infill consists in an alternation between basin-focused bodies made of incoherent reflections and more extensive high-amplitude reflectors. Attributing this alternation to eustatic variations give an age of 300-350 ka to the oldest well imaged deposits. Northwest of the Trizonia fault, the basement is imaged at shallower depth, i.e. ~450 m. The western tip of the seismic line reaches the Mornos delta, close to the northern shoreline. There, the depth to the basement is larger, reaching ~1.2 km. The infill is made of 3 units : on the basement lies a thin unit of

  3. Astor Pass Seismic Surveys Preliminary Report

    SciTech Connect

    Louie, John; Pullammanappallil, Satish; Faulds, James; Eisses, Amy; Kell, Annie; Frary, Roxanna; Kent, Graham

    2011-08-05

    In collaboration with the Pyramid Lake Paiute Tribe (PLPT), the University of Nevada, Reno (UNR) and Optim re-processed, or collected and processed, over 24 miles of 2d seismic-reflection data near the northwest corner of Pyramid Lake, Nevada. The network of 2d land surveys achieved a near-3d density at the Astor Pass geothermal prospect that the PLPT drilled during Nov. 2010 to Feb. 2011. The Bureau of Indian Affairs funded additional seismic work around the Lake, and an extensive, detailed single-channel marine survey producing more than 300 miles of section, imaging more than 120 ft below the Lake bottom. Optim’s land data collection utilized multiple heavy vibrators and recorded over 200 channels live, providing a state-of-the-art reflection-refraction data set. After advanced seismic analysis including first-arrival velocity optimization and prestack depth migration, the 2d sections show clear fault-plane reflections, in some areas as deep as 4000 ft, tying to distinct terminations of the mostly volcanic stratigraphy. Some lines achieved velocity control to 3000 ft depth; all lines show reflections and terminations to 5000 ft depth. Three separate sets of normal faults appear in an initial interpretation of fault reflections and stratigraphic terminations, after loading the data into the OpendTect 3d seismic visualization system. Each preliminary fault set includes a continuous trace more than 3000 ft long, and a swarm of short fault strands. The three preliminary normal-fault sets strike northerly with westward dip, northwesterly with northeast dip, and easterly with north dip. An intersection of all three fault systems documented in the seismic sections at the end of Phase I helped to locate the APS-2 and APS-3 slimholes. The seismic sections do not show the faults connected to the Astor Pass tufa spire, suggesting that we have imaged mostly Tertiary-aged faults. We hypothesize that the Recent, active faults that produced the tufa through hotspring

  4. Structure of a continental strike-slip fault from deep seismic reflection: Walls Boundary fault, northern British Caledonides

    NASA Astrophysics Data System (ADS)

    McBride, John H.

    1994-12-01

    Reprocessing of four offshore deep reflection profiles across the Walls Boundary strike-slip fault, postulated as the northward continuation of the Great Glen fault over the Shetland platform, provides useful constraints on the lithospheric structure of a major continental transform and some insight into the manner in which strike-slip faults deform. The reprocessing was aimed at delineating complex structure and reducing noise contamination and consisted of analyses of diffractions and amplitude variations and experimentation with seismic migration. The results demonstrate a highly variable crustal and uppermost mantle structure for the Walls Boundary fault along more than 150 km of its length. Six key observations can be made from this study. A vertical or steeply dipping structure is deduced for the fault in much of the crust and perhaps parts of the uppermost mantle; however, more diverse reflecting structures and interpreted for the lower crust, such as the Moho deflection and steeply dipping reflectors directly beneath the fault that may have been related to a localized component of transpression and resultant crustal thickening. The presence of diffractions at the level of the Moho discontinuity where the downward projection of the fault intersects it suggests points of structural 'roughness' that may be related to deformation of the Moho by late motion along the fault. Integrating the interpretation of the reflection data with previous geological studies implies that the age of the Moho deflection is post Early Cretaceous but that the dipping structure adjacent to and cut off by the fault is probably Caledonian (Silurian-Early Devonian). Although the disparate structure of the crust on opposite sides of the fault supports geologic interpretations of large-scale displacement, a major step in the Moho discontinuity directly beneath the Walls Boundary fault cannot be substantiated from the seismic data.

  5. Stochastic velocity inversion of seismic reflection/refraction traveltime data for rift structure of the southwest Barents Sea

    NASA Astrophysics Data System (ADS)

    Clark, Stephen A.; Faleide, Jan Inge; Hauser, Juerg; Ritzmann, Oliver; Mjelde, Rolf; Ebbing, Jörg; Thybo, Hans; Flüh, Ernst

    2013-05-01

    We present results from an active-source, onshore-offshore seismic reflection/refraction transect acquired as part of the PETROBAR project (Petroleum-related studies of the Barents Sea region). The 700 km-long profile is oriented NW-SE, coincident with previously published multichannel seismic reflection profiles. We utilize layer-based raytracing in a Markov Chain Monte Carlo (MCMC) inversion to determine a probabilistic velocity model constraining the sedimentary rocks, crystalline crust, and uppermost mantle in a complex tectonic regime. The profile images a wide range of crustal types and ages, from Proterozoic craton to Paleozoic to early Cenozoic rift basins; and volcanics related to Eocene continental breakup with Greenland. Our analyses indicate a complex architecture of the crystalline crust along the profile, with crystalline crustal thicknesses ranging from 43 km beneath the Varanger Peninsula to 12 km beneath the Bjørnøya Basin. Assuming an original, post-Caledonide crustal thickness of 35 km in the offshore area, we calculate the cumulative thinning (β) factors along the entire profile. The average β factor along the profile is 1.7 ± 0.1, suggesting 211-243 km of extension, consistent with the amount of overlap derived from published plate reconstructions. Local β factors approach 3, where Bjørnøya Basin reaches a depth of more than 13 km. Volcanics, carbonates, salt, diagenesis and metamorphism make deep sedimentary basin fill difficult to distinguish from original, pre-rift crystalline crust, and thus actual stretching may in places exceed our estimates. Crustal velocity structure reflects multi-stage rifting in the SW Barents Sea. A stochastic inversion is applied to the widely-used RAYINVR raytracing package. β factors peak 200 km landward of the transform margin edge. Maximum β coincides with Caledonian suture. We determine 227 ± 16 km total extension of the Barents Sea rifted margin.

  6. Determination of the tectonic evolution of the Edremit Gulf based on seismic reflection studies

    NASA Astrophysics Data System (ADS)

    Kurtuluş, C.; Doğan, B.; Sertçelik, F.; Canbay, M.; Küçük, H. M.

    2009-06-01

    The Edremit Gulf, which developed during the Neogene-Quaternary, is a seismically active graben in NW Anatolia (Turkey) surrounded by the Sakarya continent. The sedimentary deposits in the gulf overlie the bedrock unconformably and can be separated into two parts as upper and lower deposits based on similarity of their seismic characteristics, and because the contact between them is clear. The lower deposits are characterized in the seismic profiles by the absence of well defined, continuous reflectors and are strongly disturbed by faults. A tectonic map and structural model of the Edremit Gulf was derived from interpreting 21 deep seismic profiles trending NE-SW and NW-SE within the gulf. Two fault systems were distinguished on the basis of this compilation. The NNW-SSE trending parallel faults are low-angle normal faults formed after compression. They controlled and deformed the lower basin deposits. A syncline and anticline with a broad fold-curvature length resulted in folds that developed parallel to basin boundaries in the lower basin deposits. The ENE-WSW trending high-angle faults have controlled and deformed the northern basin of the Edremit Gulf. The folds developed within the northern lower deposits originated from the listric geometry of the faults. These faults are normal faults associated with regional N-S extension in western Anatolia. The Edremit Gulf began to open under the control of low-angle NNW-SSE trending faults that developed after the compression of western Anatolia in an E-W direction in the early Neogene. Subsequently, regional N-S extensional stress and high-angle