Crustal Structure, Seismic Anisotropy and Deformations of the Ediacaran/Cambrian of the Małopolska Block in SE Poland Based on Data from Two Seismic Wide-Angle Experiments

NASA Astrophysics Data System (ADS)

Środa, Piotr

2017-04-01

The area of SE Poland represents a complex contact of tectonic units of different consolidation age—from the Precambrian East European Craton, through Palaeozoic West European Platform (including Małopolska Block) to Cenozoic Carpathians and Carpathian Foredeep. In order to investigate the anisotropic properties of the upper crust of the Małopolska Block and their relation to tectonic evolution of the area, two seismic datasets were used: seismic wide-angle off-line recordings from POLCRUST-01 deep seismic reflection profile and recordings from active deep seismic experiment CELEBRATION 2000. During acquisition of deep reflection seismic profile POLCRUST-01 in 2010, a 35-km-long line of 14 recorders (PA-14), oriented perpendicularly to the profile, was deployed to record the refractions from the upper crust (Pg) at wide range of azimuths. These data were used for an analysis of the azimuthal anisotropy of the MB with the modified delay-time inversion method. The results of modelling of the off-line refractions from the MB suggest 6% HTI anisotropy of the Cambrian/Ediacaran basement, with 130º azimuth of the fast velocity axis and mean Vp of 4.9 km/s. To compare this result with previous, independent information about anisotropy at larger depth, a subset of previously modelled data from CELEBRATION 2000 experiment, recorded in the MB area, was also analysed by inversion. The recordings of Pg phase at up to 120 km offsets were analysed using anisotropic delay-time inversion, providing information down to 12 km depth. The CELEBRATION 2000 model shows 9% HTI anisotropy with 126º orientation of the fast axis. Thus, local-scale anisotropy of this part of MB confirms the large-scale anisotropy suggested by previous studies based on data from a broader area and larger depth interval. The azimuthal anisotropy (i.e. HTI symmetry of the medium) is interpreted as a result of strong compressional deformation during the accretion of terranes to the EEC margin, leading to tight (sub-vertical) folding and fracturing of intrinsically anisotropic metasediments forming the MB basement. Obtained anisotropy models are compared with data about stratal dips of the MB sequences and implications of assuming more realistic TTI model are discussed. Wide-angle recordings from off-line measurements along a reflection profile provided new information about seismic velocity and anisotropy, not available from standard near-vertical profiling, and contributed to more complete image of the upper crustal structure of Małopolska Block.

Long-period amplification in deep alluvial basins and consequences for site-specific probabilistic seismic-hazard: the case of Castelleone in the Po Plain (Northern Italy)

NASA Astrophysics Data System (ADS)

Barani, S.; Mascandola, C.; Massa, M.; Spallarossa, D.

2017-12-01

The recent Emilia seismic sequence (Northern Italy) occurred at the end of the first half of 2012 with main shock of Mw6.1 highlighted the importance of studying site effects in the Po Plain, the larger and deeper sedimentary basin in Italy. As has long been known, long-period amplification related to deep sedimentary basins can significantly affect the characteristics of the ground-motion induced by strong earthquakes. It follows that the effects of deep sedimentary deposits on ground shaking require special attention during the definition of the design seismic action. The work presented here analyzes the impact of deep-soil discontinuities on ground-motion amplification, with particular focus on long-period probabilistic seismic-hazard assessment. The study focuses on the site of Castelleone, where a seismic station of the Italian National Seismic Network has been recording since 2009. Our study includes both experimental and numerical site response analyses. Specifically, extensive active and passive geophysical measurements were carried out in order to define a detailed shear-wave velocity (VS) model to be used in the numerical analyses. These latter are needed to assess the site-specific ground-motion hazard. Besides classical seismic refraction profiles and multichannel analysis of surface waves, we analyzed ambient vibration measurements in both single and array configurations. The VS profile was determined via joint inversion of the experimental phase-velocity dispersion curve with the ellipticity curve derived from horizontal-to-vertical spectral ratios. The profile shows two main discontinuities at depths of around 160 and 1350 m, respectively. The probabilistic site-specific hazard was assessed in terms of both spectral acceleration and displacement. A partially non-ergodic approach was adopted. We have found that the spectral acceleration hazard is barely sensitive to long-period (up to 10 s) amplification related to the deeper discontinuity whereas the displacement hazard is strongly affected. Our results show that neglecting the effects of the deeper discontinuity implies an underestimation of the hazard of up to about 49% for a mean return period (MRP) of 475 years and 57% for an MRP of 2475 years, with possible consequences on the design of very tall buildings and large bridges.

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

NASA Astrophysics Data System (ADS)

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

2005-12-01

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

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

NASA Astrophysics Data System (ADS)

Cowie, L.; Kusznir, N. J.; Horn, B.

2013-12-01

Knowledge of ocean-continent transition (OCT) structure, continent-ocean boundary (COB) location and magmatic type are of critical importance for understanding rifted continental margin formation processes and in evaluating petroleum systems in deep-water frontier oil and gas exploration. The OCT structure, COB location and magmatic type of the SE Brazilian and S Angolan rifted continental margins are much debated; exhumed and serpentinised mantle have been reported at these margins. Integrated quantitative analysis using deep seismic reflection data and gravity inversion have been used to determine OCT structure, COB location and magmatic type for the SE Brazilian and S Angolan margins. Gravity inversion has been used to determine Moho depth, crustal basement thickness and continental lithosphere thinning. Residual Depth Anomaly (RDA) analysis has been used to investigate OCT bathymetric anomalies with respect to expected oceanic bathymetries and subsidence analysis has been used to determine the distribution of continental lithosphere thinning. These techniques have been validated on the Iberian margin for profiles IAM9 and ISE-01. In addition a joint inversion technique using deep seismic reflection and gravity anomaly data has been applied to the ION-GXT BS1-575 SE Brazil and ION-GXT CS1-2400 S Angola. The joint inversion method solves for coincident seismic and gravity Moho in the time domain and calculates the lateral variations in crustal basement densities and velocities along profile. Gravity inversion, RDA and subsidence analysis along the S Angolan ION-GXT CS1-2400 profile has been used to determine OCT structure and COB location. Analysis suggests that exhumed mantle, corresponding to a magma poor margin, is absent beneath the allochthonous salt. The thickness of earliest oceanic crust, derived from gravity and deep seismic reflection data is approximately 7km. The joint inversion predicts crustal basement densities and seismic velocities which are slightly less than expected for 'normal' oceanic crust. The difference between the sediment corrected RDA and that predicted from gravity inversion crustal thickness variation implies that this margin is experiencing ~300m of anomalous uplift attributed to mantle dynamic uplift. Gravity inversion, RDA and subsidence analysis have also been used to determine OCT structure and COB location along the ION-GXT BS1-575 profile, crossing the Sao Paulo Plateau and Florianopolis Ridge of the SE Brazilian margin. Gravity inversion, RDA and subsidence analysis predict the COB to be located SE of the Florianopolis Ridge. Analysis shows no evidence for exhumed mantle on this margin profile. The joint inversion technique predicts normal oceanic basement seismic velocities and densities and beneath the Sao Paulo Plateau and Florianopolis Ridge predicts crustal basement thicknesses between 10-15km. The Sao Paulo Plateau and Florianopolis Ridge are separated by a thin region of crustal basement beneath the salt interpreted as a regional transtensional structure. Sediment corrected RDAs and gravity derived 'synthetic' RDAs are of a similar magnitude on oceanic crust, implying negligible mantle dynamic topography.

The Tethys Rifting of the Valencia Trough Basin

NASA Astrophysics Data System (ADS)

Viñas, Marina; Ranero, César R.; Cameselle, Alejandra L.

2017-04-01

The western Mediterranean submarine realm is composed of several basin inferred to be formed by a common geodynamic process: upper plate extension during slab rollback of a retreating subduction zone. Although the time evolution of the geometry of the trenches is debated, all models assume that basins opened sequentially from NW (Gulf of Lions) towards the SE (Ligurian-Provençal and later Tyrrhenian basins) and SW (Valencia Trough and later Algerian-South Balearic and Alboran Basin) as trenches migrated. Basin opening history is key to reconstruct kinematics of slab retreat preferred in each model. However, the deep structure of basins is inadequately known due to the paucity of modern wide-angle and multichannel reflection seismic studies across entire systems, and absence of deep drilling in the deep-water regions of the basins, as a result, much of the opening evolution is inferred from indirect evidence. In the Valencia Trough Basin (VTB), drilling and vintage seismic data provide good knowledge of the shallow geology of the basin. However, crustal-scale information across the entire VTB has been limited to two studies (Figure 1): One in the late 80's (Valsis experiment) with three Expanded Spread Profiles that yielded local 1D velocity/depth models used to constrain 2D gravity modeling, and a few multichannel seismic profiles along the Iberian shelf and across segments of the basin. A second study in the early 90's (ESCI experiment) collected a low-resolution deep-penetration multichannel seismic reflection profile across the basin and a coincident wide-angle seismic line with numerous land stations in Iberia but a handful of widely-spaced Ocean Bottom Seismometers. In the absence of modern detailed crustal structure, the origin and evolution of the VTB is still debated. Industry multichannel seismic reflection profiles cover the SW segment of the VTB. This is a region where the basin sea floor is comparatively shallower and has numerous industry wells reaching deep into the sediment sequence, which provides an unprecedented view of the tectonic structure and distribution of synrift deposits across the entire basin, from the Iberian to the North Balearic margin (Figure 2). Here we first show that the seismic records provide full crustal-scale information. Later we discuss the tectonic and sedimentary structure that supports that crustal stretching and basin formation of the VTB occurred fundamentally during the Mesozoic times by strike-slip tectonics and not during Tertiary times by back-arc extension. We show that the current sea floor morphological configuration giving rise to the so-called Valencia Trough does not represent the changes in crystalline basement thickness related to rifting, but fundamentally a product of sediment dynamics, particularly by the development during post-Messinian times of the Ebro-river delta. Our results are significant to understand Tethyan rifting and need to be considered for plate kinematic reconstructions of the western Mediterranean.

Anisotropy and tectonic deformation in the Ordos basin revealed by an active source seismic experiment

NASA Astrophysics Data System (ADS)

Jun, W. S.; Wang, F.; Xu, T.

2016-12-01

With the purpose of exploring the Ordos block, western North China Craton, two controlled-source deep seismic transects were conducted across this region. The first one is a 650 km long profile oriented N-S; the second is 1530 km and is oriented E-W. The upper mantle P wave-velocity derived from these profiles features a 0.25 km/s difference between them. Being the E-W higher that the N-S. The results obtained from both seismic profiles indicate that the upper mantle beneath the Ordos block presents seismic anisotropy in terms of discrepancy in Pn-wave velocity, such as the apparent seismic velocities observed along the two reference profiles demonstrate. This result is consistent with SKS-wave splitting measurements in the interior of the Ordos block. This indicates that the compressive stress state in Ordos during the Mesozoic became an extensional stress state in the Cenozoic. The high-velocity anomaly in the uppermost mantle under the west-east profile suggests that the lithospheric mantle is still not water-rich. Unlike what happened in the NCC to east of the Taihang Mountains, where the lithosphere experienced its thinning and destruction since the Mesozoic, the lithosphere in the interior of Ordos has suffered less deformation and remained tectonically stable. Keywords: wide-angle seismic profiling, Pn phase, high-velocity anomaly, upper mantle anisotropy, Ordos block, North China Craton. ReferencesChen L., 2009. Lithospheric structure variations between the eastern and central North China Craton from S- and P-receiver function migration. Phys. Earth Planet. Inter. 173, 216-227. Gao S., Rudnick R.L., Xu W.L., et al., 2008. Recycling deep cratonic lithosphere and generation of intraplate magmatism in the North China Craton. Earth Planet. Sci. Lett. 270, 41-53. Xu T., Zhang Z.J., Gao E.G., et al., 2010. Segmentally iterative ray tracing in complex 2D and 3D heterogeneous block models. Bull. Seism. Soc. Am. 100, 841-850. Zhu R.X., Zheng T.Y., 2009. Destruction geodynamics of the North China Craton and its Paleoproterozoic plate tectonics. Chinese Sci. Bull. 54(14), 1950-1961 (in Chinese).

Spatial Relationship Between Crustal Structure and Mantle Seismicity in the Vrancea Seismogenic Zone of Romania

NASA Astrophysics Data System (ADS)

Knapp, C. C.; Enciu, D. M.; Knapp, J. H.

2007-12-01

Active crustal deformation and subsidence in the Southeast Carpathian foreland has previously been attributed to active foundering of thickened continental lithosphere beneath the Carpathian bend region (Knapp et al, 2005). The present study involves integration of active and passive-source seismic data in order to place constraints on the duration, timing, and scale of crustal deformation in the Carpathian foreland, and in particular to assess the genetic relationship with the Vrancea intermediate-depth seismogenic zone (VSZ). Relocated crustal earthquakes and focal mechanisms were correlated with four deep industry seismic profiles, the reprocessed DACIA PLAN deep seismic profile, and the DRACULA (Deep Reflection Acquisition Constraining Unusual Lithospheric Activity) II and III profiles. Projection of foreland crustal hypocenters onto the deep seismic lines correlates well with previously identified crustal faults such as the Trotus and Sinaia, as well as the newly identified Ialomita Fault. Specifically, results of this study (1) image the full crustal and uppermost mantle structure of the Focsani Basin in the close proximity of the VSZ, (2) show evidence for a sub-horizontal, slightly east-dipping Moho in the vicinity of the VSZ and thinning of the crust towards the Carpathian orogen, (3) illustrate the conspicuous absence of west-dipping fabrics or structures in the crust and across the Moho, (4) present evidence that the Trotus Fault is a crustal-scale active fault with a dextral sense of motion, (5) suggest that the Paleozoic age Peceneaga-Camena and Capidava-Ovidiu Faults have not been active in post-Paleozoic time, and (6) show evidence for a new active crustal scale sinistral fault, named the Ialomita fault. Both the seismogenic Vrancea body and deformation in the Focsani Basin appear to be concentrically bound by the Trotus Fault in the north and east and the Sinaia-Ialomita Fault in the south, suggesting a coupled deformation between the VSZ and the foreland deformation, possibly accommodated on these two major fault systems. These results contradict both the "subduction-in-place" and "slab- break-off" hypotheses as feasible explanations for VSZ intermediate-depth seismicity, and lend additional support to a lithospheric delamination model to explain both the origin of the VSZ and the crustal architecture of the Southeast Carpathian foreland.

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.

Seismic signatures of carbonate caves affected by near-surface absorptions

NASA Astrophysics Data System (ADS)

Rao, Ying; Wang, Yanghua

2015-12-01

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

Earth's crust model of the South-Okhotsk Basin by wide-angle OBS data

NASA Astrophysics Data System (ADS)

Kashubin, Sergey N.; Petrov, Oleg V.; Rybalka, Alexander V.; Milshtein, Evgenia D.; Shokalsky, Sergey P.; Verba, Mark L.; Petrov, Evgeniy O.

2017-07-01

Deep seismic studies of the Sea of Okhotsk region started in late 1950s. Since that time, wide-angle reflection and refraction data on more than two dozen profiles were acquired. Only five of those profiles either crossed or entered the deep-water area of the South-Okhotsk Basin (also known as the Kuril Basin or the South-Okhotsk Deep-Water Trough). Only P-waves were used to develop velocity-interface models in all the early research. Thus, all seismic and geodynamic models of the Okhotsk region were based only on the information on compressional waves. Nevertheless, the use of Vp/Vs ratio in addition to P-wave velocity allows discriminating felsic and mafic crustal layers with similar Vp values. In 2007 the Russian seismic service company Sevmorgeo acquired multi-component data with ocean bottom seismometers (OBS) along the 1700-km-long north-south 2-DV-M Profile. Only P-wave information was used previously to develop models for the entire profile. In this study, a multi-wave processing, analysis, and interpretation of the OBS data are presented for the 550-km-long southern segment of this Profile that crosses the deep-water South-Okhotsk Basin. Within this segment 50 seismometers were deployed with nominal OBS station spacing of 10-12 km. Shot point spacing was 250 m. Not only primary P-waves and S-waves but also multiples and P-S, S-P converted waves were analyzed in this study to constrain velocity-interface models by means of travel time forward modeling. In offshore deep seismic studies, thick water layer hinders an estimation of velocities in the sedimentary cover and in the upper consolidated crust. Primarily, this is due to the fact that refracted waves propagating in low-velocity solid upper layers interfere with high-amplitude direct water wave. However, in multi-component measurements with ocean bottom seismometers, it is possible to use converted and multiple waves for velocity estimations in these layers. Consequently, one can obtain P- and S-waves velocity models of the sedimentary strata and the upper consolidated crust. Velocity values in the upper consolidated crust beneath the South-Okhotsk Basin (Vp = 5.50-5.80 km/s, Vp/Vs = 1.74-1.76) allow interpretation of this 2.5-3.5-km-thick layer to be consistent with a felsic (granodioritic) crust. These results suggest that the Earth's crust in this region can be considered continental in nature, rather than previously accepted oceanic crust. Even though, the crust is thinned and stretched at this location.

Crustal structure of mountain belts and basins: Industry and academic collaboration at Cornell

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

Allmendinger, R.; Barazangi, M.; Brown, L.

1995-08-01

Interdisciplinary investigations of the large-scale structure and evolution of key basins and orogenic belts around the world are the focal point of academic-industry interaction at Cornell. Ongoing and new initiatives with significant industry involvement include: Project INDEPTH (Interdisciplinary Deep Profiling of Tibet and the Himalayas), a multinational effort to delineate deep structure across the type example of active continent-continent collision. 300 km of deep reflection profiling was collected across the Himalaya: and southern Tibet Plateau in 1992 and 1994. CAP (Cornell Andes Project), a long-standing interdisciplinary effort to understand the structure and evolution of the Andes, with a focus onmore » Argentina, Chile and Bolivia. A deep reflection profile is tentatively planned for 1997. Intra-plate Orogeny in the Middle East and North Africa is the focus of multidisciplinary regional syntheses of existing seismic reflection and other databases in Syria (Palmyrides)and Morocco (Atlas), with an emphasis on reactivation and inversion tectonics. Project URSEIS (Urals Reflection Seismic Experiment and Integrated Studies) is a collaboration with EUROPROBE to collect 500 km of vibroseis and dynamite deep reflection profiling across the southern Urals in 1995. Project CRATON, an element in COCORP`s systematic exploration of the continental US, is a nascent multi-disciplinary effort to understand the buried craton of the central US and the basins built upon it. Global Basins Research Network (GBRN) is a diversified observational and computational effort to image and model the movement of pore fluids in detail and on a regional scale for a producing oil structure in the Gulf of Mexico.« less

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

NASA Astrophysics Data System (ADS)

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

2017-12-01

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

Comparison of Earthquake Damage Patterns and Shallow-Depth Vs Structure Across the Napa Valley, Inferred From Multichannel Analysis of Surface Waves (MASW) and Multichannel Analysis of Love Waves (MALW) Modeling of Basin-Wide Seismic Profiles

NASA Astrophysics Data System (ADS)

Chan, J. H.; Catchings, R.; Strayer, L. M.; Goldman, M.; Criley, C.; Sickler, R. R.; Boatwright, J.

2017-12-01

We conducted an active-source seismic investigation across the Napa Valley (Napa Valley Seismic Investigation-16) in September of 2016 consisting of two basin-wide seismic profiles; one profile was 20 km long and N-S-trending (338°), and the other 15 km long and E-W-trending (80°) (see Catchings et al., 2017). Data from the NVSI-16 seismic investigation were recorded using a total of 666 vertical- and horizontal-component seismographs, spaced 100 m apart on both seismic profiles. Seismic sources were generated by a total of 36 buried explosions spaced 1 km apart. The two seismic profiles intersected in downtown Napa, where a large number of buildings were red-tagged by the City following the 24 August 2014 Mw 6.0 South Napa earthquake. From the recorded Rayleigh and Love waves, we developed 2-Dimensional S-wave velocity models to depths of about 0.5 km using the multichannel analysis of surface waves (MASW) method. Our MASW (Rayleigh) and MALW (Love) models show two prominent low-velocity (Vs = 350 to 1300 m/s) sub-basins that were also previously identified from gravity studies (Langenheim et al., 2010). These basins trend N-W and also coincide with the locations of more than 1500 red- and yellow-tagged buildings within the City of Napa that were tagged after the 2014 South Napa earthquake. The observed correlation between low-Vs, deep basins, and the red-and yellow-tagged buildings in Napa suggests similar large-scale seismic investigations can be performed. These correlations provide insights into the likely locations of significant structural damage resulting from future earthquakes that occur adjacent to or within sedimentary basins.

Crustal Structure of the Yakutat Microplate: Constraints from STEEP Wide-angle Seismic Data

NASA Astrophysics Data System (ADS)

Christeson, G. L.; van Avendonk, H.; Gulick, S. P.; Worthington, L.; Pavlis, T.

2008-12-01

In Fall 2008 we will conduct a seismic program focusing on the Yakutat microplate. As part of this study we plan to acquire two wide-angle profiles: an onshore-offshore northwest-southeast oriented profile extending from the Bering glacier onto the continental shelf and across the Dangerous River Zone, and an offshore northeast-southwest oriented profile extending from the ocean basin across the Transition fault and into Yakutat Bay. The sound source will be the R/V Langseth's tuned 6600 cu. in., 36 air gun array. Ocean bottom seismometers will be positioned at ~15 km spacing, and Texan seismometers at 1-4 km spacing across the Bering Glacier. Coincident deep-penetrating seismic reflection data will be acquired on the marine portion of both profiles using a 8-km, 640-channel solid hydrophone streamer. Existing models for the Yakutat microplate disagree as to whether it is a continental fragment attached to normal oceanic crust or an oceanic plateau, and if the deep structure changes from west to east across the Dangerous River Zone. In the continental fragment model uplift is concentrated along crustal-scale thrust faulting at the ocean crust boundary (Dangerous River Zone?) resulting in focused and rapid erosion. In the oceanic plateau model more distributed, regional uplift is expected which will produce widespread exhumation with net erosion potentially coupled with glacial cycles. Thus distinguishing between these models, which we expect to accomplish with our planned seismic program, is vital for linking tectonics to erosion on both spatial and temporal scales.

Instrument Correction and Dynamic Site Profile Validation at the Central United States Seismic Observatory, New Madrid Seismic Zone

NASA Astrophysics Data System (ADS)

Brengman, C.; Woolery, E. W.; Wang, Z.; Carpenter, S.

2016-12-01

The Central United States Seismic Observatory (CUSSO) is a vertical seismic array located in southwestern Kentucky within the New Madrid seismic zone. It is intended to describe the effects of local geology, including thick sediment overburden, on seismic-wave propagation, particularly strong-motion. The three-borehole array at CUSSO is composed of seismic sensors placed on the surface, and in the bedrock at various depths within the 585 m thick sediment overburden. The array's deep borehole provided a unique opportunity in the northern Mississippi embayment for the direct geological description and geophysical measurement of the complete late Cretaceous-Quaternary sediment column. A seven layer, intra-sediment velocity model is interpreted from the complex, inhomogeneous stratigraphy. The S- and P-wave sediment velocities range between 160 and 875 m/s and between 1000 and 2300 m/s, respectively, with bedrock velocities of 1452 and 3775 m/s, respectively. Cross-correlation and direct comparisons were used to filter out the instrument response and determine the instrument orientation, making CUSSO data ready for analysis, and making CUSSO a viable calibration site for other free-field sensors in the area. The corrected bedrock motions were numerically propagated through the CUSSO soil profile (transfer function) and compared, in terms of both peak acceleration and amplitude spectra, to the recorded surface observations. Initial observations reveal a complex spectral mix of amplification and de-amplification across the array, indicating the site effect in this deep sediment setting is not simply generated by the shallowest layers.

Deep structure of the Algerian margin offshore Great Kabylie: Preliminary results of an offshore-onshore seismic profile (SPIRAL campaign)

NASA Astrophysics Data System (ADS)

Chafik, Aidi; Abd el Karim, Yelles; Marie-Odile, Beslier; Frauke, Klingelhoefer; Philippe, Schnurle; Rabah, Bracene; Hamou, Djellit; Audrey, Galve; Laure, Schenini; Françoise, Sage; Abdallah, Bounif Mohand ou; Philippe, Charvis

2013-04-01

In October-November 2009 the Algerian-French SPIRAL research program (Sismique Profonde et Investigation Régionale du Nord de l'ALgérie) was conducted onboard the R/V Atalante in order to understand the deep structure and tectonic history of the Algerian Margin using multichannel and wide-angle seismic data. An extensive dataset was acquired along five regional transects off Algeria, from Arzew Bay to the west, to Annaba to the east. The profiles range from 80 to 180 km long and around 40 ocean-bottom seismometers were deployed on each profile. All profiles were extended on land up to 125 km by land-stations to better constrain the structure of the margin and the nature of the ocean-continent transition zone. We present the preliminary results from modeling of deep and superficial structures in the central Algerian margin, more precisely in the region of the Great Kabylie where a N-S transect of combined wide-angle data using a set of 40 OBS (ocean bottom seismometer) and 24 on-land seismological stations and reflection seismic data was acquired. The profile with a total length of about 260 km (140 km offshore and approximately 124 km onshore), crosses from the north to south the Algeria-Provence Basin, the central Algerian Margin and onshore the geological unit of the Great Kabylie that represents the Kabylides block and the transitional zone between the internal zone (Kabylides) and the external zone in the central Algeria. The network (OBS and seismological stations), recorded 1031 low frequency air gun shots in order to ensure good penetration in the crust. Travel time tomography of first arrivals time of OBS data has yielded a preliminary model of P wave velocities along the profile. In the oceanic domain, a relatively thin crust of about 5 km thickness was imaged overlying a mantle characterized by seismic velocities of about 8 km/s, and covered by a thin sedimentary layer of about 2 km thickness. For the study of the sedimentary cover near the margin several MCS profiles were acquired in this region during the Spiral survey and previously by the Maradja cruise. This data sets allows to image reactivation of the Algerian Margin in this region.

Crustal structure of China from deep seismic sounding profiles

USGS Publications Warehouse

Li, S.; Mooney, W.D.

1998-01-01

More than 36,000 km of Deep Seismic Sounding (DSS) profiles have been collected in China since 1958. However, the results of these profiles are not well known in the West due to the language barrier. In this paper, we summarize the crustal structure of China with a new contour map of crustal thickness, nine representative crustal columns, and maps showing profile locations, average crustal velocity, and Pn velocity. The most remarkable aspect of the crustal structure of China is the well known 70+ km thickness of the crust of the Tibetan Plateau. The thick (45-70 km) crust of western China is separated from the thinner (30-45 km) crust of eastern China by the north-south trending seismic belt (105??E). The average crustal velocity of China ranges from 6.15 to 6.45 km/s, indicating a felsic-to-intermediate bulk crustal composition. Upper mantle (Pn) velocities are 8.0 ?? 0.2 km/s, equal to the global continental average. We interpret these results in terms of the most recent thermo-tectonic events that have modified the crust. In much of eastern China, Cenoxoic crustal extension has produced a thin crust with a low average crustal velocity, similar to western Europe and the Basin and Range Province, western USA. In western China, Mesozoic and Cenoxoic arc-continent and continent-continent collisions have led to crustal growth and thickening. Inferences on the process of crustal thickening are provided by the deep crustal velocity structure as determined by DSS profiles and other seismological studies. A high velocity (7.0-7.4 km/s) lower-crustal layer has been reported in western China only beneath the southernmost Tibetan Plateau. We identity this high-velocity layer as the cold lower crust of the subducting Indian plate. As the Indian crust is injected northward into the Tibetan lower crust, it heats and assimilates by partial melting, a process that results in a reduction in the seismic velocity of the lower crust in the central and northern Tibetan Plateau. ?? 1998 Elsevier Science B.V. All rights reserved.

Constraints on the Final Stages of Breakup and Early Spreading history of the Eastern North American Margin from New Multichannel Seismic Data of the Community Seismic Experiment

NASA Astrophysics Data System (ADS)

Becel, A.

2016-12-01

In September-October 2014, the East North American Margin (ENAM) Community Seismic Experiment (CSE) acquired deep penetration multichannel seismic (MCS) reflection on a 500 km wide section of the Mid-Atlantic continental margin offshore North Carolina and Virginia. This margin formed after the Mesozoic breakup of supercontinent Pangea. One of the goals of this experiment is an improved understanding of events surrounding final stage of breakup including the relationship between the timing of rifting and the occurrence of offshore magmatism and early spreading history of this passive margin that remain poorly understood. Deep penetration MCS data were acquired with the 6600 cu.in. tuned airgun array and the 636 channel, 8-km-long streamer of the R/V Marcus Langseth. The source and the streamer were both towed at a depth of 9 m for deep imaging. Here we present initial results from MCS data along two offshore margin normal profiles (450-km long and 370-km-long, respectively), spanning from continental crust 50 km off the coast to mature oceanic crust and a 350-km-long MCS profile along the enigmatic Blake Spur Magnetic Anomaly (BSMA). Initial images reveal a major change in the basement roughness at the BSMA on both margin normal profiles. Landward of this anomaly, the basement is rough and more faulted whereas starting at the anomaly and seaward, the basement is very smooth and reflective. Clear Moho reflections are observed 2.5-3s (7.75-9.3 km assuming an average crustal velocity of 6.2 km/s) beneath the top of the basement on the seaward part of two margin normal profiles and on the margin parallel profile. Intracrustal reflections are also observed over both transitional and oceanic basement. A long-lived mantle thermal anomaly close to the ridge axis during the early opening of the Atlantic Ocean could explain the thicker than normal oceanic crust and smooth basement topography observed in the data.

Crustal structure of the northern margin of the eastern Tien Shan, China, and its tectonic implications for the 1906 M~7.7 Manas earthquake

USGS Publications Warehouse

Wang, Chun-Yong; Yang, Zhu-En; Luo, Hai; Mooney, W.D.

2004-01-01

The Tien Shan orogenic belt is the most active intracontinental mountain belt in the world. We describe an 86-km-long N–S-trending deep seismic reflection profile (which passes through the southern Junggar basin) located on the northeastern Tien Shan piedmont. Two distinct anticlines beneath the northern margin of the Tien Shan are clearly imaged in the seismic section. In addition, we have imaged two detachment surfaces at depths of ∼7 and ∼16 km. The detachment surface at 16-km depth corresponds to the main detachment that converges with the steep angle reverse fault (the Junggar Southern Marginal Fault) on which the 1906 M~7.7 Manas earthquake occurred. A 12–14-km-thick sedimentary basin is imaged beneath the southern Junggar basin near Shihezi. The crust beneath the northern margin of the Tien Shan is 50–55-km thick, and decreases beneath the Junggar basin to 40–45-km thick. The crustal image of the deep seismic reflection profile is consistent with models derived from nearby seismic refraction data and Bouguer gravity anomalies in the same region. The faulting associated with the 1906 Manas earthquake also fits within the structural framework imaged by the seismic reflection profile. Present-day micro-seismicity shows a hypocentral depth-distribution between 5 and 35 km, with a peak at 20 km. We hypothesize that the 1906 Manas earthquake initiated at a depth of ∼20 km and propagated upwards, causing northward slip on the sub-horizontal detachments beneath the southern Junggar basin. Thus, in accord with regional geological mapping, the current shortening within the eastern Tien Shan is accommodated both by high-angle reverse faulting and detachment faulting that can be clearly imaged at depth in seismic reflection data.

Structural and Depositional Evolution of the Stevenson Basin, a Gulf of Alaska Forearc Basin: Insights from Legacy Seismic and Borehole Data

NASA Astrophysics Data System (ADS)

Bhattacharya, R.; Liberty, L. M.; Almeida, R. V.; Hubbard, J.

2016-12-01

We explore the structural and depositional evolution of the Stevenson Basin, Gulf of Alaska from a dense network of 2-D marine seismic profiles that span the Gulf of Alaska continental margin. The grid of 71 seismic profiles was acquired as part of a 1975 Mineral Management Services (MMS) exploration project to assess basin architecture along the Alaska continental shelf. We obtained unmigrated and stacked seismic profiles in TIFF format. We converted the data to SEGY format and migrated each profile. Within the Stevenson Basin, we identify key seismic horizons, including the regional Eocene-Miocene unconformity, that provide insights into its depositional and structural history. Using these observations combined with stacking velocities, sonic logs from wells, and refraction velocities from the Edge profile of Ye et al. (1997), we develop a local 3D velocity model that we use to depth-convert the seismic reflection profiles. By using ties to >2.5 km deep exploration wells, we note the Stevenson Basin is one of many Eocene and younger depocenters that span the forearc between Kodiak and Prince William Sound. Well logs and seismic data suggest basal strata consist of Eocene sediments than are unconformably overlain by Neogene and younger strata. Faults that breach the sea floor suggest active deformation within and at the bounds of this basin, including on new faults that do not follow any pre-existing structural trends. This assessment is consistent with slip models that place tsunamigenic faults that ruptured during the 1964 Great Alaska earthquake in the vicinity of the basin. The catalog of faults, their slip history and the depositional evolution of the Stevenson Basin, all suggest that the basin evolution may be controlled by heterogeneities along the incoming plate.

Low frequency amplification in deep alluvial basins: an example in the Po Plain (Northern Italy) and consequences for site specific SHA

NASA Astrophysics Data System (ADS)

Mascandola, Claudia; Massa, Marco; Barani, Simone; Lovati, Sara; Santulin, Marco

2016-04-01

This work deals with the problem of long period seismic site amplification that potentially might involve large and deep alluvial basins in case of strong earthquakes. In particular, it is here presented a case study in the Po Plain (Northern Italy), one of the most extended and deep sedimentary basin worldwide. Even if the studied area shows a low annul seismicity rate with rare strong events (Mw>6.0) and it is characterized by low to medium seismic hazard conditions, the seismic risk is significant for the high density of civil and strategic infrastructures (i.e. high degree of exposition) and the unfavourable geological conditions. The aim of this work is to provide general considerations about the seismic site response of the Po Plain, with particular attention on deep discontinuities (i.e. geological bedrock), in terms of potential low frequency amplification and their incidence on the PSHA. The current results were obtained through active and passive geophysical investigations performed near Castelleone, a site where a seismic station, which is part of the INGV (National Institute for Geophysics and Volcanology) Seismic National Network, is installed from 2009. In particular, the active analyses consisted in a MASW and a refraction survey, whereas the passive ones consisted in seismic ambient noise acquisitions with single stations and arrays of increasing aperture. The results in terms of noise HVSR indicate two main peaks, the first around 0.17 Hz and the second, as already stated in the recent literature, around 0.7 Hz. In order to correlate the amplified frequencies with the geological discontinuities, the array acquisitions were processed to obtain a shear waves velocity profile, computed with a joint inversion, considering the experimental dispersion curves and the HVSR results. The obtained velocity profile shows two main discontinuities: the shallower at ~165 m of depth, which can be correlated to the seismic bedrock (i.e. Vs > 800 m/) and the deeper at ~1350 m of depth, properly associable to the geological bedrock, considering the transition between the pliocenic loose sediments and the miocenic marls observable from the available stratigraphy. Numerical 1D analyses, computed to obtain the theoretical Transfer Function at the site, support the correlation between the experimental amplification peak around 0.17 Hz and the hypothesized geological bedrock. In terms of site specific SHA, the UHS expressed in displacement (MRP: 475 years) shows a significant increase if the seismic input is located at the geological bedrock (~1350 m) instead of the seismic bedrock (~165 m). Even if this increase is not relevant for the studied site, since the seismic hazard is low, it could be significant in other part of the Po Plain, where the seismic hazard is medium-high. According to the HVSR results, obtained for other available Po Plain broadband stations, the considerations of this work could represent a warning for future seismic hazard investigations in other areas of the basin.

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

NASA Astrophysics Data System (ADS)

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

2012-04-01

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

Seismic Imaging Reveals Deep-Penetrating Fault Planes in the Wharton Basin Oceanic Mantle

NASA Astrophysics Data System (ADS)

Carton, H. D.; Singh, S. C.; Dyment, J.; Hananto, N. D.; Chauhan, A.

2011-12-01

We present images from a deep multi-channel seismic reflection survey acquired in 2006 over the oceanic lithosphere of the Wharton Basin offshore northern Sumatra, NW of Simeulue island. The main ~230-km long seismic profile is roughly parallel to the trench at ~32-66 km distance from the subduction front and crosses (at oblique angles to both flow line and isochron directions) an entire segment of 55-57 my-old fast-spread crust formed at the extinct Wharton spreading center, as well as two bounding ~N5°E trending fracture zones near its extremities; complementary data is provided by the oceanic portions of two margin-crossing profiles on either side shot during the same survey. This high-quality, 12-km streamer dataset acquired for deep reflection imaging (10000 cu in tuned airgun array and 15-m source and streamer depths) reveals the presence of mostly SE-dipping (20 to 40 degrees dip) events cutting across and extending below the oceanic Moho, down to a maximum depth below seafloor of ~37 km, at ~5 km spacing along the trench-parallel profile. Similar dipping mantle events are imaged on the oceanic portion of another long-offset profile acquired in 2009 offshore central Sumatra south of Pagai island, which will also be presented. Such events are unlikely to be imaging artefacts of the 2D acquisition, such as out-of-plane energy originating from sharp, buried basement reliefs trending obliquely to the profile. Due to their geometry, they do not seem to be associated with plate bending at the trench outer-rise, which has a relatively modest expression at the seafloor and within the incoming sedimentary section north of the Simeulue elbow. We propose that these deep-penetrating dipping reflectors are fossil fault planes formed due to compressive stresses at the beginning of the continent-continent collision between India and Eurasia, the early stages of which were responsible for the cessation of seafloor spreading at the Wharton ridge at ca 40 Ma.

Basin-centered asperities in great subduction zone earthquakes: A link between slip, subsidence, and subduction erosion?

USGS Publications Warehouse

Wells, R.E.; Blakely, R.J.; Sugiyama, Y.; Scholl, D. W.; Dinterman, P.A.

2003-01-01

Published areas of high coseismic slip, or asperities, for 29 of the largest Circum-Pacific megathrust earthquakes are compared to forearc structure revealed by satellite free-air gravity, bathymetry, and seismic profiling. On average, 71% of an earthquake's seismic moment and 79% of its asperity area occur beneath the prominent gravity low outlining the deep-sea terrace; 57% of an earthquake's asperity area, on average, occurs beneath the forearc basins that lie within the deep-sea terrace. In SW Japan, slip in the 1923, 1944, 1946, and 1968 earthquakes was largely centered beneath five forearc basins whose landward edge overlies the 350??C isotherm on the plate boundary, the inferred downdip limit of the locked zone. Basin-centered coseismic slip also occurred along the Aleutian, Mexico, Peru, and Chile subduction zones but was ambiguous for the great 1964 Alaska earthquake. Beneath intrabasin structural highs, seismic slip tends to be lower, possibly due to higher temperatures and fluid pressures. Kilometers of late Cenozoic subsidence and crustal thinning above some of the source zones are indicated by seismic profiling and drilling and are thought to be caused by basal subduction erosion. The deep-sea terraces and basins may evolve not just by growth of the outer arc high but also by interseismic subsidence not recovered during earthquakes. Basin-centered asperities could indicate a link between subsidence, subduction erosion, and seismogenesis. Whatever the cause, forearc basins may be useful indicators of long-term seismic moment release. The source zone for Cascadia's 1700 A.D. earthquake contains five large, basin-centered gravity lows that may indicate potential asperities at depth. The gravity gradient marking the inferred downdip limit to large coseismic slip lies offshore, except in northwestern Washington, where the low extends landward beneath the coast. Transverse gravity highs between the basins suggest that the margin is seismically segmented and could produce a variety of large earthquakes. Published in 2003 by the American Geophysical Union.

Near-surface structure of the Central Scandinavian Caledonides in northern Trøndelag, Norway, from correlation of seismic and MT profiles using gravity and magnetic data

NASA Astrophysics Data System (ADS)

Ebbing, J.; Goerigk, L.; Nasuti, A.; Roberts, D.; Korja, T. J.; Smirnov, M.

2014-12-01

The deep geology of northern Trøndelag is somewhat speculative as the Central Scandinavian Caledonides are intersected by the Møre-Trøndelag Fault Complex (MTFC) and only a few depth-penetrating geophysical profiles exist. Here, we correlate the mapped geological units and faults between a seismic-reflection profile and a MT profile. The seismic-reflection data were acquired in 5 segments over the period 1986-1990. The westernmost section of the seismic profile is dominated by a complex pattern of reflections and diffractions. This type of pattern is typical of polydeformed terranes with a mixture of contrasting felsic and mafic lithologies. The two steeply-dipping strands of the MTFC (Hitra-Snåsa and Verran faults) that transect the profile do not show any distinctive signature in the seismic data. The MT data were acquired in 2007 from the Swedish border to the Norwegian coast. The conductivity profile shows some distinct vertical changes as well as changes from the near-surface to shallow depths. The strands of the MTFC show especially a distinctive change in conductivity. The two profiles are almost parallel but separated by 100 km. To correlate the structures seen on both profiles, we have applied lineament analysis and 3D modelling of the gravity and magnetic field. The tilt derivative of the magnetic and isostatic gravity anomaly clearly allows us to identify and link the main geological boundaries between the profiles and to trace the strands of the MTFC from one profile to the other. This trend analysis indicates that at least the Verran Fault visibly modifies the pattern of seismic reflections. However, the main change in crustal lithology occurs farther to the west, almost at the coast where the Tarva Fault intersects the MT profile. This integrated analysis shows the benefit of combining gravity and magnetic interpretations with MT and seismic data to enable us to understand the near-surface geology and structure in more detail.

Reservoir Identification: Parameter Characterization or Feature Classification

NASA Astrophysics Data System (ADS)

Cao, J.

2017-12-01

The ultimate goal of oil and gas exploration is to find the oil or gas reservoirs with industrial mining value. Therefore, the core task of modern oil and gas exploration is to identify oil or gas reservoirs on the seismic profiles. Traditionally, the reservoir is identify by seismic inversion of a series of physical parameters such as porosity, saturation, permeability, formation pressure, and so on. Due to the heterogeneity of the geological medium, the approximation of the inversion model and the incompleteness and noisy of the data, the inversion results are highly uncertain and must be calibrated or corrected with well data. In areas where there are few wells or no well, reservoir identification based on seismic inversion is high-risk. Reservoir identification is essentially a classification issue. In the identification process, the underground rocks are divided into reservoirs with industrial mining value and host rocks with non-industrial mining value. In addition to the traditional physical parameters classification, the classification may be achieved using one or a few comprehensive features. By introducing the concept of seismic-print, we have developed a new reservoir identification method based on seismic-print analysis. Furthermore, we explore the possibility to use deep leaning to discover the seismic-print characteristics of oil and gas reservoirs. Preliminary experiments have shown that the deep learning of seismic data could distinguish gas reservoirs from host rocks. The combination of both seismic-print analysis and seismic deep learning is expected to be a more robust reservoir identification method. The work was supported by NSFC under grant No. 41430323 and No. U1562219, and the National Key Research and Development Program under Grant No. 2016YFC0601

An Idea for an Active Seismic Experiment on Mars in 2008

NASA Technical Reports Server (NTRS)

Lognonne, Ph.; Banerdt, B.; Giardini, D.; Costard, F.

2001-01-01

The detection of liquid water is of prime interest and should have deep implications in the understanding of the Martian hydrological cycle and also in exobiology. In the frame of the 2007 joint CNES-NASA mission to Mars, a set of 4 NETLANDERS developed by an European consortium is expected to be launched in June 2007. We propose to use a second spacecraft going or landing to Mars to release near one of the Netlander a series of artificial metallic meteorites, in order to perform an active seismic experiment providing a seismic profile of the crust and subsurface.

Crustal reflectivity in the Skagerrak area

NASA Astrophysics Data System (ADS)

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

1991-04-01

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

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.

Evaluation of deep moonquake source parameters: Implication for fault characteristics and thermal state

NASA Astrophysics Data System (ADS)

Kawamura, Taichi; Lognonné, Philippe; Nishikawa, Yasuhiro; Tanaka, Satoshi

2017-07-01

While deep moonquakes are seismic events commonly observed on the Moon, their source mechanism is still unexplained. The two main issues are poorly constrained source parameters and incompatibilities between the thermal profiles suggested by many studies and the apparent need for brittle properties at these depths. In this study, we reinvestigated the deep moonquake data to reestimate its source parameters and uncover the characteristics of deep moonquake faults that differ from those on Earth. We first improve the estimation of source parameters through spectral analysis using "new" broadband seismic records made by combining those of the Apollo long- and short-period seismometers. We use the broader frequency band of the combined spectra to estimate corner frequencies and DC values of spectra, which are important parameters to constrain the source parameters. We further use the spectral features to estimate seismic moments and stress drops for more than 100 deep moonquake events from three different source regions. This study revealed that deep moonquake faults are extremely smooth compared to terrestrial faults. Second, we reevaluate the brittle-ductile transition temperature that is consistent with the obtained source parameters. We show that the source parameters imply that the tidal stress is the main source of the stress glut causing deep moonquakes and the large strain rate from tides makes the brittle-ductile transition temperature higher. Higher transition temperatures open a new possibility to construct a thermal model that is consistent with deep moonquake occurrence and pressure condition and thereby improve our understandings of the deep moonquake source mechanism.

Basin analysis of North Sea viking graben: new techniques in an old basin

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

Iliffe, J.E.; Cao, S.; Lerche, I.

1987-05-01

Rapid sedimentation rates from the Upper Cretaceous to Tertiary in the North Sea require that burial history modeling account for overpressuring. Use of a quantitative fluid flow/compaction model, along with the inversion of thermal indicators to obtain independent estimates of paleoheat flu, can greatly enhance their knowledge of a basin's evolution and hydrocarbon potential. First they assess the modeling sensitivity to the quality of data and variation of other input parameters. Then application to 16 wells with vitrinite data in the Viking graben north of 59/sup 0/ latitude and to pseudo-wells derived from deep seismic profiling of BIRPA greatly enhancesmore » the study of regional variations. A Tissot generation model is run on all the wells for each potential source rock. The resulting amounts of oil and gas generated are contoured to produce a regional oil and gas provenance map for each source rock. The model results are compared and tested against the known producing fields. Finally, by restoration of the two-dimensional seismic reflection profiles, the temporal variations of basement subsidence and paleoheat flow are related to the tectonic zoning of the region and to the extensional history. The combined structural, thermal, and depositional information available due to technological progress in both modeling and deep seismic profiling allows a better understanding of previously proposed models of extension.« less

Joint the active source and passive source seismic to research the fine crustal structure of the Lushan area

NASA Astrophysics Data System (ADS)

Chen, Q.; Yu, C.

2017-12-01

On April 20, 2013, Ms7.0 strong earthquake (Lushan earthquake) occurred in Lanshan County Ya'an City, Sichuan Province. It is another earthquake that occurred in the Longmenshan fault zone after the Wenchuan earthquake. However, there is still no conclusive conclusion in relationship between the fine structure of the Lushan area and triggering seismic fault . In this study, the crustal structure, the shallow structure and the hidden faults and the focal mechanism of the Lushan earthquake were analyzed by using the deep seismic reflection profile and the broadband seismic array data. Combined with the surface geological information, the structure and fracture cause of the Lishan earthquake were discussed.We have synthetic analyzed the seismic precursors, fine locating, focal mechanism analysis and time-tomographic imaging of the broadband seismic data before and after the earthquake in Lushan earthquake, and obtained the seismic distribution, the focal mechanism and the crustal fine structure in the Lushan area. And we use these results to detailed interpreted the deep reflection seismic section of the Lushan earthquake zone.The results show that the crust of the Lushan area is characterized by a distinct structure of upper crust with thickness about 14.75km. The nature of the faults is inferred to be thrusting in the region due to the pushing of the crustal material of the Tibetan plateau into the southeast part of the rigid Sichuan basin. The shuangshi-Dachuan fault stretches from the surface to the deep crust at a low angle, and is dominated by thrusting in a form of imbricate structure with small-scale faults nearby. Whereas the Guangyuan-Dayi fault is a positive flower structure with a listric shape, consisting of six branches. Its movement is dominated by thrusting with gentle horizontal slip.

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

NASA Astrophysics Data System (ADS)

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

2018-02-01

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

2D Seismic Velocity Modelling in the Southeastern Romanian Carpathians and its Foreland (Vrancea Zone and Focsani Basin)

NASA Astrophysics Data System (ADS)

Stephenson, R.; Bocin, A.; Tryggvason, A.

2003-12-01

The DACIA-PLAN (Danube and Carpathian Integrated Action on Processes in the Lithosphere and Neotectonics) deep seismic reflection survey was performed in August-September 2001, with the objective of obtaining of new information on the deep structure of the external Carpathians nappes and the architecture of Tertiary/Quaternary basins developed within and adjacent to the seismically-active Vrancea Zone, including the rapidly subsiding Focsani Basin. The DACIA-PLAN profile is about 140 km long, having a roughly NW-SE direction, from near the southeast Transylvanian Basin, across the mountainous southeastern Carpathians and their foreland to near the Danube Dalta. A high resolution 2D velocity model of the upper crust along the seismic profile has been determined from a first-arrival tomographic inversion of the DACIA-PLAN data. The shallowing of Palaeozoic-Mesozoic basement, and related structural heterogeneity within it, beneath the eastern flank of the Focsani Basin is clearly seen. Velocity heterogeneity within the Carpathian nappe belt is also evident and is indicative of internal structural complexity, including the presence of salt bodies and basement involvement in thrusting, thus favouring some current geological models over others. The presence of basement involvement implies the compressional reactivation of pre-existing basement normal faults. Members of the DACIA-PLAN/TomoSeis Working Group (see poster) should be considered as co-authors of this presentation.

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.

Origin and nature of crystal reflections: Results from integrated seismic measurements at the KTB superdeep drilling site

NASA Astrophysics Data System (ADS)

Harjes, H.-P.; Bram, K.; Dürbaum, H.-J.; Gebrande, H.; Hirschmann, G.; Janik, M.; KlöCkner, M.; Lüschen, E.; Rabbel, W.; Simon, M.; Thomas, R.; Tormann, J.; Wenzel, F.

1997-08-01

For almost 10 years the KTB superdeep drilling project has offered an excellent field laboratory for adapting seismic techniques to crystalline environments and for testing new ideas for interpreting seismic reflections in terms of lithological or textural properties of metamorphic rock units. The seismic investigations culminated in a three-dimensional (3-D) reflection survey on a 19×19 km area with the drill site at its center. Interpretation of these data resulted in a detailed, structural model of the German Continental Deep Drilling Program (KTB) location with dominant, steep faults in the upper crust. The 3-D reflection survey was part of a suite of seismic experiments, ranging from wide-angle reflection and refraction profiles to standard vertical seismic profiles (VSP) and more sophisticated surface-to-borehole observations. It was predicted that the drill bit would meet the most prominent, steeply dipping, crustal reflector at a depth of about 6500-7000 m, and indeed, the borehole penetrated a major fault zone in the depth interval between 6850 and 7300 m. This reflector offered the rare opportunity to relate logging results, reflective properties, and geology to observed and modeled data. Post-Variscan thrusting caused cataclastic deformation, with partial, strong alterations within a steeply dipping reverse fault zone. This process generated impedance contrasts within the fault zone on a lateral scale large enough to cause seismic reflections. This was confirmed by borehole measurements along the whole 9.1 km deep KTB profile. The strongest, reflected signals originated from fluid-filled fractures and cataclastic fracture zones rather than from lithological boundaries (i.e., first-order discontinuities between different rock types) or from texture- and/or foliation-induced anisotropy. During the interpretation of seismic data at KTB several lessons were learned: Conventional processing of two-dimensional (2-D) reflection data from a presite survey showed predominantly subhorizontal layering in the upper crust with reflectivity striking in the Variscan direction. Drilling, however, revealed that all rock units are steeply dipping. This confirms that surface common depth point (CDP) seismics strongly enhances subhorizontal reflectivity and may thus produce a very misleading crustal image. Although this was shown for synthetic examples earlier, the KTB provides the experimental proof of how crucial this insight can be.

First images of the crustal structure across the central Algerian margin, off Tipaza (West Algiers) from deep penetrating seismic data: new information to constrain the opening of the Algerian basin

NASA Astrophysics Data System (ADS)

Leprêtre, A.; Deverchere, J.; Klingelhoefer, F.; Graindorge, D.; Schnurle, P.; Yelles, K.; Bracene, R.

2011-12-01

The origin of the Algerian margin remains one of the key questions still unresolved in the Western Mediterranean sea. This is related to the unknown nature and kinematics of this Neogene basin. Whereas the westernmost margin is generally assumed to have been shaped as a STEP-fault (Subduction-Transform Edge Propagator, transcurrent) margin by the westward displacement of the Alboran block, the central Algerian margin is believed to have involved a NW-SE basin opening related to a southward slab rollback. This work sheds insight on this issue, using data acquired in the context of the Algerian-French program SPIRAL (Sismique Profonde et Investigation Régionale en Algérie): a cruise conducted on the 'R/V L'Atalante' in October-November 2009. It has provided 5 new combined onshore-offshore wide-angle seismic profiles and an extensive multi-channel seismic dataset spread along the margin, from Oran to Annaba. In this work, the available structural information on the ~N-S wide-angle transect of Tipaza is presented, where the margin broadens due to the presence of a bathymetric high (the Khayr-Al-Din bank) which is assumed to represent a remaining titled block of the passive margin. Along the transect, 39 OBS and 13 landstations recorded 751 low frequency airgun shots. Travel-time tomography and forward modelling were computed using the software developed by Zelt and Barton (1998) and Zelt and Smith (1992), to obtain the velocity structure in the region. A set of multi-channel seismic reflection profiles including two coincident profiles with the wide-angle data allows a combined interpretation and extend the deep structure in the Bou Ismail Bay. MCS data outline the sedimentary sequence filling the Algerian basin depicting an intensive salt tectonic associated with the Messinan Salinity Crisis and allowing to image locally below the salt layer. The deep penetrating data SPIRAL allow to image the sedimentary sequence in the Algerian basin off Tipaza (West Algiers) and the crustal structure at the continent-ocean boundary. In the Algerian basin off Tipaza, the Moho discontinuity is identified using wide-angle modelling at 11-12 km depth which corresponds in two-way travel-time to 7-8 s. Wide-angle seismic modelling imaged a major thinning of the crust from more of 15 km in the upper margin (KADB) to only 5-6 km in the deep basin. This thinning also marks the rapid transition from a thinned continental crust at the Khayr-al-Din bank to an oceanic crust in the Algerian Basin, revealing a narrow transition zone (20-30 km) between the two domains. This work presents the deep structure of the margin West of Algiers from wide-angle and multichannel seismic data in order to discuss models of opening for the Algerian basin.

Quaternary tectonics from seismic interpretation and its potential relation with deep geothermal fluids in the Marche (Central Italy).

NASA Astrophysics Data System (ADS)

Chicco, Jessica; Invernizzi, Chiara; Pierantoni, Pietro Paolo; Costa, Mario

2017-04-01

Knowledge of the structural features is fundamental in evaluating geothermal exchange potential and in modelling geothermal systems. In particular, faults and fractures play an important role for the circulation of fluids in the crust, and structural setting can influence groundwater flow, its regime, chemistry and electrical conductivity. In this context, data coming from accurate studies of groundwater physical properties in the Marche region (Central Italy), concerning electrical conductivity above all, revealed some anomalies in several localities that could be ascribed to a strong structural control. Data acquisition and interpretation of some SW-NE seismic reflection profiles crossing the Apennine chain to the Adriatic sea and kindly provided by ENI S.p.A, highlight important deep Plio-Quaternary structures connected with minor surface ones and to hydrogeological conditions. Seismic profiles interpretation allowed to reconstruct the structural setting and to identify the recent evolution of the Apennine Marche sector in more detail with respect to what is already known. In fact, some high angle structures affecting the whole sedimentary sequence and routing at high depth were labelled. These are NW-SE sub-parallel transpressive structures bounded by SW and NE-dipping high-angle reverse faults reaching > 10 km depth (positive flower structures), and probably involving the upper crust basement. Three main alignments were identified from W to the coast line. In some cases, flower nucleation gives rise to the lifting and counter-clockwise rotation of the Pre-Pliocene substratum blocks, with the upwelling and outcropping of Upper Miocene (Messinian) evaporite deposits along the axial zone of the transpressive structural highs. Noting the analyses of groundwater properties coming from wells placed in proximity of these structures or located along the analysed seismic profiles, anomalies in electrical conductivity are relevant. The activity of the deep rooting structures observed in the seismic profiles and the high degree of fracturing that accompanies these complex and recent fault systems can facilitate the exchange between deep and superficial fluids. In other cases, like in coastal structural high, it can have a role in preventing the sea water ingression. This significant consideration can be supported also by the direct relation of electrical conductivity with the amount of rainfall revealed from studied piezometers along the carbonate Marche ridge. It should be explained through a specific behaviour (typical of carbonate aquifers, known as the "piston-flow phase") which implies an increase of groundwater mineralization as a result of transmission of the hydraulic pressure from the saturated zone, through fractures as important way for fluids circulation. Ultimately, we suggest that the structural control could be an important factor in influencing both the surface and the groundwater flow behaviours, and then convective component of the heat transport in the studied area.

The boundary between the Indian and Asian tectonic plates below Tibet

PubMed Central

Zhao, Junmeng; Yuan, Xiaohui; Liu, Hongbing; Kumar, Prakash; Pei, Shunping; Kind, Rainer; Zhang, Zhongjie; Teng, Jiwen; Ding, Lin; Gao, Xing; Xu, Qiang; Wang, Wei

2010-01-01

The fate of the colliding Indian and Asian tectonic plates below the Tibetan high plateau may be visualized by, in addition to seismic tomography, mapping the deep seismic discontinuities, like the crust-mantle boundary (Moho), the lithosphere-asthenosphere boundary (LAB), or the discontinuities at 410 and 660 km depth. We herein present observations of seismic discontinuities with the P and S receiver function techniques beneath central and western Tibet along two new profiles and discuss the results in connection with results from earlier profiles, which did observe the LAB. The LAB of the Indian and Asian plates is well-imaged by several profiles and suggests a changing mode of India-Asia collision in the east-west direction. From eastern Himalayan syntaxis to the western edge of the Tarim Basin, the Indian lithosphere is underthrusting Tibet at an increasingly shallower angle and reaching progressively further to the north. A particular lithospheric region was formed in northern and eastern Tibet as a crush zone between the two colliding plates, the existence of which is marked by high temperature, low mantle seismic wavespeed (correlating with late arriving signals from the 410 discontinuity), poor Sn propagation, east and southeast oriented global positioning system displacements, and strikingly larger seismic (SKS) anisotropy. PMID:20534567

The boundary between the Indian and Asian tectonic plates below Tibet.

PubMed

Zhao, Junmeng; Yuan, Xiaohui; Liu, Hongbing; Kumar, Prakash; Pei, Shunping; Kind, Rainer; Zhang, Zhongjie; Teng, Jiwen; Ding, Lin; Gao, Xing; Xu, Qiang; Wang, Wei

2010-06-22

The fate of the colliding Indian and Asian tectonic plates below the Tibetan high plateau may be visualized by, in addition to seismic tomography, mapping the deep seismic discontinuities, like the crust-mantle boundary (Moho), the lithosphere-asthenosphere boundary (LAB), or the discontinuities at 410 and 660 km depth. We herein present observations of seismic discontinuities with the P and S receiver function techniques beneath central and western Tibet along two new profiles and discuss the results in connection with results from earlier profiles, which did observe the LAB. The LAB of the Indian and Asian plates is well-imaged by several profiles and suggests a changing mode of India-Asia collision in the east-west direction. From eastern Himalayan syntaxis to the western edge of the Tarim Basin, the Indian lithosphere is underthrusting Tibet at an increasingly shallower angle and reaching progressively further to the north. A particular lithospheric region was formed in northern and eastern Tibet as a crush zone between the two colliding plates, the existence of which is marked by high temperature, low mantle seismic wavespeed (correlating with late arriving signals from the 410 discontinuity), poor Sn propagation, east and southeast oriented global positioning system displacements, and strikingly larger seismic (SKS) anisotropy.

First images of the crustal structure across the eastern Algerian margin, from deep penetrating seismic data.

NASA Astrophysics Data System (ADS)

Bouyahiaoui, Boualem; Abtout, Abdeslam; Sage, Françoise; Klingelhoeffer, Frauke; Collot, Jean-yves; Yelles-chaouche, Abdelkarim; Marok, Abbas; Djellit, Hamou; Galves, Audrey; Bracène, Rabah; Schnurle, Philippe; Graindorge, David; party, Scientific

2013-04-01

The Algerian continental margin North Africa presents one of only a few examples of a passive continental margin formed in a back-arc environment, which undergoes current compression and is proposed to be reactivated today. In the framework of the Algerian - French SPIRAL research program (Sismique Profonde et Investigation Regionale du nord de l'ALgérie), a seismic cruise was conducted on the R/V Atalante from September to November 2009. During the cruise, deep penetrating low frequency multichannel and wide-angle seismic data were acquired in order to study the deep structure of the Algerian margin. In this work, we present the preliminary results from wide-angle modeling of the North-east Algerian margin in the region of Annaba along a N-S transect using a data set of 42 OBS (ocean bottom seismometers) along a profile extending 117km, and 13 broadband seismological stations along a profile of 80 km length. Travel-time tomography and forward modeling were undertaken to model the velocity structure in this region. The resulting velocity models image the thickness of the sedimentary layers, which varies between a few hundred meters on the continental margin of more than 4 km in the basin. The crust is about 6 km thick in the basin, and thickens to 7-8 km between 40 and 60km distance from the margin toe. Crustal thickness increases to about 22 km at the continental slope over a distance of ~ 90 km. The nature of the crust was determined to be thin oceanic with abnormal velocity gradient in the basin, and thinned continental from around 30 km distance from the coast landward. Integration of the wide-angle seismic data with multichannel seismic, gravity and magnetic data will help to better understand the structure of the Algerian margin and the adjacent oceanic basin in the Annaba region, and to discuss the numerous cinematic models proposed in literature regarding the formation of the north-Algerian basin.

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

NASA Astrophysics Data System (ADS)

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

2001-12-01

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

POPO AGIE PRIMITIVE AREA, WYOMING.

USGS Publications Warehouse

Pearson, Robert C.; Patten, L.L.

1984-01-01

A mineral-resource appraisal was made of the Popo Agie Primitive Area and some adjoining lands. This scenic mountainous region of the Wind River Range in west-central Wyoming is composed largely of ancient granitic rocks in which virtually no evidence of mineral deposits was found. Deep crustal seismic-reflection profiles obtained across the southern Wind River Range suggest the possibility that young sedimentary rocks, similar to those at the surface along the northeast flank of the range, are present at depth beneath the granite in the Popo Agie primitive Area. If present, such buried sedimentary rocks could be petroleum bearing. Additional seismic and gravity studies would probably add valuable information, but ultimately very expensive, very deep drilling will be necessary to test this possibility.

Cordilleran front range structural features in northwest Montana interpreted from vintage seismic reflection data

NASA Astrophysics Data System (ADS)

Porter, Mason C.; Rutherford, Bradley S.; Speece, Marvin A.; Mosolf, Jesse G.

2016-04-01

Industry seismic reflection data spanning the Rocky Mountain Cordillera front ranges of northwest Montana were reprocessed and interpreted in this study. Five seismic profiles represent 160 km of deep reflection data collected in 1983 that span the eastern Purcell anticlinorium, Rocky Mountain Trench (RMT), Rocky Mountain Basal Décollement (RMBD), and Lewis thrust. The data were reprocessed using modern techniques including refraction statics, pre-stack time migration (PSTM), and pre- and post-stack depth migration. Results indicate the RMBD is 8-13 km below the Earth's surface and dip 3-10° west. Evidence for the autochthonous Mesoproterozoic Belt and basal Cambrian rocks beneath the RMBD is present in all of the profiles and appears to extend east of the RMT. The Lewis thrust was identified in the seismic profiles and appears to sole into the RMBD east of the RMT. The RMT fault system has a dip displacement of 3-4 km and forms a half graben filled with 1 km of unconsolidated Tertiary sedimentary deposits. The RMT and adjacent Flathead fault systems are interpreted to be structurally linked and may represent a synthetic, en echelon fault system.

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

NASA Astrophysics Data System (ADS)

Balling, N.

2000-12-01

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

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

NASA Astrophysics Data System (ADS)

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

2007-12-01

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

2.5D seismic velocity modelling in the south-eastern Romanian Carpathians Orogen and its foreland

NASA Astrophysics Data System (ADS)

Bocin, Andrei; Stephenson, Randell; Tryggvason, Ari; Panea, Ionelia; Mocanu, Victor; Hauser, Franz; Matenco, Liviu

2005-12-01

The DACIA-PLAN (Danube and Carpathian Integrated Action on Processes in the Lithosphere and Neotectonics) deep seismic reflection survey was performed in August-September 2001, with the objective of obtaining new information on the deep structure of the external Carpathians nappe system and the architecture of the Tertiary/Quaternary basins developed within and adjacent to the Vrancea zone, including the rapidly subsiding Focsani Basin. The DACIA-PLAN profile is about 140 km long, having a roughly WNW-ESE direction, from near the southeast Transylvanian Basin, across the mountainous south-eastern Carpathians and their foreland to near the Danube River. A high resolution 2.5D velocity model of the upper crust along the seismic profile has been determined from a tomographic inversion of the DACIA-PLAN first arrival data. The results show that the data fairly accurately resolve the transition from sediment to crystalline basement beneath the Focsani Basin, where industry seismic data are available for correlation, at depths up to about 10 km. Beneath the external Carpathians nappes, apparent basement (material with velocities above 5.8 km/s) lies at depths as shallow as 3-4 km, which is less than previously surmised on the basis of geological observations. The first arrival travel-time data suggest that there is significant lateral structural heterogeneity on the apparent basement surface in this area, suggesting that the high velocity material may be involved in Carpathian thrusting.

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

Code of Federal Regulations, 2010 CFR

2010-07-01

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

A 80 OBS and 30 Land 3-component seismometers array encompassing the 280 km segment of the Lesser Antilles subduction megathrust seismogenic zone: view of current seismicity

NASA Astrophysics Data System (ADS)

Laigle, Mireille; Sapin, Martine; Ruiz, Mario; Diaz, Jordi; Kissling, Edi; Charvis, Philippe; Flueh, Ernst; Hirn, Alfred

2010-05-01

An extensive onshore and offshore seismic station array in the Lesser Antilles subduction zone allows to monitor microearthquake activity for a period of 4 months in a region previously outside of reach for detailed observation. Such a network has been possible thanks to a cluster of 3 seismic surveys (TRAIL - F/S Merian, SISMANTILLESII - N/O Atalante, and OBSANTILLES - N/O Antea) for deploying and recovering the instruments from several pools (Geoazur, INSU-IPGP, IFM-GEOMAR, AWI ). It has been followed by an additional deployment of the 28 GeoAzur OBSs (OBSANTILLES - N/O Antea) during 5 months in the south-western half. These operations have been carried out for the seismic investigation of the Antilles megathrust seismogenic zone in the framework of the THALES WAS RIGHT european project, and with also the financial support of the french ANR Catastrophes Telluriques et Tsunamis (SUBSISMANTI) and by the EU SALVADOR Programme of IFM-GEOMAR. Onshore, 30 3-components land stations (CSIC Barcelone, IPG Paris, INSU-RLBM and -LITHOSCOPE) have been temporarily deployed. The deep seismic structure of the whole area has been investigated during these seismic surveys by wide-angle reflection and refraction seismics recorded by these instruments as well as multi-channel reflection seismic imaging (MCS) along a dense grid of crossing profiles at the OBS positions providing excellent velocity information for the upper plate. Both the location and the interpretation of the recorded earthquake activity require constraints on the deep seismic structure, which will be discussed with respect to the 3D geometry of the interplate boundary and oceanic Moho, as well as those of the forearc basement and Moho. Preliminary locations have been obtained within a simple 1D velocity model by taking into account corrections for the variable thickness of the mud- and sediments layers beneath each OBS. The latter are estimated for both P- and S-waves to compensate for the huge structural heterogeneity on the arrival times and their effects will be discussed in map and along vertical cross-sections aligned with the seismic profiles. A first order result is that the previously unsampled seaward region remains aseismic through the whole period of observation. Another main result, at least in a model not yet accounting for deep structural heterogeneity, is that the seismicity is principally located deeper than the contact between the forearc crust and the subducting oceanic crust as derived from the refraction-reflection approaches in the general project, and in both plates. Data are being prepared for a joint inversion of earthquake locations, shot first arrival times and 3D heterogeneity.

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 to assess the geological hazards linked to the neotectonic activity within the Africa-Eurasia plate boundary. * SISMAR Group includes the authors and Amhrar M., Camurri F., Contrucci I., Diaz J., El Archi A., Gutscher M.A., Jaffal M., Klingelhöfer F., Legall B., Maillard A., Mehdi K., Mercier E., Moulin M., Olivet J.L., Ouajhain B., Perrot J., Rolet J., Ruellan E., Sibuet J.C., Zourarah B.

Seismic stratigraphy of the Heuksan mud belt in the southeastern Yellow Sea, Korea

NASA Astrophysics Data System (ADS)

Lee, Gwang-Soo; Yoo, Dong Geun; Bae, Sung Ho; Min, Gun-Hong; Kim, Seong-Pil; Choi, Hunsoo

2015-12-01

To establish the seismic stratigraphy of the Heuksan mud belt (HMB) and reconstruct its depositional history, approximately 1,600 km of high-resolution seismic data were newly obtained using chirp acoustic sub-bottom profiler, sparker, and air-gun seismic systems. Based on seismic stratigraphic analysis, the HMB can be divided into three major seismic units (I, II, and III, from top to bottom) and four subunits (II-a, II-b, III-a, and III-b) overlying transgressive sands, pre-last glacial maximum (LGM) deposits, and the acoustic basement. Each unit and subunit show different seismic facies and geometry, being clearly separated from each other by bounding surfaces formed since the LGM. The spatial distribution, thicknesses and volumes of the seismic units were determined and plotted to document the sequential formation of the HMB. The correlation between deep drill core data (HMB-101, HMB-102, HMB-103, YSDP-101, and YSDP-102) and the seismic data suggests that subunits III-b and III-a were formed by the continuous accumulation of fine-grained sediment with partial sandy sediment in an estuarine/deltaic environment during the early to middle transgressive stage, accompanied by landward migration of the shoreline. Subunits II-b and II-a were probably formed by re-deposition of large volumes of sediment eroded from unit III during the middle transgressive to early highstand stage. Unit I is interpreted as the most recent mud deposit representing the highstand systems tract when sea-level rise terminated. The careful definition of seismic units and their interpretation proposed in this study, on the basis of the large and partly new seismic dataset covering the entire HMB together with deep drill core data, have been instrumental in reconstructing the depositional environment and formation mechanisms of the HMB.

Experience from the ECORS program in regions of complex geology

NASA Astrophysics Data System (ADS)

Damotte, B.

1993-04-01

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

Seismic stratigraphy of the Mianwali and Bannu depressions, north-western Indus foreland basin

NASA Astrophysics Data System (ADS)

Farid, Asam; Khalid, Perveiz; Ali, Muhammad Y.; Iqbal, Muhammad Asim; Jadoon, Khan Zaib

2017-11-01

Regional seismic reflection profiles, deep exploratory wells, and outcrop data have been used to study the structure and stratigraphic architecture of the Mianwali and Bannu depressions, north-western Indus foreland basin. Synthetic seismograms have been used to identify and tie the seismic horizons to the well data. Nine mappable seismic sequences are identified within the passive and active margin sediments. In general, the Mianwali and Bannu depressions deepens towards north due to the flexure generated by the loading and southward shifting of the thrust sheets of the North-western Himalayan Fold and Thrust Belt. The seismic profiles show a classic wedge shaped foreland basin with a prominent angular unconformity which clearly differentiates the active and passive margin sediments. The onlap patterns in the Late Cretaceous sediments suggest the initial onset of foreland basin formation when the Indian Plate collided with Eurasian Plate. As the collision progressed, the lithospheric flexure caused an uplift along the flexural bulge which resulted in onlaps within the Paleocene and Eocene sequences. The tectonic activity reached to its maximum during Oligocene with the formation of a prominent unconformity, which caused extensive erosion that increases towards the flexural bulge.

The crustal structures from Wuyi-Yunkai orogen to Taiwan orogen: the onshore-offshore wide-angle seismic experiment of TAIGER and ATSEE projects

NASA Astrophysics Data System (ADS)

Kuochen, H.; Kuo, N. Y. W.; Wang, C. Y.; Jin, X.; Cai, H. T.; Lin, J. Y.; Wu, F. T.; Yen, H. Y.; Huang, B. S.; Liang, W. T.; Okaya, D. A.; Brown, L. D.

2015-12-01

The crustal structure is key information for understanding the tectonic framework and geological evolution in the southeastern China and its adjacent area. In this study, we integrated the data sets from the TAIGER and ATSEE projects to resolve onshore-offshore deep crustal seismic profiles from the Wuyi-Yunkai orogen to the Taiwan orogen in southeastern China. Totally, there are three seismic profiles resolved and the longest profile is 850 km. Unlike 2D and 3D first arrival travel-time tomography from previous studies, we used both refracted and reflected phases (Pg, Pn, PcP, and PmP) to model the crustal structures and the crustal reflectors. 40 shots, 2 earthquakes, and about 1,950 stations were used and 15,319 arrivals were picked among three transects. As a result, the complex crustal evolution since Paleozoic era are shown, which involved the closed Paleozoic rifted basin in central Fujian, the Cenozoic extension due to South China sea opening beneath the coastline of southern Fujian, and the on-going collision of the Taiwan orogen.

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

NASA Astrophysics Data System (ADS)

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

2017-10-01

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

Deep Shear Wave Velocity of Southern Bangkok and Vicinity

NASA Astrophysics Data System (ADS)

Wongpanit, T.; Hayashi, K.; Pananont, P.

2017-09-01

Bangkok is located on the soft marine clay in the Lower Chao Phraya Basin which can amplify seismic wave and can affect the shaking of buildings during an earthquake. Deep shear wave velocity of the sediment in the basin are useful for study the effect of the soft sediment on the seismic wave and can be used for earthquake engineering design and ground shaking estimation, especially for a deep basin. This study aims to measure deep shear wave velocity and create 2D shear wave velocity profile down to a bedrock in the southern Bangkok by the Microtremor measurements with 2 seismographs using Spatial Autocorrelation (2-SPAC) technique. The data was collected during a day time on linear array geometry with offsets varying between 5-2,000 m. Low frequency of natural tremor (0.2-0.6 Hz) was detected at many sites, however, very deep shear wave data at many sites are ambiguous due to man-made vibration noises in the city. The results show that shear wave velocity of the sediment in the southern Bangkok is between 100-2,000 ms-1 and indicate that the bedrock depth is about 600-800 m, except at Bang Krachao where bedrock depth is unclear.

Receiver Function Imaging of Crustal and Lithospheric Structure Beneath the Jalisco Block and Western Michoacan, Mexico.

NASA Astrophysics Data System (ADS)

Reyes Alfaro, G.; Cruz-Atienza, V. M.; Perez-Campos, X.; Reyes Dávila, G. A.

2014-12-01

We used a receiver function technique for imaging western Mexico, a unique area with several active seismic and volcanic zones like the triple junction of Rivera, Cocos and North American plates and the Colima volcano complex (CVC), the most active in Mexico. Clear images of the distribution of the crust and the lithosphere-asthenosphere boundary are obtained using P-to-S receiver functions (RF) from around ~80 broadband stations recorded by the Mapping the Rivera Subduction Zone (MARS), the Colima Volcano Deep Seismic Experiment (CODEX) and a local network (RESCO) that allowed us to considerably increase the teleseismic database used in the project. For imaging, we constructed several 2-D profiles of depth transformed RFs to delineate the seismic discontinuities of the region. Low seismic velocities associated with the Michoacan-Guanajuato and the Mascota-Ayutla-Tapalpa volcanic fields are also observed. Most impressive, a large and well delineated magma body 100 km underneath CVC is recognized along a surely related depression of the moho discontinuity just above it. We bring more tools for a better understanding of the deep processes that ultimately control eruptive behavior in the region.

Data report for onshore-offshore wide-angle seismic recordings in the Bering-Chukchi Sea, Western Alaska and eastern Siberia

USGS Publications Warehouse

Brocher, Thomas M.; Allen, Richard M.; Stone, David B.; Wolf, Lorraine W.; Galloway, Brian K.

1995-01-01

This report presents fourteen deep-crustal wide-angle seismic reflection and refraction profiles recorded onland in western Alaska and eastern Siberia from marine air gun sources in the Bering-Chukchi Seas. During a 20-day period in August, 1994, the R/V Ewing acquired two long (a total of 3754 km) deep-crustal seismic-reflection profiles on the continental shelf of the Bering and Chukchi Seas, in a collaborative project between Stanford University and the United States Geological Survey (USGS). The Ewing's 137.7 liter (8355 cu. in.) air gun array was the source for both the multichannel reflection and the wide-angle seismic data. The Ewing, operated by the Lamont-Doherty Earth Observatory, steamed northward from Nunivak Island to Barrow, and returned, firing the air gun array at intervals of either 50 m or 75 m. About 37,700 air gun shots were fired along the northward directed Lines 1 and 2, and more than 40,000 air gun shots were fired along the southward directed Line 3. The USGS and the University of Alaska, Fairbanks (UAF), deployed an array of twelve 3-component REFTEK and PDAS recorders in western Alaska and eastern Siberia which continuously recorded the air gun signals fired during the northward bound Lines 1 and 2. Seven of these recorders also continuously recorded the southward bound Line 3. These wide-angle seismic data were acquired to: (1) image reflectors in the upper to lower crust, (2) determine crustal and upper mantle refraction velocities, and (3) provide important constraints on the geometry of the Moho along the seismic lines. In this report, we describe the land recording of wide-angle data conducted by the USGS and the UAF, describe in detail how the wide-angle REFTEK and PDAS data were reduced to common receiver gather seismic sections, and illustrate the wide-angle seismic data obtained by the REFTEKs and PDAS's. Air gun signals were observed to ranges in excess of 400 km, and crustal and upper /mantle refractions indicate substantial variation in the crustal thickness along the transect.

Calibration of Seismic Sources during a Test Cruise with the new RV SONNE

NASA Astrophysics Data System (ADS)

Engels, M.; Schnabel, M.; Damm, V.

2015-12-01

During autumn 2014, several test cruises of the brand new German research vessel SONNE were carried out before the first official scientific cruise started in December. In September 2014, BGR conducted a seismic test cruise in the British North Sea. RV SONNE is a multipurpose research vessel and was also designed for the mobile BGR 3D seismic equipment, which was tested successfully during the cruise. We spend two days for calibration of the following seismic sources of BGR: G-gun array (50 l @ 150 bar) G-gun array (50 l @ 207 bar) single GI-gun (3.4 l @ 150 bar) For this experiment two hydrophones (TC4042 from Reson Teledyne) sampling up to 48 kHz were fixed below a drifting buoy at 20 m and 60 m water depth - the sea bottom was at 80 m depth. The vessel with the seismic sources sailed several up to 7 km long profiles around the buoy in order to cover many different azimuths and distances. We aimed to measure sound pressure level (SPL) and sound exposure level (SEL) under the conditions of the shallow North Sea. Total reflections and refracted waves dominate the recorded wave field, enhance the noise level and partly screen the direct wave in contrast to 'true' deep water calibration based solely on the direct wave. Presented are SPL and RMS power results in time domain, the decay with distance along profiles, and the somehow complicated 2D sound radiation pattern modulated by topography. The shading effect of the vessel's hull is significant. In frequency domain we consider 1/3 octave levels and estimate the amount of energy in frequency ranges not used for reflection seismic processing. Results are presented in comparison of the three different sources listed above. We compare the measured SPL decay with distance during this experiment with deep water modeling of seismic sources (Gundalf software) and with published results from calibrations with other marine seismic sources under different conditions: E.g. Breitzke et al. (2008, 2010) with RV Polarstern, Tolstoy et al. (2004) with RV Ewing and Tolstoy et al. (2009) with RV Langseth, and Crone et al. (2014) with RV Langseth.

Recent Russian Geophysical and Geological Investigations on Siberian Continental Margin

NASA Astrophysics Data System (ADS)

P. v., A.; K. v., D.; B. v., V.

2007-12-01

In July-August, 2005 new geophysical and geological data were acquired in the Mendeleev Rise (MR) region during "Arctic-2005" cruise aboard M/V "Akademik Fedorov". The study was concentrated in the southern part of MR in the area of its junction with East Siberian shelf. On-ice deep seismic sounding investigations (with offsets up to 250 km) and helicopter-supported seismic reflection soundings were performed along 600 km-long sub- longitudinal profile. Seismic survey was accompanied by on-ice gravity observations and geological sampling. Air-borne magnetic and air gravity measurements at scale 1:1,000,000 were also performed within a 100 km- wide corridor along the central seismic profile. Processing and analysis of new evidence included the compilation of deep seismic section, 2D seismic-gravity modeling of the Earth crust, 3D modeling of basement and Moho relief, and estimation of sediment and earth crust thickness. The results were integrated with earlier data and used for advanced structural and tectonic interpretations. The following main conclusions were obtained: Thickness of sediment cover along seismic line varies from 12 km in the south (in the North-Chukchi Trough) to 3-4 km in the northern MR. Crust thickness beneath MR is on the order of 30-35 km with a maximum value of 38 km in its southern part. The thinnest crust (28 km) is observed in the North-Chukchi Trough. Potential fields indicate existence of several blocks differing in gravity and magnetic anomalies. In the southern MR these blocks appear separated by grabens and display distinct continental characteristics accentuated by thickness of the crust, its seismic velocities and potential field pattern. At some of the shallowest (possibly eroded?) bathymetric highs the results of bottom sampling seem to point to the possibility of local derivation of coarse bottom debris. The proposed tectonic model implies structural continuity between MR and the adjacent East Siberian shelf. Brief information about the latest Russian geophysical and geological cruise "Arctic-2007" to the Lomonosov Ridge and its transition to the Siberian shelf will also be presented.

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

USGS Publications Warehouse

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

1999-01-01

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

Improving our understanding of the evolution of mountain belts via the Collisional Orogeny in the Scandinavian Caledonides (COSC) project: Results from seismic investigations and plans for the 2.5 km deep COSC-2 borehole

NASA Astrophysics Data System (ADS)

Juhlin, C.; Almqvist, B. S. G.; Buske, S.; Giese, R.; Hedin, P.; Lorenz, H.

2017-12-01

Mountain belts (orogens) have influenced, and do influence, geological processes and climatic conditions considerably, perhaps more than any other natural phenomenon. The Alpine-Himalayan mountain belt is the prime example of a collisional orogen today. However, research in an active orogen is mostly constrained to observe and interpret the expression of processes at the surface, while the driving processes act at depth, often at mid-crustal levels (20 km) and deeper. About 440 million years ago, an orogen comparable in dimension and tectonic setting to today's Alpine-Himalayan orogen was developing in what is western Scandinavia today. Since then, erosion has removed much of the overburden and exposed the deep interior of the orogen, facilitating direct observation of rocks that are deep in the crust in modern orogens. In the COSC project we study how large rock volumes (allochthons) were transported during the collision of two continents and the associated deformation. The emplacement of high-grade metamorphic allochthons during orogeny has been the focus of COSC-1 research, centered on a 2.5 km deep fully cored borehole drilled in the summer of 2014 through the lower part of the high-grade Seve Nappe Complex near the town of Åre in western Sweden. The planned COSC-2 borehole (also fully cored to 2.5 km) will complement the COSC-1 borehole and allow a 5 km deep tectonostratigraphic column of the Caledonides to be constructed. The rock volume in the proximity of the COSC-2 borehole will be imaged with a combination of very-high and high-resolution geophysical experiments, such as a combination of high frequency seismics; zero offset and walk-away vertical seismic profiling (VSP); and a sparse 3D coverage around the drill site combined with 2D seismic profiles of several kilometers length in different directions. Downhole geophysical logging will provide additional information on the in-situ rock physical properties. Data from surface surveys will be calibrated against and integrated with the borehole data and the geological interpretation of the drill core. The COSC-1 and COSC-2 boreholes will provide a field laboratory for investigating mountain building processes, how plates and rock units deform, what structures and units are formed and their physical properties.

United States crustal thickness

NASA Technical Reports Server (NTRS)

Allenby, R. J.; Schnetzler, C. C.

1983-01-01

The thickness of the crust, the thickness of the basal (intermediate or lower) crustal layer, and the average velocity at the top of the mantle have been mapped using all available deep-penetrating seismic-refraction profiles in the conterminous United States and surrounding border areas. These profiles are indexed to their literature data sources. The more significant long wavelength anomalies on the three maps are briefly discussed and analyzed. An attempt to use Bouguer gravity to validate mantle structure was inconclusive.

Velocity model of the crust and upper mantle at the southern margin of the East European Craton (Azov Sea-Crimea-Black Sea area), DOBRE-2 & DOBRE'99 transect

NASA Astrophysics Data System (ADS)

Starostenko, Vitaly; Janik, Tomasz; Stephenson, Randell; Gryn, Dmytro; Tolkunov, Anatoliy; Czuba, Wojciech; Środa, Piotr; Sydorenko, Grigoriy; Lysynchuk, Dmytro; Omelchenko, Victor; Grad, Marek; Guterch, Aleksander; Kolomiyets, Katerina; Thybo, Hans; Dannowski, Anke; Flűh, Ernst R.; Legostaeva, Olga

2013-04-01

The southern part of the eastern European continental landmass consists mainly of a thick platform of Vendian and younger sediments overlying Precambrian basement, part of the East European Craton (EEC). The Scythian Platform (SP) lies between the EEC and the (mainly Alpine) deformed belt running from Dobrudja (Romania) to Crimea (Ukraine) and the Greater Caucasus (Russia), along the northern margin of the Black Sea. Hard constraints on the Palaeozoic history on the SP are very sparse and little is known of its crustal structure in this area. The poster presents the seismic results of a multidisciplinary project that fills some of this gap. The project is called DOBRE-2 (as it forms a prolongation of the successful DOBRE project executed in 1999-2001). The main objectives of DOBRE-2 were to elucidate the deep-seated structure of the lithosphere and geodynamic setting of the shelf zones of the Azov and Black seas and the Crimean peninsula and to study the deep controls on the structure of basement and sedimentary cover. DOBRE-2 traverses a number of major faults and suture zones separating the EEC from the SP, the Crimean Mountains, and the Black Sea depression. Significant hydrocarbon reserves occur in the basins traversed by DOBRE-2. Deep seismic reflection profiling (30 second, Vibroseis) has been completed on a 100-km segment of the profile on the Azov massif (part of the Ukrainian Shield) as well as a 47-km segment in Crimea. These are complemented by refraction profiling on the shelf zones of the Azov (~53 km) and Black (~160 km) seas and coincident near-vertical (CDP) in the Black Sea, using a combination of onshore seismograph stations, ocean-bottom seismometers, onshore explosive energy sources (6 shot points), as well as ship-borne seismic acquisition. We present a 2-D seismic velocity model (Vp in the crust, depth to the Moho and depth to the intracrustal reflectors) along (~780 km) the DOBRE-2 & DOBRE'99 transect. Our model extends the model published for the DOBRE'99 profile (The DOBREfraction'99 Working Group, 2003) to the southwest. The Moho dips in this direction, from a depth of 40 km below the Azov Sea to ~47 km, below Crimea. A short segment of a reflector interpreted to represent Moho was detected at a depth of ~37 km in the Black Sea part of the profile. We also present a comparison of the DOBRE-2 velocity model with an interpretation of a coincident CDP profile.

Insights into the Lurking Structures and Related Intraplate Earthquakes in the Region of Bay of Bengal Using Gravity and Full Gravity Gradient Tensor

NASA Astrophysics Data System (ADS)

Dubey, C. P.; Tiwari, V. M.; Rao, P. R.

2017-12-01

Comprehension of subsurface structures buried under thick sediments in the region of Bay of Bengal is vital as structural features are the key parameters that influence or are caused by the subsurface deformation and tectonic events like earthquakes. Here, we address this issue using the integrated analysis and interpretation of gravity and full gravity gradient tensor with few seismic profiles available in the poorly known region. A 2D model of the deep earth crust-mantle is constructed and interpreted with gravity gradients and seismic profiles, which made it possible to obtain a visual image of a deep seated fault below the basement associated with thick sediments strata. Gravity modelling along a NE-SW profile crossing the hypocentre of the earthquake of 21 May 2014 ( M w 6.0) in the northern Bay of Bengal suggests that the location of intraplate normal dip fault earthquake in the upper mantle is at the boundary of density anomalies, which is probably connected to the crustal fault. We also report an enhanced structural trend of two major ridges, the 85°E and the 90°E ridges hidden under the sedimentary cover from the computed full gravity gradients tensor components.

Structural variation along the southwestern Nankai seismogenic zone related to various earthquake phenomena

NASA Astrophysics Data System (ADS)

Nakanishi, A.; Shimomura, N.; Kodaira, S.; Obana, K.; Takahashi, T.; Yamamoto, Y.; Sato, T.; Kashiwase, K.; Fujimori, H.; Kaneda, Y.; Mochizuki, K.; Kato, A.; Iidaka, T.; Kurashimo, E.; Shinohara, M.; Takeda, T.; Shiomi, K.

2011-12-01

In the Nankai Trough subduction seismogenic zone, the Nankai and Tonankai earthquakes had often occurred simultaneously, and caused a great event. In order to reduce a great deal of damage to coastal area from both strong ground motion and tsunami generation, it is necessary to understand rupture synchronization and segmentation of the Nankai megathrust earthquake. For a precise estimate of the rupture area of the Nankai megathrust event, it is important to know the geometry of the subducting Philippine Sea plate and deep subduction structure along the Nankai Trough. To obtain the deep subduction structure of the coseismic rupture area of the Nankai earthquake in 1946 off Shikoku area, the large-scale high-resolution wide-angle seismic study was conducted in 2009 and 2010. In this study, 201 and 200 ocean bottom seismographs were deployed off the Shikoku Island and the Kii channel respectively. A tuned airgun system (7800 cu. in.) shot every 200m along 13 profiles. Airgun shots were also recorded along an onshore seismic profile (prepared by ERI, univ. of Tokyo and NIED) prolonged from the offshore profile off the Kii Peninsula. Long-term observation was conducted for ~9 months by 21 OBSs off the Shikoku area and 20 OBSs off the Kii channel.This research is part of 'Research concerning Interaction Between the Tokai, Tonankai and Nankai Earthquakes' funded by Ministry of Education, Culture, Sports, Science and Technology, Japan. Structural images of the overriding plate indicate the old accreted sediments (the Cretaceous-Tertiary accretionary prism) with the velocity greater than 6km/s extend seaward from off the Shikoku to the Hyuga-nada. Moreover, the young accreted sediments become relatively thinner eastward from off the cape Ashizuri to Muroto. These structural variations might be related to the different rupture pattern of the Nankai event. Structural image of the deep low frequency earthquakes and tremors is shown by using the airgun shots recorded at onshore Hi-net (NIED, Japan) data located along prolongation of the offshore seismic profiles.

Anomalies of rupture velocity in deep earthquakes

NASA Astrophysics Data System (ADS)

Suzuki, M.; Yagi, Y.

2010-12-01

Explaining deep seismicity is a long-standing challenge in earth science. Deeper than 300 km, the occurrence rate of earthquakes with depth remains at a low level until ~530 km depth, then rises until ~600 km, finally terminate near 700 km. Given the difficulty of estimating fracture properties and observing the stress field in the mantle transition zone (410-660 km), the seismic source processes of deep earthquakes are the most important information for understanding the distribution of deep seismicity. However, in a compilation of seismic source models of deep earthquakes, the source parameters for individual deep earthquakes are quite varied [Frohlich, 2006]. Rupture velocities for deep earthquakes estimated using seismic waveforms range from 0.3 to 0.9Vs, where Vs is the shear wave velocity, a considerably wider range than the velocities for shallow earthquakes. The uncertainty of seismic source models prevents us from determining the main characteristics of the rupture process and understanding the physical mechanisms of deep earthquakes. Recently, the back projection method has been used to derive a detailed and stable seismic source image from dense seismic network observations [e.g., Ishii et al., 2005; Walker et al., 2005]. Using this method, we can obtain an image of the seismic source process from the observed data without a priori constraints or discarding parameters. We applied the back projection method to teleseismic P-waveforms of 24 large, deep earthquakes (moment magnitude Mw ≥ 7.0, depth ≥ 300 km) recorded since 1994 by the Data Management Center of the Incorporated Research Institutions for Seismology (IRIS-DMC) and reported in the U.S. Geological Survey (USGS) catalog, and constructed seismic source models of deep earthquakes. By imaging the seismic rupture process for a set of recent deep earthquakes, we found that the rupture velocities are less than about 0.6Vs except in the depth range of 530 to 600 km. This is consistent with the depth variation of deep seismicity: it peaks between about 530 and 600 km, where the fast rupture earthquakes (greater than 0.7Vs) are observed. Similarly, aftershock productivity is particularly low from 300 to 550 km depth and increases markedly at depth greater than 550 km [e.g., Persh and Houston, 2004]. We propose that large fracture surface energy (Gc) value for deep earthquakes generally prevent the acceleration of dynamic rupture propagation and generation of earthquakes between 300 and 700 km depth, whereas small Gc value in the exceptional depth range promote dynamic rupture propagation and explain the seismicity peak near 600 km.

Characterization of the structure of the Salar de Atacama Basin through gravimetric profiles and interval velocity analysis.

NASA Astrophysics Data System (ADS)

Becerra, J.; Bascunan, S. A.; Maksymowicz, A.; Martínez, F.; Arriagada, C.

2017-12-01

The structure of the basins found in the Preandean Depression in the northern Central Andes has remained elusive, partly due to a poor understanding of the structural styles and stratigraphy beneath their surface. An independent approach to the multiple interpretations of seismic lines available is the analysis of 2D gravity profiles. An E-W profile was performed across the basin, closely matching the surficial trace of previous seismic lines. The profile shows three gravimetric lows, the most relevant being one beneath the Llano de la Paciencia- Cordillera de la Sal, comprised of deformed evaporitic and terrigenous deposits of Oligocene-Early Miocene age. The structure which bounds this gravity low has a steeper dip on its eastern side, bounding the eastern side of the Cordillera de la Sal, which is at odds with previous studies that interpreted its western contact with Cretaceous outcrops as the possible basin boundary. The 3-D analyses of seismic interval velocity data around the gravimetric survey reveal a major vertical contrast in the eastern portion of the profile, interpreted as the bottom of the evaporite successions, followed to the west by a complex, narrow and deep zone of low velocities. Westward, the Cretaceous rocks record higher velocities than its post-Paleocene counterparts, and an almost uniform increase in velocity with depth. The major gravity anomaly is closely related to the Cordillera de la Sal, which consists of an array of folds and reverse faults involving Oligocene to recent deposits. We propose that the faults which generated Oligocene extension are not at the western border of the basin, but around the Cordillera de la Sal, which is the result of Miocene inversion of the same system. Strike-slip deformation was also probably a major contributor in basin formation, as shown by the narrow yet deep shape of the depocenter.

Passive seismic experiment and receiver functions analysis to determine crustal structure at the contact of the northern Dinarides and southwestern Pannonian Basin

NASA Astrophysics Data System (ADS)

Šumanovac, Franjo; Hegedűs, Endre; Orešković, Jasna; Kolar, Saša; Kovács, Attila C.; Dudjak, Darko; Kovács, István J.

2016-06-01

Passive seismic experiment was carried out at the SW contact of the Dinarides and Pannonian basin to determine the crustal structure and velocity discontinuities. The aim of the experiment was to define the relationship between the Adriatic microplate and the Pannonian segment as a part of the European plate. Most of the temporary seismic stations were deployed in Croatia along the Alp07 profile-a part of the active-source ALP 2002 project. About 300-km-long profile stretches from Istra peninsula to the Drava river, in a WSW-ESE direction. Teleseismic events recorded on 13 temporary seismic stations along the profile were analysed by P-receiver function method. Two types of characteristic receiver functions (RF) have been identified, belonging to Dinaridic and Pannonian crusts as defined on the Alp07 profile, while in transitional zone there are both types. Three major crustal discontinuities can be identified for the Dinaridic type: sedimentary basement, intracrustal discontinuity and Mohorovičić discontinuity, whereas the Pannonian type revealed only two discontinuities. The intracrustal discontinuity was not observed in the Pannonian type, thus pointing to a single-layered crust in the Pannonian basin. Two interpretation methods were applied: forward modelling of the receiver functions and H-κ stacking method, and the results were compared with the active-source seismic data at deep refraction profile Alp07. The receiver function modelling has given reliable results of the Moho depths that are in accordance with the seismic refraction results at the end of the Alp07 profile, that is in the area of Pannonian crust characterized by simple crustal structure and low seismic velocities (Vp between 5.9 and 6.2 km s-1). In the Dinarides and its peripheral parts, receiver function modelling regularly gives greater Moho depths, up to +15 per cent, due to more complex crustal structure. The depths of the Moho calculated by the H-κ stacking method vary within wide limits (±13 km), due to band limited data of short-period stations. The results at five stations have to be rejected because of huge deviations in comparison with all previous results, while at the other seven stations the Moho depths vary within ±15 per cent around the Moho discontinuity of the Alp07 profile.

Deep continental margin reflectors

USGS Publications Warehouse

Ewing, J.; Heirtzler, J.; Purdy, M.; Klitgord, Kim D.

1985-01-01

In contrast to the rarity of such observations a decade ago, seismic reflecting and refracting horizons are now being observed to Moho depths under continental shelves in a number of places. These observations provide knowledge of the entire crustal thickness from the shoreline to the oceanic crust on passive margins and supplement Consortium for Continental Reflection Profiling (COCORP)-type measurements on land.

Imaging Seafloor Massive Sulphides at the TAG hydrothermal fields, from the Blue Mining seismic project

NASA Astrophysics Data System (ADS)

Gil de la Iglesia, Alba; Vardy, Mark; Bialas, Jörg; Dannowski, Anke; Schröder, Henning; Minshull, Tim; Chidlow, Kasia; Murton, Bramly

2017-04-01

The Trans-Atlantic Geotraverse (TAG) hydrothermal field, located at the Mid-Atlantic Ridge (26°N), is known for the existence of Seafloor Massive Sulphides (SMS) discovered by the Trans-Atlantic Geotraverse cruise (Rona et al., 1986). The TAG comprises a low-temperature alteration zone, five inactive, high-temperature hydrothermal deposits, and the hydrothermal active TAG mound. TAG is also known for being one of the eight known SMS with a size larger than 2M tones (Hannington et al., 2011). The known SMS deposits do not have the same dimensions as the Massive Sulphides (MS) found on land, covering areas from 10s-100s m2 and their accessibility is more complicated, being located at 800-6000 m water depth. Although they do not seem to be economically exploitable at present, those deep-sea mineral resources could be important targets in the near future. One of the aims of the European-funded Blue Mining project is to identify the SMS deposit dimensions for the future environmentally sustainable and clean deep-sea mining. The Blue Mining project is focused on the extinct Seafloor Massive Sulphides (eSMS) in the TAG hydrothermal field, in particular Shinkai, Southern and Shimmering mounds. In May/June 2016 the German RV METEOR carried out a seismic refraction/reflection wide-angle (WA) experiment acquiring thirty multichannel seismic (MCS) profiles crossing the TAG hydrothermal field. GEOMAR's 2-unit air-gun array with a total volume of 760 cubic-inches was used, triggering seismic pulses every 12 s along the MCS profiles. Reflected and refracted events from the shallow-towed sources were recorded by 20 Ocean Bottom Seismometers (OBS) and 5 Ocean Bottom Hydrophones (OBH). To obtain the internal velocities and gross geometries of these deposits, 10 of 20 OBS were located on top of the eSMS, Shinaki and Southern mounds, while the other 10 instruments were located in extension of the profiles, covering Shimmering mounds and regional targets. In this presentation, we present results from controlled-source seismic forward modelling along two 5 km North-South profiles and a 10 km East-West profile. The 10 km profile cross over two eSMS (Shinkai and Southern mounds) deposits, while the other two 5 km profiles, pass through Shimmering and Shinkai mounds, and Southern mound, respectively. Despite the small size of all mounds we have been able to image their dimensions by using forward modelling. From Pg, PcP and PmP arrivals, we could model one 100 m and two 120 m thick deposits in 500 m slow thin upper crust layer (2900-5400 m/s), followed by 1500 m lower crust (6400-7200 m/s).

Retroarc extension in the last 6 Ma in the South-Central Andes (36°S-40°S) evaluated through a 3-D gravity modelling

NASA Astrophysics Data System (ADS)

Folguera, A.; Alasonati Tašárová, Z.; Götze, H.-J.; Rojas Vera, E.; Giménez, M.; Ramos, V. A.

2012-12-01

The Andean retroarc between 35° and 40°S is the locus of debate regarding its Pliocene to Quaternary tectonic setting. Retroarc volcanic eruptions since 6 Ma to the Present are, based on some hypotheses, associated with widespread extension. In these works, geological data point to the existence of normal faults affecting previous (Late Cretaceous to Miocene) contractional structures. In order to evaluate such interpretations we have collected data from various geological and geophysical studies and scales. Based on these data, an existing large-scale 3-D gravity model could be improved and used to investigate the lithospheric structure of this region. Moreover, using the gravity model, an attenuated crust could be localized and quantified throughout the retroarc area. Deep seismic data available from this region are limited to the forearc - arc area, while in general the retroarc zone lacks deep seismic constraints. The only deep seismic profile extending to the retroarc is a receiver function profile at 39°S, showing crustal attenuation. This observation correlates with the extensional activity recognized at the surface. When analysing the gravity field, positive residual anomalies are observed. They correlate with crustal attenuation at the areas of extension. Also, computed elastic thickness in the retroarc shows good correlation between the areas of crustal stretching and low flexural rigidity, explained by thermal processes. The present extensional deformation reflected in positive residual gravity anomalies points to the influence of reactivated Triassic rifting inherited from early phases of Pangea break-up. Finally, the present local uplift and consequent fluvial incision at the retroarc zone are explained by crustal stretching and not by crustal shortening, the common mechanism in Andean orogenesis.

Integrated geologic and geophysical studies of North American continental intraplate seismicity

USGS Publications Warehouse

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

2007-01-01

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

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

PubMed

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

2017-12-12

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

Prominent reflector beneath around the segmentation boundary between Tonankai-Nankai earthquake area

NASA Astrophysics Data System (ADS)

Nakanishi, A.; Shimomura, N.; Fujie, G.; Kodaira, S.; Obana, K.; Takahashi, T.; Yamamoto, Y.; Yamashita, M.; Takahashi, N.; Kaneda, Y.; Mochizuki, K.; Kato, A.; Iidaka, T.; Kurashimo, E.; Shinohara, M.; Takeda, T.; Shiomi, K.

2013-12-01

In the Nankai Trough subduction seismogenic zone, the Nankai and Tonankai earthquakes had often occurred simultaneously, and caused a great event. In most cases, first break of such large events of Nankai Trough usually begins from southwest off the Kii Peninsula so far. The idea of split Philippine Sea plate between the Kii Peninsula and the Shikoku Island, which explains seismicity, tectonic background, receiver function image and historical plate motion, was previously suggested. Moreover, between the Kii Peninsula and the Shikoku Island, there is a gap of deep low-frequency events observed in the belt-like zone along the strike of the subducting Philippine Sea plate. In 2010 and 2011, we conducted the large-scale high-resolution wide-angle and reflection (MCS) seismic study, and long-term observation from off Shikoku and Kii Peninsula. Marine active source seismic data have been acquired along grid two-dimensional profiles having the total length of ~800km/year. A three-dimensional seismic tomography using active and passive seismic data observed both land and ocean bottom stations have been also performed. From those data, we found a possible prominent reflector imaged in the offshore side in the Kii channel at the depth of ~18km. The velocity just beneath the reflector cannot be determined due to the lack of ray paths. Based of the amplitude information, we interpret the reflector as the forearc Moho based on the velocity gap (from ~6.4km/s to ~7.4km/s). However, the reflector is shallower than the forearc Moho of other area along the Nankai Trough. Similar reflectors are recognized along other seismic profiles around the Kii channel. In this presentation, we will show the result of structure analysis to understand the peculiar structure including the prominent reflector around the Kii channel. Relation between the structure and the existence of the segmentation of the Nankai megathrust earthquake or seismic gap of the deep low-frequency events will be also discussed. This study is part of 'Research concerning Interaction Between the Tokai, Tonankai and Nankai Earthquakes' funded by Ministry of Education, Culture, Sports, Science and Technology, Japan.

Early evolution of salt structures in north Louisiana salt basin

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

Lobao, J.J.; Pilger, R.H. Jr.

1986-05-01

Several salt diapirs and pillows in southern and central north Louisiana have been studied using approximately 355 mi (570 km) of seismic reflection data and information from 57 deep well holes. Using seismic profiles with deep well-hole data is the most advantageous method to document regional salt tectonism through time. The following conclusions were reached on diapirism in the North Louisiana Salt basin. (1) The diapiric event began early (early Coahuilan) in the southern and central part of the basin, and later (late Coahuilan to Comanchean) in the northern part. (2) The initial diapiric event is much more abrupt andmore » intense in the southern and central diapirs when compared with the later diapiric event in the northern diapirs. (3) Regional depocenter shifting, relative sea level, local erosion with salt extrusion, and rapid depositional loading of sediments are the major controls on diapirism in the basin.« less

Lateral evolution of the deep crustal structure of the Lesser Antilles Island arc from wide-angle seismic modelling.

NASA Astrophysics Data System (ADS)

Klingelhoefer, F.; Laurencin, M.; Marcaillou, B.; Graindorge, D.; Evain, M.; Lebrun, J. F.

2016-12-01

One of the goals of the Antithesis cruises (2013 and 2016) was investigating the deep structure of the Lesser Antilles subduction zone in order to: 1) constrain the possible along-strike variations of deep margin structures and slab geometry, 2) assess the nature of the crust and 3) discuss the potential impact of these structures on seismic hazard. Four combined wide-angle and multichannel seismic profiles were acquired between Barbuda and the Virgin Islands using 66 ocean bottom seismometers, a 4.5 km digital streamer and a 7200 cu inch seismic source. Along every line, we performed forward modelling of the wide-angle seismic data, gravity models and synthetic data calculations. The 5-7-km-thick subducting Atlantic oceanic plate is modelled with a single layer along every profile. The sedimentary prism fill is globally thin with maximal 5 km thick and 20-30 km wide. The 18-km-thick Caribbean crust is subdivided in 2 or 3 layers interpreted, from top to bottom, as following. A 2 to 4 km thick upper layer with velocity ranging from 2.5 to 3.5 km/s possibly consists of consolidate sediments or a carbonate platform. The underlying 4 to 6 km thick layer, with velocity ranging from 4.7 to 6.15 km/s might correspond to volcanic products. The lower 15 km thick lower crustal layer shows velocity up to 7.4 km/s, typical of basal velocities in oceanic crust. The structure and velocity model is thus closely consistent with a possibly overthickened oceanic crust. Our southernmost model, offshore of Barbuda, reveal a general crust structure and slab geometry which appear very to those described South of Guadeloupe along a line proposed by Kopp et al. (2011). It suggests an overall homogeneity for these structural features within the central segment of the Lesser Antilles (Martinique - Antigua). When the overall structure of the Caribbean plate is stable, the deep structure of the frontal margin and slab geometry is evolving from south to north. The wideness and thickness of the prism decrease toward the north as a consequence of the presence of blocking ridges and less sediment inputs. Frontal bending of the slab is also decreasing toward the north leading to a less steep slab within the first 30 kilometers as a consequence of increasing obliquity of subduction in the northern Antilles. This phenomena may increase the wideness of a seismogenic zone?

Deep seismic reflection images of the Wharton Basin oceanic crust and uppermost mantle offshore Northern Sumatra: Relation with active and past deformation

NASA Astrophysics Data System (ADS)

Carton, Hélène; Singh, Satish C.; Hananto, Nugroho D.; Martin, James; Djajadihardja, Yusuf S.; Udrekh; Franke, Dieter; Gaedicke, Christoph

2014-01-01

present deep seismic reflection images along two profiles collected in 2006 in the Wharton Basin offshore Northern Sumatra. The main profile is located subparallel to the Sumatran trench at a distance of 32-66 km. Faulting of the entire sedimentary section (strike-slip deformation sometimes accompanied by a dip-slip component) is imaged over two fracture zones of the extinct Wharton Spreading Center that prior studies have shown to be reactivated as left-lateral faults. The western fracture zone is associated with a wide region of strong basement topography, a difference in crustal thickness of 1.5 km, and an age offset of 9 Ma. The epicenters of the 11 April 2012 Mw 8.6 great strike-slip earthquake, its Mw 7.2 foreshock, and Mw 8.2 aftershock align along this major structure > 100 km south of the profile intersection. Our high-quality long-offset seismic reflection data also reveal bright dipping reflections extending down to a maximum of 24 km into the oceanic mantle ( 37 km below sea level). Apparent dips are mostly 25-35°, corresponding to 30-55° along either N-S to NNE-SSW or E-W to WNW-ESE directions, which encompass the directions of plate fabric and nodal planes of the Mw 8.6 event. We suggest that these enigmatic reflections arise from presently inactive dip-slip fault planes reaching for the deepest ones to the base of the brittle layer. Possible origins include extension related to plate bending or an episode of now inactive thrust-type deformation reactivating paleonormal faults, similar to that taking place in the Central Indian Basin.

Crustal structure and tectonics of the northern part of the Southern Granulite Terrane, India

USGS Publications Warehouse

Rao, V.V.; Sain, K.; Reddy, P.R.; Mooney, W.D.

2006-01-01

Deep seismic reflection studies investigating the exposed Archean lower continental crust of the Southern Granulite Terrane, India, yield important constraints on the nature and evolution of the deep crust, including the formation and exhumation of granulites. Seismic reflection images along the Kuppam-Bhavani profile reveal a band of reflections that dip southward from 10.5 to 15.0??s two-way-time (TWT), across a distance of 50??km. The bottom of these reflections beneath the Dharwar craton is interpreted as the Moho. Further south, another reflection band dipping northward is observed. These bands of reflectivity constitute a divergent reflection fabric that converges at the Moho boundary observed at the Mettur shear zone. Reflection fabrics that intersect at a steep angle are interpreted as a collisional signature due to the convergence of crustal blocks, which we infer resulted in crustal thickening and the formation of granulites. Anomalous gravity and magnetic signatures are also observed across the Mettur shear zone. The gravity model derived from the Bouguer gravity data corroborates seismic results. The tectonic regime and seismic reflection profiles are combined in a 3-D representation that illustrates our evidence for paleo-subduction at a collision zone. The structural dissimilarities and geophysical anomalies suggest that the Mettur shear zone is a suture between the Dharwar craton in the north and another crustal block in the south. This study contributes significantly to our understanding of the operation of Archean plate tectonics, here inferred to involve collision and subduction. Furthermore, it provides an important link between the Gondwanaland and global granulite evolution occurring throughout the late Archean. ?? 2006 Elsevier B.V. All rights reserved.

The eastern arm of the Midcontinent Rift: Progress and problems

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

Hinze, W.J.

1994-04-01

The extent and nature of the Midcontinent Rift System (MCR) was initially determined by potential-field mapping and extrapolation of geologic information from the Lake Superior region. Early interpretation suggested a rift origin which is well supported by deep crustal reflection seismic data and isotopic evidence from the related volcanic rocks that became available during the past decade. A rift origin of the eastern arm of the MCR was corroborated by sub-Phanerozoic drilling into the clastic sediment and volcanic rocks in the McClure-Sparks drill hole located on a massive anticlinal feature in the Precambrian rocks mapped by seismic reflection data. Subsequentmore » seismic profiling further detailed the character of the rift. However, these studies also indicate that the eastern arm is unlike the western, e.g., adjacent clastic rock basins are absent, late-stage compressional features are present, but definite evidence for high-angle reverse faulting is missing, and volcanic basins are not continuous. The termination of this arm of the rift also remains problematic. There is no direct evidence of the rift SE of the McClure-Sparks hole in central Michigan. Geophysical anomalies and deep drilling in the Howell anticline region suggest that the 1,100 Ma old rift is covered by Grenville-age thrusts. If the rift extends farther to the SE, its nature must have been altered by the Grenville orogeny. The hypothesized extension across Ohio east of the Grenville Front is unsupported by seismic reflection profiling and anomaly modeling. Grabens identified at the basement surface in Ohio and to the south are of unknown age, but appear to be more clearly related to late-stage Grenville activity and/or continuation of Eocambrian rifts of the Mississippi Embayment.« less

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.

Crustal structure of the Central-Eastern Greenland: results from the TopoGreenland refraction profile

NASA Astrophysics Data System (ADS)

Shulgin, Alexey; Thybo, Hans

2014-05-01

Until present, seismic surveys have only been carried out offshore and near the coasts of Greenland, where the crustal structure is affected by oceanic break-up. We present the deep seismic structure of the crust of the interior of Greenland, based on the new and the only existing so far seismic refraction/wide-angle reflection profile. The seismic data was acquired by a team of six people during a two-month long experiment in summer of 2011 on the ice cap in the interior of central-eastern Greenland. The presence of an up to 3.4 km thick ice sheet, permanently covering most of the land mass, made acquisition of geophysical data logistically complicated. The profile extends 310 km inland in E-W direction from the approximate edge of the stable ice cap near the Scoresby Sund across the center of the ice cap. 350 Reftek Texan receivers recorded high-quality seismic data from 8 equidistant shots along the profile. Explosive charge sizes were 1 ton at the ends and ca. 500 kg along the profile, loaded with about 125 kg at 35-85 m depth in individual boreholes. Given that the data acquisition was affected by the thick ice sheet, we questioned the quality of seismic records in such experiment setup. We have developed an automatic routine to check the amplitudes and spectra of the selected seismic phases and to check the differences/challenges in making seismic experiments on ice and the effects of ice on data interpretation. Using tomographic inversion and forward ray tracing modelling we have obtained the two-dimensional velocity model down to a 50 km depth. The model shows a decrease of crustal thickness from 47 km below the centre of Greenland in the western part of the profile to 40 km in its eastern part. Relatively high lower crustal velocities (Vp 6.8 - 7.3 km/s) in the western part of the TopoGreenland profile may result from past collision tectonics or, alternatively, may be related to the speculated passage of the Iceland mantle plume. Comparison of our results with the new receiver function studies (Kraft et al., personal communication) suggests the possibility for a massive underplating along the profile. The origin of the pronounced circum-Atlantic mountain ranges in Norway and eastern Greenland, which have average elevation above 1500 m with peak elevations of more than 3.5 km near the Scoresby Sund in Eastern Greenland, is unknown. Our new results on the crustal structure provide constraints for assessment of the isostatic balance of the crust in Greenland, as well as for examining possible links between crustal composition, rifting history and present-day topography of the North Atlantic Region.

Integrated geological-geophysical models of unstable slopes in seismogenic areas in NW and SE Europe

NASA Astrophysics Data System (ADS)

Mreyen, Anne-Sophie; Micu, Mihai; Onaca, Alexandru; Demoulin, Alain; Havenith, Hans-Balder

2017-04-01

We will present a series of new integrated 3D models of landslide sites that were investigated in distinctive seismotectonic and climatic contexts: (1) along the Hockai Fault Zone in Belgium, with the 1692 Verviers Earthquake (M 6 - 6.5) as most prominent earthquake that occurred in that fault zone and (2) in the seismic region of Vrancea, Romania, where four earthquakes with Mw > 7.4 have been recorded during the last two centuries. Both sites present deep-seated failures located in more or less seismically active areas. In such areas, slope stability analyses have to take into account the possible contributions to ground failure. Our investigation methods had to be adapted to capture the deep structure as well as the physico-mechanical characteristics that influence the dynamic behaviour of the landslide body. Field surveys included electrical resistivity tomography profiles, seismic refraction profiles (analysed in terms of both seismic P-wave tomography and surface waves), ambient noise measurements to determine the soil resonance frequencies through H/V analysis, complemented by geological and geomorphic mapping. The H/V method, in particular, is more and more used for landslide investigations or sites marked by topographic relief (in addition to the more classical applications on flat sites). Results of data interpretation were compiled in 3D geological-geophysical models supported by high resolution remote sensing data of the ground surface. Data and results were not only analysed in parallel or successively; to ensure full integration of all inputs-outputs, some data fusion and geostatistical techniques were applied to establish closer links between them. Inside the 3D models, material boundaries were defined in terms of surfaces and volumes. Those models were used as inputs for 2D dynamic numerical simulations completed with the UDEC (Itasca) software. For some sites, a full back-analysis was carried out to assess the possibility of a seismic triggering of the landslides.

High-Resolution 3D P-Wave Velocity Model in the Trans-European Suture Zone in Poland

NASA Astrophysics Data System (ADS)

Polkowski, M.; Grad, M.; Ostaficzuk, S.

2014-12-01

Poland is located on conjunction of major European tectonic units - the Precambrian East European Craton and the Paleozoic Platform of Central and Western Europe. This conjunction is known as Trans-European Suture Zone (TESZ). Geological and seismic structure under area of Poland is well studied by over one hundred thousand boreholes, over thirty deep seismic refraction and wide angle reflection profiles and other methods: vertical seismic profiling, magnetic, gravity, magnetotelluric, thermal. Compilation of these studies allows creation of detailed, high-resolution 3D P-wave velocity model for entire Earth's crust in the area of Poland. Model provides detailed six layer sediments (Tertiary and Quaternary, Cretaceous, Jurassic, Triassic, Permian, old Paleozoic), consolidated / crystalline crust and uppermost mantle. Continental suturing is a fundamental part of the plate tectonic cycle, and knowing its detailed structure allows understanding plate tectonic cycle. We present a set of crustal cross sections through the TESZ, illustrating differentiation in the structure between Precambrian and Wariscan Europe. National Science Centre Poland provided financial support for this work by NCN grant DEC- 2011/02/A/ST10/00284.

Seismic expression of the Chesapeake Bay impact crater: Structural and morphologic refinements based on new seismic data

USGS Publications Warehouse

Poag, C. Wylie; Hutchinson, Deborah R.; Colman, Steve M.; Lee, Myung W.; Dressler, B.O.; Sharpton, V.L.

1999-01-01

This work refines previous interpretations of the structure and morphology of the Chesapeake Bay impact crater on the basis of more than 1,200 km of multichannel and single-channel seismic reflection profiles collected in the bay and on the adjacent continental shelf. The outer rim, formed in sedimentary rocks, is irregularly circular, with an average diameter of ~85 km. A 20–25-km-wide annular trough separates the outer rim from an ovate, crystalline peak ring of ~200 m of maximum relief. The inner basin is 35–40 km in diameter, and at least 1.26 km deep. A crystalline(?) central peak, approximately 1 km high, is faintly imaged on three profiles, and also is indicated by a small positive Bouguer gravity anomaly. These features classify the crater as a complex peak-ring/central peak crater. Chesapeake Bay Crater is most comparable to the Ries and Popigai Craters on Earth; to protobasins on Mars, Mercury, and the Moon; and to type D craters on Venus.

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

NASA Astrophysics Data System (ADS)

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

2015-04-01

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

Wide-angle seismic data from the East Sicily margin: Imaging the deep structure of a Tethyan transform margin and the modern Calabria subduction lateral slab tear.

NASA Astrophysics Data System (ADS)

Dellong, D.; Klingelhoefer, F.; Kopp, H.; Gutscher, M. A.

2016-12-01

It is generally accepted that a STEP fault (Subduction Tear Edge Propagator) has accommodated the roll back of the Ionian Slab along the eastern Sicily Margin since 6 to 7 Ma. However the location of this lithospheric scale tear fault, and its surface expression is controversial. Constrain by numerous bathymetric imaging and shallow sub-surface multi-channels seismic (MCS) studies, variety of fault geometry was proposed. Moreover the role of the Malta Escarpment in this geodynamic system also remain the object of debates. It may be linked to the opening of the Ionian basin during a phase of strike-slip rifting since more than 180 Ma. Here we present the results of modelling of two wide-angle seismic profiles from the DIONYSUS survey (R/V Meteor, Oct. 2014). The first profile (DY-P3) was recorded by 25 Ocean- Bottom-Seismometers (OBS) and 3 land stations, and the second profile (DY-P1) by 52 OBS. Forward modelling of both profiles reveals a zone of abrupt crustal thinning from about 30 km below the Hyblean plateau and East-Sicily continental domain, to values of 8-15 km over a short lateral distance of 20-30 km. In the northern profile (DY-P3) the crust east of this abrupt thinning is of transitional thickness (15 km) and characterized by seismic velocities and velocity gradients similar to thinned continental crust. In the southern profile (DY-P1) this crust is 6-8 km thick, and the velocity gradients are close to those of oceanic crust. On this profile about 50-60 km eastward from the base of the Malta Escarpment, a lateral change of crustal velocities was modelled. Here a recent shallow transtensional deformation has been observed in MCS data at the position of this structure and linked to an elongated basin visible in the bathymetry and was linked to the STEP fault location. The results of the wide-angle seismic modelling suggest an ancient origin for the Malta Escarpment, formed as a transform margin during opening of the Ionian Basin about 180 Ma ago. The geometry of the modern day STEP fault is largely obscured in the northern profile because of the superposition of the structures with the ancient Tethyan transform Margin. In the southern wide-angle seismic profile these two structures are distinct and this allow us to conclude that the Malta Escarpment offshore SE Sicily has not been re-activated by the recent STEP-fault activity.

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

USGS Publications Warehouse

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

2008-01-01

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

GONAF - A borehole Geophysical Observatory around the North Anatolian Fault in the Eastern Sea of Marmara

NASA Astrophysics Data System (ADS)

Bohnhoff, Marco; Dresen, Georg; Ceken, Ulubey; Tuba Kadarioglu, Filiz; Feyiz Kartal, Recai; Kilic, Tugbay; Nurlu, Murat; Yanik, Kenan; Acarel, Digdem; Bulut, Fatih; Ito, Hisao; Johnson, Wade; Malin, Peter Eric; Mencin, Dave

2017-04-01

The Marmara section of the North Anatolian Fault Zone (NAFZ) runs under water and is located less than 20 km from the 15-million-person population center of Istanbul at its eastern portion. Based on historical seismicity data, recurrence times forecast an impending magnitude M>7 earthquake for this region. The permanent GONAF Geophysical Observatory at the North Anatolian Fault has been installed around this section to help capture the seismic and strain activity preceding, during, and after such an anticipated event. The GONAF observatory is currently comprised of seven 300 m deep vertical seismic profiling stations and four collocated 100 m deep borehole strainmeters. Five of the stations are located on the land surrounding the Princes Islands segment below the eastern Sea of Marmara and two are on the near-fault Princes Islands south of Istanbul. The 300 m boreholes have 1, 2, and 15 Hz 3-C seismometers near their bottoms. Above this are vertical, 1 Hz, seismometers at 210, 140, and 70 m depths. The strainmeter boreholes are located within a few meters of the seismometer boreholes and contain horizontal strain tensor sensors and 2 Hz 3-C seismometers at their bottoms. This selection of instruments and depths was done so as to ensure high-precision and broad-frequency earthquake monitoring and vertical profiling, all under low-noise conditions. GONAF is the first ICDP-driven project with a primarily focus on long-term monitoring of fault-zone dynamics. It has already contributed to earthquake hazard studies in the Istanbul area in several ways. Combining GONAF recordings with existing regional seismic stations now allows monitoring of the NAFZ offshore Istanbul down to magnitudes M<0. GONAF also improves the resolution of earthquake hypocenters and source parameters, better defining local fault branches, their seismicity, and earthquake potential. Using its vertical distribution of sensors, it has directly measured depth-dependent seismic site-effects for ground shaking studies. GONAF is starting to address fundamental questions related to earthquake nucleation, rupture dynamics, temporal changes of material properties and strain.

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 Mohamed, KLINGELÖFER Fraucke, LANDURÉ Jean Yves, LEGALL Bernard, MAILLARD-LENOIR Agnès, MARTIN Christophe, MEHDI Khalid, MERCIER Eric, MOULIN Maryline, OUAJHAIN Brahim, PERROT Julie, ROLET Joël, RUELLAN Etienne, TEIXIRA Fernando, TERRINHA Pedro, ZOURARAH Bendehhou.

Active tectonics of the Imperial Valley, southern California: fault damage zones, complex basins and buried faults

NASA Astrophysics Data System (ADS)

Persaud, P.; Ma, Y.; Stock, J. M.; Hole, J. A.; Fuis, G. S.; Han, L.

2016-12-01

Ongoing oblique slip at the Pacific-North America plate boundary in the Salton Trough produced the Imperial Valley. Deformation in this seismically active area is distributed across a complex network of exposed and buried faults resulting in a largely unmapped seismic hazard beneath the growing population centers of El Centro, Calexico and Mexicali. To better understand the shallow crustal structure in this region and the connectivity of faults and seismicity lineaments, we used data primarily from the Salton Seismic Imaging Project (SSIP) to construct a P-wave velocity profile to 15 km depth, and a 3-D velocity model down to 8 km depth including the Brawley Geothermal area. We obtained detailed images of a complex wedge-shaped basin at the southern end of the San Andreas Fault system. Two deep subbasins (VP <5.65 km/s) are located in the western part of the larger Imperial Valley basin, where seismicity trends and active faults play a significant role in shaping the basin edge. Our 3-D VP model reveals previously unrecognized NE-striking cross faults that are interacting with the dominant NW-striking faults to control deformation. New findings in our profile include localized regions of low VP (thickening of a 5.65-5.85 km/s layer) near faults or seismicity lineaments interpreted as possibly faulting-related. Our 3-D model and basement map reveal velocity highs associated with the geothermal areas in the eastern valley. The improved seismic velocity model from this study, and the identification of important unmapped faults or buried interfaces will help refine the seismic hazard for parts of Imperial County, California.

Seismicity, shear failure and modes of deformation in deep subduction zones

NASA Technical Reports Server (NTRS)

Lundgren, Paul R.; Giardini, Domenico

1992-01-01

The joint hypocentral determination method is used to relocate deep seismicity reported in the International Seismological Center catalog for earthquakes deeper than 400 km in the Honshu, Bonin, Mariannas, Java, Banda, and South America subduction zones. Each deep seismic zone is found to display planar features of seismicity parallel to the Harvard centroid-moment tensor nodal planes, which are identified as planes of shear failure. The sense of displacement on these planes is one of resistance to deeper penetration.

Active Structures in the Georgia Basin, NW Washington State, USA, and SW British Columbia, Canada

NASA Astrophysics Data System (ADS)

Polivka, P.; Riedel, M.; Pratt, T. L.

2013-12-01

The Georgia basin is a local depression in the Cascadia forearc straddling the USA-Canadian border that hosts Canada's largest west coast population. The basin contains late Pleistocene and Holocene sediments overlying a thick sequence of Eocene and Cretaceous sedimentary rocks and is currently experiencing N-S shortening. Tectonic structures capable of accommodating this N-S shortening are recognized in Oregon and Washington; however, none have been identified in southwest Canada despite multiple independent geodetic studies indicating that shortening continues further north. This conflict of observed shortening over a region without recognized active structures suggests that seismic hazard may be underestimated in Canada. We combine multiple seismic reflection surveys and multibeam bathymetry with published geophysical data and on-shore mapping to identify active structures and assess seismic hazard. Reflection datasets span the USA-CA border and include those from the deep 1998 Seismic Hazards Investigations of Puget Sound (SHIPS), high resolution 2002 SHIPS, localized sparker, and deep industry lines. These data are augmented by digitized paper records of past reflection surveys. The 1998 SHIPS and industry lines show strong reflections of folded and faulted Cretaceous and Eocene sedimentary bedrock to 5 km depth. Shallow sediment deformation is imaged on the 2002 SHIPS and sparker lines. Combining these profiles, bathymetry, and surficial bedrock mapping in a 3-D interpretation program facilitated the correlation of features across multiple 2-D seismic lines, allowing us to interpret four new regional stratigraphic and tectonic characteristics. (1) The 1997 ML4.6 Gabriola Island earthquake was a north-side up thrust event occurring 30 km west of Vancouver at ~3.5 km depth. The event was previously correlated with a zone of low coherence on the SHIPS 1998 line. We reprocessed the line and imaged distinct reflector terminations. A generally E-W strike is interpreted from regional bedrock fault trends and shallow sediment deformation imaged on the 2002 SHIPS lines. (2) Kelsey et al. (2012, JGR) identified three subparallel NW-striking faults in NW Washington. We use the industry lines to constrain the subsurface geometries of these faults to >4 km depth. (3) Interpreting on-shore mapping, bathymetric bedrock ridges, and intersecting deep seismic profiles, we conclude that the E-K boundary is an angular unconformity across and along the length of the basin. (4) We correlate kinks in bathymetric bedrock ridges with bedrock folds on the intersecting SHIPS 1998 profile to re-interpret previously identified NE-trending 'secondary faults' as blind and broken-through fault-propagation folds. These faults are orthogonal to the subduction margin and collectively deemed the Vancouver Fold and Thrust Belt. The Gabriola Island earthquake indicates that the fault system is active, and likely accommodates at least part of the strain measured on GPS networks but not accounted for in previous tectonic models.

The Ural-Herirud transcontinental postcollisional strike-slip fault and its role in the formation of the Earth's crust

NASA Astrophysics Data System (ADS)

Leonov, Yu. G.; Volozh, Yu. A.; Antipov, M. P.; Kheraskova, T. N.

2015-11-01

The paper considers the morphology, deep structure, and geodynamic features of the Ural-Herirud postorogenic strike-slip fault (UH fault), along which the Moho (the "M") shifts along the entire axial zone of the Ural Orogen, then further to the south across the Scythian-Turan Plate to the Herirud sublatitudinal fault in Afghanistan. The postcollisional character of dextral displacements along the Ural-Herirud fault and its Triassic-Jurassic age are proven. We have estimated the scale of displacements and made an attempt to make a paleoreconstruction, illustrating the relationship between the Variscides of the Urals and the Tien Shan before tectonic displacements. The analysis of new data includes the latest generation of 1: 200000 geological maps and the regional seismic profiling data obtained in the most elevated part of the Urals (from the seismic profile of the Middle Urals in the north to the Uralseis seismic profile in the south), as well as within the sedimentary cover of the Turan Plate, from Mugodzhary to the southern boundaries of the former water area of the Aral Sea. General typomorphic signs of transcontinental strike-slip fault systems are considered and the structural model of the Ural-Herirud postcollisional strike-slip fault is presented.

Outokumpu Deep Drill Hole: Window to the Precambrian bedrock

NASA Astrophysics Data System (ADS)

Heinonen, Suvi; Kietäväinen, Riikka; Ahonen, Lasse; Kukkonen, Ilmo

2017-04-01

Outokumpu Deep Drill Hole is located in eastern Finland, at latitude 62°43'4'' N and longitude 29°3'43'' E. This 2516 m long and fully cored deep hole has been utilized as a geolaboratory open for researchers worldwide since it was drilled in 2004-2005. The 220 mm diameter drill hole is open without a casing (excluding the uppermost 40 m) and thus provides a direct access to in situ conditions to 2.5 km depth. There is a wide range of wire-line logs carried out by the drilling contractor and later by ICDP (International Continental Scientific Drilling Program) in several logging sessions for geothermal, hydrogeological and deep biosphere studies. Lithology, metamorphism, fluid inclusions, density, magnetic properties, seismic velocities and thermal properties of the drill core have been studied by several international groups. The hole has kept open since the end of drilling enabling future studies to be conducted in it. The drill hole is situated in the southwestern part of the Outokumpu historical mining district famous for its Cu-Co-Zn sulfide deposits. These sulfide deposits are hosted by 1.96 Ga old ophiolitic rock types, known as the Outokumpu assemblage, also penetrated by the deep drill hole at 1314-1515 m depth. Laboratory and in situ petrophysical measurements have provided valuable information about physical properties of the typical rocks of the area that can be utilized in the mineral exploration efforts. The drill site of Outokumpu was chosen based on strong reflectivity observed in the high resolution seismic profiles acquired earlier in the area. Outokumpu Deep Drill Hole revealed that these reflections originate from the acoustic impedance variations caused by the ore hosting Outokumpu assemblage. In 2006, surface seismic reflection and vertical seismic profiling (VSP) data were measured in the drill site, and these data show that not only is Outokumpu assemblage rocks reflective but also water bearing fracture at 965 m depth is observed as a strong reflector. This fracture, as well as other fractures penetrated by the drill hole, contains saline water and gases, mainly methane, nitrogen, hydrogen and helium. Salinity of water in the deeper part (>1000 m) of the drill hole has continuously increased since the drilling. Gas-rich water slowly seeps upward and bubble out at the water table. In total, five different water types have been discerned along the drill hole by geochemical and isotopic methods and residence times up to 58 Ma indicated by the accumulation of noble gases. Microbiological studies in the Outokumpu Deep Drill Hole show that not only do different fracture zones act as places for shift in groundwater chemistry but also in the microbial communities. After a decade of research, Outokumpu drill hole site is geologically well known and thus provides a good environment to test new tools developed for exploration, microbiological or hydrogeological purposes, for example. Geological Survey of Finland is open for new research collaboration projects related to the drill site.

A Deep-towed Digital Multichannel Seismic Streamer For Very High-resolution Studies Of Marine Subsurface Structures

NASA Astrophysics Data System (ADS)

Breitzke, M.; Bialas, J.; Inggas Working Group

A deep-towed digital multichannel seismic streamer and side scan sonar system has been developed to collect marine seismic data with a very high lateral in- and cross- line resolution particularly in regions of special interest for gas hydrate research. As marine seismic sources conventional air-, GI or waterguns will be shot close to the sea surface. A depressor of about 2 tons weight ensures the slightly buoyant deep-towed system to keep in depth. The streamer is a modular digital system which can be operated in water depths up to 6000 m. At this stage of development, it consists of a 50 m lead-in cable towed behind the side scan sonar fish and 26 single nodes for each channel. Each node houses a sin- gle hydrophone, low- and high-cut filter, preamplifier and 24-bit AD converter. Three special engineering nodes additionally include a pressure sensor and compass which provide information on the depth of the node and on its geographical position relative to the ship. Nodes are interchangeable and can arbitrarily be connected by cables of 1 or 6.5 m length. A minimum sample interval of 0.25 ms allows to use sufficiently high- frequency seismic sources to guarantee both a very high vertical and lateral resolution. Data are stored both underwater on a linux-based PC with 120 GB storage capacity installed in a pressure vessel mounted on the side scan sonar fish, and onboard on a PC running a data acquisition program and a DLT device. Data are transferred between underwater and onboard systems via telemetry controlled by a second linux-based PC onboard, using coaxial cable or fibre optic technology. The exact position of the side scan sonar fish is determined by the ultra-short base line (USBL) Posidonia system. It mainly consists of a hull-mounted acoustic unit (antenna) and a responder mounted on the side scan sonar fish. Additionally, the three engineering nodes measure the depth and heading of the streamer at three positions relative to the side scan sonar fish. All deep-towed and laboratory components are synchronized by DGPS time based trigger signals. This deep-towed system will first be tested during the SO162 cruise of RV Sonne (21.2. - 12.3.02) off Peru and Ecuador along profile lines where conventional multi- channel seismic reflection data have already been collected during a fomer cruise.

Double seismic zone for deep earthquakes in the izu-bonin subduction zone.

PubMed

Iidaka, T; Furukawa, Y

1994-02-25

A double seismic zone for deep earthquakes was found in the Izu-Bonin region. An analysis of SP-converted phases confirms that the deep seismic zone consists of two layers separated by approximately 20 kilometers. Numerical modeling of the thermal structure implies that the hypocenters are located along isotherms of 500 degrees to 550 degrees C, which is consistent with the hypothesis that deep earthquakes result from the phase transition of metastable olivine to a high-pressure phase in the subducting slab.

Investigation of the deep structure of the Sivas Basin (innereast Anatolia, Turkey) with geophysical methods

NASA Astrophysics Data System (ADS)

Onal, K. Mert; Buyuksarac, Aydin; Aydemir, Attila; Ates, Abdullah

2008-11-01

Sivas Basin is the easternmost and third largest basin of the Central Anatolian Basins. In this study, gravity, aeromagnetic and seismic data are used to investigate the deep structure of the Sivas Basin, together with the well seismic velocity data, geological observations from the surface and the borehole data of the Celalli-1 well. Basement depth is modeled three-dimensionally (3D) using the gravity anomalies, and 2D gravity and magnetic models were constructed along with a N-S trending profile. Densities of the rock samples were obtained from the distinct parts of the basin surface and in-situ susceptibilities were also measured and evaluated in comparison with the other geophysical and geological data. Additionally, seismic sections, in spite of their low resolution, were used to define the velocity variation in the basin in order to compare depth values and geological cross-section obtained from the modeling studies. Deepest parts of the basin (12-13 km), determined from the 3D model, are located below the settlement of Hafik and to the south of Zara towns. Geometry, extension and wideness of the basin, together with the thickness and lithologies of the sedimentary units are reasonably appropriate for further hydrocarbon exploration in the Sivas Basin that is still an unexplored area with the limited number of seismic lines and only one borehole.

Evolution of Northeast Atlantic Magmatic Continental Margins from an Ethiopian-Afar Perspective

NASA Astrophysics Data System (ADS)

England, R. W.; Cornwell, D. G.; Ramsden, A. M.

2014-12-01

One of the major problems interpreting the evolution of magmatic continental margins is that the structure which should record the pre-magmatic evolution of the rift and which potentially influences the character of the rifting process is partially or completely obscured by thick basalt lava flows and sills. A limited number of deep reflection seismic profiles acquired with tuned seismic sources have penetrated the basalts and provide an image of the pre-magmatic structure, otherwise the principle data are lower resolution wide-angle/refraction profiles and potential field models which have greater uncertainties associated with them. In order to sidestep the imaging constraints we have examined the Ethiopian - Afar rift system to try to understand the rifting process. The Main Ethiopian rift contains an embryonic magmatic passive margin dominated by faulting at the margins of the rift and en-echelon magmatic zones at the centre. Further north toward Afar the rift becomes in-filled with extensive lava flows fed from fissure systems in the widening rift zone. This rift system provides, along its length, a series of 'snapshots' into the possible tectonic evolution of a magmatic continental margin. Deep seismic profiles crossing the NE Atlantic margins reveal ocean dipping reflector sequences (ODRS) overlying extended crust and lower crustal sill complexes of intruded igneous rock, which extend back beneath the continental margin. The ODRS frequently occur in fault bounded rift structures along the margins. We suggest, by analogy to the observations that can be made in the Ethiopia-Afar rift that these fault bounded basins largely form at the embryonic rift stage and are then partially or completely filled with lavas fed from fissures which are now observed as the ODRS. Also in the seismic profiles we identify volcanic constructs on the ODRS which we interpret as the equivalent of the present day fissure eruptions seen in Afar. The ocean ward dip on the ODRS is predominantly the result of post-eruption differential subsidence, as opposed to syn-eruption extension. The timing of intrusion of the lower crustal sill complexes remains unclear but they are most likely to have been emplaced as the supply of magma increased, which implies they are a late stage addition.

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

NASA Astrophysics Data System (ADS)

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

2017-12-01

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

Structure of the Middle America trench in Oaxaca, Mexico

NASA Astrophysics Data System (ADS)

Nava, F.; Núñez-Cornú, F.; Córdoba, D.; Mena, M.; Ansorge, J.; González, J.; Rodríguez, M.; Banda, E.; Mueller, S.; Udías, A.; García-García, M.; Calderón, G.; the Mexican Working GroupDeep Seismic Profiling

1988-11-01

Deep seismic profiling was carried out in south and central Oaxaca as a multinational (Mexico, Spain and Switzerland) project. Sixteen sea-bottom explosions, ranging from 20 to 1000 kg were recorded by thirty portable instruments along three profiles, two along the coast and one going inland in an approximate N-S direction. Gravity surveys were carried out over the seismic profile lines, and the resulting Bouguer anomalies are interpreted together with the seismic data. Preliminary results indicate changes in the crustal thickness along the coast, near the town of Pinotepa Nacional, from 23.5 km in the northwest to 19 km in the southeast, reaching a minimum of some 15 km near the middle of the profile, about 140 km northwest of Puerto Angel. The coastal structure section consists roughly of two layers, an upper one with P-wave velocities that range from 5.1-5.4 to 5.8-6.0 km/s and a lower one where the P velocity range is from 6.0-6.2 to 6.3-6.4 km/s, overlying material with P-wave velocities of 7.45 km/s. Along the coast from Puerto Angel to Salina Cruz, the dip of the Cocos plate appears to be much less than it is to the northwest. A low-velocity zone, which corresponds to the top of the subducted oceanic crust, with P-wave velocities of 6.5-6.9 km/s, is found beneath the 2-3 km thick 7.45 km/s layer. The possible presence of an intrusive body is suggested by anomalous seismic arrivals and by a large gravimetric anomaly near Puerto Angel, close to the southern tip of Mexico.

Evolution of the continental margin of southern Spain and the Alboran Sea

USGS Publications Warehouse

Dillon, William P.; Robb, James M.; Greene, H. Gary; Lucena, Juan Carlos

1980-01-01

Seismic reflection profiles and magnetic intensity measurements were collected across the southern continental margin of Spain and the Alboran basin between Spain and Africa. Correlation of the distinct seismic stratigraphy observed in the profiles to stratigraphic information obtained from cores at Deep Sea Drilling Project site 121 allows effective dating of tectonic events. The Alboran Sea basin occupies a zone of motion between the African and Iberian lithospheric plates that probably began to form by extension in late Miocene time (Tortonian). At the end of Miocene time (end of Messinian) profiles show that an angular unconformity was cut, and then the strata were block faulted before subsequent deposition. The erosion of the unconformity probably resulted from lowering of Mediterranean sea level by evaporation when the previous channel between the Mediterranean and Atlantic was closed. Continued extension probably caused the block faulting and, eventually the opening of the present channel to the Atlantic through the Strait of Gibraltar and the reflooding of the Mediterranean. Minor tectonic movements at the end of Calabrian time (early Pleistocene) apparently resulted in minor faulting, extensive transgression in southeastern Spain, and major changes in the sedimentary environment of the Alboran basin. Active faulting observed at five locations on seismic profiles seems to form a NNE zone of transcurrent movement across the Alboran Sea. This inferred fault trend is coincident with some bathymetric, magnetic and seismicity trends and colinear with active faults that have been mapped on-shore in Morocco and Spain. The faults were probably caused by stresses related to plate movements, and their direction was modified by inherited fractures in the lithosphere that floors the Alboran Sea.

A New Analysis of the Two Classical ZZ Ceti White Dwarfs GD 165 and Ross 548. II. Seismic Modeling

NASA Astrophysics Data System (ADS)

Giammichele, N.; Fontaine, G.; Brassard, P.; Charpinet, S.

2016-03-01

We present the second of a two-part seismic analysis of the bright, hot ZZ Ceti stars GD 165 and Ross 548. In this second part, we report the results of detailed searches in parameter space for identifying an optimal model for each star that can account well for the observed periods, while being consistent with the spectroscopic constraints derived in our first paper. We find optimal models for each target that reproduce the six observed periods well within ∼0.3% on the average. We also find that there is a sensitivity on the core composition for Ross 548, while there is practically none for GD 165. Our optimal model of Ross 548, with its thin envelope, indeed shows weight functions for some confined modes that extend relatively deep into the interior, thus explaining the sensitivity of the period spectrum on the core composition in that star. In contrast, our optimal seismic model of its spectroscopic sibling, GD 165 with its thick envelope, does not trap/confine modes very efficiently, and we find weight functions for all six observed modes that do not extend into the deep core, hence accounting for the lack of sensitivity in that case. Furthermore, we exploit after the fact the observed multiplet structure that we ascribe to rotation. We are able to map the rotation profile in GD 165 (Ross 548) over the outermost ∼20% (∼5%) of its radius, and we find that the profile is consistent with solid-body rotation.

Collision tectonics of the Central Indian Suture zone as inferred from a deep seismic sounding study

USGS Publications Warehouse

Mall, D.M.; Reddy, P.R.; Mooney, W.D.

2008-01-01

The Central Indian Suture (CIS) is a mega-shear zone extending for hundreds of kilometers across central India. Reprocessing of deep seismic reflection data acquired across the CIS was carried out using workstation-based commercial software. The data distinctly indicate different reflectivity characteristics northwest and southeast of the CIS. Reflections northwest of the CIS predominantly dip southward, while the reflection horizons southeast of the CIS dip northward. We interpret these two adjacent seismic fabric domains, dipping towards each other, to represent a suture between two crustal blocks. The CIS itself is not imaged as a sharp boundary, probably due to the disturbed character of the crust in a 20 to 30-km-wide zone. The time sections also show the presence of strong bands of reflectors covering the entire crustal column in the first 65??km of the northwestern portion of the profile. These reflections predominantly dip northward creating a domal structure with the apex around 30??km northwest of the CIS. There are a very few reflections in the upper 2-2.5??s two-way time (TWT), but the reflectivity is good below 2.5??s TWT. The reflection Moho, taken as the depth to the deepest set of reflections, varies in depth from 41 to 46??km and is imaged sporadically across the profile with the largest amplitude occurring in the northwest. We interpret these data as recording the presence of a mid-Proterozoic collision between two micro-continents, with the Satpura Mobile Belt being thrust over the Bastar craton. ?? 2008.

A New Moonquake Catalog from Apollo 17 Seismic Data II: Lunar Surface Gravimeter: Implications of Expanding the Passive Seismic Array

NASA Astrophysics Data System (ADS)

Phillips, D.; Dimech, J. L.; Weber, R. C.

2017-12-01

Apollo 17's Lunar Surface Gravimeter (LSG) was deployed on the Moon in 1972, and was originally intended to detect gravitational waves as a confirmation of Einstein's general theory of relativity. Due to a design problem, the instrument did not function as intended. However, remotely-issued reconfiguration commands permitted the instrument to act effectively as a passive seismometer. LSG recorded continuously until Sept. 1977, when all surface data recording was terminated. Because the instrument did not meet its primary science objective, little effort was made to archive the data. Most of it was eventually lost, with the exception of data spanning the period March 1976 until Sept. 1977, and a recent investigation demonstrated that LSG data do contain moonquake signals (Kawamura et al., 2015). The addition of useable seismic data at the Apollo 17 site has important implications for event location schemes, which improve with increasing data coverage. All previous seismic event location attempts were limited to the four stations deployed at the Apollo 12, 14, 15, and 16 sites. Apollo 17 extends the functional aperture of the seismic array significantly to the east, permitting more accurate moonquake locations and improved probing of the lunar interior. Using the standard location technique of linearized arrival time inversion through a known velocity model, Kawamura et al. (2015) used moonquake signals detected in the LSG data to refine location estimates for 49 deep moonquake clusters, and constrained new locations for five previously un-located clusters. Recent efforts of the Apollo Lunar Surface Experiments Package Data Recovery Focus Group have recovered some of the previously lost LSG data, spanning the time period April 2, 1975 to June 30, 1975. In this study, we expand Kawamura's analysis to the newly recovered data, which contain over 200 known seismic signals, including deep moonquakes, shallow moonquakes, and meteorite impacts. We have completed initial data processing and verified the presence of deep moonquake signals in the recovered data. This positions us well for the application of automated event-detection techniques that have been successfully applied to the Apollo 16 Passive Seismic Experiment data as well as the Apollo 17 Lunar Seismic Profiling Experiment data.

Seismic imaging of the geodynamic activity at the western Eger rift in central Europe

NASA Astrophysics Data System (ADS)

Mullick, N.; Buske, S.; Hrubcova, P.; Ruzek, B.; Shapiro, S.; Wigger, P.; Fischer, T.

2015-04-01

The western Eger rift at the Czech-German border in central Europe is an important geodynamically active area within the European Cenzoic rift system (ECRS) in the forelands of the Alps. Along with two other active areas of the ECRS, the French Massif Central and the east and west Eifel volcanic fields, it is characterized by numerous CO2-rich fluid emission points and frequent micro-seismicity. Existence of a plume(s) is indicated in the upper mantle which may be responsible for these observations. Here we reprocess a pre-existing deep seismic reflection profile '9HR' and interpret the subsurface structures as mapped by seismic reflectivity with previous findings, mainly from seismological and geochemical studies, to investigate the geodynamic activity in the subsurface. We find prominent hints of pathways which may allow magmatic fluids originating in the upper mantle to rise through the crust and cause the observed fluid emanations and earthquake activity.

Seismic evidence of Quaternary faulting in the Benton Hills area, southeast Missouri

USGS Publications Warehouse

Palmer, J.R.; Shoemaker, M.; Hoffman, D.; Anderson, N.L.; Vaughn, J.D.; Harrison, R.W.

1997-01-01

Two reflection seismic profiles at English Hill, across the southern edge of the Benton Hills escarpment, southeast Missouri, establish that geologic structures at English Hill are of tectonic origin. The lowland area to the south of the escarpment is relatively undisturbed. The geology at English Hill is structurally complex, and reflection seismic and geologic data indicate extensive and episodic faulting of Paleozoic, Cretaceous, Tertiary, and Quaternary strata. The individual faults have near-vertical fault surfaces with maximum vertical separations on the order of 15 m. They appear to be clustered in north-northeast trending zones that essentially parallel one of the dominant Benton Hills structural trends. These observations suggest that previously mapped Quaternary faults at English Hill are deep-seated and tectonic in origin. This paper documents recent faulting at English Hill and is the first time late Quaternary, surface-rupture faulting has been recognized in the middle Mississippi River Valley region outside of the New Madrid seismic zone. This has important implications for earthquake assessment in the midcontinent.

Drilling the centre of the Thuringian Basin, Germany, to decipher potential interrelation between shallow and deep fluid systems

NASA Astrophysics Data System (ADS)

Kukowski, Nina; Totsche, Kai Uwe; Abratis, Michael; Habisreuther, Annett; Ward, Timothy; Influins Drilling-Team

2014-05-01

To shed light on the coupled dynamics of near surface and deep fluids in a sedimentary basin on various scales, ranging from the pore scale to the extent of an entire basin, is of paramount importance to understand the functioning of sedimentary basins fluid systems and therefore e.g. drinking water supply. It is also the fundamental goal of INFLUINS (INtegrated FLuid dynamics IN Sedimentary basins), a research initiative of several groups from Friedrich-Schiller University of Jena and their partners. This research association is focusing on the nearby Thuringian basin, a well confined, small intra-continental sedimentary basin in Germany, as a natural geo laboratory. In a multidisciplinary approach, embracing different fields of geophysics like seismic reflection profiling or airborne geomagnetics, structural geology, sedimentology, hydrogeology, hydrochemistry and hydrology, remote sensing, microbiology and mineralogy, among others, and including both, field-based, laboratory-based and computer-based research, an integral INFLUINS topic is the potential interaction of aquifers within the basin and at its rims. The Thuringian basin, which is composed of sedimentary rocks from the latest Paleozoic and mainly Triassic, is particularly suited to undertake such research as it is of relative small size, about 50 to 100 km, easily accessible, and quite well known from previous studies, and therefore also a perfect candidate for deep drilling. After the acquisition of 76 km seismic reflection data in spring 2011, to get as much relevant data as possible from a deep drilling at the cross point between two seismic profiles with a limited financial budget, an optimated core sampling and measuring strategy including partial coring, borehole geophysics and pump tests as well as a drill hole design, which enables for later continuation of drilling down to the basement, had been developed. Drilling Triassic rocks from Keuper to lower Buntsandstein was successfully realised down to a final depth of 1179 m from late June to mid-September 2013. Here, we give an introduction into the layout of INFLUINS deep drilling together with a summary of preliminary results, e.g. on the nature of the boundaries between Muschelkalk and Buntsandstein, and between upper and middle Buntsandstein, a complete core recovery of upper Buntsandstein saliniferous formations as well as unexpectedly low porosity and permeability of potential aquifers.

Tectonic evolution of the Qumran Basin from high-resolution 3.5-kHz seismic profiles and its implication for the evolution of the northern Dead Sea Basin

NASA Astrophysics Data System (ADS)

Lubberts, Ronald K.; Ben-Avraham, Zvi

2002-02-01

The Dead Sea Basin is a morphotectonic depression along the Dead Sea Transform. Its structure can be described as a deep rhomb-graben (pull-apart) flanked by two block-faulted marginal zones. We have studied the recent tectonic structure of the northwestern margin of the Dead Sea Basin in the area where the northern strike-slip master fault enters the basin and approaches the western marginal zone (Western Boundary Fault). For this purpose, we have analyzed 3.5-kHz seismic reflection profiles obtained from the northwestern corner of the Dead Sea. The seismic profiles give insight into the recent tectonic deformation of the northwestern margin of the Dead Sea Basin. A series of 11 seismic profiles are presented and described. Although several deformation features can be explained in terms of gravity tectonics, it is suggested that the occurrence of strike-slip in this part of the Dead Sea Basin is most likely. Seismic sections reveal a narrow zone of intensely deformed strata. This zone gradually merges into a zone marked by a newly discovered tectonic depression, the Qumran Basin. It is speculated that both structural zones originate from strike-slip along right-bending faults that splay-off from the Jordan Fault, the strike-slip master fault that delimits the active Dead Sea rhomb-graben on the west. Fault interaction between the strike-slip master fault and the normal faults bounding the transform valley seems the most plausible explanation for the origin of the right-bending splays. We suggest that the observed southward widening of the Dead Sea Basin possibly results from the successive formation of secondary right-bending splays to the north, as the active depocenter of the Dead Sea Basin migrates northward with time.

Seismic Reflection Profiles Image the Rodgers Creek Fault and Cotati Basin Beneath Urban Santa Rosa, California

NASA Astrophysics Data System (ADS)

Williams, R. A.; Langenheim, V. E.; McLaughlin, R. J.; Stephenson, W. J.; Odum, J. K.

2008-12-01

The USGS in collaboration with the Network for Earthquake Engineering Simulation (NEES) group at the University of Texas, Austin, the Sonoma County Water Agency, the city of Santa Rosa, and with support from NSF, collected 13-km of high-resolution seismic-reflection data in two profiles on the Santa Rosa Plain. The purpose of this survey was to image basin structure and stratigraphy in this seismically-active area and to provide constraints for earthquake hazard assessment. We acquired the data using a 9,990 kg minivib I truck in P-wave mode, which swept from 15 to 120 Hz, along city streets and creek-side roads. The common- midpoint spacing of these data is 2.5 m while nominal fold is 36 traces. The Rodgers Creek fault, a northward extension of the Hayward fault which passes through the city of Santa Rosa, has not been imaged previously by seismic reflection data. The east-west trending Santa Rosa Creek profile images several faults including the steeply dipping Rodgers Creek fault as it passes near Doyle Elementary School. In this vicinity the fault zone appears to consist of at least two strands with a set of arched reflectors between them. West of the Rodgers Creek fault, and in general agreement with preexisting gravity data and geologic mapping, we interpret a sedimentary basin more than 1 km deep that underlies downtown Santa Rosa, which was heavily damaged in the 1906 earthquake. This basin shallows to the west as the profile crosses the southeastern side of Trenton Ridge, a concealed basement high. Reflectors within the basin show a thickening sequence of layered strata and apparent dips of about 10 degrees east in the 400 to 800 m depth range that decrease to about 1 degree at 50 m depth. These new data will help to constrain existing seismic velocity models for this area which currently show only flat-lying basin fill.

Imaging the Subsurface of the Thuringian Basin (Germany) on Different Spatial Scales

NASA Astrophysics Data System (ADS)

Goepel, A.; Krause, M.; Methe, P.; Kukowski, N.

2014-12-01

Understanding the coupled dynamics of near surface and deep fluid flow patterns is essential to characterize the properties of sedimentary basins, to identify the processes of compaction, diagenesis, and transport of mass and energy. The multidisciplinary project INFLUINS (Integrated FLUid dynamics IN Sedimentary basins) aims for investigating the behavior of fluids in the Thuringian Basin, a small intra-continental sedimentary basin in Germany, at different spatial scales, ranging from the pore scale to the extent of the entire basin. As hydraulic properties often significantly vary with spatial scales, e.g. seismic data using different frequencies are required to gain information about the spatial variability of elastic and hydraulic subsurface properties. For the Thuringian Basin, we use seismic and borehole data acquired in the framework of INFLUINS. Basin-wide structural imaging data are available from 2D reflection seismic profiles as well as 2.5D and 3D seismic travel time tomography. Further, core material from a 1,179 m deep drill hole completed in 2013 is available for laboratory seismic experiments on mm- to cm-scale. The data are complemented with logging data along the entire drill hole. This campaign yielded e.g. sonic and density logs allowing the estimation of in-situ P-velocity and acoustic impedance with a spatial resolution on the cm-scale and provides improved information about petrologic and stratigraphic variability at different scales. Joint interpretation of basin scale structural and elastic properties data with laboratory scale data from ultrasound experiments using core samples enables a detailed and realistic imaging of the subsurface properties on different spatial scales. Combining seismic travel time tomography with stratigraphic interpretation provides useful information of variations in the elastic properties for certain geological units and therefore gives indications for changes in hydraulic properties.

Deep-towed high resolution seismic imaging II: Determination of P-wave velocity distribution

NASA Astrophysics Data System (ADS)

Marsset, B.; Ker, S.; Thomas, Y.; Colin, F.

2018-02-01

The acquisition of high resolution seismic data in deep waters requires the development of deep towed seismic sources and receivers able to deal with the high hydrostatic pressure environment. The low frequency piezoelectric transducer of the SYSIF (SYstème Sismique Fond) deep towed seismic device comply with the former requirement taking advantage of the coupling of a mechanical resonance (Janus driver) and a fluid resonance (Helmholtz cavity) to produce a large frequency bandwidth acoustic signal (220-1050 Hz). The ability to perform deep towed multichannel seismic imaging with SYSIF was demonstrated in 2014, yet, the ability to determine P-wave velocity distribution wasn't achieved. P-wave velocity analysis relies on the ratio between the source-receiver offset range and the depth of the seismic reflectors, thus towing the seismic source and receivers closer to the sea bed will provide a better geometry for P-wave velocity determination. Yet, technical issues, related to the acoustic source directivity, arise for this approach in the particular framework of piezoelectric sources. A signal processing sequence is therefore added to the initial processing flow. Data acquisition took place during the GHASS (Gas Hydrates, fluid Activities and Sediment deformations in the western Black Sea) cruise in the Romanian waters of the Black Sea. The results of the imaging processing are presented for two seismic data sets acquired over gas hydrates and gas bearing sediments. The improvement in the final seismic resolution demonstrates the validity of the velocity model.

The role of thermal effect on mantle seismic anomalies from observations of GIA

NASA Astrophysics Data System (ADS)

Wu, P.; Wang, H. S.; Steffen, H.

2012-04-01

Recent advance in seismic tomography reveals the structure inside the mantle. An outstanding issue is the role of thermal versus non-thermal (e.g. compositional, partial melting) contribution to seismic velocity anomalies. Here we use observations of Glacial Isostatic Adjustment (GIA), e.g. global relative sea level data, GRACE observations (with recent hydrology contributions removed) and GPS crustal uplift rates in combination with 3D GIA models to address this issue. Both ICE-4G and ICE-5G models are tested, but ICE-4G gives much better overall fit to these observations. Also, several 1-D background viscosity profiles, with different viscosity contrast at 670 km depth have also been tested and the one that gives consistent results is model RF3 which has a moderate viscosity increase across 670 km. Lateral mantle viscosity variation is inferred from Ekstrom & Dziewonski's S20A seismic tomography model using a scaling law that includes both the effect of anharmonicity and anelasticity. Thermal contribution to seismic tomography appears as the beta factor in the scaling law. The values of beta in the upper mantle, shallow part of the lower mantle and the deep part of the lower mantle are allowed to be different and the solution space of the beta values is searched to find the best combination that gives the best fit to the GIA observations simultaneously. The result of our best model (RF3 with lateral heterogeneity) shows that thermal effect increases from about 65% in the upper mantle to 80% in the shallow part of the lower mantle and to about 100% in the deep lower mantle above the D" layer. This is consistent with temperature excess in the lower mantle from high core heating. However, the uncertainty increases from < 1% in the upper mantle to 20% in the shallow lower mantle and is not very well constrained in the deep lower mantle.

Mantle Subduction and Uplift of Intracontinental Mountains: A Case Study from the Chinese Tianshan Mountains within Eurasia.

PubMed

Li, Jinyi; Zhang, Jin; Zhao, Xixi; Jiang, Mei; Li, Yaping; Zhu, Zhixin; Feng, Qianwen; Wang, Lijia; Sun, Guihua; Liu, Jianfeng; Yang, Tiannan

2016-06-29

The driving mechanism that is responsible for the uplift of intracontinental mountains has puzzled geologists for decades. This study addresses this issue by using receiver function images across the Chinese Tianshan Mountains and available data from both deep seismic profiles and surface structural deformation. The near-surface structural deformation shows that the Tianshan crust experienced strong shortening during the Cenozoic. The receiver function image across the Tianshan Mountains reveals that the lithosphere of the Junggar Basin to the north became uncoupled along the Moho, and the mantle below the Moho subducted southwards beneath the northern part of the Tianshan Mountains, thereby thickening the overlying crust. Similar deep structures, however, are not observed under the Tarim Basin and the adjacent southern Tianshan Mountains. This difference in the deep structures correlates with geomorphological features in the region. Thus, a new model of mantle subduction, herein termed M-type subduction, is proposed for the mountain-building processes in intracontinental compressional settings. The available geomorphological, geological and seismic data in the literatures show that this model is probably suitable for other high, linear mountains within the continent.

Mantle Subduction and Uplift of Intracontinental Mountains: A Case Study from the Chinese Tianshan Mountains within Eurasia

PubMed Central

Li, Jinyi; Zhang, Jin; Zhao, Xixi; Jiang, Mei; Li, Yaping; Zhu, Zhixin; Feng, Qianwen; Wang, Lijia; Sun, Guihua; Liu, Jianfeng; Yang, Tiannan

2016-01-01

The driving mechanism that is responsible for the uplift of intracontinental mountains has puzzled geologists for decades. This study addresses this issue by using receiver function images across the Chinese Tianshan Mountains and available data from both deep seismic profiles and surface structural deformation. The near-surface structural deformation shows that the Tianshan crust experienced strong shortening during the Cenozoic. The receiver function image across the Tianshan Mountains reveals that the lithosphere of the Junggar Basin to the north became uncoupled along the Moho, and the mantle below the Moho subducted southwards beneath the northern part of the Tianshan Mountains, thereby thickening the overlying crust. Similar deep structures, however, are not observed under the Tarim Basin and the adjacent southern Tianshan Mountains. This difference in the deep structures correlates with geomorphological features in the region. Thus, a new model of mantle subduction, herein termed M-type subduction, is proposed for the mountain-building processes in intracontinental compressional settings. The available geomorphological, geological and seismic data in the literatures show that this model is probably suitable for other high, linear mountains within the continent. PMID:27353861

Crustal insights from gravity and aeromagnetic analysis: Central North Slope, Alaska

USGS Publications Warehouse

Saltus, R.W.; Potter, C.J.; Phillips, J.D.

2006-01-01

Aeromagnetic and gravity data are processed and interpreted to reveal deep and shallow information about the crustal structure of the central North Slope, Alaska. Regional aeromagnetic anomalies primarily reflect deep crustal features. Regional gravity anomalies are more complex and require detailed analysis. We constrain our geophysical models with seismic data and interpretations along two transects including the Trans-Alaska Crustal Transect. Combined geophysical analysis reveals a remarkable heterogeneity of the pre-Mississippian basement. In the central North Slope, pre-Mississippian basement consists of two distinct geophysical domains. To the southwest, the basement is dense and highly magnetic; this basement is likely mafic and mechanically strong, possibly acting as a buttress to basement involvement in Brooks Range thrusting. To the northeast, the central North Slope basement consists of lower density, moderately magnetic rocks with several discrete regions (intrusions?) of more magnetic rocks. A conjugate set of geophysical trends, northwest-southeast and southwest-northeast, may be a factor in the crustal response to tectonic compression in this domain. High-resolution gravity and aeromagnetic data, where available, reflect details of shallow fault and fold structure. The maps and profile models in this report should provide useful guidelines and complementary information for regional structural studies, particularly in combination with detailed seismic reflection interpretations. Future challenges include collection of high-resolution gravity and aeromagnetic data for the entire North Slope as well as additional deep crustal information from seismic, drilling, and other complementary methods. Copyrights ?? 2006. The American Association of Petroleum Geologists. All rights reserved.

Seismic imaging of the Formosa Ridge cold seep site offshore of southwestern Taiwan

NASA Astrophysics Data System (ADS)

Hsu, Ho-Han; Liu, Char-Shine; Morita, Sumito; Tu, Shu-Lin; Lin, Saulwood; Machiyama, Hideaki; Azuma, Wataru; Ku, Chia-Yen; Chen, Song-Chuen

2017-12-01

Multi-scale reflection seismic data, from deep-penetration to high-resolution, have been analyzed and integrated with near-surface geophysical and geochemical data to investigate the structures and gas hydrate system of the Formosa Ridge offshore of southwestern Taiwan. In 2007, dense and large chemosynthetic communities were discovered on top of the Formosa Ridge at water depth of 1125 m by the ROV Hyper-Dolphin. A continuous and strong BSR has been observed on seismic profiles from 300 to 500 ms two-way-travel-time below the seafloor of this ridge. Sedimentary strata of the Formosa Ridge are generally flat lying which suggests that this ridge was formed by submarine erosion processes of down-slope canyon development. In addition, some sediment waves and mass wasting features are present on the ridge. Beneath the cold seep site, a vertical blanking zone, or seismic chimney, is clearly observed on seismic profiles, and it is interpreted to be a fluid conduit. A thick low velocity zone beneath BSR suggests the presence of a gas reservoir there. This "gas reservoir" is shallower than the surrounding canyon floors along the ridge; therefore as warm methane-rich fluids inside the ridge migrate upward, sulfate carried by cold sea water can flow into the fluid system from both flanks of the ridge. This process may drive a fluid circulation system and the active cold seep site which emits both hydrogen sulfide and methane to feed the chemosynthetic communities.

Comparison of Shear-wave Profiles for a Compacted Fill in a Geotechnical Test Pit

NASA Astrophysics Data System (ADS)

Sylvain, M. B.; Pando, M. A.; Whelan, M.; Bents, D.; Park, C.; Ogunro, V.

2014-12-01

This paper investigates the use of common methods for geological seismic site characterization including: i) multichannel analysis of surface waves (MASW),ii) crosshole seismic surveys, and iii) seismic cone penetrometer tests. The in-situ tests were performed in a geotechnical test pit located at the University of North Carolina at Charlotte High Bay Laboratory. The test pit has dimensions of 12 feet wide by 12 feet long by 10 feet deep. The pit was filled with a silty sand (SW-SM) soil, which was compacted in lifts using a vibratory plate compactor. The shear wave velocity values from the 3 techniques are compared in terms of magnitude versus depth as well as spatially. The comparison was carried out before and after inducing soil disturbance at controlled locations to evaluate which methods were better suited to captured the induced soil disturbance.

EAGLE The controlled source experiment

NASA Astrophysics Data System (ADS)

Maguire, P. K. H.; Eagle Controlled Source Group

2003-04-01

In January 2003, a wide-angle reflection / refraction seismic project was carried out over the north-eastern section of the Main Ethiopian Rift as part of the international EAGLE (Ethiopia Afar Geoscientific Lithospheric Experiment) programme. EAGLE comprises a combination of passive and controlled source seismic experiments to determine the geometry and kinematics of a continental rift immediately prior to break-up, enabling the development of magmatic margin break-up models. A total of ˜900 seismic instruments were deployed along two 450km profiles, one along the axis of the Ethiopian Rift into the south-west corner of Afar; and a second across the rift, extending north and south across the uplifted, flood basalt covered, Ethiopian plateau. The two profiles intersect over the Nazret volcanic segment in the rift. This may be indicative of the transition from continental style rifting in which strain is accommodated on the rift bounding border faults, to a state where strain and magmatism have migrated to a narrow zone within the rift, a necessary pre-cursor to break-up. A further ˜300 instruments were deployed in a 100x100km^2 array around the intersection of the two profiles. A total of 16 borehole and 2 lake shots were fired into the network over a period of four days. The principal objectives of the controlled source project were to examine crustal strain, the distribution of crustal magmatic intrusions, the influence of pre-rift crustal property variations on rift development and also to provide a crustal seismic velocity distribution to improve images of the deep mantle, as well as earthquake locations derived from the EAGLE passive arrays.

IODP Expedition 340T: Borehole Logging at Atlantis Massif Oceanic Core Complex

NASA Astrophysics Data System (ADS)

Blackman, D.; Slagle, A.; Harding, A.; Guerin, G.; McCaig, A.

2013-03-01

Integrated Ocean Drilling Program (IODP) Expedition 340T returned to the 1.4-km-deep Hole U1309D at Atlantis Massif to carry out borehole logging including vertical seismic profiling (VSP). Seismic, resistivity, and temperature logs were obtained throughout the geologic section in the footwall of this oceanic core complex. Reliable downhole temperature measurements throughout and the first seismic coverage of the 800-1400 meters below seafloor (mbsf) portion of the section were obtained. Distinct changes in velocity, resistivity, and magnetic susceptibility characterize the boundaries of altered, olivine-rich troctolite intervals within the otherwise dominantly gabbroic se-quence. Some narrow fault zones also are associated with downhole resistivity or velocity excursions. Small deviations in temperature were measured in borehole fluid adjacent to known faults at 750 mbsf and 1100 mbsf. This suggests that flow of seawater remains active along these zones of faulting and rock alteration. Vertical seismic profile station coverage at zero offset now extends the full length of the hole, including the uppermost 150 mbsf, where detachment processes are expected to have left their strongest imprint. Analysis of wallrock properties, together with alteration and structural characteristics of the cores from Site U1309, highlights the likely interplay between lithology, structure, lithospheric hydration, and core complex evolution. doi:10.2204/iodp.sd.15.04.2013

Analyzing structural variations along strike in a deep-water thrust belt

NASA Astrophysics Data System (ADS)

Totake, Yukitsugu; Butler, Robert W. H.; Bond, Clare E.; Aziz, Aznan

2018-03-01

We characterize a deep-water fold-thrust arrays imaged by a high-resolution 3D seismic dataset in the offshore NW Borneo, Malaysia, to understand the kinematics behind spatial arrangement of structural variations throughout the fold-thrust system. The seismic volume used covers two sub-parallel fold trains associated with a series of fore-thrusts and back-thrusts. We measured fault heave, shortening value, fold geometries (forelimb dip, interlimb angle and crest depth) along strike in individual fold trains. Heave plot on strike projection allows to identify individual thrust segments showing semi-elliptical to triangular to bimodal patterns, and linkages of these segments. The linkage sites are marked by local minima in cumulative heave. These local heave minima are compensated by additional structures, such as small imbricate thrusts and tight folds indicated by large forelimb dip and small interlimb angle. Complementary profiles of the shortening amount for the two fold trains result in smoother gradient of total shortening across the structures. We interpret this reflects kinematic interaction between two fold-thrust trains. This type of along-strike variation analysis provides comprehensive understanding of a fold-thrust system and may provide an interpretative strategy for inferring the presence of complex multiple faults in less well-imaged parts of seismic volumes.

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

NASA Astrophysics Data System (ADS)

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

2015-12-01

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

Seismic evidence for silicate melt atop the 410-km mantle discontinuity

USGS Publications Warehouse

Revenaugh, Justin; Sipkin, S.A.

1994-01-01

LABORATORY results demonstrating that basic to ultrabasic melts become denser than olivine-rich mantle at pressures above 6 GPa (refs 1-3) have important implications for basalt petrogenesis, mantle differentiation and the storage of volatiles deep in the Earth. A density cross-over between melt and solid in the extensively molten Archaean mantle has been inferred from komatiitic volcanism and major-element mass balances, but present-day evidence of dense melt below the seismic low-velocity zone is lacking. Here we present mantle shear-wave impedance profiles obtained from multiple-ScS reverberation mapping for corridors connecting western Pacific subduction zone earthquakes with digital seismograph stations in eastern China, imaging a ~5.8% impedance decrease roughly 330 km beneath the Sea of Japan, Yellow Sea and easternmost Asia. We propose that this represents the upper surface of a layer of negatively buoyant melt lying on top of the olivine ??? ??- phase transition (the 410-km seismic discontinuity). Volatile-rich fluids expelled from the partial melt zone as it freezes may migrate upwards, acting as metasomatic agents and perhaps as the deep 'proto-source' of kimberlites. The remaining, dense, crystalline fraction would then concentrate above 410 km, producing a garnet-rich layer that may flush into the transition zone.

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

NASA Astrophysics Data System (ADS)

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

2018-03-01

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

Seismic imaging of a transform segment of the Maranhão-Barreirinhas-Ceará margin, NW Brazil

NASA Astrophysics Data System (ADS)

Schnurle, Philippe; Moulin, Maryline; Gallais, Flora; Afilhado, Alexandra; Afonso Dias, Nuno; Soares, José; Loureiro, Afonso; Fuck, Reinhardt; Cupertino, José; Viana, Adriano; Matias, Luís; Evain, Mikael; Aslanian, Daniel

2017-04-01

The structure of the North-East equatorial Brazilian margin was investigated during the MAGIC (Margins of brAzil, Ghana and Ivory Coast) seismic experiment, a project conducted by IFREMER (Institut Francais de Recherche pour l'Exploration de la Mer), UnB (University of Brasilia), FCUL (Faculdade de Ciências da Universidade de Lisboa) and Petrobras. The survey consists of 5 deep seismic profiles totaling 1900 km of marine multi-channel seismic reflection and wide angle acquisition with 143 deployments of short-period OBS's from the IFREMER pool. Three of the profiles were extended into land using Land Seismic Stations (LSS) from the Brazilian pool at a total of 50 points. This study focuses on the MC1 and MC5 wide-angle profiles: MC5 spans NW-SE 720 km in length, from the São Paulo Double Fracture Zone to the Borborema-Cearà margin. MC-1 spans parallel east of MC5, 360 km in length, in the presumed oceanic domain. Our main objective is to understand the fundamental processes which lead to the thinning and finally to the breakup of the continental crust in a specific context of a pull-apart system with two strike-slip borders. The experiment was devised to obtain the 2D structure along the profiles from joint pre-stack depth migration of the reflection data, and tomography and forward modeling of the OBS records. Along the MC1/MC5 wide-angle transects, 5 major sectors are identified: - the São Paulo Double Fracture Zone and the volcanic line associated to the southern São Paulo strike-slip zone presenting a 4.5 km thick volcano-sedimentary basin on top of a 5.5 km thick basement; - the intermediate domain, formed by the 4.5 km thick Basin III, the 7.5 km thick Basin II (interleaved by a 0.5-1 km thick volcanic layer), and the 5.5 km thick Basin I composing the continental slope. While the crust remains about 6 km thick, its acoustic velocity evolves from two-layer typical (4.8-6 km/s and 6.1-6.8 km/s) beneath Basin III to two-layer high velocity (6.1-6.8 km/s and 7.2-7.4 km/s) beneath Basin II and I, interpreted as exhumed lower continental crust; - to the east, the oceanic crust, evolves to an 2 layers crust 5 km thick, characterized by typical oceanic crustal velocities and also overlain by 5.5 km of sedimentary deposits, spanning between the two main fracture zones that fringe the Maranhão-Barreirinhas-Ceará segment; - the 50 km wide necking zone, forming the Parnaiba Platform and associated Ceará Basins, where the upper and lower crust thin abruptly; - the Medio Coreaù and Ceará Central thrust belt, where the unthinned continental crust thickness reaches 32 km. Keywords: North-East equatorial Brazil, transform margin, deep seismic structure

Stress on the seismogenic and deep creep plate interface during the earthquake cycle in subduction zones

NASA Astrophysics Data System (ADS)

Ruff, Larry J.

2001-04-01

The deep creep plate interface extends from the down-dip edge of the seismogenic zone down to the base of the overlying lithosphere in subduction zones. Seismogenic/deep creep zone interaction during the earthquake cycle produces spatial and temporal variations in strains within the surrounding elastic material. Strain observations in the Nankai subduction zone show distinct deformation styles in the co-seismic, post-seismic, and inter-seismic phases associated with the 1946 great earthquake. The most widely used kinematic model to match geodetic observations has been a 2-D Savage-type model where a plate interface is placed in an elastic half-space and co-seismic slip occurs in the upper seismogenic portion of the interface, while inter-seismic deformation is modeled by a locked seismogenic zone and a constant slip velocity across the deep creep interface. Here, I use the simplest possible 2-D mechanical model with just two blocks to study the stress interaction between the seismogenic and deep creep zones. The seismogenic zone behaves as a stick-slip interface where co-seismic slip or stress drop constrain the model. A linear constitutive law for the deep creep zone connects the shear stress (σ) to the slip velocity across the plate interface (s') with the material property of interface viscosity (ζ ) as: σ = ζ s'. The analytic solution for the steady-state two-block model produces simple formulas that connect some spatially-averaged geodetic observations to model quantities. Aside from the basic subduction zone geometry, the key observed parameter is τ, the characteristic time of the rapid post-seismic slip in the deep creep interface. Observations of τ range from about 5 years (Nankai and Alaska) to 15 years (Chile). The simple model uses these values for τ to produce estimates for ζ that range from 8.4 × 1013 Pa/m/s (in Nankai) to 6.5 × 1014 Pa/m/s (in Chile). Then, the model predicts that the shear stress acting on deep creep interface averaged over the earthquake cycle ranges from 0.1 MPa (Nankai) to 1.7 MPa (Chile). These absolute stress values for the deep creep zone are slightly smaller than the great earthquake stress drops. Since the great earthquake recurrence time ( T recur) is much larger than τ for Nankai, Alaska, and Chile, the model predicts that rapid post-seismic creep should re-load the seismogenic zone to about (1/3) of the co-seismic change; geodetically observed values range from about (1/10) to more than (1/2). Also, for the case of (Trecur/τ) ≫1, the model predicts that the slip velocity across the deep creep interface during the inter-seismic phase should be about (2/3) the plate tectonic velocity (R). Thus the deep creep velocity used in Savage-type models should be less than R. Even complex 3-D models with non-linear creep laws should make a similar prediction for inter-seismic deep creep rates. At present, it seems that geodetic observations at Nankai and other subduction zones are more consistent with a deep creep rate of R rather than (2/3) R. This discrepancy is quite puzzling and is difficult to explain in the context of a 2-D steady-state earthquake cycle model. Future observational and modeling studies should examine this apparent discrepancy to gain more understanding of the earthquake cycle in subduction zones.

2.5D S-wave velocity model of the TESZ area in northern Poland from receiver function analysis

NASA Astrophysics Data System (ADS)

Wilde-Piorko, Monika; Polkowski, Marcin; Grad, Marek

2016-04-01

Receiver function (RF) locally provides the signature of sharp seismic discontinuities and information about the shear wave (S-wave) velocity distribution beneath the seismic station. The data recorded by "13 BB Star" broadband seismic stations (Grad et al., 2015) and by few PASSEQ broadband seismic stations (Wilde-Piórko et al., 2008) are analysed to investigate the crustal and upper mantle structure in the Trans-European Suture Zone (TESZ) in northern Poland. The TESZ is one of the most prominent suture zones in Europe separating the young Palaeozoic platform from the much older Precambrian East European craton. Compilation of over thirty deep seismic refraction and wide angle reflection profiles, vertical seismic profiling in over one hundred thousand boreholes and magnetic, gravity, magnetotelluric and thermal methods allowed for creation a high-resolution 3D P-wave velocity model down to 60 km depth in the area of Poland (Grad et al. 2016). On the other hand the receiver function methods give an opportunity for creation the S-wave velocity model. Modified ray-tracing method (Langston, 1977) are used to calculate the response of the structure with dipping interfaces to the incoming plane wave with fixed slowness and back-azimuth. 3D P-wave velocity model are interpolated to 2.5D P-wave velocity model beneath each seismic station and synthetic back-azimuthal sections of receiver function are calculated for different Vp/Vs ratio. Densities are calculated with combined formulas of Berteussen (1977) and Gardner et al. (1974). Next, the synthetic back-azimuthal sections of RF are compared with observed back-azimuthal sections of RF for "13 BB Star" and PASSEQ seismic stations to find the best 2.5D S-wave models down to 60 km depth. National Science Centre Poland provided financial support for this work by NCN grant DEC-2011/02/A/ST10/00284.

Structure Deformation of the Minjiang and Huya Fault, the Eastern Margin of the Tibetan Plateau Revealed by Deep Seismic Reflection Profiles

NASA Astrophysics Data System (ADS)

Gao, R.; Wang, H.; Li, W.; Li, H.

2014-12-01

The Minshan region, located along the eastern margin of the Tibetan Plateau north of the Sichuan Basin, provides an important natural laboratory in which to study the patterns of deformation and their relationship to mountain building at the margin of the plateau. The Minshan range is bounded by the Minjiang fault to the west and Huya fault to the east. Evidence from the Neotectonics sediments suggests that deformation along the western Min Shan may reflect the surface response to thickening of a weak lower crust at the margin of the Tibetan Plateau (Kirby et al., 2000). In 2014, two deep seismic profiles was carried out across the Minjiang fault (55 km long) and Huya fault (45 km long) respectively, supported by China geological survey project (No.1212011220260) and Crust Probe Project of China (SinoProbe-02-01). The recording of seismic waves from 4 big shots (500kg), 100 middle shots (120 kg) and 400 small shots (36 kg) were employed. The geophones spacing is 50 m. The preliminary stack sections provide us a detailed deformation mechanism of the Minshan region for the first time. The result shows that: (1) The Huya fault section shows different reflection characteristics on the west and east flank. (2) The Moho reflection beneath the Huya fault, which appeared at 12-13 s two-way time, tilts from the east to the west. (3) The Minjiang fault shows as a series of thrust nappe in the upper crust. (4) A strong reflector appears in the middle crust of the Minjiang section at 8-9 s two-way times, and it dips down to the lower crust from west to east.

Interpretations from multichannel seismic-reflection profiles of the deep crust crossing South Carolina and Georgia from the Appalachian Mountains to the Atlantic Coast

USGS Publications Warehouse

Behrendt, John C.

1985-01-01

The Appalachian décollement does not appear continuous from the Appalachian Mountains to the coast but rather appears to extend southeastward only to the Carolina slate belt. A series of reflections on lines S4, S6, and S8 and on the COCORP line is interpreted as evidence of southeastward-dipping imbricate faults, from the Brevard fault on the northwest to beyond the Augusta fault, which marks the southeastern extent of the Eastern Piedmont fault zone. The Carolina slate belt is characterized on the four seismic profiles by a complex series of diffractions and reflections extending from less than 1 s to 8 s. These arrivals are possibly the result of layering in the metasedimentary rocks complexly disrupted by the imbricate faults. A number of Triassic (?) basins are apparent in the reflection data for the rifted Charleston terrane identified from low-gradient magnetic anomalies.

Deployment of the Oklahoma borehole seismic experiment

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

Harben, P.E.; Rock, D.W.

1989-01-20

This paper discusses the Oklahoma borehole seismic experiment, currently in operation, set up by members of the Lawrence Livermore National Laboratory Treaty Verification Program and the Oklahoma Geophysical Observatory to determine deep-borehole seismic characteristics in geology typical of large regions in the Soviet Union. We evaluated and logged an existing 772-m deep borehole on the Observatory site by running caliper, cement bonding, casing inspection, and hole-deviation logs. Two Teledyne Geotech borehole-clamping seismometers were placed at various depths and spacings in the deep borehole. Currently, they are deployed at 727 and 730 m. A Teledyne Geotech shallow-borehole seismometer was mounted inmore » a 4.5-m hole, one meter from the deep borehole. The seismometers' system coherency were tested and found to be excellent to 35 Hz. We have recorded seismic noise, quarry blasts, regional earthquakes and teleseisms in the present configuration. We will begin a study of seismic noise and attenuation as a function of depth in the near future. 7 refs., 18 figs.« less

Fault zone characteristics and basin complexity in the southern Salton Trough, California

USGS Publications Warehouse

Persaud, Patricia; Ma, Yiran; Stock, Joann M.; Hole, John A.; Fuis, Gary S.; Han, Liang

2016-01-01

Ongoing oblique slip at the Pacific–North America plate boundary in the Salton Trough produced the Imperial Valley (California, USA), a seismically active area with deformation distributed across a complex network of exposed and buried faults. To better understand the shallow crustal structure in this region and the connectivity of faults and seismicity lineaments, we used data primarily from the Salton Seismic Imaging Project to construct a three-dimensional P-wave velocity model down to 8 km depth and a velocity profile to 15 km depth, both at 1 km grid spacing. A VP = 5.65–5.85 km/s layer of possibly metamorphosed sediments within, and crystalline basement outside, the valley is locally as thick as 5 km, but is thickest and deepest in fault zones and near seismicity lineaments, suggesting a causative relationship between the low velocities and faulting. Both seismicity lineaments and surface faults control the structural architecture of the western part of the larger wedge-shaped basin, where two deep subbasins are located. We estimate basement depths, and show that high velocities at shallow depths and possible basement highs characterize the geothermal areas.

Evidence of post-Pleistocene faults on New Jersey Atlantic outer continental shelf

USGS Publications Warehouse

Sheridan, R.E.; Knebel, H.J.

1976-01-01

Recently obtained high-resolution seismic profiles (400-4,000-Hz band) show evidence of faults in shallow sedimentary strata near the edge of the Atlantic continental shelf off New Jersey. Apparent normal faults having a throw of about 1.5 m displace sediments to within 7 m of the sea floor. The faults appear to be overlain by undeformed horizontal beds of relatively recent age. Several faults 1 to 2 km apart strike approximately N70°E and dip northwest. The data suggest that the faults are upthrown on the southeast.Projection of the faults on the high-resolution profiles to a nearby multichannel seismic-reflection profile indicates that these shallow faults might be the near-surface expression of a more fundamental deep-seated fault. Several prominent reflectors in the multichannel records are offset by a high-angle normal fault reaching depths of 4.0 to 5.0 sec (6.0 to 6.5 km). The deep fault on the multichannel line also is upthrown on the southeast. Throws of as much as 90 m are apparent at depth, but offsets of as much as 10 m could be present in the shallower parts of the section that may not be resolved in the multichannel data.The position and strike of these faults coincide with and parallel the East Coast magnetic anomaly interpreted as the fundamental seaward basement boundary of the Baltimore Canyon trough. Recurring movements along such boundary faults are expected theoretically if the marginal basins are subsiding in response to the plate rotation of North America and seafloor spreading in the Atlantic.

The Crustal Structure And CTBT Monitoring Of India: New Insights From Deep Seismic Profiling

DTIC Science & Technology

2000-09-01

transitional type crust as a major source of Deccan trap flows. The Narmada-Son lineament is the most conspicuous linear geological feature in the... Deccan proto-continents) buckling of the upper and middle crustal layers of the proto-continents took place, resulting in the western block’s lower...crustal column subducting below the Deccan proto-continents. Thus, the collision process was of such severe magnitude that the impact was seen in both

Remote sensing in marine environment - acquiring, processing, and interpreting GLORIA sidescan sonor images of deep sea floor

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

O'Leary, D.W.

1989-03-01

The US Geological Survey's remote sensing instrument for regional imaging of the deep sea floor (> 400 m water depth) is the GLORIA (Geologic Long-Range Inclined Asdic) sidescan sonar system, designed and operated by the British Institute of Oceanographic Sciences. A 30-sec sweep rate provides for a swath width of approximately 45 km, depending on water depth. The return signal is digitally recorded as 8 bit data to provide a cross-range pixel dimension of 50 m. Postcruise image processing is carried out by using USGS software. Processing includes precision water-column removal, geometric and radiometric corrections, and contrast enhancement. Mosaicking includesmore » map grid fitting, concatenation, and tone matching. Seismic reflection profiles, acquired along track during the survey, are image correlative and provide a subsurface dimension unique to marine remote sensing. Generally GLORIA image interpretation is based on brightness variations which are largely a function of (1) surface roughness at a scale of approximately 1 m and (2) slope changes of more than about 4/degrees/ over distances of at least 50 m. Broader, low-frequency changes in slope that cannot be detected from the Gloria data can be determined from seismic profiles. Digital files of bathymetry derived from echo-sounder data can be merged with GLORIA image data to create relief models of the sea floor for geomorphic interpretation of regional slope effects.« less

Does seismic activity control carbon exchanges between transform-faults in old ocean crust and the deep sea? A hypothesis examined by the EU COST network FLOWS

NASA Astrophysics Data System (ADS)

Lever, M. A.

2014-12-01

The European Cooperation in Science and Technology (COST)-Action FLOWS (http://www.cost.eu/domains_actions/essem/Actions/ES1301) was initiated on the 25th of October 2013. It is a consortium formed by members of currently 14 COST countries and external partners striving to better understand the interplay between earthquakes and fluid flow at transform-faults in old oceanic crust. The recent occurrence of large earthquakes and discovery of deep fluid seepage calls for a revision of the postulated hydrogeological inactivity and low seismic activity of old oceanic transform-type plate boundaries, and indicates that earthquakes and fluid flow are intrinsically associated. This Action merges the expertise of a large number of research groups and supports the development of multidisciplinary knowledge on how seep fluid (bio)chemistry relates to seismicity. It aims to identify (bio)geochemical proxies for the detection of precursory seismic signals and to develop innovative physico-chemical sensors for deep-ocean seismogenic faults. National efforts are coordinated through Working Groups (WGs) focused on 1) geophysical and (bio)geochemical data acquisition; 2) modelling of structure and seismicity of faults; 3) engineering of deep-ocean physico-chemical seismic sensors; and 4) integration and dissemination. This poster will illustrate the overarching goals of the FLOWS Group, with special focus to research goals concerning the role of seismic activity in controlling the release of carbon from the old ocean crust into the deep ocean.

Delineation of faulting and basin geometry along a seismic reflection transect in urbanized San Bernardino Valley, California

USGS Publications Warehouse

Stephenson, W.J.; Odum, J.K.; Williams, R.A.; Anderson, M.L.

2002-01-01

Fourteen kilometers of continuous, shallow seismic reflection data acquired through the urbanized San Bernardino Valley, California, have revealed numerous faults between the San Jacinto and San Andreas faults as well as a complex pattern of downdropped and uplifted blocks. These data also indicate that the Loma Linda fault continues northeastward at least 4.5 km beyond its last mapped location on the southern edge of the valley and to within at least 2 km of downtown San Bernardino. Previously undetected faults within the valley northeast of the San Jacinto fault are also imaged, including the inferred western extension of the Banning fault and several unnamed faults. The Rialto-Colton fault is interpreted southwest of the San Jacinto fault. The seismic data image the top of the crystalline basement complex across 70% of the profile length and show that the basement has an overall dip of roughly 10?? southwest between Perris Hill and the San Jacinto fault. Gravity and aeromagnetic data corroborate the interpreted location of the San Jacinto fault and better constrain the basin depth along the seismic profile to be as deep as 1.7 km. These data also corroborate other fault locations and the general dip of the basement surface. At least 1.2 km of apparent vertical displacement on the basement is observed across the San Jacinto fault at the profile location. The basin geometry delineated by these data was used to generate modeled ground motions that show peak horizontal amplifications of 2-3.5 above bedrock response in the 0.05- to 1.0-Hz frequency band, which is consistent with recorded earthquake data in the valley.

The complex emplacement dynamics and tsunami genesis of the 1888 Ritter Island sector collapse from 3D seismic data

NASA Astrophysics Data System (ADS)

Urlaub, M.; Karstens, J.; Berndt, C.; Watt, S. F.; Micallef, A.; Klaucke, I.; Klaeschen, D.; Brune, S.; Kühn, M.

2017-12-01

On March 13 1888, a large sector of the subaerial and submarine edifice of Ritter Island (Papua New Guinea) collapsed and slid into the Bismarck Sea, triggering a tsunami with run-up heights of more than 25 m on the neighboring islands. The tsunami traveled for more than 600 km and caused destruction in several settlements. German colonists described in detail the timing of the arriving waves. During research cruise SO252 onboard RV Sonne, we collected a comprehensive set of multibeam and sediment echosounder data, seafloor video footage, rock samples, 2D seismic profiles, and a 60 km2 high-resolution Pcable 3D seismic cube. This dataset, combined with the historic eyewitness accounts, allows detailed reconstruction of the large-scale volcanic sector collapse and the associated tsunami genesis. The 3D seismic cube reveals a change of emplacement dynamics during the collapse of the volcanic edifice. The initial failure occurred along a deep slide plane extending from the volcanic cone up to 300 m deep into the seafloor sediments adjacent to the volcanic edifice. Movement of large, intact sediment blocks and shortening characterize this deep-rooted mass-movement. In contrast to the well-preserved mobilization structures in the deep part of the volcanic edifice related to the initial phase of mass movement, there are hardly any deposits of the upper part of the volcanic cone comprising of well-stratified volcaniclastic layers. The 2 km3 cone was mobilized in the final stage of the sector collapse and its highly energetic slide mass eroded deeply into the previously emplaced slide deposits. The fast moving mass was channelized between two volcanic ridges, transported into the basin west of Sakar Island, and then deposited more than 30 km away from its source. We interpret the separation into two phases as the result of decoupling of the sliding mass of the cone from the deeper volcanic edifice. This process may be explained by gravitational acceleration of the sliding mass or a phreatomagmatic explosion due to the contact of the magmatic conduit with seawater.

Automatic Seismic-Event Classification with Convolutional Neural Networks.

NASA Astrophysics Data System (ADS)

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

2017-12-01

Active volcanoes exhibit a wide range of seismic signals, providing vast amounts of unlabelled volcano-seismic data that can be analyzed through the lens of artificial intelligence. However, obtaining high-quality labelled data is time-consuming and expensive. Deep neural networks can process data in their raw form, compute high-level features and provide a better representation of the input data distribution. These systems can be deployed to classify seismic data at scale, enhance current early-warning systems and build extensive seismic catalogs. In this research, we aim to classify spectrograms from seven different seismic events registered at "Volcán de Fuego" (Colima, Mexico), during four eruptive periods. Our approach is based on convolutional neural networks (CNNs), a sub-type of deep neural networks that can exploit grid structure from the data. Volcano-seismic signals can be mapped into a grid-like structure using the spectrogram: a representation of the temporal evolution in terms of time and frequency. Spectrograms were computed from the data using Hamming windows with 4 seconds length, 2.5 seconds overlapping and 128 points FFT resolution. Results are compared to deep neural networks, random forest and SVMs. Experiments show that CNNs can exploit temporal and frequency information, attaining a classification accuracy of 93%, similar to deep networks 91% but outperforming SVM and random forest. These results empirically show that CNNs are powerful models to classify a wide range of volcano-seismic signals, and achieve good generalization. Furthermore, volcano-seismic spectrograms contains useful discriminative information for the CNN, as higher layers of the network combine high-level features computed for each frequency band, helping to detect simultaneous events in time. Being at the intersection of deep learning and geophysics, this research enables future studies of how CNNs can be used in volcano monitoring to accurately determine the detection and location of seismic events.

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

NASA Astrophysics Data System (ADS)

Juhojuntti, Niklas; Bergman, Stefan; Olsson, Sverker

2013-04-01

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

New Inquiry into Distribution and Mechanism of Deep Moonquakes with Recently Identified Seismic Events

NASA Technical Reports Server (NTRS)

Nakamura, Yosio

2005-01-01

The objectives of the project were (1) to complete our preceding effort, supported by NASA grant NAGS-1 1619, of searching for deep moonquakes in the far hemisphere of the Moon among the seismic events detected by the Apollo seismic array; and (2) to re-examine the distribution and mechanism of deep moonquakes in the light of the newly identified deep moonquakes. The project was originally planned for completion in three years, of which only the first year, covered by this report, was funded. As a result, we were able to address only the first objective during the period, and the major part of the second objective was left for the future.

Crust structure of the Northern Margin of North China Craton and adjacent region from Sinoprobe-02 North China seismic WAR/R experiment

NASA Astrophysics Data System (ADS)

Li, W.; Gao, R.; Keller, G. R.; Li, Q.; Cox, C. M.; Hou, H.; Guan, Y.

2011-12-01

The Central Asian Orogen Belt (CAOB) or Altaids, situated between the Siberian craton(SC) to the north and north China craton (NCC) with tarim to the south, is one of the world's largest accretionary orogens formed by subduction and accretion of juvenile material from the Neoproterozoic through the Paleozoic. The NCC is the oldest craton in China, which suffered Yanshan intercontinental orogenic process and lithosphere thinning in Mesozoic. In the past 20 years, remarkable studies about this region have been carried out and different tectonic models were proposed, however, some crucial geologic problems remain controversial. In order to obtain better knowledge of deep structure and properties of crust on the northern margin of north China craton, a 450 km long WAR/R section was completed jointly by Institute of Geology, CAGS and University of Oklahoma. Our 450 km long NW-SE WAR/R line extends from west end of the Yanshan orogen, across the Bainaimiao arc, Ondor sum subduction accretion complex to the Solonker suture zone. The recording of seismic waves from 8 explorations was conducted in 4 deployments of 300 reftek-125A records and single-channel 4.5Hz geophones with station spacing of 1km. The shooting procedure was employ 500 or 1500kg explosives in 4-5 or 15-23 boreholes at 40-45m depth. The sampling rate was 100 HZ, and recording time window was 1200s. The P wave field on the sections got high quality data for most part of the profile, but have low signal-to-noise for the south end, where closed to Beijing with a lot of ambient noise from traffic, industry and human activity. Arrivals from of refracted and reflected waves from sediments and basement (Pg), intracrust (Pcp, Plp) and Moho (Pmp) were typically observed, but Pn phase through the upper most mantle was only observed for 2 shots. Identification and correlation of seismic phases was done manually on computer screen Zplot software. Each trace has been bandpass filtered (1-20Hz) and normalized with AGC. The records were cut to 60s and reduced by 8 km/s. The initial velocity model began with a subhorizontal multilayer frame, in which the velocity was constructed and modified from adjacent deep seismic sounding sections for the profile, and the structure was constrained by the high-resolution deep seismic reflection stack section alone the same profile. The 2D ray-tracing program RAYINVR was used for forward modeling and inversion of travel times (Zelt, 1992), and VMED was used for creating and modifying velocity models. The travel time modeling was done using the top to bottom approach layer by layer. The velocity model was altered by trial and error, and travel times were calculated many times until the agreement between observed and calculated travel times were acceptable. Subsequently, the forward model was updated by damped least-squares inversion for the velocity and interface nodes. In our modeling, calculated travel times fit observed travel times for all trace with RMS of 0.1-0.2.The final velocity models derived for the profile reveals large variations both in structure and velocity. Supported by Sinoprobe-02 and US NSF PIRE grant (0730154)

New seismic Vp- and Vp/Vs- models of HUKKA 2007 wide-angle reflection and refraction profile in northern Fennoscandian Shield

NASA Astrophysics Data System (ADS)

Tiira, T.; Janik, T.; Kozlovskaya, E.; Grad, M.; Korja, A.; Komminaho, K.; Hegedüs, E.; Kovács, C. A.; Silvennoinen, H.; Brückl, E.

2012-04-01

We study the block structure within accreationary orogens. We present an example from northern part of the Fennoscandian Shield transected by deep seismic sounding profile HUKKA 2007. The 455 km long profile runs in NNW-SSE direction from Kittilä in northwestern Finnish Lapland to Kostamush in Russia near central part of the border between Finland and Russia. We present 2-D seismic velocity model (Vp and Vp/Vs ratio in the crust, depth to the Moho and depth to the intracrustal reflectors) along HUKKA 2007 wide-angle reflection and refraction profile in northern Finland. Commercial and military chemical explosions at 7 shot points were used as sources of the seismic energy. The shots were recorded by 115 recording stations deployed along the profile with an average station spacing of 3.45 km. The field recordings were cut and sorted into shot gathers. The 2-D velocity model of the HUKKA 2007 profile was developed by SEIS83 forward raytracing package using arrivals of major refracted and reflected P- and S-wave phases. In general the velocities vary in the upper crust between 5.8 and 6.1 km/s. Interesting features are three high P wave velocity (6.30-6.35 km/s) bodies in the upper crust. Two small bodies lie close to surface at first 100 km and the third one can be followed from 200 to 350 km along the profile reaching depth of 5-10 km. The central part of the profile (between 120 and 220 km) has a zone of low (lower than 6 km/s) P-wave velocity in the uppermost crust. This zone is about 4 km thick. In addition, the velocity model along the HUKKA 2007 profile shows significant difference in crustal velocity structure between the northern (up to 120 km) and southern parts of the profile. The differences in P-wave velocities and Vp/Vs ratio can be followed throughout the crust down to the Moho boundary. This suggests that the HUKKA 2007 profile transects a major terrane boundary. However, the position of this boundary with respect to major crustal units is controversial. It may be the boundary that separates the pristine parts of the Archean Karelian craton from those parts reworked in the Paleoproterozoic. Alternatively, it can be the boundary that separates the Karelian craton from the Belomorian mobile belt.

Geophysical evidence for a transform margin offshore Western Algeria: a witness of a subduction-transform edge propagator?

NASA Astrophysics Data System (ADS)

Badji, Rabia; Charvis, Philippe; Bracene, Rabah; Galve, Audrey; Badsi, Madjid; Ribodetti, Alessandra; Benaissa, Zahia; Klingelhoefer, Frauke; Medaouri, Mourad; Beslier, Marie-Odile

2015-02-01

For the first time, a deep seismic data set acquired in the frame of the Algerian-French SPIRAL program provides new insights regarding the origin of the westernmost Algerian margin and basin. We performed a tomographic inversion of traveltimes along a 100-km-long wide-angle seismic profile shot over 40 ocean bottom seismometers offshore Mostaganem (Northwestern Algeria). The resulting velocity model and multichannel seismic reflection profiles show a thin (3-4 km thick) oceanic crust. The narrow ocean-continent transition (less than 10 km wide) is bounded by vertical faults and surmounted by a narrow almost continuous basin filled with Miocene to Quaternary sediments. This fault system, as well as the faults organized in a negative-flower structure on the continent side, marks a major strike-slip fault system. The extremely sharp variation of the Moho depth (up to 45 ± 3°) beneath the continental border underscores the absence of continental extension in this area. All these features support the hypothesis that this part of the margin from Oran to Tenes, trending N65-N70°E, is a fossil subduction-transform edge propagator fault, vestige of the propagation of the edge of the Gibraltar subduction zone during the westward migration of the Alborán domain.

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).

The Investigation of a Sinkhole Area in Germany by Near-Surface Active Seismic Tomography

NASA Astrophysics Data System (ADS)

Tschache, S.; Becker, D.; Wadas, S. H.; Polom, U.; Krawczyk, C. M.

2017-12-01

In November 2010, a 30 m wide and 17 m deep sinkhole occurred in a residential area of Schmalkalden, Germany, which fortunately did not harm humans, but led to damage of buildings and property. Subsequent geoscientific investigations showed that the collapse was naturally caused by the subrosion of sulfates in a depth of about 80 m. In 2012, an early warning system was established including 3C borehole geophones deployed in 50 m depth around the backfilled sinkhole. During the acquisition of two shallow 2D shear wave seismic profiles, the signals generated by a micro-vibrator at the surface were additionally recorded by the four borehole geophones of the early warning system and a VSP probe in a fifth borehole. The travel time analysis of the direct arrivals enhanced the understanding of wave propagation in the area. Seismic velocity anomalies were detected and related to structural seismic images of the 2D profiles. Due to the promising first results, the experiment was further extended by distributing vibration points throughout the whole area around the sinkhole. This time, micro-vibrators for P- and S-wave generation were used. The signals were recorded by the borehole geophones and temporary installed seismometers at surface positions close to the boreholes. The travel times and signal attenuations are evaluated to detect potential instable zones. Furthermore, array analyses are performed. The first results reveal features in the active tomography datasets consistent with structures observed in the 2D seismic images. The advantages of the presented method are the low effort and good repeatability due to the permanently installed borehole geophones. It has the potential to determine P-wave and S-wave velocities in 3D. It supports the interpretation of established investigation methods as 2D surface seismics and VSP. In our further research we propose to evaluate the suitability of the method for the time lapse monitoring of changes in the seismic wave propagation, which could be related to subrosion processes.

Crustal architecture of an inverted back arc rift basin, Niigata, central Japan

NASA Astrophysics Data System (ADS)

Sato, H.; Abe, S.; Kawai, N.; Saito, H.; Kato, N.; Ishiyama, T.; Iwasaki, T.; Kurashimo, E.; Inaba, M.; Van Horne, A.

2012-04-01

A back arc rift basin, formed during the Miocene opening of the Japan Sea, now uplifted and exposed in Niigata, central Japan, provides an exceptional opportunity to study a back arc rift formed on a short time scale and in a still active setting for the present day shortening deformation. Due to stress build up before the 2011 Tohoku earthquake (M9), two damaging earthquakes (M6.8) occurred in 2004 and 2007 in this inverted rift basin. Deep seismic profiling was performed along four seismic lines between 2008 and 2011. We used onshore-offshore deep seismic reflection profiling to examine the crustal architecture of the back arc basin, in particular the geometry of the source faults. We further applied refraction tomography analysis to distinguish between previously undifferentiated syn-rift volcanics and pre-rift Mesozoic rock based on P-wave velocity. Our findings indicate that the Miocene rift structure created during the extensional phase regulates the style of deformation and the geometry of the source faults in the current compressional regime. Syn-rift volcanics with a maximum thickness of 6 km filled the fault controlled basins as rifting proceeded. The volcanism was bimodal, comprising a reflective unit of mafic rocks around the rift axis and a non-reflective unit of felsic rocks near the margins of the basins. Once rifting ended, thermal subsidence, and subsequently, mechanical subsidence related to the onset of the compressional regime, allowed deposition of up to 5 km of post-rift, deep marine to fluvial sedimentation, including the Teradomari Formation, an over-pressured mudstone in the middle of the section that later became an important shallow detachment layer. Continued compression has caused fault-related fold and wedge thrusting in the post-rift sedimentary strata which are highly deformed by thin-skin style deformation. Since the Pliocene, normal faults created during the rift phase have been reactivated as reverse faults, including a shallow detachment in the Teradomari Formation which forms a complicated shortened deformation structure. Quaternary geomorphology suggests ongoing shortening. Transform faults inherited from the rift stage control the extent of present day reverse source faults and more importantly, earthquake magnitude.

The GEORIFT 2013 wide-angle seismic profile, along Pripyat-Dnieper-Donets Basin

NASA Astrophysics Data System (ADS)

Starostenko, Vitaliy; Janik, Tomasz; Yegorova, Tamara; Czuba, Wojciech; Sroda, Piotr; Lysynchuk, Dmytro; Aizberg, Roman; Garetsky, Radim; Karataev, German; Gribik, Yaroslav; Farfuliak, Lliudmyla; Kolomiyets, Katerina; Omelchenko, Victor; Gryn, Dmytro; Guterch, Aleksander; Komminaho, Kari; Legostaeva, Olga; Thybo, Hans; Tiira, Timo; Tolkunov, Anatoly

2017-04-01

The GEORIFT 2013 deep seismic sounding (DSS) experiment was carried in August 2013 on territory of Belarus and Ukraine in wide international co-operation. The aim of the work is to study basin architecture and the deep structure of the Pripyat-Dnieper-Donets Basin (PDDB), which is the deepest and best studied Palaeozoic rift basin in Europe. The PDDB locates in the southern part of the East European Craton (EEC) and crosses in NW direction the Sarmatia, the southernmost of three major segments forming the EEC. The long PDDB was formed by Late Devonian rifting in the arch of the ancient Sarmatian shield. During the Late Devonian, rifting, associated with domal basement uplift and magmatism, was widespread in the EEC from the PDDB rift basin in the south to Eastern Barents Sea in the north. The GEORIFT 2013 runs in NW-SE direction along the PDDB and crosses the Pripyat Trough and Dnieper Graben separated by Bragin uplift of the basement. The total profile length was 675 km: 315 km on the Belarusian territory and 360 km in Ukraine. The field acquisition included 14 shot points (charge 600-1000 kg of TNT), and 309 recording stations every 2.2 km. The data quality of the data was good, with visible first arrivals even up to 670 km. We present final model of the structure to the depth of 80 km. Ray-tracing forward modelling (SEIS83 package) was used for the modelling of the seismic data. The thickness of the sedimentary layer (Vp < 6.0 km/s) changes along the profile from 1-4 km in the NW, through 5 km in the central part, to 10-13 km in the SE part of the profile. In 330-530 km distance range, an updoming of the lower crust (with Vp of 7.1 km/s) to 25 km depth is observed. Large variations in the internal structure of the crust and the Moho topography were detected. The depth of the Moho varies from 47 km in the northwestern part of the model, to 40 km in central part, and to 38 km in the southeastern part of the profile. The sub-Moho velocities are 8.25 km/s. Second, near-horizontal mantle discontinuity was found in the northwestern part of the profile at the depth of 50-47 km. It dips to the depth of 60 km at distances of 360-405 km, similarly as on crossing EUROBRIDGE'97 profile (Thybo et al., 2003). In the central part of the profile (distances 180-330 km and 300-480 km) two reflectors were found in the lower lithosphere at depths of about 62 km and 75 km, respectively.

Sedimentation in the Kane fracture zone, western North Atlantic

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

Jaroslow, G.E.

1991-03-01

The Kane fracture zone, a deep narrow trough in oceanic crust, has provided an ideal depocenter for reservation on the seismic stratigraphic record of the North Atlantic basin. The acoustic stratigraphy in single-channel and multichannel seismic reflection profiles crossing the Kane fracture zone in the western North Atlantic has been examined in order to scrutinize age processes within a fracture zone. Maps of total sediment thickness have provided insight into overall sediment distribution and the influence of topography on sedimentation. Eight reflectors have been traced and correlated with lithostratigraphy at Deep Sea Drilling Project (DSDP) sites. The Bermuda Rise, amore » prominent topographic feature, has had a profound effect on the distribution of sediments within the fracture zone. Since late Eocene, the rise has blocked transport by turbidity currents of terrigenous sediments to distal portions of the fracture valley. A 1,000-m-thick turbidite pond within the fracture zone east of the Bermuda Rise has been determined to have been derived from local sources. Within the ponded sequence a seismic discontinuity is estimated to be early Oligocene and postdates the emergence of the Bermuda Rise, adding an independent age constraint on the development of the rise. The pond terminates against a structural dam at 55{degree}20W, east of which the fracture zone is essentially sediment starved.« less

Mountain Building in the Uralides: Pangea to the Present

NASA Astrophysics Data System (ADS)

Brown, Dennis; Juhlin, Christopher; Puchkov, Victor

Extending for more than 2000 kilometers from the islands of Novaya Zemlya in the north to the Aral Sea in the south, the Uralide orogen forms the geographical and geological divide between Europe and Asia. For more than a century the Uralides have been one of the key areas of geological research in Russia, and have provided much of its mineral and petroleum wealth for the last 50 years. Nevertheless, the geology and tectonic evolution of the Uralide orogen were relatively unknown in the international literature until recently, when EUROPROBE and GEODE (European Science Foundation scientific programmes) brought together Russian, European, and American earth scientists to work in the Uralides project and the Urals Mineral Province project, respectively. Much of the recent research has focused around two deep seismic surveys, Europrobe's Seismic Reflection Profiling in the Urals (ESRU) survey in the Middle Urals and the multicomponent Urals Seismic Experiment and Integrated Studies (URSEIS) survey in the South Urals. These experiments were accompanied by a large number of geological, geochemical, geochronological, and geophysical studies.

Preface

NASA Astrophysics Data System (ADS)

Brown, Dennis; Juhlin, Christopher; Puchkov, Victor

Extending for more than 2000 kilometers from the islands of Novaya Zemlya in the north to the Aral Sea in the south, the Uralide orogen forms the geographical and geological divide between Europe and Asia. For more than a century the Uralides have been one of the key areas of geological research in Russia, and have provided much of its mineral and petroleum wealth for the last 50 years. Nevertheless, the geology and tectonic evolution of the Uralide orogen were relatively unknown in the international literature until recently, when EUROPROBE and GEODE (European Science Foundation scientific programmes) brought together Russian, European, and American earth scientists to work in the Uralides project and the Urals Mineral Province project, respectively. Much of the recent research has focused around two deep seismic surveys, Europrobe's Seismic Reflection Profiling in the Urals (ESRU) survey in the Middle Urals and the multicomponent Urals Seismic Experiment and Integrated Studies (URSEIS) survey in the South Urals. These experiments were accompanied by a large number of geological, geochemical, geochronological, and geophysical studies.

High resolution seismic stratigraphy and sedimentological signature of the Late Quaternary deposits in the northern Western Basin (Ross Sea, Antarctica)

NASA Astrophysics Data System (ADS)

Corradi, N.; Finocchiaro, F.; Ivaldi, R.; Melis, R.; Pittà, A.

2003-04-01

The northern Western Basin is a sector of the continental shelf of the Western Ross Sea that is considered to be the natural northward extension of the Drygalski Basin by many authors. The literature provides a general model of the evolution of the basin and the recent papers propose a seismic stratigraphy for the post-Miocene sedimentation. However, the sedimentary processes during the Late Quaternary and, in particular, the Last Glacial Maximum (LGM) are still little understood (Brambati et al., 2001). In this paper we present the preliminary results of the very high-resolution seismic surveys (Sub Bottom Profiler, Huntec Deep Tow Boomer and Sparker) and their calibration with the sediment samples collected during the three Marine Geology Campaigns of the PNRA (XIII, XIV and XVII), with the scientific objective of the research to investigate the role of the East Antarctic Ice Sheet (EAIS) in the morphogenesis and deposition of the Late Quaternary sedimentary series.

Joint inversion of time-lapse VSP data for monitoring CO2 injection at the Farnsworth EOR field in Texas

NASA Astrophysics Data System (ADS)

Zhang, M.; Gao, K.; Balch, R. S.; Huang, L.

2016-12-01

During the Development Phase (Phase III) of the U.S. Southwest Regional Partnership on Carbon Sequestration (SWP), time-lapse 3D vertical seismic profiling (VSP) data were acquired to monitor CO2 injection/migration at the Farnsworth Enhanced Oil Recovery (EOR) field, in partnership with the industrial partner Chaparral Energy. The project is to inject a million tons of carbon dioxide into the target formation, the deep oil-bearing Morrow Formation in the Farnsworth Unit EOR field. Quantitative time-lapse seismic monitoring has the potential to track CO2 movement in geologic carbon storage sites. Los Alamos National Laboratory (LANL) has recently developed new full-waveform inversion methods to jointly invert time-lapse seismic data for changes in elastic and anisotropic parameters in target monitoring regions such as a CO2 reservoir. We apply our new joint inversion methods to time-lapse VSP data acquired at the Farnsworth EOR filed, and present some preliminary results showing geophysical properties changes in the reservoir.

Opening of the Central Atlantic Ocean: Implications for Geometric Rifting and Asymmetric Initial Seafloor Spreading after Continental Breakup

NASA Astrophysics Data System (ADS)

Klingelhoefer, F.; Biari, Y.; Sahabi, M.; Funck, T.; Benabdellouahed, M.; Schnabel, M.; Reichert, C. J.; Gutscher, M. A.; Bronner, A.; Austin, J. A., Jr.

2017-12-01

The structure of conjugate passive margins provides information about rifting styles, the initial phases of the opening of an ocean and the formation of its associated sedimentary basins. The study of the deep structure of conjugate passive continental margins combined with precise plate kinematic reconstructions can provide constraints on the mechanisms of rifting and formation of initial oceanic crust. In this study the Central Atlantic conjugate margins are compared, based on compilation of wide-angle seismic profiles from the NW-Africa Nova Scotian and US passive margins. Plate cinematic reconstructions were used to place the profiles in the position at opening and at the M25 magnetic anomaly. The patterns of volcanism, crustal thickness, geometry, and seismic velocities in the transition zone. suggest symmetric rifting followed by asymmetric oceanic crustal accretion. Conjugate profiles in the southern Central Atlantic image differences in the continental crustal thickness. While profiles on the eastern US margin are characterized by thick layers of magmatic underplating, no such underplate was imaged along the NW-African continental margin. It has been proposed that these volcanic products form part of the CAMP (Central Atlantic Magmatic Province). In the north, two wide-angle seismic profiles acquired in exactly conjugate positions show that the crustal geometry of the unthinned continental crust and the necking zone are nearly symmetric. A region including seismic velocities too high to be explained by either continental or oceanic crust is imaged along the Nova Scotia margin off Eastern Canada, corresponding on the African side to an oceanic crust with slightly elevated velocities. These might result from asymmetric spreading creating seafloor by faulting the existing lithosphere on the Canadian side and the emplacement of magmatic oceanic crust including pockets of serpentinite on the Moroccan margin. A slightly elevated crustal thickness along the African margin can be explained by the influence of the Canary hotspot between 60 and 30 Ma in the study region. After isochron M25, a large-scale plate reorganization may then have led to an increase in spreading velocity and the production of a more typical but thin magmatic crust on both sides.

Seismic Imaging of the Deep Crust in the Pull-Apart Basin off Maranhão-Barreirinhas-Ceará Margin, NW Brazil

NASA Astrophysics Data System (ADS)

Afilhado, Alexandra; Gallais, Flora; Moulin, Maryline; Schnürle, Philippe; Afonso Dias, Nuno; Soares, José; Loureiro, Afonso; Fuck, Reinhardt; Cupertino, José; Viana, Adriano; Matias, Luis; Evain, Mikael; Aslanian, Daniel

2017-04-01

Five profiles, with coincident multi-chanel and wide-angle seismic, were acquired during the MAGIC (Margins of brAsil, Ganha and Ivory Coast) cruise, in order to image the Maranhão-Barreirinhas-Ceará segment of the Brazilian Margins. The seismic experiment was conducted by Ifremer (Institut Français de Recherche pour l'Exploration de la Mer), UnB (University of Brasilia), FCUL (Faculdade de Ciencias da Universidade de Lisboa) and Petrobras. The main objective of the experiment is to understand the fundamental processes which lead to the thinning and breakup of the continental crust in a specific context of a pull-apart system, limited by two strike-slip borders. We present the main results evidenced by two of these profiles, MC3 and MC4, oriented in the directions of flow lines (E-W) and margin segmentation (SW-NE), respectively. The profile MC3 spans from the continental crust, near Sao Luis Craton, to the oceanic basin, north of Ceara. 31 Ocean Bottom Seismometers (OBS) from the Ifremer pool and 8 small arrays of 6 RefTek Land Seismic Stations (LSS) from the Brazilian pool were deployed in this profile, jointly with 400 km multi channel seismic acquisition. The profile MC4 spans from the Parnaiba and Barreirinhas Basins onshore to the oceanic basin, South of the Northern Brazilian Ridge. The MC4 seismic data includes 225 km multi channel seismic data and wide-angle data acquired in 19 OBS and 21 arrays of 3 LSS each, totaling a maximum source-receiver offset of 400 km. The analysis of these profiles evidence a NW-SE segmentation of the margin following the opening direction of this pull-apart basin, from unthinned continental crust (about 40 km thick) to thin oceanic crust. The width of the necking zone increases from about 50 km in the direction of flow-lines (MC3-Ilha da Santana margin), to more than 125 km in the direction of segmentation (MC4-Barreirinhas margin), at the corner of the pull-apart system, with two steps first in the upper crust then in middle/lower crust. The intermediate domain, is formed by a thick sedimentary basin overlying a substratum of 5 km- thickness, with velocity ranging from 6.2 to 6.6 km/s. Below, a 2-3 km thick layer with very high velocity (7.4-7.6 km/s) and marked by reflections at the top and base, is followed continuously towards the continent beneath the Parnaiba-Barreirinhas province, at the corner of the system. These observations favor a lower continental crust nature for this domain, in relation to its flow and exhumation in the flow-lines direction. Publication supported by FCT- project UID/GEO/50019/2013 - Instituto Dom Luiz

Contourite drifts on early passive margins as an indicator of established lithospheric breakup

NASA Astrophysics Data System (ADS)

Soares, Duarte M.; Alves, Tiago M.; Terrinha, Pedro

2014-09-01

The Albian-Cenomanian breakup sequence (BS) offshore Northwest Iberia is mapped, described and characterised for the first time in terms of its seismic and depositional facies. The interpreted dataset comprises a large grid of regional (2D) seismic-reflection profiles, complemented by Industry and ODP/DSDP borehole data. Within the BS are observed distinct seismic facies that reflect the presence of: (a) black shales and fine-grained turbidites, (b) mass-transport deposits (MTDs) and coarse-grained turbidites, and (c) contourite drifts. Borehole data show that these depositional systems developed as mixed carbonate-siliciclastic sediments proximally, and as organic-carbon-rich mudstones (black shales) distally on the Northwest Iberia margin. MTDs and turbidites tend to occur on the continental slope, frequently in association with large-scale olistostromes. Distally, these change into interbedded fine-grained turbidites and black shales showing widespread evidence of deep-water current activity towards the top of the BS. Current activity is expressed by intra-BS erosional surfaces and sediment drifts. The results in this paper are important as they demonstrate that contourite drifts are ubiquitous features in the study area after Aptian-Albian lithospheric breakup. Therefore, we interpret the recognition of contourite drifts in Northwest Iberia as having significant palaeogeographic implications. Contourite drifts materialise the onset of important deep-water circulation marking the establishment of oceanic gateways between two fully separated continental margins. As a corollary, we postulate the generation of deep-water geostrophic currents to have had significant impact on North Atlantic climate and ocean circulation during the Albian-Cenomanian, with the record of such impacts being preserved in the contourite drifts analysed in this work.

Coseismic and blind fault of the 2015 Pishan Mw 6.5 earthquake: Implications for the sedimentary-tectonic framework of the western Kunlun Mountains, northern Tibetan Plateau

NASA Astrophysics Data System (ADS)

Lu, Renqi; Xu, Xiwei; He, Dengfa; Liu, Bo; Tan, Xibin; Wang, Xiaoshan

2016-04-01

On 3 July 2015, the Mw 6.5 Pishan earthquake occurred in the western Kunlun Mountains front, at the northern margin of the Tibetan Plateau. To reveal the sedimentary-tectonic framework of the seismically active structure, three high-resolution seismic reflection profiles and well drilling data were collected for seismic interpretation. The western Kunlun Mountains and Tarim Basin have two gypseous detachments and one basement detachment that control the tectonic framework and structural deformation. The upper gypseous detachment (D1) is in the lower Paleocene, and the middle gypseous detachment (D2) is in the Middle to Lower Cambrian. A Neogene shallow thrust system is developing above D1 and includes the Zepu fault (F2) and Mazar Tagh fault (F3). A deep thrust system is developing between D1 and D2 and forms a large-scale structural wedge beneath the western Kunlun Mountains front. The Pishan Mw 6.5 earthquake was triggered on a frontal blind fault of this deep thrust system. The lower detachment is in the Proterozoic basement (D3), which extends into the Tarim Basin and develops another deep thrust (F4) beneath the F3 belt. D1, D2, D3, and the Tiekelike fault (F1) merge together at depth. Crustal shortening of the western Kunlun Mountains front continues for approximately 54 km. Two tectonic evolutionary stages have occurred since the Miocene according to sedimentary unconformity, axial analysis, and fault interpretation. The results of this study indicate a regime of episodic growth of the western Kunlun Mountains and Tarim Basin during the Cenozoic.

Seismic imaging of small horizontal scale structures of the shallow thermocline on the western Brittany continental shelf (North-East Atlantic)

NASA Astrophysics Data System (ADS)

Piete, H.; Marié, L.; Marsset, B.; Gutscher, M.

2012-12-01

The recent development of the seismic oceanography technique has made possible the imaging of a variety of deep oceanographic structures (Holbrook et al., 2003); however, until now this method has remained ill suited for the study of shallow (<200m) thermohaline structures. This difficulty is partly due to the fact that both important seismic trace lengths and large offsets that characterize the acoustic receiver device (seismic streamer) cause significant signal attenuations through an induced antenna filter effect. Further difficulties are related to limitations of currently employed seismic sources, which do not conciliate 1- high power (essential to the imaging of weakly reflective structures in a noisy environment) and 2- spectral contents offering high vertical resolutions (relevant to the mapping of small vertical wavelength structures). In this study we defined and tested a new experimental seismic acquisition system capable of imaging the ~10 m thick seasonal thermocline on the western Brittany continental shelf. To accomplish this task, we pursued two complementary approaches: 1. Analysis of legacy seismic data (multi-channel seismic reflection profiles acquired on the East-Corsican margin, Bahamas Plateau and Gulf of Cadiz in various oceanographic environments) featuring reflectors at depths between 25 and 150 m, in order to identify and quantify the influence of acquisition parameters (seismic trace length, offsets, emission level and frequency content). 2. Incorporation of new oceanographic data acquired during the FROMVAR cruise (July 28th to August 10th 2010) on the western Brittany shelf in thermally stratified waters for use in the simulation of the seismic acquisition, in order to further define the optimal parameters for the system. Finally a 3D seismic system has emerged and was tested during the ASPEX scientific cruise led from June 17th to 19th 2012 across the western Brittany shelf. The device featured: i- four seismic streamers, each consisting of 6 traces at a spacing of 1.80 m; ii- a 1000 J SIG Sparker producing a 400 Hz signal with a 220 dB re 1μPa @1m level of emission, towed at a 8 m distance of the first seismic trace. This survey provided high lateral resolution images of the seasonal thermocline located at a 30 m depth with vertical displacements induced by internal waves. References Holbrook, W.S., Paramo, P., Pearse, S. and Schmitt, R.W., 2003. Thermohaline Fine Structure in an Oceanographic Front from Seismic Reflection Profiling. Science, 301(5634): 821.

Using geophysical data to assess scour development

USGS Publications Warehouse

Placzek, Gary; Haeni, Peter F.; Trent, Roy; ,

1993-01-01

The development of scour holes in the Connecticut River near the new Baldwin Bridge has been documented by comparing geophysical records collected before (1989), during (1990), and after (1992) bridge construction. Eight piers that support the 570-m (meter) span over the Connecticut River were protected by 12-m wide cofferdams during construction. The maximum flow during the study was equivalent to a 3-year recurrence-interval flood, indicating no significant floods. Fathometer data indicate that deep scour holes, 1.5 to 6.4 m deep, developed north of piers 6, 7, and 8. Scour holes, less than 1.3 m-deep, developed south of these piers. The deepest scour hole was north of pier 7, where data show a flat river bottom in 1989, a scour 3.3-m deep in 1990, and a scour hole 6.4-m deep in 1992. Continuous seismic-profiling (CSP) data show that a 1.5 -m deep scour hole north of pier 6 in 1990 was filled in with 1.5-m of material by 1992. No infilling was detected in the scour holes north of piers 7 and 8. Numerous subbottom reflectors from geologic layers, up to 7.6 -m deep were identified in the CSP records.

Detailed structure and tectonics of the Ninetyeast Ridge near Site ODP 758 (on new geophysical data from KNOX06RR cruise of R/V Roger Revelle)

NASA Astrophysics Data System (ADS)

Levchenko, O.; Eisin, A. E.; Ivanenko, A. N.; Marinova, J. G.; Paul, C. F.; Sborshchikov, I. M.; Sager, W. W.

2008-12-01

Detailed geophysical survey was carried out during the NSF-funded KNOX06RR cruise of R/V Roger Revelle in July 2007 over the ~70×70 km area near ODP Site 758, the northern Ninetyeast Ridge (NER). In addition to multibeam echo-sounder bathymetry, 3.5 kHz echo-sounder profiles, magnetic, and gravity data, high-resolution multichannel seismic reflection data were collected on eight orthogonal profiles of total length ~270 km. Large NE-trending depressions with complicated horst and graben morphology dominate the whole detailed survey area. The numerous basement faults extend upward into overlying sediments filling out these depressions. Thickness of the sedimentary fill is highly variable due to very rough basement topography, and is up to 800 m maximum. This fill is divided in two clear sedimentary layers: transparent pelagic sediments above and stratified shallow-water ones below. Two high ~400-450 m isometric seamounts extend from the surrounding NER seafloor. High-resolution seismic records show that these igneous basement highs are covered by thin transparent pelagic sediments which hamper the dredging of volcanic rocks. Seismic stratigraphy analyses for sedimentary cover over the seamounts buried slopes suggest that they seem to be recent volcanoes superimposed on the main NER edifice. Both volcanoes are clearly delineated in the constructed map of total anomaly magnetic field. Since water depths are ~2.5 km above these seamounts, the lower edge of the magnetic body in these volcanoes is situated deep at ~7 km under sea level. That appears to represent deep roots of the volcanoes. Preliminary magnetic modeling shows that they were generated during negative chron of the geomagnetic scale rather not long ago and not far from their present location, seeming to confirm the inference that these volcanoes are recent in origin. In general, one may assume a secondary phase of magmatic activity on the NER. It is important to reveal, any recent phase of tectonic and magnetic activity occurred over the northern NER during the same time of well-known intense intraplate deformation in the Central Indian Basin which was initiated ~8 Ma in response to growing regional compression due to continental collision Hindustan and Eurasia. It appears to be nonrandom that this NER segment is located in an anomalous zone of high oceanic intraplate seismicity. Seismic stratigraphy analyses of high-resolution seismic records over the fault features simultaneously with careful study of reflectors on the buried slopes of the recent volcanoes will allow us to examine this problem.

Integrated Potential-field Studies in Support of Energy Resource Assessment in Frontier Areas of Alaska

NASA Astrophysics Data System (ADS)

Phillips, J. D.; Saltus, R. W.; Potter, C. J.; Stanley, R. G.; Till, A. B.

2008-05-01

In frontier areas of Alaska, potential-field studies play an important role in characterizing the geologic structure of sedimentary basins having potential for undiscovered oil and gas resources. Two such areas are the Yukon Flats basin in the east-central interior of Alaska, and the coastal plain of the Arctic National Wildlife Refuge (ANWR) in northeastern Alaska. The Yukon Flats basin is a potential source of hydrocarbon resources for local consumption and possible export. Knowledge of the subsurface configuration of the basin is restricted to a few seismic reflection profiles covering a limited area and one well. The seismic profiles were reprocessed and reinterpreted in preparation for an assessment of the oil and gas resources of the basin. The assessment effort required knowledge of the basin configuration away from the seismic profiles, as well as an understanding of the nature of the underlying basement. To extend the interpretation of the basin thickness across the entire area of the basin, an iterative Jachens-Moring gravity inversion was performed on gridded quasi-isostatic residual gravity anomaly data. The inversion was constrained to agree with the interpreted basement surface along the seismic profiles. In addition to the main sedimentary depocenter interpreted from the seismic data as having over 8 km of fill, the gravity inversion indicated a depocenter with over 7 km of fill in the Crooked Creek sub-basin. Results for the Crooked Creek sub-basin are consistent with magnetic and magnetotelluric modeling, but they await confirmation by drilling or seismic profiling. Whether hydrocarbon source rocks are present in the pre-Cenozoic basement beneath Yukon Flats is difficult to determine because extensive surficial deposits obscure the bedrock geology, and no deep boreholes penetrate basement. The color and texture patterns in a red-green-blue composite image consisting of reduced-to-the-pole aeromagnetic data (red), magnetic potential (blue), and basement gravity (green) highlight domains with common geophysical characteristics and, by inference, lithology. The observed patterns suggest that much of the basin is underlain by Devonian to Jurassic oceanic rocks that probably have little or no potential for hydrocarbon generation. The coastal plain surficial deposits in the northern part of ANWR conceal another frontier basin with hydrocarbon potential. Proprietary aeromagnetic and gravity data were used, along with seismic reflection profiles, to construct a structural and stratigraphic model of this highly deformed sedimentary basin for use in an energy resource assessment. Matched-filtering techniques were used to separate short-wavelength magnetic and gravity anomalies attributed to sources near the top of the sedimentary section from longer-wavelength anomalies attributed to deeper basin and basement sources. Models along the seismic reflection lines indicate that the primary sources of the short-wavelength anomalies are folded and faulted sedimentary beds truncated at the Pleistocene erosion surface. In map view, the aeromagnetic and gravity anomalies produced by the sedimentary units were used to identify possible structural trapping features and geometries, but they also indicated that these features may be significantly disrupted by faulting.

Surface wave tomography of the European crust and upper mantle from ambient seismic noise

NASA Astrophysics Data System (ADS)

LU, Y.; Stehly, L.; Paul, A.

2017-12-01

We present a high-resolution 3-D Shear wave velocity model of the European crust and upper mantle derived from ambient seismic noise tomography. In this study, we collect 4 years of continuous vertical-component seismic recordings from 1293 broadband stations across Europe (10W-35E, 30N-75N). We analyze group velocity dispersion from 5s to 150s for cross-correlations of more than 0.8 million virtual source-receiver pairs. 2-D group velocity maps are estimated using adaptive parameterization to accommodate the strong heterogeneity of path coverage. 3-D velocity model is obtained by merging 1-D models inverted at each pixel through a two-step data-driven inversion algorithm: a non-linear Bayesian Monte Carlo inversion, followed by a linearized inversion. Resulting S-wave velocity model and Moho depth are compared with previous geophysical studies: 1) The crustal model and Moho depth show striking agreement with active seismic imaging results. Moreover, it even provides new valuable information such as a strong difference of the European Moho along two seismic profiles in the Western Alps (Cifalps and ECORS-CROP). 2) The upper mantle model displays strong similarities with published models even at 150km deep, which is usually imaged using earthquake records.

Deep sea sedimentation processes and geomorphology: Northwest Atlantic continental margin

NASA Astrophysics Data System (ADS)

Mosher, David; Campbell, Calvin; Gardner, Jim; Chaytor, Jason; Piper, David; Rebesco, Michele

2017-04-01

Deep-sea sedimentation processes impart a fundamental control on the morphology of the western North Atlantic continental margin from Blake Spur to Hudson Strait. This fact is illustrated by the variable patterns of cross-margin gradients that are based on extensive new multibeam echo-sounder data informed by subbottom profiler and seismic reflection data. Erosion by off-shelf sediment transport in turbidity currents creates gullies, canyons and channels and a steep upper slope. Amalgamation of these conduits produces singular channels and turbidite fan complexes on the lower slope, flattening slope-profile gradients. The effect is an exponentially decaying "graded" slope profile. Comparatively, sediment mass failure produces steeper upper slopes due to head scarp development and a wedging architecture to the lower slope as deposits thin in the downslope direction. This process results in either a "stepped" slope, and/or a significant downslope gradient change where MTDs pinch out. Large drift deposits created by geostrophic currents are developed all along the margin. Blake Ridge, Sackville Spur, and Hamilton Spur are large detached drifts on disparate parts of the margin. They form a linear "above grade" profile along their crests from the shelf to abyssal plain. Deeper portions of the US continental margin are dominated by the Chesapeake Drift and Hatteras Outer Ridge; both plastered elongate mounded drifts. Farther north, particularly on the Grand Banks margin, are plastered and separated drifts. These drifts form "stepped" slope profiles, where they onlap the margin. Trough-mouth fan complexes become more common along the margin with increasing latitude. Sediment deposition and retention, particularly those dominated by glacigenic debris flows, characterize these segments producing an "above grade" slope profile. Understanding these geomorphological consequences of deep sea sedimentation processes is important to extended continental shelf mapping in which gradients and gradient change is a critical metric.

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

NASA Astrophysics Data System (ADS)

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

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

Changing sediment physical properties at the Agulhas Plateau (IODP Site U1475): indications for the long-term variability of deepwater circulation over the last 7 Ma

NASA Astrophysics Data System (ADS)

Gruetzner, Jens; Lathika, Nambiyathodi; Jimenez Espejo, Francisco J.; Uenzelmann-Neben, Gabriele

2017-04-01

The gateway south of South Africa constitutes an integral inter-ocean link in the global thermohaline circulation (THC) since it allows the exchange of shallow- and deepwater masses between the Indian and the Atlantic. Thus understanding past variations of this current system is important for improving our knowledge of the global climate. The long-term changes in deepwater flow in the Atlantic-Indian gateway during the Cenozoic have been initially studied using reflection seismic profiles. But in many cases the seismic stratigraphy is poorly constrained and not further resolved within the time period from the late Miocene to present. In particular, there are limited Pliocene records that can be used to investigate the influence of climatic (e.g. Antartic ice volume) and tectonic (e.g. closure of the central American seaway) on the deep-water variability. Here we focus on the bottom water flow around the Agulhas Plateau, a location proximal to the entrance of North Atlantic Deep Water (NADW) to the Southern Ocean and South Indian Ocean. IODP Expedition 361 (SAFARI) Site U1475 was drilled in 2669 m water depth into a sediment drift that is deposited on the southwestern flank of Agulhas Plateau and comprises a complete stratigraphic section of the last 7 Ma. We present cleaned, edited, and spliced high-resolution data sets of sediment physical properties measured at Site U1475. Synthetic seismograms generated from the velocity and bulk density core scanning records allow a detailed correlation oft the drilling results with the Site survey seismic reflection profiles. Seismic reflectors at 3.75 and 3.87 s (two-way-traveltime) correspond to major increases in acoustic impedance at 110 and 216 meters below seafloor. Based on the preliminary shipboard biostratigraphic age model sediments at these depths have ages of 4.0 and 5.1 Ma, respectively. Furthermore spectral analyses of physical property records such as natural gamma radiation and colour reflectance reveal climate variability on orbital and suborbital timescales.

Extension style in the Orphan Basin during the Mesozoic North Atlantic rifting

NASA Astrophysics Data System (ADS)

Gouiza, Mohamed; Hall, Jeremy

2013-04-01

The Orphan Basin, lying along the Newfoundland passive continental margin, has formed in Mesozoic time during the opening of the North Atlantic Ocean and the breakup of Iberia/Eurasia from North America. Regional deep seismic reflection profiles across the basin indicate that the Neoproterozoic basement has been affected by repeated extensional episodes between the Late Triassic/Jurassic and the Early Cretaceous. Deformation initiated in the eastern part of the Orphan basin in the Jurassic and migrated toward the west in the Early Cretaceous, resulting in numerous rift structures filled with Jurassic-Lower Cretaceous syn-rift successions and sealed by thick Upper Cretaceous-Cenozoic post-rift sediments. The seismic data show an extremely attenuated crust underneath the eastern and western part of the deep basin, forming two sub-basins associated with the development of rifting. The two sub-basins are separated by a wide structural high with a relatively thick crust and are bounded to the west by the continental shelf domain. Restoration of the Orphan Basin along a 2D crustal section (520 km long), yields a total amount of stretching of about 144 km, while the total crustal thinning indicates an extension of around 250 km, assuming mass conservation along the section and an initial crustal thickness of 28 km. Brittle deformation accommodated by normal faults is documented in the seismic profiles and affected essentially the present-day upper portion of the crust, and represents only 60% of the total extension which thinned the Orphan crust. The remaining crustal thinning must involve other deformation processes which are not (easily) recognizable in the seismic data. We propose two models that could explain discrepancies between brittle deformation and total crustal thinning during lithospheric extension. The first model assumes the reactivation of pre-rift inherited structures, which act as crustal-scale detachments during the early stages of rifting. The second model uses depth-dependent extension of a 20 km thick crust characterized by a strong upper crust and a weak lower crust. Both models raise secondary issues that are discussed around the order of rifting events and the original crustal thickness.

The shallow sedimentary and structural deformation in the southern Longmen Shan: constraints on the seismotectonics of the 2013 Lushan Mw6.7 Earthquake

NASA Astrophysics Data System (ADS)

Lu, R.; Xu, X.; He, D.; Suppe, J.

2017-12-01

On April 20, 2013, an unexpected Mw 6.7 earthquake occurred in Lushan County at the southern Longmen Shan, the eastern margin of the Tibetan Plateau. After this Lushan earthquake, whether the seismogenic fault is a high-angle or low-angle fault? The structural characteristics, attribution, and the seismotectonic model of this earthquake have many debates and problems. In this study, a high-resolution seismic reflection profile was combined with near-surface geological data, earthquake relocation and geodetic measurements, and a recent deep artificial seismic reflection profile to identify the active fault and seismotectonics of this earthquake. Three-dimensional imaging of the aftershocks was used to identify two planar faults that together form a y-shape (f1 and f2). Seismic interpretations suggest that the seismogenic fault f1 is a typical basement blind fault that did not penetrate into the overlying Mesozoic and Cenozoic units, and it is not a Shuangshi-Dachuan fault (F4) or the frontal Dayi buried fault (F6). Geodetic measurements suggest that the coseismic deformation is consistent with the geometry and kinematics of shear fault-bend folding (FBF). The history of tectonic evolution since the Paleozoic in Longmen Shan area also referred. There are three major detachments control the structural deformation of the upper crust in the Longmen Shan and Western Sichuan Basin, resulting in multiple superimposed deformation events. Deep seismic data indicate the syndepositional nature of fault f1 a preexisting normal fault older than the Triassic, which underwent positive inversion tectonics during the Late Cenozoic. A thrust fault f3 converges with f1 at a depth of approximately12 km with an accumulated slip 3.6 km. This 2013 Lushan earthquake triggered by blind faults is a hidden earthquake. Since the Late Cenozoic, with the strong and on-going compression of the Qinghai-Tibet Plateau to the Sichuan Basin, the early-period normal faults were activated after inversion and triggered Lushan earthquakes. Blind and reactivated faults increase the potential risk and uncertainty related to earthquakes in the eastern margin of the Tibetan Plateau.

Elasticity of the Earth's Lower Mantle Minerals at High Pressures: Implications to Understanding Seismic Observations of the Deep Mantle

NASA Astrophysics Data System (ADS)

Lin, J. F.; Yang, J.; Fu, S.

2017-12-01

Elasticity of the candidate lower-mantle minerals at relevant P-T conditions of the region provides critical information in understanding seismic profiles, compositional and mineralogical models, and geodynamic processes of the Earth's interior. Here we will discuss recent major research advances in the investigation of the elasticity of major lower-mantle minerals in a high-pressure diamond anvil cell coupled with Brillouin Light Scattering, Impulsive Stimulated Scattering (ISS), and X-ray diffraction. These have permitted direct and reliable measurements of both Vp and Vs to derive full elastic constants of single-crystal ferropericlase and (Fe, Al)-bearing bridgmanite as well as velocity profiles of polycrystalline silicate post-perovskite at relevant lower-mantle pressures. The effects of the spin transition on the single-crystal elasticity of ferropericlase are now well understood experimentally and theoretically1,2: the spin transition causes drastic softening in elastic constants involving the compressive stress component (C11 and C12) due to the additional Gibbs free energy term arising from the mixing of the high-spin and low-spin states, while the elastic constant(s) related to the shear stress component (C44) is not affected. This leads to significant reduction in VP/VS ratio within the spin transition of ferropericlase in the mid-lower mantle. The derived single-crystal Cij of bridgmanite at lower mantle pressures display relatively small elastic Vp and Vs anisotropies as compared to the ferropericlase counterpart. Using thermoelastic modelling, we will discuss the application of the elasticity of ferropericlase, bridgmanite, and silicate post-perovskite at relevant conditions of the Earth's lower mantle to differentiate the role of the thermal vs. chemical perturbations as well as the spin transition and iron partitioning effects in the reported seismic lateral heterogeneity in lower mantle as well as the D″ zone region3,4. We will address how recent elasticity results are applied to advance our understanding of seismic structures, mineralogical models, and geodynamic processes of the deep Earth's interior. References: 1Yang et al., Sci. Rep., 2015; 2Fu et al., Phys. Rev. Lett., 2017; 3Yang et al., J. Geophys. Res., 2016; 4Wu et al., Nature Comm., 2017.

Comparison of publically available Moho depth and crustal thickness grids with newly derived grids by 3D gravity inversion for the High Arctic region.

NASA Astrophysics Data System (ADS)

Lebedeva-Ivanova, Nina; Gaina, Carmen; Minakov, Alexander; Kashubin, Sergey

2016-04-01

We derived Moho depth and crustal thickness for the High Arctic region by 3D forward and inverse gravity modelling method in the spectral domain (Minakov et al. 2012) using lithosphere thermal gravity anomaly correction (Alvey et al., 2008); a vertical density variation for the sedimentary layer and lateral crustal variation density. Recently updated grids of bathymetry (Jakobsson et al., 2012), gravity anomaly (Gaina et al, 2011) and dynamic topography (Spasojevic & Gurnis, 2012) were used as input data for the algorithm. TeMAr sedimentary thickness grid (Petrov et al., 2013) was modified according to the most recently published seismic data, and was re-gridded and utilized as input data. Other input parameters for the algorithm were calibrated using seismic crustal scale profiles. The results are numerically compared with publically available grids of the Moho depth and crustal thickness for the High Arctic region (CRUST 1 and GEMMA global grids; the deep Arctic Ocean grids by Glebovsky et al., 2013) and seismic crustal scale profiles. The global grids provide coarser resolution of 0.5-1.0 geographic degrees and not focused on the High Arctic region. Our grids better capture all main features of the region and show smaller error in relation to the seismic crustal profiles compare to CRUST 1 and GEMMA grids. Results of 3D gravity modelling by Glebovsky et al. (2013) with separated geostructures approach show also good fit with seismic profiles; however these grids cover the deep part of the Arctic Ocean only. Alvey A, Gaina C, Kusznir NJ, Torsvik TH (2008). Integrated crustal thickness mapping and plate recon-structions for the high Arctic. Earth Planet Sci Lett 274:310-321. Gaina C, Werner SC, Saltus R, Maus S (2011). Circum-Arctic mapping project: new magnetic and gravity anomaly maps of the Arctic. Geol Soc Lond Mem 35, 39-48. Glebovsky V.Yu., Astafurova E.G., Chernykh A.A., Korneva M.A., Kaminsky V.D., Poselov V.A. (2013). Thickness of the Earth's crust in the deep Arctic Ocean: results of a 3D gravity modeling Russian Geology and Geophysics 54, 247-262. Jakobsson M, Mayer L, Coakley B, Dowdeswell JA, Forbes S, Fridman B, Hodnesdal H, Noormets R, Pedersen R, Rebesco M, Schenke HW, Zarayskaya Y, Accettella D, Armstrong A, Anderson RM, Bienhoff P, Camerlenghi A, Church I, Edwards M, Gardner JV, Hall JK, Hell B, Hestvik O, Krist-offersen Y, Marcussen C, Mohammad R, Mosher D, Nghiem SV, Pedrosa MT, Travaglini PG, Weatherall P (2012). The international bathymetric chart of the Arctic Ocean (IBCAO) version 3.0. Geophys Res Lett 39, L12609. Laske, G., Masters., G., Ma, Z. and Pasyanos, M. (2013). Update on CRUST1.0 - A 1-degree Global Model of Earth's Crust, Geophys. Res. Abstracts, 15, Abstract EGU2013-2658, 2013. Minakov A, Faleide JI, Glebovsky VY, Mjelde R (2012) Structure and evolution of the northern Barents-Kara Sea continental margin from integrated analysis of potential fields, bathymetry and sparse seismic data. Geophys J Int 188, 79-102. Petrov O., Smelror M., Shokalsky S., Morozov A., Kashubin S., Grikurov G., Sobolev N., Petrov E., (2013). A new international tectonic map of the Arctic (TeMAr) at 1:5 M scale and geodynamic evolution in the Arctic region. EGU2013-13481. Reguzzoni, M., & Sampietro, D. (2014). GEMMA: An Earth crustal model based on GOCE satellite data. International Journal of Applied Earth Observation and Geoinformation Spasojevic S. & Gurnis M., (2012). Sea level and vertical motion of continents from dynamic earth models since the late Cretaceous. American Association of Petroleum Geologists Bulletin, 96, pp. 2037-2064.

Insights upon upper crustal arhitecture of a subduction zone and its surroundings - Vrancea Zone and Focsani Basin - substantiated by geophysical studies

NASA Astrophysics Data System (ADS)

Bocin, A.; Stephenson, R.; Mocanu, V.

2007-12-01

The DACIA PLAN (Danube and Carpathian Integrated Action on Processes in the Lithosphere and Neotectonics) deep seismic reflection survey was performed in August-September 2001, with the proposed objective of obtaining new information on the deep structure of the external Carpathians nappes and the architecture of Tertiary/Quaternary basin developed within and adjacent to the Vrancea zone, including the rapidly subsiding Focsani Basin. The DACIA-PLAN profile is about 140 km long, having a roughly NW-SE direction, from near the southeast Transylvanian Basin, across the mountainous southeastern Carpathians and their foreland to near the Danube River. A high resolution 2.5D velocity model of the upper crust along the seismic profile has been determined from a tomographic inversion and a 2D ray tracing forward modelling of the DACIA PLAN first arrival data. Peculiar shallow high velocities indicate that pre-Tertiary basement in the Vrancea Zone (characterised by velocities greater than 5.6 km/s) is involved in Carpathian thrusting while rapid alternance, vertically or horizontally, of velocity together with narrowingly contemporary crustal events suggests uplifting. Further to the east, at the foreland basin-thrust belt transition zone (well defined within velocity values), the velocity model suggests a nose of the Miocene Subcarpathians nappe being underlain by Focsani Basin units. A Miocene and younger Focsani Basin sedimentary succession of ~10 km thickness is ascertained by a gradual increase of velocities and strongly defined velocity boundaries.

New seismic images of the cascadia subduction zone from cruise SO 108-ORWELL

USGS Publications Warehouse

Flueh, E.R.; Fisher, M.A.; Bialas, J.; Childs, J. R.; Klaeschen, D.; Kukowski, Nina; Parsons, T.; Scholl, D. W.; ten Brink, Uri S.; Trehu, A.M.; Vidal, N.

1998-01-01

In April and May 1996, a geophysical study of the Cascadia continental margin off Oregon and Washington was conducted aboard the German R/V Sonne. This cooperative experiment by GEOMAR and the USGS acquired wide-angle reflection and refraction seismic data, using ocean-bottom seismometers (OBS) and hydrophones (OBH), and multichannel seismic reflection (MCS) data. The main goal of this experiment was to investigate the internal structure and associated earthquake hazard of the Cascadia subduction zone and to image the downgoing plate. Coincident MCS and wide-angle profiles along two tracks are presented here. The plate boundary has been imaged precisely beneath the wide accretionary wedge close to shore at c13km depth. Thus, the downgoing plate dips more shallowly than previously assumed. The dip of the plate changes from 2?? to 4?? at the eastern boundary of the wedge on the northern profile, whereas approximately 3km of sediment is entering the subduction zone. On the southern profile, where the incoming sedimentary section is about 2.2km thick, the plate dips about 0.5?? to 1.5?? near the deformation front and increases to 3.5?? further landwards. On both profiles, the deformation of the accretionary wedge has produced six ridges on the seafloor, three of which represent active faulting, as indicated by growth folding. The ridges are bordered by landward verging faults which reach as deep as the top of the oceanic basement. Thus, the entire incoming sediment package is being accreted. At least two phases of accretion are evident, and the rocks of the older accretionary phase(s) forms the backstop for the younger phase, which started around 1.5 Ma ago. This documents that the 30 to 50km wide frontal part of the accretionary wedge, which is characterized by landward vergent thrusts, is a Pleistocene feature which was formed in response to the high input of sediment building the fans during glacial periods. Velocities increase quite rapidly within the wedge, both landward and downward. At the toe of the deformation front, velocities are higher than 4.0 km/s, indicating extensive dewatering of deep, oceanic sediment. Further landward, considerable velocity variation is found, which indicates major breaks throughout the accretionary history.

Sunda-Banda Arc Transition: Marine Multichannel Seismic Profiling

NASA Astrophysics Data System (ADS)

Lueschen, E.; Mueller, C.; Kopp, H.; Djajadihardja, Y.; Ehrhardt, A.; Engels, M.; Lutz, R.; Planert, L.; Shulgin, A.; Working Group, S.

2008-12-01

After the Indian Ocean Mw 9.3 earthquake and tsunami on December 26, 2004, intensive research activities focussed on the Sunda Arc subduction system offshore Sumatra. For this area a broad database is now available interpreted in terms of plate segmentation and outer arc high evolution. In contrast, the highly active easternmost part of this subduction system, as indicated by the south of Java Mw 7.7 earthquake and tsunami on July 17, 2006, has remained almost unexplored until recently. During RV SONNE cruise SO190 from October until December 2006 almost 5000 km of marine geophysical profiles have been acquired at the eastern Sunda Arc and the transition to the Banda Arc. The SINDBAD project (Seismic and Geoacoustic Investigations along the Sunda-Banda Arc Transition) comprises 30-fold multichannel reflection seismics with a 3-km streamer, wide-angle OBH/OBS refraction seismics for deep velocity control (see poster of Shulgin et al. in this session), swath bathymetry, sediment echosounder, gravimetric and geomagnetic measurements. We present data and interpretations of several 250-380 km long, prestack depth-migrated seismic sections, perpendicular to the deformation front, based on velocity models from focussing analysis and inversion of OBH/OBS refraction data. We focus on the variability of the lower plate and the tectonic response of the overriding plate in terms of outer arc high formation and evolution, forearc basin development, accretion and erosion processes at the base of the overriding plate. The subducting Indo-Australian Plate is characterized by three segments: i) the Roo Rise with rough topography offshore eastern Java ii) the Argo Abyssal Plain with smooth oceanic crust offshore Bali, Lombok, and Sumbawa, and iii) the Scott Plateau with continental crust colliding with the Banda island arc. The forearc responds to differences in the incoming oceanic plate with the absence of a pronounced forearc basin offshore eastern Java and with development of the 4000 m deep forearc Lombok Basin offshore Bali, Lombok, and Sumbawa. The eastern termination of the Lombok Basin is formed by Sumba Island, which shows evidence for recent uplift, probably associated with the collision of the island arc with the continental Scott Plateau. The Sumba area represents the transition from subduction to collision. Our seismic profiles image the bending of the oceanic crust seaward of the trench and associated normal faulting. Landward of the trench, they image the subducting slab beneath the outer arc high, where the former bending-related normal faults appear to be reactivated as reverse faults introducing vertical displacements in the subducting slab. The accretionary prism and the outer arc high are characterized by an ocean-verging system of imbricate thrust sheets with major thrust faults connecting seafloor and detachment. Compression results in shortening and steepening of the imbricated thrust sheets building up the outer arc high. Tilted piggy-back basins and downlaps of tilted sediments in the southern Lombok forearc basin indicate ongoing uplift of the entire outer arc high, abrupt displacements, and recent tectonic activity.

The seismic stratigraphy of Okanagan Lake, British Columbia; a record of rapid deglaciation in a deep 'fiord-lake' basin

NASA Astrophysics Data System (ADS)

Eyles, Nicholas; Mullins, Henry T.; Hine, Albert C.

1991-09-01

This paper presents the first detailed data regarding the newly discovered deep infill of Okanagan Lake. Okanagan Lake (50°00'N, 119°30'W) is 120 km long, ˜ 3-5 km wide and occupies a glacially overdeepened bedrock basin in the southern interior of British Columbia. This basin, and other elongate lakes of the region (e.g. Shuswap, Kootenay, Kalamalka, Canim and Mahood lakes), mark the site of westward flowing ice streams within successive Cordilleran ice sheets. An air gun seismic survey of Okanagan Lake shows that the bedrock floor is nearly 650 m below sea-level, more than 2000 m below the rim of the surrounding plateau. The maximum thickness of Pleistocene sediment in Okanagan Lake basin approaches 800 m. Forty-six seismic reflection traverses and an axial profile show a relatively simple stratigraphy composed of three seismic sequences argued to be no older than the last glacial cycle (< 30 ka). A discontinuous basal unit (sequence I) characterized by large-scale diffractions, and up to 460 m thick, infills the narrow, V-shaped bedrock floor of the basin and is interpreted as a boulder gravel deposited by subglacial meltwaters. Overlying seismic sequence II is composed of two sub-sequences. Sub-sequence IIa is a chaotic to massive facies up to 736 m thick. Lakeshore exposures close to where this unit reaches lake level show deformed and chaotically-bedded glaciolacustrine silts containing gravel lens and large ice-rafted boulders. The surface topography of this sub-sequence is irregular and in general mimics the form of the underlying bedrock as a result of compaction. This sequence passes laterally into stratified facies (sub-sequence IIb) at the northern end of the basin. Seismic sequence II appears to record rapid ice-proximal dumping of glaciolacustrine silt as the Okanagan glacier backwasted upvalley in a deep lake. A thin (60 m max.) laminated seismic sequence (III) drapes the hummocky surface of sequence II and represents postglacial sedimentation from fan-deltas. The extreme thickness of sequences I and II in Okanagan Lake reflects the focussing of large volumes of meltwater and sediment into the basin during deglaciation; pre-existing sediments that pre-date the last glacial cycle appear to have been completely eroded. Glaciological conditions during sedimentation may have been similar to marine-based outlet glaciers calving in deep water in fiord basins. In contrast to marine settings where ice bergs are free to disperse, large volumes of dead ice were trapped within the basin; structural evidence for sedimentation around dead ice blocks has been previously used to argue that the Cordilleran Ice Sheet downwasted in situ. We emphasize in contrast, the trapping of dead ice left behind by rapidly calving lake-based outlet glaciers.

2D and 3D high resolution seismic imaging of shallow Solfatara crater in Campi Flegrei (Italy): new insights on deep hydrothermal fluid circulation processes

NASA Astrophysics Data System (ADS)

De Landro, Grazia; Gammaldi, Sergio; Serlenga, Vincenzo; Amoroso, Ortensia; Russo, Guido; Festa, Gaetano; D'Auria, Luca; Bruno, Pier Paolo; Gresse, Marceau; Vandemeulebrouck, Jean; Zollo, Aldo

2017-04-01

Seismic tomography can be used to image the spatial variation of rock properties within complex geological media such as volcanoes. Solfatara is a volcano located within the Campi Flegrei still active caldera, characterized by periodic episodes of extended, low-rate ground subsidence and uplift called bradyseism accompanied by intense seismic and geochemical activities. In particular, Solfatara is characterized by an impressive magnitude diffuse degassing, which underlines the relevance of fluid and heat transport at the crater and prompted further research to improve the understanding of the hydrothermal system feeding the surface phenomenon. In this line, an active seismic experiment, Repeated Induced Earthquake and Noise (RICEN) (EU Project MEDSUV), was carried out between September 2013 and November 2014 to provide time-varying high-resolution images of the structure of Solfatara. In this study we used the datasets provided by two different acquisition geometries: a) A 2D array cover an area of 90 x 115 m ^ 2 sampled by a regular grid of 240 vertical sensors deployed at the crater surface; b) two 1D orthogonal seismic arrays deployed along NE-SW and NW-SE directions crossing the 400 m crater surface. The arrays are sampled with a regular line of 240 receiver and 116 shots. We present 2D and 3D tomographic high-resolution P-wave velocity images obtained using two different tomographic methods adopting a multiscale strategy. The 3D image of the shallow (30-35 m) central part of Solfatara crater is performed through the iterative, linearized, tomographic inversion of the P-wave first arrival times. 2D P-wave velocity sections (60-70 m) are obtained using a non-linear travel-time tomography method based on the evaluation of a posteriori probability density with a Bayesian approach. The 3D retrieved images integrated with resistivity section and temperature and CO2 flux measurements , define the following characteristics: 1. A depth dependent P-wave velocity layer down to 14 m, with Vp<700m/s typical of poorly-consolidated tephra and affected by CO2 degassing; 2. An intermediate layer, deepening towards the mineralized liquid-saturated area (Fangaia), interpreted as permeable deposits saturated with condensed water; 3. A deep, confined high velocity anomaly associated with a CO2 reservoir. With the 2D profiles we can image up to around 70 m depth: the first 30 m are characterized by features and velocities comparable to those of the 3D profiles, deeper, between 40-60 m depth, were found two low velocity anomalies, that probably indicate a preferential via for fluid degassing. These features are expression of an area located between the Fangaia, which is water saturated and replenished from deep aquifers, and the main fumaroles that are the superficial relief of deep rising CO2 flux. So, the changes in the outgassing rate greatly affects the shallow hydrothermal system, which can be used as a near-surface "mirror" of fluid migration processes occurring at greater depths.

Survey evaluation and design (SED): A case study in Garden Banks, Gulf of Mexico

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

Johnson, G.; Hannan, A.; Mann, A.D.

1995-12-31

Hydrocarbon exploration in the Gulf of Mexico has reached its mature stages. Exploration objectives such as deep stratigraphic and pre-salt traps are becoming more dominant. As the exploration targets change, earlier 3D seismic surveys, designed for different objectives, become less able to meet the demands of the present day explorations. Some areas of the Gulf of Mexico will require reacquisition of new 3D seismic data, redesigned to meet new objectives. Garden Banks is one such area. A major advantage of performing a survey evaluation design (SED) in a mature area is the amount and diversity of available data. Geological profiles,more » reservoir characterizations, borehole wireline and surface seismic data, all serve to aid in the survey design. Given the exploration history and geological objectives, the geophysical analyses of resolution, signal loss, noise, fold, acquisition geometry, migration aperture, velocity anisotropy and others, may now be carried out in a much more specific manner. A thorough SED ensures that overall survey objectives will be met and reduces the possibility of over design on critical parameters. This generates the highest quality seismic survey for the most reasonable cost.« less

Free Surface Downgoing VSP Multiple Imaging

NASA Astrophysics Data System (ADS)

Maula, Fahdi; Dac, Nguyen

2018-03-01

The common usage of a vertical seismic profile is to capture the reflection wavefield (upgoing wavefield) so that it can be used for further well tie or other interpretations. Borehole Seismic (VSP) receivers capture the reflection from below the well trajectory, traditionally no seismic image information above trajectory. The non-traditional way of processing the VSP multiple can be used to expand the imaging above the well trajectory. This paper presents the case study of using VSP downgoing multiples for further non-traditional imaging applications. In general, VSP processing, upgoing and downgoing arrivals are separated during processing. The up-going wavefield is used for subsurface illumination, whereas the downgoing wavefield and multiples are normally excluded from the processing. In a situation where the downgoing wavefield passes the reflectors several times (multiple), the downgoing wavefield carries reflection information. Its benefit is that it can be used for seismic tie up to seabed, and possibility for shallow hazards identifications. One of the concepts of downgoing imaging is widely known as mirror-imaging technique. This paper presents a case study from deep water offshore Vietnam. The case study is presented to demonstrate the robustness of the technique, and the limitations encountered during its processing.

Preliminary potential-field constraints on the geometry of the San Fernando basin, Southern California

USGS Publications Warehouse

Langenheim, V.E.; Griscom, Andrew; Jachens, R.C.; Hildenbrand, T.G.

2000-01-01

Gravity and magnetic data provide new insights on the structural underpinnings of the San Fernando Basin region, which may be important to ground motion models. Gravity data indicate that a deep basin (>5 km) underlies the northern part of the San Fernando Valley; this deep basin is required to explain the lowest gravity values over the Mission Hills thrust fault. Gravity modeling, constrained by well data and density information, shows that the basin may reach a thickness of 8 km, coinciding with the upper termination of the 1994 Northridge earthquake mainshock rupture. The basin is deeper than previous estimates by 2 to 4 km; this estimate is the result of high densities for the gravels of the Pliocene-Pleisocene Saugus Formation. The geometry of the southern margin of the deep basin is not well-constrained by the gravity data, but may dip to the south. Recently acquired seismic data along the LARSE (Los Angeles Regional Seismic Experiment) II profile may provide constraints to determine the location and attitude of the basin edge. Gravity and aeromagnetic models across the eastern margin of the San Fernando Valley indicate that the Verdugo fault may dip to the southwest along its southern extent and therefore have a normal fault geometry whereas it clearly has a thrust fault geometry along its northern strand.

Seismic images of an extensional basin, generated at the hangingwall of a low-angle normal fault: The case of the Sansepolcro basin (Central Italy)

NASA Astrophysics Data System (ADS)

Barchi, Massimiliano R.; Ciaccio, Maria Grazia

2009-12-01

The study of syntectonic basins, generated at the hangingwall of regional low-angle detachments, can help to gain a better knowledge of these important and mechanically controversial extensional structures, constraining their kinematics and timing of activity. Seismic reflection images constrain the geometry and internal structure of the Sansepolcro Basin (the northernmost portion of the High Tiber Valley). This basin was generated at the hangingwall of the Altotiberina Fault (AtF), an E-dipping low-angle normal fault, active at least since Late Pliocene, affecting the upper crust of this portion of the Northern Apennines. The dataset analysed consists of 5 seismic reflection lines acquired in the 80s' by ENI-Agip for oil exploration and a portion of the NVR deep CROP03 profile. The interpretation of the seismic profiles provides a 3-D reconstruction of the basin's shape and of the sedimentary succession infilling the basin. This consisting of up to 1200 m of fluvial and lacustrine sediments: this succession is much thicker and possibly older than previously hypothesised. The seismic data also image the geometry at depth of the faults driving the basin onset and evolution. The western flank is bordered by a set of E-dipping normal faults, producing the uplifting and tilting of Early to Middle Pleistocene succession along the Anghiari ridge. Along the eastern flank, the sediments are markedly dragged along the SW-dipping Sansepolcro fault. Both NE- and SW-dipping faults splay out from the NE-dipping, low-angle Altotiberina fault. Both AtF and its high-angle splays are still active, as suggested by combined geological and geomorphological evidences: the historical seismicity of the area can be reasonably associated to these faults, however the available data do not constrain an unambiguous association between the single structural elements and the major earthquakes.

Salton Seismic Imaging Project Line 6: San Andreas Fault and Northern Coachella Valley Structure, Riverside and San Bernardino Counties, California

NASA Astrophysics Data System (ADS)

Catchings, R. D.; Fuis, G.; Rymer, M. J.; Goldman, M.; Tarnowski, J. M.; Hole, J. A.; Stock, J. M.; Matti, J. C.

2012-12-01

The Salton Seismic Imaging Project (SSIP) is a large-scale, active- and passive-source seismic project designed to image the San Andreas fault (SAF) and adjacent basins (Imperial and Coachella Valleys) in southernmost California. Data and preliminary results from many of the seismic profiles are reported elsewhere (including Fuis et al., Rymer et al., Goldman et al., Langenheim et al., this meeting). Here, we focus on SSIP Line 6, one of four 2-D seismic profiles that were acquired across the Coachella Valley. The 44-km-long, SSIP-Line-6 seismic profile extended from the east flank of Mt. San Jacinto northwest of Palm Springs to the Little San Bernardino Mountains and crossed the SAF (Mission Creek (MCF), Banning (BF), and Garnet Hill (GHF) strands) roughly normal to strike. Data were generated by 10 downhole explosive sources (most spaced about 3 to 5 km apart) and were recorded by approximately 347 Texan seismographs (average spacing 126 m). We used first-arrival refractions to develop a P-wave refraction tomography velocity image of the upper crust along the seismic profile. The seismic data were also stacked and migrated to develop low-fold reflection images of the crust. From the surface to about 7 km depth, P-wave velocities range from about 2.5 km/s to about 7.2 km/s, with the lowest velocities within an ~2-km-deep, ~20-km-wide basin, and the highest velocities below the transition zone from the Coachella Valley to Mt. San Jacinto and within the Little San Bernardino Mountains. The BF and GHF strands bound a shallow sub-basin on the southwestern side of the Coachella Valley, but the underlying shallow-depth (~4 km) basement rocks are P-wave high in velocity (~7.2 km/s). The lack of a low-velocity zone beneath BF and GHF suggests that both faults dip northeastward. In a similar manner, high-velocity basement rocks beneath the Little San Bernardino Mountains suggest that the MCF dips vertically or southwestward. However, there is a pronounced low-velocity zone in basement rocks between about 2 and 7 km depth beneath and southwest of the MCF, suggesting a vertical or slightly southwest-dipping MCF. The apparent northeast dip of the BF and the apparent vertical or southwest dip of the MCF suggests that the two main strands of the SAF (MCF and BF) merge at about 10 km depth. A plot of double-difference earthquake hypocenters (Hauksson, 2000) along the seismic profile shows events that occurred between 1980-2000 (excluding those in 1992, prior to and after the Joshua Tree and Landers earthquakes) are largely confined to the vicinity of the basement low-velocity zone between the MCF and BF. However, a separate alignment of hypocenters occurs southwest of the BF and projects toward the surface beneath Mt. San Jacinto. Collectively, the velocity images and the seismicity data suggest the BF strand of the SAF dips to the northeast at about 50 degrees in the upper 10 km, and the MCF strand is either vertical or dips southwestward about 80 degrees, with both strands merging at about 10 km depth and forming a near-vertical zone of faults to at least 15 km depth. The SSIP Line 6 data are consistent with structures interpreted by Catchings et al. (2009).

Deep Segmentation from 2D Forward Modeling and 3D Tomography of the Maranhão-Barreirinhas-Ceará Margin, NW Brazil

NASA Astrophysics Data System (ADS)

Afonso Dias, Nuno; Afilhado, Alexandra; Schnürle, Philippe; Gallais, Flora; Soares, José; Fuck, Reinhardt; Cupertino, José; Viana, Adriano; Moulin, Maryline; Aslanian, Daniel; Matias, Luís; Evain, Mikael; Loureiro, Afonso

2017-04-01

The deep crustal structure of the North-East equatorial Brazilian margin, was investigated during the MAGIC (Margins of brAzil, Ghana and Ivory Coast) joint project, conducted in 2012. The main goal set to understand the fundamental processes leading to the thinning and finally breakup of the continental crust, in a context of a Pull-apart system with two strike-slip borders. The offshore Barreirinhas Basin, was probed by a set of 5 intersecting deep seismic wide-angle profiles, with the deployment of short-period OBS's from IFREMER and land stations from the Brazilian pool. The experiment was devoted to obtain the 2D structure along the directions of flow lines, parallel to margin segmentation and margin segmentation, from tomography and forward modeling. The OBS's deployed recorded also lateral shooting along some profiles, allowing a 3D tomography inversion complementing the results of 2D modeling. Due to the large variation of the water column thickness, heterogeneous crustal structure and Moho depth, several approaches were tested to generate initial input models, to set the grid parameterization and inversion parameters. The assessment of the 3D model was performed by standard synthetic tests and comparison with the obtained 2D forward models. The results evidence a NW-SE segmentation of the margin, following the opening direction of this pull-apart basin, and N-S segmentation that marks the passage between Basins II-III. The signature of the segmentation is evident in the tomograms, where the shallowing of the basement from Basin II towards the oceanic domain is well marked by a NW-SE velocity gradient. Both 2D forward modeling and 3D tomographic inversion indicate a N-S segmentation in the proto-oceanic and oceanic domains, at least at the shallow mantle level. In the southern area the mantle is much faster than on the north. In all profiles crossing Basin II, a deep layer with velocities of 7-4-7.6 km/s generates both refracted as well as reflected phases from its boundaries, in agreement with the 3D model, which indicate a much more gradual transition of crustal velocities to mantle-velocities, than in the remaining segments. The intersection of Basins II, III and proto-oceanic crust is well marked by the absence of seismic energy propagation at deep crust to mantle levels, with no lateral arrival being recorded. Publication supported by FCT- project UID/GEO/50019/2013 - Instituto Dom Luiz.

Processing and attenuation of noise in deep seismic-reflection data from the Gulf of Maine

USGS Publications Warehouse

Hutchinson, D.R.; Lee, M.W.

1989-01-01

The U.S. Geological Survey deep crustal studies reflection profile across the Gulf of Maine off southeastern New England was affected by three sources of noise: side-scattered noise, multiples, and 20-Hz whale sounds. The special processing most effective in minimizing this noise consisted of a combination of frequency-wavenumber (F-K) filtering, predictive deconvolution, and spectral whitening, each applied in the shot domain (prestack). Application of the F-K filter to remove side-scatter noise in the poststack domain resulted in a much poorer quality profile. The prestack noise suppression processing techniques resulted in a reflection profile with good signal-to-noise ratios and reliable strong reflections, especially at depths equivalent to the lower crust (24-34 km). Certain geologic features, such as a buried rift basin and a crustal fault are resolved much better within the upper crust after this processing. Finite difference migration of these data using realistic velocities produced excellent results. Migration was essential to distinguish between abundant dipping and subhorizontal reflections in the lower crust as well as to show an essentially transparent upper mantle. ?? 1989 Kluwer Academic Publishers.

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

Toksoz, M N; Kuleli, S; Gurbuz, C

The objective of this project is to calibrate regional travel-times and propagation characteristics of seismic waves in Turkey and surrounding areas in the Middle East in order to enhance detection and location capabilities in the region. Important data for the project will be obtained by large calibration shots in central and eastern Turkey. The first, a two-ton shot, was fired in boreholes near Keskin in central Anatolia on 23 November 2002. The explosives were placed in 14 holes, each 80 m deep, arranged in concentric circular arrays. Ninety temporary seismic stations were deployed within a 300 km radius around themore » shot. The permanent stations of the Turkish National Seismic Network provided a good azimuthal coverage as well as three radial traverses. Most stations within a radius of 200 km recorded the shot. Travel-time data have been analyzed to obtain a detailed crustal model under the shot and along the profiles. The model gives a 35 km thick crust, characterized by two layers with velocities of 5.0 and 6.4 km/s. The P{sub n} velocity was found to be 7.8 km/s. The crustal thickness decreases to the north where the profile crosses the North Anatolian fault. There is a slight increase in crustal velocities, but no change in crustal thickness to the west. Data analysis effort is continuing to refine the regional velocity models and to obtain station corrections.« less

Marine Physical Laboratory Multi-Disciplinary Ocean Science and Technology Program

DTIC Science & Technology

1991-04-01

ambierit noise were made with the advent of large. of 3800 m. Reflection profiles and drill logs from this hole scale seismome ter arrays." Sensor arrays...Deaion. and S C Webb."A deep-sea differential pressure frequency. The array was too limited in extent to make spa- gauge ." J. Aimos Ocean Tech. 2. 237...75, 847-864 (1985). 2"P. K Spudich andi I A. Orcutt," Petrology and porcisit% of tn oceanic "M E Dougherty and R. A. Stephen."Seismic energy

Reprocessing and Interpretation of Vintage Seismic Reflection Data: Evidence for the Tectonic History of the Rocky Mountain Trench, Northwest Montana.

NASA Astrophysics Data System (ADS)

Porter, M.; Speece, M. A.; Rutherford, B. S.; Constenius, K. N.

2014-12-01

In 1983 Techno, Inc. collected five seismic reflection profiles in the region between Whitefish, Montana and the United States-Canada border. The poulter method was used to gather four of these profiles and one profile was collected using a vibroseis source. We are currently reprocessing these data in order to construct a regional geological interpretation. The profiles cover a key position in the hinterland of the Cordillera in the lee of the Lewis thrust salient where the east-northeast verging Lewis thrust fault system translated (horizontal displacement >100 km) and inverted a thick, strong slab of primarily Belt-Purcell rocks out of a deep Precambrian depositional basin onto a cratonic platform. In this event, Belt-Purcell rocks were thrust over complexly imbricated Phanerozoic strata in the foreland. Late Mesozoic compressional deformation was followed by Cenozoic extensional collapse of the over-thickened Cordillera and subsequent basin and range style deformation that produced an array of northwest trending grabens. Three of the seismic profiles cross the Rocky Mountain Trench; the Trench is a linear structure of regional dimension that is an expression of the extensional fragmentation of the Cordillera. Strong reflections, interpreted as sills encased within Lower Belt rocks (encountered in the Arco-Marathon 1 Paul Gibbs borehole), outline the complexly folded and faulted structure of the eastern limb of the Purcell anticlinorium. East of the Rocky Mountain Trench stratified reflections within Belt rocks clearly outline the Wigwam Thrust. Beneath the Whitefish Range, an apparent inflection in the strongly reflective basal Cambrian veneer marks the westerly increase in dip of the Rocky Mountain Basal Detachment. The dip contrast between the foreland and hinterland might be a manifestation of the tectonic loading of the Belt basin margin and the loading might have localized extension across the Rocky Mountain Trench.

Seismicity in the source areas of the 1896 and 1933 Sanriku earthquakes and implications for large near-trench earthquake faults

NASA Astrophysics Data System (ADS)

Obana, Koichiro; Nakamura, Yasuyuki; Fujie, Gou; Kodaira, Shuichi; Kaiho, Yuka; Yamamoto, Yojiro; Miura, Seiichi

2018-03-01

In the northern part of the Japan Trench, the 1933 Showa-Sanriku earthquake (Mw 8.4), an outer-trench, normal-faulting earthquake, occurred 37 yr after the 1896 Meiji-Sanriku tsunami earthquake (Mw 8.0), a shallow, near-trench, plate-interface rupture. Tsunamis generated by both earthquakes caused severe damage along the Sanriku coast. Precise locations of earthquakes in the source areas of the 1896 and 1933 earthquakes have not previously been obtained because they occurred at considerable distances from the coast in deep water beyond the maximum operational depth of conventional ocean bottom seismographs (OBSs). In 2015, we incorporated OBSs designed for operation in deep water (ultradeep OBSs) in an OBS array during two months of seismic observations in the source areas of the 1896 and 1933 Sanriku earthquakes to investigate the relationship of seismicity there to outer-rise normal-faulting earthquakes and near-trench tsunami earthquakes. Our analysis showed that seismicity during our observation period occurred along three roughly linear trench-parallel trends in the outer-trench region. Seismic activity along these trends likely corresponds to aftershocks of the 1933 Showa-Sanriku earthquake and the Mw 7.4 normal-faulting earthquake that occurred 40 min after the 2011 Tohoku-Oki earthquake. Furthermore, changes of the clarity of reflections from the oceanic Moho on seismic reflection profiles and low-velocity anomalies within the oceanic mantle were observed near the linear trends of the seismicity. The focal mechanisms we determined indicate that an extensional stress regime extends to about 40 km depth, below which the stress regime is compressional. These observations suggest that rupture during the 1933 Showa-Sanriku earthquake did not extend to the base of the oceanic lithosphere and that compound rupture of multiple or segmented faults is a more plausible explanation for that earthquake. The source area of the 1896 Meiji-Sanriku tsunami earthquake is characterized by an aseismic region landward of the trench axis. Spatial heterogeneity of seismicity and crustal structure might indicate the near-trench faults that could lead to future hazardous events such as the 1896 and 1933 Sanriku earthquakes, and should be taken into account in assessment of tsunami hazards related to large near-trench earthquakes.

The lithosphere architecture and geodynamic of the Middle and Lower Yangtze metallogenic belt in eastern China: constraints from integrated geophysical data

NASA Astrophysics Data System (ADS)

Lü, Qingtian; Shi, Danian; Jiang, Guoming; Dong, Shuwen

2014-05-01

The lithosphere structure and deep processes are keys to understanding mineral system and ore-forming processes. Lithosphere-scale process could create big footprints or signatures which can be observed by geophysics methods. SinoProbe has conducted an integrated deep exploration across middle and lower reaches of Yangtze Metallogenic Belt (YMB) in Eastern China, these included broadband seismic, reflection seismic, wide-angle reflection and magnetotellurics survey. Seismic reflection profiles and MT survey were also performed in Luzong, Tongling and Ningwu ore districts to construct 3D geological model. The resulting geophysical data provides new information which help to better understanding the lithosphere structure, geodynamic, deformation and heat and mass transportation that lead to the formation of the Metallogenic Belt. The major results are: (1) Lower velocity body at the top of upper mantle and a SE dipping high velocity body were imaged by teleseismic tomography beneath YMB; (2) Shear wave splitting results show NE parallel fast-wave polarization direction which parallel with tectonic lineament; (3) The reflection seismic data support the crustal-detachment model, the lower and upper crust was detached during contraction deformation near Tanlu fault and Ningwu volcanic basin; (4) Broadband and reflection seismic confirm the shallow Moho beneath YMB; (5) Strong correlation of lower crust reflectivity with magmatism; (6) The lower crust below Luzong Volcanics shows obvious reflective anisotropy both at the crust-mantle transition and the brittle-ductile transition in the crust. All these features suggest that introcontinental subduction, lithosphere delamination, mantle sources magmatic underplating, and MASH process are responsible for the formation of this Mesozoic metallogenic belt. Acknowledgment: We acknowledge the financial support of SinoProbe by the Ministry of Finance and Ministry of Land and Resources, P. R. China, under Grant sinoprobe-03, and financial support by National Natural Science Foundation of China under Grant 40930418

Slab seismicity in the Western Hellenic Subduction Zone: Constraints from tomography and double-difference relocation

NASA Astrophysics Data System (ADS)

Halpaap, Felix; Rondenay, Stéphane; Ottemöller, Lars

2016-04-01

The Western Hellenic subduction zone is characterized by a transition from oceanic to continental subduction. In the southern oceanic portion of the system, abundant seismicity reaches intermediate depths of 100-120 km, while the northern continental portion rarely exhibits deep earthquakes. Our study aims to investigate how this oceanic-continental transition affects fluid release and related seismicity along strike, by focusing on the distribution of intermediate depth earthquakes. To obtain a detailed image of the seismicity, we carry out a tomographic inversion for P- and S-velocities and double-difference earthquake relocation using a dataset of unprecedented spatial coverage in this area. Here we present results of these analyses in conjunction with high-resolution profiles from migrated receiver function images obtained from the MEDUSA experiment. We generate tomographic models by inverting data from 237 manually picked, well locatable events recorded at up to 130 stations. Stations from the permanent Greek network and the EGELADOS experiment supplement the 3-D coverage of the modeled domain, which covers a large part of mainland Greece and surrounding offshore areas. Corrections for the sphericity of the Earth and our update to the SIMULR16 package, which now allows S-inversion, help improve our previous models. Flexible gridding focusses the inversion on the domains of highest gradient around the slab, and we evaluate the resolution with checker board tests. We use the resulting velocity model to relocate earthquakes via the Double-Difference method, using a large dataset of differential traveltimes obtained by crosscorrelation of seismograms. Tens of earthquakes align along two planes forming a double seismic zone in the southern, oceanic portion of the subduction zone. With increasing subduction depth, the earthquakes appear closer to the center of the slab, outlining probable deserpentinization of the slab and concomitant eclogitization of dry crustal rocks. Against expectations, we relocate one robust deep event at ≈70 km depth in the northern, continental part of the subduction zone.

Investigating the ocean generated acoustic/seismic wavefields in NE Atlantic

NASA Astrophysics Data System (ADS)

Le Pape, F.; Bean, C. J.; Craig, D.; Jousset, P.; Donne, S. E.; Möllhoff, M.

2017-12-01

In this study, we look at the comparison of 3D simulations of acoustic and seismic waves propagation with OBS data recorded across the shelf offshore Ireland and out into the Rockall Trough. Real and synthetic observations are combined to characterize both acoustic and seismic wavefields in the marine environment and particularly study secondary microseisms propagation from deep to shallow water to the land. Whereas the recorded OBS data show a strong change in the energy of "noise events" in the primary microseism band from the shelf to the land, the secondary microseism band is associated with stronger signal in the deep water compared to the shelf area. Furthermore, the data also highlight seasonal variations in the seismic and acoustic wavefields likely related to changes in noise source locations. The 3D simulations of acoustic and seismic waves propagation in the Rockall Trough look promising to reconcile deep ocean, shelf and land seismic observations as well as the effect of the water column and sediments thickness on "seismic ambient noise" generation and propagation. For instance, the simulations reveal interesting results on the acoustic/seismic coupling and its implication on the secondary microseisms source origin. This project is part of the Irish Centre for Research in Applied Geoscience (ICRAG), funded under the SFI Research Centres Programme and is co-funded under the European Regional Development Fund.

Seismic stability of the survey areas of potential sites for the deep geological repository of the spent nuclear fuel

NASA Astrophysics Data System (ADS)

Kaláb, Zdeněk; Šílený, Jan; Lednická, Markéta

2017-07-01

This paper deals with the seismic stability of the survey areas of potential sites for the deep geological repository of the spent nuclear fuel in the Czech Republic. The basic source of data for historical earthquakes up to 1990 was the seismic website [1-]. The most intense earthquake described occurred on September 15, 1590 in the Niederroesterreich region (Austria) in the historical period; its reported intensity is Io = 8-9. The source of the contemporary seismic data for the period since 1991 to the end of 2014 was the website [11]. It may be stated based on the databases and literature review that in the period from 1900, no earthquake exceeding magnitude 5.1 originated in the territory of the Czech Republic. In order to evaluate seismicity and to assess the impact of seismic effects at depths of hypothetical deep geological repository for the next time period, the neo-deterministic method was selected as an extension of the probabilistic method. Each one out of the seven survey areas were assessed by the neo-deterministic evaluation of the seismic wave-field excited by selected individual events and determining the maximum loading. Results of seismological databases studies and neo-deterministic analysis of Čihadlo locality are presented.

Imaging a Hydrate-Related Cold Vent Offshore Vancouver Island From Deep-Towed Multichannel Seismic Data

DTIC Science & Technology

2009-02-20

vent). 2500 2600 2700 Distance (m) 2800 2900 3000 1.791 Figure 11. Southeast-northwest seismic section, showing hydrate cap details from DTI 6. The...line DT16 Line DTI 6 continues as a long transit line extending to the north- west. The 1999 COAMS (Canadian Ocean Acoustic Measurement System) grid...inline IN26 is coincident with DTI 6 (Figure 1). A com- bination of the surface-towed seismic data and the deep-towed DTAGS data is needed to provide

Understanding Seismic Anisotropy in Hunt Well of Fort McMurray, Canada

NASA Astrophysics Data System (ADS)

Malehmir, R.; Schmitt, D. R.; Chan, J.

2014-12-01

Seismic imaging plays vital role in geothermal systems as a sustainable energy resource. In this paper, we acquired and processed zero-offset and walk-away VSP and logging as well as surface seismic in Athabasca oil sand area, Alberta. Seismic data were highly processed to make better image geothermal system. Through data processing, properties of natural fractures such as orientation and width were studied and high probable permeable zones were mapped along the deep drilled to the depth of 2363m deep into crystalline basement rocks. In addition to logging data, seismic data were processed to build a reliable image of underground. Velocity analysis in high resolution multi-component walk-away VSP informed us about the elastic anisotropy in place. Study of the natural and induced fracture as well as elastic anisotropy in the seismic data, led us to better map stress regime around the well bore. The seismic image and map of fractures optimizes enhanced geothermal stages through hydraulic stimulation. Keywords: geothermal, anisotropy, VSP, logging, Hunt well, seismic

Identification of deep subaqueous co-seismic scarps through specific coeval sedimentation in Lesser Antilles: implication for seismic hazard

NASA Astrophysics Data System (ADS)

Beck, C.; Reyss, J.-L.; Leclerc, F.; Moreno, E.; Feuillet, N.; Barrier, L.; Beauducel, F.; Boudon, G.; Clément, V.; Deplus, C.; Gallou, N.; Lebrun, J.-F.; Le Friant, A.; Nercessian, A.; Paterne, M.; Pichot, T.; Vidal, C.

2012-05-01

During the GWADASEIS cruise (Lesser Antilles volcanic arc, February-March 2009) a very high resolution (VHR) seismic-reflection survey was performed in order to constrain Late Quaternary to Present faulting. The profiles we obtained evidence frequent "ponding" of reworked sediments in the deepest areas, similar to the deposition of Mediterranean "homogenites". These bodies are acoustically transparent (few ms t.w.t. thick) and are often deposited on the hanging walls of dominantly normal faults, at the base of scarps. Their thickness appears sufficient to compensate (i.e. bury) co-seismic scarps between successive earthquakes, resulting in a flat and horizontal sea floor through time. In a selected area (offshore Montserrat and Nevis islands), piston coring (4 to 7 m long) was dedicated to a sedimentological analysis of the most recent of these particular layers. It corresponds to non-stratified homogenous calcareous silty sand (reworked calcareous plankton and minor volcanoclastics). This layer can be up to 2 m thick, and overlies fine-grained hemipelagites. The upper centimeters of the latter represent the normal RedOx water/sediment interface. 210Pb and 137Cs activities lack in the massive sands, while a normal profile of unsupported 210Pb decrease is observed in the hemipelagite below, together with a 137Cs peak corresponding to the Atmospheric Nuclear Experiments (1962). The RedOx level was thus capped by a recent instantaneous major sedimentary event considered as post-1970 AD; candidate seismic events to explain this sedimentary deposits are either the 16 March 1985 earthquake or the 8 October 1974 one (Mw = 6.3 and Mw = 7.4, respectively). This leads to consider that the syntectonic sedimentation in this area is not continuous but results from accumulation of thick homogenites deposited after the earthquakes (as observed in the following weeks after Haiti January 2010 event, McHugh et al., 2011). The existence of such deposits suggests that, in the area of study, vertical throw likely results from cumulated effects of separated earthquakes rather than from aseismic creep. Examination of VHR profiles shows that all major co-seismic offsets are recorded in the fault growth sequence and that co-seismic offsets can be precisely estimated. By using a sedimentation rate deduced from 210Pb decrease curve (0.5 mm yr-1) and taking into account minor reworking events detected in cores, we show that the Redonda system may have been responsible for five >M6 events during the last 34 000 yr. The approach presented in this work differs from fault activity analyses using displaced sets of isochronous surfaces and postulating co-seismic offsets. Combining VHR seismic imagery and coring we can decipher co-seismic vs. slow continuous displacement, and thus actually estimate the amplitude and the time distribution of major co-seismic offsets.

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

USGS Publications Warehouse

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

1995-01-01

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

Preliminary results from combined wide-angle and reflection seismic data in the Natal Valley, South Mozambique margin across the Almirante Leite volcanic ridge : MZ2 profile (MOZ3/5 cruise).

NASA Astrophysics Data System (ADS)

Verrier, Fanny; Leprêtre, Angélique; Evain, Mikael; Schnurle, Philippe; Watremez, Louise; Aslanian, Daniel; De Clarens, Philippe; Afonso Dias, Nuno; Afilhado, Alexandra; Leroy, Sylvie; d'Acremont, Elia; Castilla, Raymi; Moulin, Maryline

2017-04-01

The study of South Mozambique passive margin is essential to understand its rifting evolution and better constrain kinematic reconstructions model of the Indian Ocean. MOZ3-5 oceanographic cruises (2016) is part of the PAMELA project (PAssive Margin Exploration LAboratory), conducted by TOTAL, IFREMER, in collaboration with Université de Bretagne Occidentale, Université Rennes 1, Université Pierre and Marie Curie, CNRS et IFPEN. These campaigns allowed the acquisition of wide-angle and multichannel seismic data as well as high resolution bathymetric data, dredges, magnetic and gravimetric data. This work focuses on the deep structure of the northern segment of the Natal Valley which was investigated along a 300 km long E-W seismic transect cross-cutting the Almirante Leite volcanic ridge (MZ2 profile). The wide-angle data set is composed of 23 OBS (Ocean Bottom Seismometers) and 19 LSS (Land Seismic Station) spaced by about 12 km and 4-5 km respectively. Forward modelling of the wide-angle data led to a preliminary 2D P-waves velocity model revealing the sedimentary architecture, crustal and lithospherical structures and shallow high velocity material at the volcanic ridge. The aim of this work is to present the first results on the crustal structure from P-waves velocity modeling along the profile MZ2, in order to discuss the sedimentary sequences, the geometry and nature of the crust (oceanic or continental) as well as structures associated with volcanism, and to better understand the margin's evolution. The post-doc of Fanny Verrier is co-funded by TOTAL and IFREMER as part of the PAMELA (Passive Margin Exploration Laboratories) scientific project. Moulin, M., Aslanian, D., 2016. PAMELA-MOZ03 cruise, RV Pourquoi pas ?, http://dx.doi.org/10.17600/16001600 Moulin, M., Evain, M., 2016. PAMELA-MOZ05 cruise, RV Pourquoi pas ?, http://dx.doi.org/10.17600/16009500

A crustal model of the ultrahigh-pressure Dabie Shan orogenic belt, China, derived from deep seismic refraction profiling

USGS Publications Warehouse

Wang, Chun-Yong; Zeng, Rong-Sheng; Mooney, W.D.; Hacker, B.R.

2000-01-01

We present a new crustal cross section through the east-west trending ultrahigh-pressure (UHP) Dabie Shan orogenic belt, east central China, based on a 400-km-long seismic refraction profile. Data from our profile reveal that the cratonal blocks north and south of the orogen are composed of 35-km-thick crust consisting of three layers (upper, middle, and lower crust) with average seismic velocities of 6.0±0.2 km/s, 6.5±0.1 km/s, and 6.8±0.1 km/s. The crust reaches a maximum thickness of 41.5 km beneath the northern margin of the orogen, and thus the present-day root beneath the orogen is only 6.5 km thick. The upper mantle velocity is 8.0±0.1 km/s. Modeling of shear wave data indicate that Poisson's ratio increases from 0.24±0.02 in the upper crust to 0.27±0.03 in the lower crust. This result is consistent with a dominantly felsic upper crustal composition and a mafic lower crustal composition within the amphibolite or granulite metamorphic facies. Our seismic model indicates that eclogite, which is abundant in surface exposures within the orogen, is not a volumetrically significant component in the middle or lower crust. Much of the Triassic structure associated with the formation of the UHP rocks of the Dabie Shan has been obscured by post-Triassic igneous activity, extension and large-offset strike-slip faulting. Nevertheless, we can identify a high-velocity (6.3 km/s) zone in the upper (<5 km depth) crustal core of the orogen which we interpret as a zone of ultrahigh-pressure rocks, a north dipping suture, and an apparent Moho offset that marks a likely active strike-slip fault.

Analysis and seismic tests of composite shear walls with CFST columns and steel plate deep beams

NASA Astrophysics Data System (ADS)

Dong, Hongying; Cao, Wanlin; Wu, Haipeng; Zhang, Jianwei; Xu, Fangfang

2013-12-01

A composite shear wall concept based on concrete filled steel tube (CFST) columns and steel plate (SP) deep beams is proposed and examined in this study. The new wall is composed of three different energy dissipation elements: CFST columns; SP deep beams; and reinforced concrete (RC) strips. The RC strips are intended to allow the core structural elements — the CFST columns and SP deep beams — to work as a single structure to consume energy. Six specimens of different configurations were tested under cyclic loading. The resulting data are analyzed herein. In addition, numerical simulations of the stress and damage processes for each specimen were carried out, and simulations were completed for a range of location and span-height ratio variations for the SP beams. The simulations show good agreement with the test results. The core structure exhibits a ductile yielding mechanism characteristic of strong column-weak beam structures, hysteretic curves are plump and the composite shear wall exhibits several seismic defense lines. The deformation of the shear wall specimens with encased CFST column and SP deep beam design appears to be closer to that of entire shear walls. Establishing optimal design parameters for the configuration of SP deep beams is pivotal to the best seismic behavior of the wall. The new composite shear wall is therefore suitable for use in the seismic design of building structures.

Subduction zone seismicity and the thermo-mechanical evolution of downgoing lithosphere

NASA Astrophysics Data System (ADS)

Wortel, M. J. R.; Vlaar, N. J.

1988-09-01

In this paper we discuss characteristic features of subduction zone seismicity at depths between about 100 km and 700 km, with emphasis on the role of temperature and rheology in controlling the deformation of, and the seismic energy release in downgoing lithosphere. This is done in two steps. After a brief review of earlier developments, we first show that the depth distribution of hypocentres at depths between 100 km and 700 km in subducted lithosphere can be explained by a model in which seismic activity is confined to those parts of the slab which have temperatures below a depth-dependent critical value T cr. Second, the variation of seismic energy release (frequency of events, magnitude) with depth is addressed by inferring a rheological evolution from the slab's thermal evolution and by combining this with models for the system of forces acting on the subducting lithosphere. It is found that considerable stress concentration occurs in a reheating slab in the depth range of 400 to 650 700 km: the slab weakens, but the stress level strongly increases. On the basis of this stress concentration a model is formulated for earthquake generation within subducting slabs. The model predicts a maximum depth of seismic activity in the depth range of 635 to 760 km and, for deep earthquake zones, a relative maximum in seismic energy release near the maximum depth of earthquakes. From our modelling it follows that, whereas such a maximum is indeed likely to develop in deep earthquake zones, zones with a maximum depth around 300 km (such as the Aleutians) are expected to exhibit a smooth decay in seismic energy release with depth. This is in excellent agreement with observational data. In conclusion, the incoroporation of both depth-dependent forces and depth-dependent rheology provides new insight into the generation of intermediate and deep earthquakes and into the variation of seismic activity with depth. Our results imply that no barrier to slab penetration at a depth of 650 700 km is required to explain the maximum depth of seismic activity and the pattern of seismic energy release in deep earthquake zones.

The Sensitivity of Joint Inversions of Seismic and Geodynamic Data to Mantle Viscosity

NASA Astrophysics Data System (ADS)

Lu, C.; Grand, S. P.; Forte, A. M.; Simmons, N. A.

2017-12-01

Seismic tomography has mapped the existence of large scale mantle heterogeneities in recent years. However, the origin of these velocity anomalies in terms of chemical and thermal variations is still under debate due to the limitations of tomography. Joint inversion of seismic, geodynamic, and mineral physics observations has proven to be a powerful tool to decouple thermal and chemical effects in the deep mantle (Simmons et al. 2010). The approach initially attempts to find a model that can be explained assuming temperature controls lateral variations in mantle properties and then to consider more complicated lateral variations that account for the presence of chemical heterogeneity to further fit data. The geodynamic observations include Earth's free air gravity field, tectonic plate motions, dynamic topography and the excess ellipticity of the core. The sensitivity of the geodynamic observables to density anomalies, however, depends on an assumed radial mantle viscosity profile. Here we perform joint inversions of seismic and geodynamic data using a number of published viscosity profiles. The goal is to test the sensitivity of joint inversion results to mantle viscosity. For each viscosity model, geodynamic sensitivity kernels are calculated and used to jointly invert the geodynamic observations as well as a new shear wave data set for a model of density and seismic velocity. Also, compared with previous joint inversion studies, two major improvements have been made in our inversion. First, we use a nonlinear inversion to account for anelastic effects. Applying the very fast simulate annealing (VFSA) method, we let the elastic scaling factor and anelastic parameters from mineral physics measurements vary within their possible ranges and find the best fitting model assuming thermal variations are the cause of the heterogeneity. We also include an a priori subducting slab model into the starting model. Thus the geodynamic and seismic signatures of short wavelength subducting slabs are better accounted for in the inversions. Reference: Simmons, N. A., A. M. Forte, L. Boschi, and S. P. Grand (2010), GyPSuM: A joint tomographic model of mantle density and seismic wave speeds, Journal of Geophysical Research: Solid Earth, 115(B12), B12310

Linking magma transport structures at Kīlauea volcano

USGS Publications Warehouse

Wech, Aaron G.; Thelen, Weston A.

2015-01-01

Identifying magma pathways is important for understanding and interpreting volcanic signals. At Kīlauea volcano, seismicity illuminates subsurface plumbing, but the broad spectrum of seismic phenomena hampers event identification. Discrete, long-period events (LPs) dominate the shallow (5-10 km) plumbing, and deep (40+ km) tremor has been observed offshore. However, our inability to routinely identify these events limits their utility in tracking ascending magma. Using envelope cross-correlation, we systematically catalog non-earthquake seismicity between 2008-2014. We find the LPs and deep tremor are spatially distinct, separated by the 15-25 km deep, horizontal mantle fault zone (MFZ). Our search corroborates previous observations, but we find broader-band (0.5-20 Hz) tremor comprising collocated earthquakes and reinterpret the deep tremor as earthquake swarms in a volume surrounding and responding to magma intruding from the mantle plume beneath the MFZ. We propose the overlying MFZ promotes lateral magma transport, linking this deep intrusion with Kīlauea’s shallow magma plumbing.

Evolution of basin and range structure in the Ruby Mountains and vicinity, Nevada

NASA Technical Reports Server (NTRS)

Blackwell, D. D.; Reese, N. M.; Kelley, S. A.

1985-01-01

Results from various age dating techniques, seismic reflection profiling hydrocarbon maturation studies, and structural analysis were used to evaluate the Cenozoic deformation in the Ruby Mountains and adjoining ranges (pinyon Range and Cortez Range) in Elko and Eureka Counties, Nevada. Age dating techniques used include potassium-argon ages of biotites from granites published by Kistler et al. (1981) and fission track ages from apatite and zircon. Fission track ages from apatite reflect a closing temperature of 100 plus or minus 20 deg C. Zircon fission track ages reflect a closing temperature of 175 plus or minus 25 deg C and potassium-argon ages from brotite reflect a closing temperature of 250 plus or minus 30 deg C. Thus these results allow a reasonably precise tracking of the evolution of the ranges during the Cenozoic. Seismic reflection data are available from Huntington Valley. Access to seismic reflection data directly to the west of the Harrison Pass Pluton in the central Ruby Mountains was obtained. In addition results are available from several deep exploration holes in Huntington Valley.

Seismic tomography as a tool for measuring stress in mines

USGS Publications Warehouse

Scott, Douglas F.; Williams, T.J.; Denton, D.K.; Friedel, M.J.

1999-01-01

Spokane Research Center personnel have been investigating the use of seismic tomography to monitor the behavior of a rock mass, detect hazardous ground conditions and assess the mechanical integrity of a rock mass affected by mining. Seismic tomography can be a valuable tool for determining relative stress in deep, >1,220-m (>4,000-ft), underground pillars. If high-stress areas are detected, they can be destressed prior to development or they can be avoided. High-stress areas can be monitored with successive seismic surveys to determine if stress decreases to a level where development can be initiated safely. There are several benefits to using seismic tomography to identify high stress in deep underground pillars. The technique is reliable, cost-effective, efficient and noninvasive. Also, investigators can monitor large rock masses, as well as monitor pillars during the mining cycle. By identifying areas of high stress, engineers will be able to assure that miners are working in a safer environment.Spokane Research Center personnel have been investigating the use of seismic tomography to monitor the behavior of a rock mass, detect hazardous ground conditions and assess the mechanical integrity of a rock mass affected by mining. Seismic tomography can be a valuable tool for determining relative stress in deep, >1,200-m (>4,000-ft), underground pillars. If high-stress areas are detected, they can be destressed prior to development or they can be avoided. High-stress areas can be monitored with successive seismic surveys to determine if stress decreases to a level where development can be initiated safely. There are several benefits to using seismic tomography to identify high stress in deep underground pillars. The technique is reliable, cost-effective, efficient and noninvasive. Also, investigators can monitor large rock masses, as well as monitor pillars during the mining cycle. By identifying areas of high stress. engineers will be able to assure that miners are working in a safer environment.

Discriminating between natural versus induced seismicity from long-term deformation history of intraplate faults.

PubMed

Magnani, Maria Beatrice; Blanpied, Michael L; DeShon, Heather R; Hornbach, Matthew J

2017-11-01

To assess whether recent seismicity is induced by human activity or is of natural origin, we analyze fault displacements on high-resolution seismic reflection profiles for two regions in the central United States (CUS): the Fort Worth Basin (FWB) of Texas and the northern Mississippi embayment (NME). Since 2009, earthquake activity in the CUS has increased markedly, and numerous publications suggest that this increase is primarily due to induced earthquakes caused by deep-well injection of wastewater, both flowback water from hydrofracturing operations and produced water accompanying hydrocarbon production. Alternatively, some argue that these earthquakes are natural and that the seismicity increase is a normal variation that occurs over millions of years. Our analysis shows that within the NME, faults deform both Quaternary alluvium and underlying sediments dating from Paleozoic through Tertiary, with displacement increasing with geologic unit age, documenting a long history of natural activity. In the FWB, a region of ongoing wastewater injection, basement faults show deformation of the Proterozoic and Paleozoic units, but little or no deformation of younger strata. Specifically, vertical displacements in the post-Pennsylvanian formations, if any, are below the resolution (~15 m) of the seismic data, far less than expected had these faults accumulated deformation over millions of years. Our results support the assertion that recent FWB earthquakes are of induced origin; this conclusion is entirely independent of analyses correlating seismicity and wastewater injection practices. To our knowledge, this is the first study to discriminate natural and induced seismicity using classical structural geology analysis techniques.

Discriminating between natural versus induced seismicity from long-term deformation history of intraplate faults

PubMed Central

Magnani, Maria Beatrice; Blanpied, Michael L.; DeShon, Heather R.; Hornbach, Matthew J.

2017-01-01

To assess whether recent seismicity is induced by human activity or is of natural origin, we analyze fault displacements on high-resolution seismic reflection profiles for two regions in the central United States (CUS): the Fort Worth Basin (FWB) of Texas and the northern Mississippi embayment (NME). Since 2009, earthquake activity in the CUS has increased markedly, and numerous publications suggest that this increase is primarily due to induced earthquakes caused by deep-well injection of wastewater, both flowback water from hydrofracturing operations and produced water accompanying hydrocarbon production. Alternatively, some argue that these earthquakes are natural and that the seismicity increase is a normal variation that occurs over millions of years. Our analysis shows that within the NME, faults deform both Quaternary alluvium and underlying sediments dating from Paleozoic through Tertiary, with displacement increasing with geologic unit age, documenting a long history of natural activity. In the FWB, a region of ongoing wastewater injection, basement faults show deformation of the Proterozoic and Paleozoic units, but little or no deformation of younger strata. Specifically, vertical displacements in the post-Pennsylvanian formations, if any, are below the resolution (~15 m) of the seismic data, far less than expected had these faults accumulated deformation over millions of years. Our results support the assertion that recent FWB earthquakes are of induced origin; this conclusion is entirely independent of analyses correlating seismicity and wastewater injection practices. To our knowledge, this is the first study to discriminate natural and induced seismicity using classical structural geology analysis techniques. PMID:29202029

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

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

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

1986-08-01

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

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

NASA Astrophysics Data System (ADS)

Chen, N.; Li, C. F.

2017-12-01

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

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

NASA Astrophysics Data System (ADS)

Fillerup, Melvin A.

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

Investigation on the real-time prediction of ground motions using seismic records observed in deep boreholes

NASA Astrophysics Data System (ADS)

Miyakoshi, H.; Tsuno, S.

2013-12-01

The present method of the EEW system installed in the railway field of Japan predicts seismic ground motions based on the estimated earthquake information about epicentral distances and magnitudes using initial P-waves observed on the surface. In the case of local earthquakes beneath the Tokyo Metropolitan Area, however, a method to directly predict seismic ground motions using P-waves observed in deep boreholes could issue EEWs more simply and surely. Besides, a method to predict seismic ground motions, using S-waves observed in deep boreholes and S-wave velocity structures beneath seismic stations, could show planar distributions of ground motions for train operation control areas in the aftermath of earthquakes. This information is available to decide areas in which the emergency inspection of railway structures should be performed. To develop those two methods, we investigated relationships between peak amplitudes on the surface and those in deep boreholes, using seismic records of KiK-net stations in the Kanto Basin. In this study, we used earthquake accelerograms observed in boreholes whose depths are deeper than the top face of Pre-Neogene basement and those on the surface at 12 seismic stations of KiK-net. We selected 243 local earthquakes whose epicenters are located around the Kanto Region. Those JMA magnitudes are in the range from 4.5 to 7.0. We picked the on-set of P-waves and S-waves using a vertical component and two horizontal components, respectively. Peak amplitudes of P-waves and S-waves were obtained using vertical components and vector sums of two horizontal components, respectively. We estimated parameters which represent site amplification factors beneath seismic stations, using peak amplitudes of S-waves observed in the deep borehole and those on the surface, to minimize the residuals between calculations by the theoretical equation and observations. Correlation coefficients between calculations and observations are high values in the range from 0.8 to 0.9. This result suggests that we could predict ground motions with the high accuracy using peak amplitudes of S-waves in deep boreholes and site amplification factors based on S-wave velocity structures. Also, we estimated parameters which represent radiation coefficients and the P/S velocity ratios around hypocentral regions, using peak amplitudes of P-waves and S-waves observed in deep boreholes, to minimize the residuals between calculations and observations. Correlation coefficients between calculations and observations are slightly lower values in the range from 0.7 to 0.9 than those for site amplification factors. This result suggests that the variability of radiation patterns for individual earthquakes affects the accuracy to predict ground motions using P-waves in deep boreholes.

High-resolution and Deep Crustal Imaging Across The North Sicily Continental Margin (southern Tyrrhenian Sea)

NASA Astrophysics Data System (ADS)

Agate, M.; Bertotti, G.; Catalano, R.; Pepe, F.; Sulli, A.

Three multichannel seismic reflection profiles across the North Sicily continental mar- gin have been reprocessed and interpreted. Data consist of an unpublished high pene- tration seismic profile (deep crust Italian CROP Project) and a high-resolution seismic line. These lines run in the NNE-SSW direction, from the Sicilian continental shelf to the Tyrrhenian abyssal plain (Marsili area), and are tied by a third, high penetration seismic line MS104 crossing the Sisifo High. The North Sicily continental margin represents the inner sector of the Sicilian-Maghrebian chain that is collapsed as con- sequence of extensional tectonics. The chain is formed by a tectonic wedge (12-15 km thick. It includes basinal Meso-Cenozoic carbonate units overthrusting carbonate platform rock units (Catalano et al., 2000). Presently, main culmination (e.g. Monte Solunto) and a number of tectonic depressions (e.g. Cefalù basin), filled by >1000 m thick Plio-Pleistocene sedimentary wedge, are observed along the investigated tran- sect. Seismic attributes and reflector pattern depicts a complex crustal structure. Be- tween the coast and the M. Solunto high, a transparent to diffractive band (assigned to the upper crust) is recognised above low frequency reflective layers (occurring be- tween 9 and 11 s/TWT) that dips towards the North. Their bottom can be correlated to the seismological (African?) Moho discontinuity which is (26 km deep in the Sicilian shelf (Scarascia et al., 1994). Beneath the Monte Solunto ridge, strongly deformed re- flectors occurring between 8 to 9.5 s/TWT (European lower crust?) overly the African (?) lower crust. The resulting geometry suggests underplating of the African crust respect to the European crust (?). The already deformed crustal edifice is dissected by a number of N-dipping normal faults that open extensional basins and are associ- ated with crustal thinning. The Plio-Pleistocene fill of the Cefalù basin can be subdi- vided into three subunits by well-developed unconformities. The stratal pattern of the lower subunit (Early Pliocene?) points out thrust-top basin. The intermediate subunit (Middle-Late Pliocene?) shows a wide sedimentary lateral accretion with syntectonic growth geometries. Upper Pliocene layers are overlain by well-stratified sediments of supposedly Pleistocene to Recent age, which drape and smooth underlying features (Pepe et al., 2000). Crustal thinning is (2 in the Cefalù basin and reach (3.54 north of Sisifo volcano, where crustal separation occurs and oceanic crust emplaced (Marsili 1 basin). In this area the Moho is located at (8 s/TWT, corresponding to 10-km depth. References Catalano R., Franchino A., Merlini S. e Sulli A., 2000. Mem. Soc. Geol. It., 55, 5-16. Pepe F., Bertotti G., Cella F. Marsella E., 2000. Tectonics, 19, 241-257. Scarascia S., Lozej A. Cassinis R., 1994. Boll. Geof. Teor. Appl., 36 (141-144), 5-19. 2

First seismic shear wave velocity profile of the lunar crust as extracted from the Apollo 17 active seismic data by wavefield gradient analysis

NASA Astrophysics Data System (ADS)

Sollberger, David; Schmelzbach, Cedric; Robertsson, Johan O. A.; Greenhalgh, Stewart A.; Nakamura, Yosio; Khan, Amir

2016-04-01

We present a new seismic velocity model of the shallow lunar crust, including, for the first time, shear wave velocity information. So far, the shear wave velocity structure of the lunar near-surface was effectively unconstrained due to the complexity of lunar seismograms. Intense scattering and low attenuation in the lunar crust lead to characteristic long-duration reverberations on the seismograms. The reverberations obscure later arriving shear waves and mode conversions, rendering them impossible to identify and analyze. Additionally, only vertical component data were recorded during the Apollo active seismic experiments, which further compromises the identification of shear waves. We applied a novel processing and analysis technique to the data of the Apollo 17 lunar seismic profiling experiment (LSPE), which involved recording seismic energy generated by several explosive packages on a small areal array of four vertical component geophones. Our approach is based on the analysis of the spatial gradients of the seismic wavefield and yields key parameters such as apparent phase velocity and rotational ground motion as a function of time (depth), which cannot be obtained through conventional seismic data analysis. These new observables significantly enhance the data for interpretation of the recorded seismic wavefield and allow, for example, for the identification of S wave arrivals based on their lower apparent phase velocities and distinct higher amount of generated rotational motion relative to compressional (P-) waves. Using our methodology, we successfully identified pure-mode and mode-converted refracted shear wave arrivals in the complex LSPE data and derived a P- and S-wave velocity model of the shallow lunar crust at the Apollo 17 landing site. The extracted elastic-parameter model supports the current understanding of the lunar near-surface structure, suggesting a thin layer of low-velocity lunar regolith overlying a heavily fractured crust of basaltic material showing high (>0.4 down to 60 m) Poisson's ratios. Our new model can be used in future studies to better constrain the deep interior of the Moon. Given the rich information derived from the minimalistic recording configuration, our results demonstrate that wavefield gradient analysis should be critically considered for future space missions that aim to explore the interior structure of extraterrestrial objects by seismic methods. Additionally, we anticipate that the proposed shear wave identification methodology can also be applied to the routinely recorded vertical component data from land seismic exploration on Earth.

Saudi Arabian seismic deep-refraction profiles; final project report

USGS Publications Warehouse

Healy, J.H.; Mooney, W.D.; Blank, H.R.; Gettings, M.E.; Kohler, W.M.; Lamson, R.J.; Leone, L.E.

1983-01-01

In February 1978 a seismic deep-refraction profile was recorded by the U.S. Geological Survey along a 1000-km line across the Arabian Shield in western Saudi Arabia. The line begins in Mesozoic cover rocks near Riyadh on the Arabian Platform, leads southwesterly across three major Precambrian tectonic provinces, traverses Cenozoic rocks of the coastal plain near Jizan (Tihamat-Asir), and terminates at the outer edge of the Farasan Bank in the southern Red Sea. More than 500 surveyed recording sites were occupied, including 19 in the Farasan Islands. Six shot points were used: five on land, with most charges placed below the water table in drill holes, and one at sea, with charges placed on the sea floor and detonated from a ship. Slightly more than 61 metric tons of explosives were used in 19 discrete firings. Seismic energy was recorded by 100 newly-developed portable seismic stations deployed in approximately 200 km-long arrays for each firing. Each station consisted of a standard 2-Hz vertical component geophone coupled to a self-contained analog recording instrument equipped with a magnetic-tape cassette. In this final report, we fully document the field and data-processing procedures and present the final seismogram data set as both a digital magnetic tape and as record sections for each shot point. Record sections include a normalized set of seismograms, reduced at 6 km/s, and a true-amplitude set, reduced at 8 km/s, which have been adjusted for amplifier gain, individual shot size, and distance from the shot point. Appendices give recorder station and shot information, digital data set descriptions, computer program listings, arrival times used in the interpretation, and a bibliography of reports published as a result of this project. We used two-dimensional ray-tracing techniques in the data analysis, and our interpretation is based primarily on horizontally layered models. The Arabian Shield is composed, to first-order, of two layers, each about 20 km thick, with average velocities of 6.3 km/s and 7.0 km/s, respectively. At the western shield margin the crust thins to less than 20 km total thickness, beyond which the Red Sea shelf and coastal plain are interpreted to be underlain by oceanic crust. A major crustal lateral velocity inhomogeneity northeast of Sabhah in the Shammar Tectonic Province is interpreted as the suture zone of two crustal blocks of different composition. Several high-velocity anomalies in the upper crust correlate with mapped gneissic dome structures. Two intra-crustal reflectors at13 km depth are interpreted as the tops of mafic intrusives. The Mohorovicic discontinuity beneath the shield varies from 43 km depth in the northeast with 8.2 km/s mantle velocity to 38 km depth in the southwest with 8.0 km/s mantle velocity. Two velocity discontinuities are identified in the upper mantle, at 59 and 70 km depth. We suggest further work, including refined analyses of the data employing filtering and synthetic seismogram techniques, as well as consideration of attenuation properties. Extension of the seismic refraction profile to the Arabian Gulf and some short profiles perpendicular to the existing profile would be fruitful areas for future field work.

Advanced Seismic While Drilling System

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

Robert Radtke; John Fontenot; David Glowka

A breakthrough has been discovered for controlling seismic sources to generate selectable low frequencies. Conventional seismic sources, including sparkers, rotary mechanical, hydraulic, air guns, and explosives, by their very nature produce high-frequencies. This is counter to the need for long signal transmission through rock. The patent pending SeismicPULSER{trademark} methodology has been developed for controlling otherwise high-frequency seismic sources to generate selectable low-frequency peak spectra applicable to many seismic applications. Specifically, we have demonstrated the application of a low-frequency sparker source which can be incorporated into a drill bit for Drill Bit Seismic While Drilling (SWD). To create the methodology ofmore » a controllable low-frequency sparker seismic source, it was necessary to learn how to maximize sparker efficiencies to couple to, and transmit through, rock with the study of sparker designs and mechanisms for (a) coupling the sparker-generated gas bubble expansion and contraction to the rock, (b) the effects of fluid properties and dynamics, (c) linear and non-linear acoustics, and (d) imparted force directionality. After extensive seismic modeling, the design of high-efficiency sparkers, laboratory high frequency sparker testing, and field tests were performed at the University of Texas Devine seismic test site. The conclusion of the field test was that extremely high power levels would be required to have the range required for deep, 15,000+ ft, high-temperature, high-pressure (HTHP) wells. Thereafter, more modeling and laboratory testing led to the discovery of a method to control a sparker that could generate low frequencies required for deep wells. The low frequency sparker was successfully tested at the Department of Energy Rocky Mountain Oilfield Test Center (DOE RMOTC) field test site in Casper, Wyoming. An 8-in diameter by 26-ft long SeismicPULSER{trademark} drill string tool was designed and manufactured by TII. An APS Turbine Alternator powered the SeismicPULSER{trademark} to produce two Hz frequency peak signals repeated every 20 seconds. Since the ION Geophysical, Inc. (ION) seismic survey surface recording system was designed to detect a minimum downhole signal of three Hz, successful performance was confirmed with a 5.3 Hz recording with the pumps running. The two Hz signal generated by the sparker was modulated with the 3.3 Hz signal produced by the mud pumps to create an intense 5.3 Hz peak frequency signal. The low frequency sparker source is ultimately capable of generating selectable peak frequencies of 1 to 40 Hz with high-frequency spectra content to 10 kHz. The lower frequencies and, perhaps, low-frequency sweeps, are needed to achieve sufficient range and resolution for realtime imaging in deep (15,000 ft+), high-temperature (150 C) wells for (a) geosteering, (b) accurate seismic hole depth, (c) accurate pore pressure determinations ahead of the bit, (d) near wellbore diagnostics with a downhole receiver and wired drill pipe, and (e) reservoir model verification. Furthermore, the pressure of the sparker bubble will disintegrate rock resulting in an increased overall rates of penetration. Other applications for the SeismicPULSER{trademark} technology are to deploy a low-frequency source for greater range on a wireline for Reverse Vertical Seismic Profiling (RVSP) and Cross-Well Tomography. Commercialization of the technology is being undertaken by first contacting stakeholders to define the value proposition for rig site services utilizing SeismicPULSER{trademark} technologies. Stakeholders include national oil companies, independent oil companies, independents, service companies, and commercial investors. Service companies will introduce a new Drill Bit SWD service for deep HTHP wells. Collaboration will be encouraged between stakeholders in the form of joint industry projects to develop prototype tools and initial field trials. No barriers have been identified for developing, utilizing, and exploiting the low-frequency SeismicPULSER{trademark} source in a variety of applications. Risks will be minimized since Drill Bit SWD will not interfere with the drilling operation, and can be performed in a relatively quiet environment when the pumps are turned off. The new source must be integrated with other Measurement While Drilling (MWD) tools. To date, each of the oil companies and service companies contacted have shown interest in participating in the commercialization of the low-frequency SeismicPULSER{trademark} source. A technical paper has been accepted for presentation at the 2009 Offshore Technology Conference (OTC) in a Society of Exploration Geologists/American Association of Petroleum Geophysicists (SEG/AAPG) technical session.« less

A preliminary regional assessment of earthquake-induced landslide susceptibility for Vrancea Seismic Region

NASA Astrophysics Data System (ADS)

Micu, Mihai; Balteanu, Dan; Ionescu, Constantin; Havenith, Hans; Radulian, Mircea; van Westen, Cees; Damen, Michiel; Jurchescu, Marta

2015-04-01

In seismically-active regions, earthquakes may trigger landslides enhancing the short-to-long term slope denudation and sediment delivery and conditioning the general landscape evolution. Co-seismic slope failures present in general a low frequency - high magnitude pattern which should be addressed accordingly by landslide hazard assessment, with respect to the generally more frequent precipitation-triggered landslides. The Vrancea Seismic Region, corresponding to the curvature sector of the Eastern Romanian Carpathians, represents the most active sub-crustal (focal depth > 50 km) earthquake province of Europe. It represents the main seismic energy source throughout Romania with significant transboundary effects recorded as far as Ukraine and Bulgaria. During the last 300 years, the region featured 14 earthquakes with M>7, among which seven events with magnitude above 7.5 and three between 7.7 and 7.9. Apart from the direct damages, the Vrancea earthquakes are also responsible for causing numerous other geohazards, such as ground fracturing, groundwater level disturbances and possible deep-seated landslide occurrences (rock slumps, rock-block slides, rock falls, rock avalanches). The older deep-seated landslides (assumed to have been) triggered by earthquakes usually affect the entire slope profile. They often formed landslide dams strongly influencing the river morphology and representing potential threats (through flash-floods) in case of lake outburst. Despite the large potential of this research issue, the correlation between the region's seismotectonic context and landslide predisposing factors has not yet been entirely understood. Presently, there is a lack of information provided by the geohazards databases of Vrancea that does not allow us to outline the seismic influence on the triggering of slope failures in this region. We only know that the morphology of numerous large, deep-seated and dormant landslides (which can possibly be reactivated in future) with head scarps near mountain tops and close to faults is similar to the one of large mass movements for which a seismic origin is proved (such as in the Tien Shan, Pamir, Longmenshan, etc.). Thus, correlations between landslide occurrence and combined seismotectonic and climatic factors are needed to support a regional multi-hazard risk assessment. The purpose of this paper is to harmonize for the first time at a regional scale the landslide predisposing factors and seismotectonic triggers and to present a first qualitative insight into the earthquake-induced landslide susceptibility for the Vrancea Seismic Region in terms of a GIS-based analysis of Newmark displacement (ND). In this way, it aims at better defining spatial and temporal distribution patterns of earthquake-triggered landslides. Arias Intensity calculation involved in the assessment considers both regional seismic hazard aspects and singular earthquake scenarios (adjusted by topography amplification factors). The known distribution of landslides mapped through digital stereographic interpretation of high-resolution aerial photos is compared with digital active fault maps and the computed ND maps to statistically outline the seismotectonic influence on slope stability in the study area. The importance of this approach resides in two main outputs. The fist one, of a fundamental nature, by providing the first regional insight into the seismic landslides triggering framework, is allowing us to understand if deep-focus earthquakes may trigger massive slope failures in an area with a relatively smooth relief (compared to the high mountain regions in Central Asia, the Himalayas), considering possible geologic and topographic site effects. The second one, more applied, will allow a better accelerometer instrumentation and monitoring of slopes and also will provide a first correlation of different levels of seismic shaking with precipitation recurrences, an important relationship within a multi-hazard risk preparedness and prevention framework.

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.

Images for the base of the Pacific lithospheric plate beneath Wellington, New Zealand, from 500 kg dynamite shots recorded on a 100 km-long, 1000 seismometer array

NASA Astrophysics Data System (ADS)

Stern, T. A.; Henrys, S. A.; Sato, H.; Okaya, D. A.

2012-12-01

Seismic P and S-wave reflections are recorded from a west-dipping horizon at depth of 105 km beneath Wellington, New Zealand. From the depth and dip of this horizon we interpret this horizon to be the bottom of the subducting Pacific plate. In May 2011 the Seismic Array on Hikurangi margin Experiment (SAHKE) recorded reflections on a ~100 km-long high-resolution seismic line across the lower North Island of New Zealand. The main goal of this experiment was to provide a detailed image of the west dipping subducted Pacific plate beneath the Wellington city region. The seismic line had ~1000 seismographs spaced between 50-100 m apart and the 500 kg shots were in 50 m-deep, drill holes. An exceptionally high-resolution image for the top of the subducting Pacific Plate at a depth of 20-25 km beneath the Wellington region is seen. In addition, on most of the shots are a pair of 10-14 Hz reflections between 27 and 29 s two-way-travel-time (twtt) at zero offset. The quality of this reflection pair varies from shot to shot. When converted to depth and ray-traced the best solution for these deep events is a west-dipping ( ~ 15 degrees) horizon at a depth of about 105 km. This is consistent with the dip of the upper surface of the plate beneath Wellington, and therefore we argue that the deep (~105 km) reflector is the base of the Pacific plate. On two of the shots another pair 5-8 Hz reflections can also be seen between 47 and 52 s, and the move-out of these events is consistent with them being S-wave reflections from the same 105 km deep, west-dipping, boundary for a Vp/Vs ~ 1.74. Both the P-and S-wave reflections occur in pairs of twtt-thickness of 2 and 5 s, respectively and appear to define a ~ 6-8 km thick channel at the base of the plate if the Vp/Vs ratio~ 5/2 or 2.5. Such a high value of Vp/Vs is consistent with the channel containing fluids or partial melt of an unknown percent. Although we can't rule out the double reflections in both P and S as being multiples, this seems unlikely as multiples are not seen any where else in the shot gathers. Thus the lithosphere-asthenosphere boundary (LAB), at least in this setting, appears to be a sharp boundary, less than 10 km thick. As the top of the subduction zone is 20-25 km deep beneath our profile, the total thickness of the plate beneath Wellington is about 80 km. This is consistent with the thickness of old oceanic plates measured elsewhere with passive seismic methods.

Salton Seismic Imaging Project Line 5—the San Andreas Fault and Northern Coachella Valley Structure, Riverside County, California

NASA Astrophysics Data System (ADS)

Rymer, M. J.; Fuis, G.; Catchings, R. D.; Goldman, M.; Tarnowski, J. M.; Hole, J. A.; Stock, J. M.; Matti, J. C.

2012-12-01

The Salton Seismic Imaging Project (SSIP) is a large-scale, active- and passive-source seismic project designed to image the San Andreas Fault (SAF) and the adjacent basins (Imperial and Coachella Valleys) in southern California. Here, we focus on SSIP Line 5, one of four 2-D NE-SW-oriented seismic profiles that were acquired across the Coachella Valley. The 38-km-long SSIP-Line-5 seismic profile extends from the Santa Rosa Ranges to the Little San Bernardino Mountains and crosses both strands of the SAF, the Mission Creek (MCF) and Banning (BF) strands, near Palm Desert. Data for Line 5 were generated from nine buried explosive sources (most spaced about 2 to 8 km apart) and were recorded on approximately 281 Texan seismographs (average spacing 138 m). First-arrival refractions were used to develop a refraction tomographic velocity image of the upper crust along the seismic profile. The seismic data were also stacked and migrated to develop low-fold reflection images of the crust. From the surface to about 8 km depth, P-wave velocities range from about 2 km/s to more than 7.5 km/s, with the lowest velocities within a well-defined (~2-km-deep, 15-km-wide) basin (< 4 km/s), and the highest velocities below the transition from the Coachella Valley to the Santa Rosa Ranges on the southwest and within the Little San Bernardino Mountains on the northeast. The MCF and BF strands of the SAF bound an approximately 2.5-km-wide horst-type structure on the northeastern side of the Coachella Valley, beneath which the upper crust is characterized by a pronounced low-velocity zone that extends to the bottom of the velocity image. Rocks within the low-velocity zone have significantly lower velocities than those to the northeast and the southwest at the same depths. Conversely, the velocities of rocks on both sides of the Coachella Valley are greater than 7 km/s at depths exceeding about 4 km. The relatively narrow zone of shallow high-velocity rocks between the surface traces of the MCF and BF strands is associated with a zone of uplifted strata. Along SSIP Line 5, we infer that the MCF and BF strands are steeply dipping and merge at about 2 km depth. We base our interpretation on a prominent basement low-velocity zone (fault zone) that is centered southwest of the MCF and BF strands and extends to at least 8 km depth.

Initiation and evolution of the Oligo-Miocene rift basins of southwestern Europe: Contribution of deep seismic reflection profiling

NASA Astrophysics Data System (ADS)

Bois, C.

1993-11-01

Southwestern European Oligo-Miocene rift basins have recently been investigated by deep seismic reflection profiling. The study of these data, together with other geophysical and geological data, shows that the rifts, which run from the Rhinegraben to the western Mediterranean, do not form a single clearcut system. The N-trending rifts (Rhinegraben, Bresse and Limagne) were developed on a cold and rigid lithosphere affected by the Alpine collision. The NE-trending rifts (southeastern France, Gulf of Lions and Valencia Trough) were formed slightly later in a backarc basin associated with an active segment of the European-Iberian plate that was heated, affected by widespread calcalkaline volcanism and probably weakened. All the southwestern European rifts and basins together may, however, be related to a common heritage represented by the boundary between the European-Iberian and African-Apulian plates that was created in the Jurassic with the initiation of the Tethys Ocean. The present features of the southwestern European Oligo-Miocène rift basins may be explained by a combination of three geodynamic mechanisms: mechanical stretching of the lithosphere, active mantle uplifting, and subordinate lithospheric flexuring. All the rifts were probably initiated by passive stretching. A systematic discrepancy between stretching derived from fault analysis and attenuation of the crust has been observed in all the rifts. This suggests that these rifts were subsequently reworked by one or several active mantle upwelling events associated with late shoulder uplift, asthenosphere upwelling and anomalous P-wave velocities in the lowermost crust and the uppermost mantle. Crustal attenuation may have been achieved by mantle intrusion, metamorphism of the deep crust and/or its delamination. Some of the rifts were affected by lithospheric flexuring. Combinations, in various proportions, of a small number of geodynamic mechanisms probably controlled many basins in the world. This explains the unique characteristics of each basin, difficulties in basin classification and the frequent failure of single-mechanism models to explain the geological observations.

The new Nam Co Multichannel Seismic Campaign in June/July 2016 - Fresh Results and Perspectives for a Future ICDP Drilling Campaign

NASA Astrophysics Data System (ADS)

Daut, G.; Spiess, V.; Haberzettl, T.; Schwenk, T.; Schulze, N.; Haberkern, J.; Bergmann, F.; Gernhardt, F.; Wang, J.; Ju, J.; Huang, L.; Zhu, L.

2016-12-01

In June/July 2016, a multichannel seismic survey was executed on Lake Nam Co to further explore the opportunities for a deep drilling ICDP project. For acquisition, a streamer (Teledyne Inc.) of 64 m active length with 32 single hydrophone was used and sound emission was carried out with a mini GI Gun of 2 x 0.1 L chamber volume, operated at pressures between 50 bar and 140 bar, providing frequencies between 50 Hz and >600 Hz. The data acquired with the MaMuCS recording system were sampled with 1/8 ms for a length of 2 seconds. Additionally, all survey lines were recorded with a parametric echosounder (Innomar SES 200 light) to cover the uppermost ca. 25 m of the sediment sequence (last glacial-Holocene period) in high resolution. These data can serve as a modern analogs for interpreting the deep seismic lines in terms of older glacial-interglacial cycles. 91 seismic profiles were shot using shot rates between 6 and 14 with ship's speed around 4.5 knots during most of the survey, ensuring a good signal/noise ratios and complete coverage of the lake basin. Selected profiles were shot at a speed of 3.0 knots to allow lower frequencies down to 50 Hz to be recorded and to penetrate deeper (>500 ms TWT) into the sedimentary sequence. The basin formation appears to be controlled by the overall tectonic framework revealing significant activity in the latest Quaternary. Extensional, strike-slip and presumably flower structures indicate a complex fault and subsidence pattern, which could not yet be resolved in detail during the field work, but awaits further post-expedition analyses. The dense grid near the thickest sediment packages, assumed to reach back at least to MIS 5 in age, will allow a detailed investigation of sedimentary structures, sediment transport and dispersal patterns. In particular periods of higher and lower lake level can be identified and used as preliminary stratigraphic markers due to their characteristic seismic facies, revealing very low amplitudes at high stand, while lowstand deposits are characterized by higher amplitudes and irregular reflectors. Although the post-processing is still ongoing, the preliminary results show that the data allow to identify promising drilling targets, thus the campaign turned out to be a full success for the anticipated goal of motivating and preparing a potential ICDP drilling proposal.

Heat-flow measurements at shot points along the 1978 Saudi Arabia seismic deep-refraction line; Part I, Results of the measurements

USGS Publications Warehouse

Gettings, M.E.; Showail, Abdullah

1982-01-01

Heat-flow measurements were made at five onland shot points of the 1978 Saudi Arabian seismic deep-refraction line, which sample major tectonic elements of the Arabian Shield along a profile from Ar Riyad to the Farasan Islands. Because of the pattern drilling at each shot point, several holes (60 m deep) could be logged for temperature at each site and thus allow a better estimate of the geothermal gradient. Each site was mapped and sampled in detail, and modal and. chemical analyses of representative specimens were made in the laboratory. Thermal conductivities were computed from the modal analyses and single-mineral conductivity data. The resulting heat-flow values, combined with published values for the Red Sea and coastal plain, indicate a three-level pattern, with a heat flow of about 4.5 heat-flow unit (HFU) over the Red Sea axial trough, about 3.0 HFU over the shelf and coastal plain, and an essentially constant 1.0 HFU over the Arabian Shield at points well away from the suture zone with the oceanic crust. At three sites where the rocks are granitic, gamma-ray spectrometry techniques were employed to estimate thorium, potassium, and uranium concentrations. The resulting plot of heat generation versus heat flow suggests that in the Arabian Shield the relationship between heat flow and heat production is not linear. More heat-flow data are essential to establish or reject this conclusion.

Gravity anomaly and crustal structure characteristics in North-South Seismic Belt of China

NASA Astrophysics Data System (ADS)

Shen, Chongyang; Xuan, Songtbai; Yang, Guangliang; Wu, Guiju

2017-04-01

The North-South Seismic Belt (NSSB) is the binary system boundary what is formed by the western Indian plate subduction pushing and the eastern west Pacific asthenosphere rising, and it is one of the three major seismic belts (Tianshan, Taiwan and NSSB) and mainly located between E102°and E107°. And it is mainly composed of topographic gradient zones, faults, cenozoic basins and strong earthquake zones, which form two distinct parts of tectonic and physical features in the west and east. The research results of geophysical and deep tectonic setting in the NSSB show that it is not only a gravity anomaly gradient zone, it is but also a belt of crustal thickness increasing sharply westward of abrupt change. Seismic tomography results show that the anomaly zone is deeper than hundreds of kilometers in the NSSB, and the composition and structure of the crust are more complex. We deployed multiple Gravity and GNSS synchronous detection profiles in the NSSB, and these profiles crossed the mainly faults structure and got thousands of points data. In the research, source analysis, density structure inversion, residual gravity related imaging and normalized full gradient methods were used, and analyzed gravity field, density and their structure features in different positions, finally obtained the crustal density structure section characteristics and depth structure differences. The research results showed that the gravity Bouguer anomaly is similar to the existing large scale result. The Bouguer anomaly is rising significantly from west to east, its trend variation coincides well with the trend change of Moho depth, which is agreeing with the material flows to the peripheral situation of the Tibetan plateau. The obvious difference changes of the residual anomaly is relative to the boundary of structure or main tectonics, it's also connected with the stop degree of the eurasian plate when the material migrates around. The density structure of the gravity profiles mainly reflects basic frame work of the regional crust structure. The earth's crust basically present three layer structure, nearly horizontally distributes, undulation of Moho is obvious, which is consistent with the results of seismic sounding and seismic array detection; in the local area, there are lower density layer zonal distribution in the earth's crust what accelerates the lateral movement in up and middle crust; when the substance of the Tibetan plateau spreads around, the integrity in up and middle crust is well, and it is basically a coupling movement together; in the lower crust, the thickness of the Tibetan plateau is outward gradually thinning, there is decoupling phenomenon in crust-mantle; The results of the gravity and the crustal density structure show that the research area can be divided into several part such as Qinghai-Tibet Plateau, Sichuan-Yunnan block, Ordos block and Alxa block, the transitional zones of the Qinghai-Tibet Plateau and Sichuan basin, and Alxa and Ordos are complex, and Moho slope is bigger, where is the part of strong tectonic activity and strong earthquakes occur easily. The research is of great significance for study the crustal deep structure, geodynamic evolution process and environment of earthquake gestation of the NSSB region.

Using Vertical electrical sounding survey and refraction seismic survey for determining the geological layers depths, the structural features and assessment groundwater in Aqaba area in South Jordan.

NASA Astrophysics Data System (ADS)

Akawwi, Emad; Alzoubi, Abdallah; Ben Abraham, Zvi; Rahamn Abo Alades, Abdel; Alrzouq, Rami; Tiber, Gidon; Neimi, Tina

2010-05-01

The study area is the Aqaba region (Southern wadi Araba basin). Aqaba region area located at 87900 and 89000 North and 147000 and 158000 East (Palestine grid). Tectonically Aqaba area lies within the tectonic plate boundary along the Arabian and African plate slide. This plate boundary comprises numerous and shot fault segments. The main aims of this study are to assessing the groundwater potential and its quality, to explain the subsurface geological conditions and support the ongoing geological, environmental and hydrogeological studies. Therefore, it was anticipated that the results of the geophysical surveying will give many different important parameters as The subsurface geological features, thicknesses of the different lithological units, depth to the bed rocks and depth to the water table. The groundwater can apply an important role in ensuring sustainable water supply in the area. This study was carried out in order to assess groundwater condition, geological layers thicknesses and structural features in Aqaba area by using vertical electrical sounding (VES) surveys and refraction seismic techniques. There are three geoelectrical cross section were carried out at different sites by using the Schlumberger array. The first cross section indicated three layers of different resistivity. The second cross section indicated four layers of different resistivity. The third geoelectrical cross sections indicated three layers. The refraction seismic method also has been conducted in the same area as VES. About 12 refraction seismic profiles have been carried out in the study area. The length of the first profile was 745 m at the direction N-S. This profile indicated two different layers with a different velocities. The length of the second profile was 1320 m with E-W direction. This profile indicated two different layers. The length of the third profile was about 515 m with a direction SE-NW. It recognized two different layers with a different velocities. The fourth profile was N-S direction and the length of this profile was 950 m. Two different layers were recognized along this profile. The fifth profile was located N-S with length about 340 m. Two layers were recognized from this profile. The sixth profile was located N-S direction and the length about 575 m. Three layers were recognized from this profile. The direction of the seventh profile was N-S with a length of about 235 m. two different layers were recognized the top layer was unconsolidated alluvium. The profile number 8 was located N-S with length about 232 m. two layers were conducted from this profile. The direction of ninth profile was NW-SE with length about 565 m. two layers were conducted along this profile. The length of the tenth profile was 235 m and the direction was N-S. Two layers with a different velocities were detected along this profile. Profile number eleven was located SW-NE with length about 475 m. two layers were recognized from this profile. The length of the last profile was 375 m with direction SE-NW. Two layers were conducted from this profile. It was found that the shallow aquifers exist at a depths ranging from 4 to 19 m and the relatively deep aquifers from 24 to 60 m below the ground surface. Keywords: Vertical electrical sounding, Aqaba, Resistivity, Groundwater, Layer depth, Geoelectrical.

Seismic-sequence stratigraphy and geologic structure of the Floridan aquifer system near "Boulder Zone" deep wells in Miami-Dade County, Florida

USGS Publications Warehouse

Cunningham, Kevin J.

2015-01-01

In addition to the preceding seismic-reflection analysis, interpretation of geophysical well log data from four effluent injection wells at the North District “Boulder Zone” Well Field delineated a narrow karst collapse structure beneath the injection facility that extends upward about 900 ft from the top of the Boulder Zone to about 125 ft above the top of the uppermost major permeable zone of the Lower Floridan aquifer. No karst collapse structures were identified in the seismic-reflection profiles acquired near the North District “Boulder Zone” Well Field. However, karst collapse structures at the level of the lowermost major permeable zone of the Lower Floridan aquifer at the South District “Boulder Zone” Well Field are present at three locations, as indicated by seismic-reflection data acquired in the C–1 Canal bordering the south side of the injection facility. Results from the North District “Boulder Zone” Well Field well data indicate that a plausible hydraulic connection between faults and stratiform permeability zones may contribute to the upward transport of effluent, terminating above the base of the deepest U.S. Environmental Protection Agency designated underground source of drinking water at the North District “Boulder Zone” Well Field.

Integration of 2D and 3D reflection seismic data with deep boreholes in the Kevitsa Ni-Cu-PGE deposit, northern Finland

NASA Astrophysics Data System (ADS)

Koivisto, Emilia; Malehmir, Alireza; Voipio, Teemu; Wijns, Chris

2013-04-01

Kevitsa is a large disseminated sulphide Ni-Cu-PGE deposit hosted by the Kevitsa mafic-ultramafic intrusion in northern Finland and dated as about 2.06 Ga old. The Geological Survey of Finland first discovered the Kevitsa deposit in 1987. Open pit mining by Kevitsa Mining Oy/First Quantum Minerals Ltd. commenced in June 2012. The final pit depth is planned to be 550-600 m. The estimated ore reserves of the Kevitsa intrusion are about 240 million tones (using a nickel cut-off grade of 0.1%). The expected life-of-mine is 20-30 years. More than 400 hundred holes have been drilled in the Kevitsa area, but most are concentrated close to the known deposit and do not provide a comprehensive understanding of the extent of the intrusion. The basal contact of the intrusion is penetrated by only about 30 drill holes, most of which are shallow. A better knowledge of the geometry of the intrusion would provide a framework for near-mine and deep exploration in the area. An exact knowledge on the basal contact of the intrusion would also provide an exploration target for the contact-type mineralization that is often more massive and richer in Ni-Cu. In December 2007, a series of 2D reflection seismic profiles was acquired in the Kevitsa area. It consisted of four connected survey lines between 6 and 11 km long. In 2010, the initial positive results of the 2D seismic survey led Kevitsa Mining Oy/First Quantum Minerals Ltd. to initiate a 3D reflection seismic survey. The 3D seismic survey is limited to the closer vicinity of the known deposit, while the 2D seismic survey was designed to provide a more regional view of the Kevitsa intrusive complex. The main aims of the 2D and 3D seismic surveys were to delineate the shape and extent of the ore-bearing Kevitsa intrusion and the geometry of some of the host rock and surrounding units, and extract information about the larger-scale structures and structures important for mine-planning purposes. The 2D and 3D seismic data were used to create a 3D lithological and structural model for the architecture of the whole complex. The information on the extent of the ore-bearing Kevitsa intrusion can be used for more effective exploration in the area. The base of the intrusion is particularly clear in the northern and eastern sectors. Toward the east, the base is mostly defined by disruption of the reflectors internal to the intrusion. The 2D seismic data, which extend beyond the 3D seismic study, reveal that the prominent reflectors at the base of the intrusion continue deeper toward the south-southwest. This has been interpreted as a previously unknown southern continuation of the intrusion. Furthermore, the data reveal strong reflectors at the base of the intrusion that have been penetrated by two deep drill holes in the area. These drill holes reveal contact-type mineralization at the onset of the reflectors. Thus, the seismic data can be directly used for exploration of the contact-type mineralization.

Regional two-dimensional magnetotelluric profile in West Bohemia/Vogtland reveals deep conductive channel into the earthquake swarm region

NASA Astrophysics Data System (ADS)

Muñoz, Gerard; Weckmann, Ute; Pek, Josef; Kováčiková, Světlana; Klanica, Radek

2018-03-01

The West Bohemia/Vogtland region, characterized by the intersection of the Eger (Ohře) Rift and the Mariánské Lázně fault, is a geodynamically active area exhibiting repeated occurrence of earthquake swarms, massive CO2 emanations and mid Pleistocene volcanism. The Eger Rift is the only known intra-continental region in Europe where such deep seated, active lithospheric processes currently take place. We present an image of electrical resistivity obtained from two-dimensional inversion of magnetotelluric (MT) data acquired along a regional profile crossing the Eger Rift. At the near surface, the Cheb basin and the aquifer feeding the mofette fields of Bublák and Hartoušov have been imaged as part of a region of very low resistivity. The most striking resistivity feature, however, is a deep reaching conductive channel which extends from the surface into the lower crust spatially correlated with the hypocentres of the seismic events of the Nový Kostel Focal Zone. This channel has been interpreted as imaging a pathway from a possible mid-crustal fluid reservoir to the surface. The resistivity model reinforces the relation between the fluid circulation along deep-reaching faults and the generation of the earthquakes. Additionally, a further conductive channel has been revealed to the south of the profile. This other feature could be associated to fossil hydrothermal alteration related to Mýtina and/or Neualbenreuth Maar structures or alternatively could be the signature of a structure associated to the suture between the Saxo-Thuringian and Teplá-Barrandian zones, whose surface expression is located only a few kilometres away.

Source and dynamics of a volcanic caldera unrest: Campi Flegrei, 1983-84.

PubMed

De Siena, Luca; Chiodini, Giovanni; Vilardo, Giuseppe; Del Pezzo, Edoardo; Castellano, Mario; Colombelli, Simona; Tisato, Nicola; Ventura, Guido

2017-08-14

Despite their importance for eruption forecasting the causes of seismic rupture processes during caldera unrest are still poorly reconstructed from seismic images. Seismic source locations and waveform attenuation analyses of earthquakes in the Campi Flegrei area (Southern Italy) during the 1983-1984 unrest have revealed a 4-4.5 km deep NW-SE striking aseismic zone of high attenuation offshore Pozzuoli. The lateral features and the principal axis of the attenuation anomaly correspond to the main source of ground uplift during the unrest. Seismic swarms correlate in space and time with fluid injections from a deep hot source, inferred to represent geochemical and temperature variations at Solfatara. These swarms struck a high-attenuation 3-4 km deep reservoir of supercritical fluids under Pozzuoli and migrated towards a shallower aseismic deformation source under Solfatara. The reservoir became aseismic for two months just after the main seismic swarm (April 1, 1984) due to a SE-to-NW directed input from the high-attenuation domain, possibly a dyke emplacement. The unrest ended after fluids migrated from Pozzuoli to the location of the last caldera eruption (Mt. Nuovo, 1538 AD). The results show that the high attenuation domain controls the largest monitored seismic, deformation, and geochemical unrest at the caldera.

Mega-thrust and Intra-slab Earthquakes Beneath Tokyo Metropolitan Area

NASA Astrophysics Data System (ADS)

Hirata, N.; Sato, H.; Koketsu, K.; Hagiwara, H.; Wu, F.; Okaya, D.; Iwasaki, T.; Kasahara, K.

2006-12-01

In central Japan the Philippine Sea plate (PSP) subducts beneath the Tokyo Metropolitan area, the Kanto region, where it causes mega-thrust earthquakes, such as the 1703 Genroku earthquake (M8.0) and the 1923 Kanto earthquake (M7.9) which had 105,000 fatalities. The vertical proximity of this down going lithospheric plate is of concern because the greater Tokyo urban region has a population of 42 million and is the center of approximately 40% of the nation's economic activities. A M7+ earthquake in this region at present has high potential to produce devastating loss of life and property with even greater global economic repercussions. The M7+ earthquake is evaluated to occur with a probability of 70% in 30 years by the Earthquake Research Committee of Japan. In 2002, a consortium of universities and government agencies in Japan started the Special Project for Earthquake Disaster Mitigation in Urban Areas, a project to improve information needed for seismic hazards analyses of the largest urban centers. Assessment in Kanto of the seismic hazard produced by the Philippine Sea Plate (PSP) mega-thrust earthquakes requires identification of all significant faults and possible earthquake scenarios and rupture behavior, regional characterizations of PSP geometry and the overlying Honshu arc physical properties (e.g., seismic wave velocities, densities, attenuation), and local near-surface seism ic site effects. Our study addresses (1) improved regional characterization of the PSP geometry based on new deep seismic reflection profiles (Sato etal.,2005), reprocessed off-shore profiles (Kimura et al.,2005), and a dense seismic array in the Boso peninsular (Hagiwara et al., 2006) and (2) identification of asperities of the mega-thrust at the top of the PSP. We qualitatively examine the relationship between seismic reflections and asperities inferred by reflection physical properties. We also discuss the relation between deformation of PSP and intra-slab M7+ earthquakes: the PSP is subducting beneath the Hoshu arc and also colliding with the Pacific plate. The subduction and collision both contribute active seismicity in the Kanto region. We present a high resolution tomographic image to show a low velocity zone which suggests a possible internal failure of the slab; a source region of the M7+ intra-slab earthquake. Our study contributes a new assessment of the seismic hazard in the Tokyo metropolitan area. tokyo.ac.jp/daidai/index-J.html

Combining mineral physics with seismic observations: What can we deduce about the thermochemical structure of the Earth's deep interior?

NASA Astrophysics Data System (ADS)

Cobden, L. J.

2017-12-01

Mineral physics provides the essential link between seismic observations of the Earth's interior, and laboratory (or computer-simulated) measurements of rock properties. In this presentation I will outline the procedure for quantitative conversion from thermochemical structure to seismic structure (and vice versa) using the latest datasets from seismology and mineralogy. I will show examples of how this method can allow us to infer major chemical and dynamic properties of the deep mantle. I will also indicate where uncertainties and limitations in the data require us to exercise caution, in order not to "over-interpret" seismic observations. Understanding and modelling these uncertainties serves as a useful guide for mineralogists to ascertain which mineral parameters are most useful in seismic interpretation, and enables seismologists to optimise their data assembly and inversions for quantitative interpretations.

Test of high-resolution 3D P-wave velocity model of Poland by back-azimuthal sections of teleseismic receiver function

NASA Astrophysics Data System (ADS)

Wilde-Piorko, Monika; Polkowski, Marcin; Grad, Marek

2015-04-01

Geological and seismic structure under area of Poland is well studied by over one hundred thousand boreholes, over thirty deep seismic refraction and wide angle reflection profiles and by vertical seismic profiling, magnetic, gravity, magnetotelluric and thermal methods. Compilation of these studies allowed to create a high-resolution 3D P-wave velocity model down to 60 km depth in the area of Poland (Polkowski et al. 2014). Model also provides details about the geometry of main layers of sediments (Tertiary and Quaternary, Cretaceous, Jurassic, Triassic, Permian, old Paleozoic), consolidated/crystalline crust (upper, middle and lower) and uppermost mantle. This model gives an unique opportunity for calculation synthetic receiver function and compering it with observed receiver function calculated for permanent and temporary seismic stations. Modified ray-tracing method (Langston, 1977) can be used directly to calculate the response of the structure with dipping interfaces to the incoming plane wave with fixed slowness and back-azimuth. So, 3D P-wave velocity model has been interpolated to 2.5D P-wave velocity model beneath each seismic station and back-azimuthal sections of components of receiver function have been calculated. Vp/Vs ratio is assumed to be 1.8, 1.67, 1.73, 1.77 and 1.8 in the sediments, upper/middle/lower consolidated/crystalline crust and uppermost mantle, respectively. Densities were calculated with combined formulas of Berteussen (1977) and Gardner et al. (1974). Additionally, to test a visibility of the lithosphere-asthenosphere boundary phases at receiver function sections models have been extended to 250 km depth based on P4-mantle model (Wilde-Piórko et al., 2010). National Science Centre Poland provided financial support for this work by NCN grant DEC-2011/02/A/ST10/00284 and by NCN grant UMO-2011/01/B/ST10/06653.

Seismic reflection imaging with conventional and unconventional sources

NASA Astrophysics Data System (ADS)

Quiros Ugalde, Diego Alonso

This manuscript reports the results of research using both conventional and unconventional energy sources as well as conventional and unconventional analysis to image crustal structure using reflected seismic waves. The work presented here includes the use of explosions to investigate the Taiwanese lithosphere, the use of 'noise' from railroads to investigate the shallow subsurface of the Rio Grande rift, and the use of microearthquakes to image subsurface structure near an active fault zone within the Appalachian mountains. Chapter 1 uses recordings from the land refraction and wide-angle reflection component of the Taiwan Integrated Geodynamic Research (TAIGER) project. The most prominent reflection feature imaged by these surveys is an anomalously strong reflector found in northeastern Taiwan. The goal of this chapter is to analyze the TAIGER recordings and to place the reflector into a geologic framework that fits with the modern tectonic kinematics of the region. Chapter 2 uses railroad traffic as a source for reflection profiling within the Rio Grande rift. Here the railroad recordings are treated in an analogous way to Vibroseis recordings. These results suggest that railroad noise in general can be a valuable new tool in imaging and characterizing the shallow subsurface in environmental and geotechnical studies. In chapters 3 and 4, earthquakes serve as the seismic imaging source. In these studies the methodology of Vertical Seismic Profiling (VSP) is borrowed from the oil and gas industry to develop reflection images. In chapter 3, a single earthquake is used to probe a small area beneath Waterboro, Maine. In chapter 4, the same method is applied to multiple earthquakes to take advantage of the increased redundancy that results from multiple events illuminating the same structure. The latter study demonstrates how dense arrays can be a powerful new tool for delineating, and monitoring temporal changes of deep structure in areas characterized by significant seismic activity.

The Oceanic Crustal Structure of the Southwestern Subbasin in the South China Sea

NASA Astrophysics Data System (ADS)

Wu, Z.; Ruan, A.; Li, J.; Lee, C.

2012-12-01

Located at the southwestern part of the South China Sea (SCS) among the Zhongsha Islands(Macclesfield Bank), the east subbasin, the Nansha Islands(Dangerous Ground), the V type southwest subbasin (SWSB) is an unique ocean basin in all the three subbasins of SCS. The crustal structure is one of the key problems to study the formation and evolution of SWSB. During December 2010 to March 2011, Ocean Bottom Seismometers (OBSs) experiment has been carried out in the SWSB to get the deep crustal structure information, especially under the fossil spreading center. Three types of OBS, Sedis IV type, I-4C type and MicrOBS type have been used in the experiment, and the energy source was supplied by 6000 inch3 large volume air-gun. High quality seismic data of four 2D profiles which covered the fossil spreading center of SWSB have been acquired. The data of the experiment can supply evidence for the study of oceanic crustal structure of the SWSB and seafloor spreading course, etc. The profile 1 extended 130 km in length. A total of 8 OBSs were deployed at intervals of 10 or 15 km and 7 OBSs were recovered. The data of the 7 stations of profile 1 have been processed, which shows that the seismic records are clear and seismic phases are abundance, and the air-guns have enough energy supply. The velocity model was obtained by using an interactive trial-and-error 2D ray-tracing method. The crustal structure indicates that the crustal thickness under the SWSB is about 6 km, and the moho depth is about 10km. The results reveal that the crust of SWSB is normal oceanic crust with a thin sedimentary layer on the seamount and shallow moho surface. The crustal velocity under the spreading center is extremely low, which shows the characteristic of the deep crustal structure of the fossil spreading center. Acknowledgements This study was supported by the National Natural Science Foundation of China (Grant No. 91028006, 41106053, 41176046), Scientific Research Fund of the Second Institute of Oceanography, SOA(Grant No. JT1101) References: Ruan A G, Qiu X L, Li J B, et al. Wide aperture seismic sounding in the margin seas of China. South China Journal of Seismology,2009,29:10-18(in Chinese). Li J B, Jin X L, Gao J Y. Morpho-tectonic study on late-stage spreading of the Eastern Subbasin of South China Sea. Sci China Ser D-Earth Sci,2002, 45:978-989 WU Z L, LI J B, RUAN A G, et al. Crustal structure of the northwestern sub-basin, South China Sea: Results from a wide-angle seismic experiment[J]. Sci China Earth Sci, 2012,55:159-172. doi: 10.1007/s11430-011-4324-9.

Tectonic History and Deep Structure of the Demerara Plateau from Combined Wide-Angle and Reflection Seismic Data and Plate Kinematic Reconstructions

NASA Astrophysics Data System (ADS)

Klingelhoefer, F.; Museur, T.; Roest, W. R.; Graindorge, D.; Chauvet, F.; Loncke, L.; Basile, C.; Poetisi, E.; Deverchere, J.; Lebrun, J. F.; Perrot, J.; Heuret, A.

2017-12-01

Many transform margins have associated intermediate depth marginal plateaus, which are commonly located between two oceanic basins. The Demerara plateau is located offshore Surinam and French Guiana. Plate kinematic reconstructions show that the plateau is located between the central and equatorial Atlantic in a position conjugate to the Guinean Plateau. In the fall of 2016, the MARGATS cruise acquired geophysical data along the 400 km wide Demerara plateau. The main objective of the cruise was to image the deep structure of the Demerara plateau and to study its tectonic history. A set of 4 combined wide-angle and reflection seismic profiles was acquired along the plateau, using 80 ocean-bottom seismometers, a 3 km long seismic streamer and a 8000 cu inch tuned airgun array. Forward modelling of the wide-angle seismic data on a profile, located in the eastern part of the plateau and oriented in a NE-SW direction, images the crustal structure of the plateau, the transition zone and the neighbouring crust of oceanic origin, up to a depth of 40 km. The plateau itself is characterised by a crust of 30 km thickness, subdivided into three distinct layers. However, the velocities and velocity gradients do not fit typical continental crust, with a lower crustal layer showing untypically high velocities and an upper layer having a steep velocity gradient. From this model we propose that the lowermost layer is probably formed from volcanic underplated material and that the upper crustal layer likely consists of the corresponding extrusive volcanic material, forming thick seaward-dipping reflector sequences on the plateau. A basement high is imaged at the foot of the slope and forms the ocean-continent transition zone. Further oceanward, a 5-6 km thick crust is imaged with velocities and velocity gradients corresponding to a thin oceanic crust. A compilation of magnetic data from the MARGATS and 3 previous cruises shows a high amplitude magnetic anomaly along the northern edge of the plateau thereby strengthening the hypothesis of an volcanic origin of at least part of the structure. We propose, that the plateau was formed by large-scale volcanism, possibly intruding into a thinner existing continental crust.

Crustal-scale alpine tectonic evolution of the western Pyrenees - eastern Cantabrian Mountains (N Spain) from integration of structural data, low-T thermochronology and seismic constraint

NASA Astrophysics Data System (ADS)

DeFelipe, I.; Pedreira, D.; Pulgar, J. A.; Van der Beek, P.; Bernet, M.; Pik, R.

2017-12-01

The Pyrenean-Cantabrian Mountain belt extends in an E-W direction along the northern border of Spain and resulted from the convergence between the Iberian and European plates from the Late Cretaceous to the Miocene, in the context of the Alpine orogeny. The main aim of this work is to characterize the tectonic evolution at a crustal-scale of the transition zone from the Pyrenees to the Cantabrian Mountains, in the eastern Basque-Cantabrian Basin (BCB). We integrate structural work, thermochronology (apatite fission track and zircon (U-Th)/He) and geophysical information (shallow seismic reflection profiles, deep seismic refraction/wide-angle reflection profiles and seismicity distribution) to propose an evolutionary model since the Jurassic to the present. During the Albian, hyperextension related to the opening of the Bay of Biscay yielded to mantle unroofing to the base of the BCB. This process was favored by a detachment fault that connected the mantle in its footwall with the base of a deep basin in its hanging wall. During this process, the basin experienced HT metamorphism and fluid circulation caused the serpentinization of the upper part of the mantle. There is no evidence of seafloor mantle exhumation before the onset of the Alpine orogeny. The thermochronological study points to a N-vergent phase of contractional deformation in the late Eocene represented by the thin-skinned Leiza fault system followed in the early Oligocene by the S-vergent, thick-skinned, Ollín thrust. Exhumation rates for the late Eocene-early Oligocene are of 0.2-0.7 km/Myr. After that period, deformation continues southwards until the Miocene. The crustal-scale structure resultant of the Alpine orogeny consists of an Iberian plate that subducts below the European plate. The crust is segmented into four blocks separated by three S-vergent crustal faults inherited from the Cretaceous extensional period. The P-wave velocities in this transect show anomalous values (7.4 km/s) in the deepest part of the Iberian crust that may correspond to serpentinized mantle formed during the Cretaceous and later subducted. The Alpine shortening in this transect is estimated in ca. 90 km. Integration of structural, geophysical and thermochronological data, allows a more precise reconstruction of the crustal-scale Alpine cycle in the eastern BCB.

Preliminary results of layered modelling of seismic refraction data at the East Limpopo Margin, Mozambique (PAMELA project, MOZ3/5 cruise)

NASA Astrophysics Data System (ADS)

Watremez, Louise; Evain, Mikael; Leprêtre, Angélique; Verrier, Fanny; Aslanian, Daniel; Leroy, Sylvie; Dias, Nuno; Afilhado, Alexandra; Schnurle, Philippe; d'Acremont, Elia; de Clarens, Philippe; Castilla, Raymi; Moulin, Maryline

2017-04-01

The East Limpopo Margin is a continental margin located offshore southern Mozambique, in the Mozambique Channel. The southern Mozambique margin has not been studied much until now, but its formation is assumed to be the result of the separation of the African plate from the Antarctica plate. A new geophysical survey MOZ3/5 (February-April 2016; PAMELA project*) allowed the acquisition of seven wide-angle reflection and refraction seismic profiles across the southernmost Mozambique margin. In this work, we show the first results obtained from the layered modelling of an approximately 400 km long transect crossing the East Limpopo Margin and including information from 22 ocean-bottom seismometers and 18 land seismometers. The velocity model, compared to coincident seismic reflection data, allows to observe (1) the variations of seismic velocities together with the variations of reflectivity characteristics in the sediments, including the occurrence of some magmatism, (2) some deep features located below the acoustic basement and that can be related to the pre-to-syn-rift history of the margin, (3) the velocities and Moho depths in the different areas of the crust, from the thick continental crust to the clear oceanic crust (magnetic anomalies), helping to define the nature of the crust and the presence of magmatic features along the whole profile, and (4) some velocity information in the uppermost mantle. These results will allow us to (1) understand the deep structures of the East Limpopo Margin and to have better constraints on the formation of the margin, helping kinematic reconstructions, improving the quantification of the magmatism along this margin, and (2) improve the knowledge of both the thermal evolution of the sediments and the potential magmatic sources in the study area. *The PAMELA project (PAssive Margin Exploration Laboratories) is a scientific project led by Ifremer and TOTAL in collaboration with Université de Bretagne Occidentale, Université Rennes 1, Université Pierre and Marie Curie, CNRS and IFPEN. Moulin, M., Aslanian, D., et al 2016. PAMELA-MOZ03 cruise, RV Pourquoi pas ?, http://dx.doi.org/10.17600/16001600 Moulin, M., Evain, M., et al. 2016. PAMELA-MOZ05 cruise, RV Pourquoi pas ?, http://dx.doi.org/10.17600/16009500

Maps Showing Seismic Landslide Hazards in Anchorage, Alaska

USGS Publications Warehouse

Jibson, Randall W.; Michael, John A.

2009-01-01

The devastating landslides that accompanied the great 1964 Alaska earthquake showed that seismically triggered landslides are one of the greatest geologic hazards in Anchorage. Maps quantifying seismic landslide hazards are therefore important for planning, zoning, and emergency-response preparation. The accompanying maps portray seismic landslide hazards for the following conditions: (1) deep, translational landslides, which occur only during great subduction-zone earthquakes that have return periods of =~300-900 yr; (2) shallow landslides for a peak ground acceleration (PGA) of 0.69 g, which has a return period of 2,475 yr, or a 2 percent probability of exceedance in 50 yr; and (3) shallow landslides for a PGA of 0.43 g, which has a return period of 475 yr, or a 10 percent probability of exceedance in 50 yr. Deep, translational landslide hazard zones were delineated based on previous studies of such landslides, with some modifications based on field observations of locations of deep landslides. Shallow-landslide hazards were delineated using a Newmark-type displacement analysis for the two probabilistic ground motions modeled.

Maps showing seismic landslide hazards in Anchorage, Alaska

USGS Publications Warehouse

Jibson, Randall W.

2014-01-01

The devastating landslides that accompanied the great 1964 Alaska earthquake showed that seismically triggered landslides are one of the greatest geologic hazards in Anchorage. Maps quantifying seismic landslide hazards are therefore important for planning, zoning, and emergency-response preparation. The accompanying maps portray seismic landslide hazards for the following conditions: (1) deep, translational landslides, which occur only during great subduction-zone earthquakes that have return periods of =300-900 yr; (2) shallow landslides for a peak ground acceleration (PGA) of 0.69 g, which has a return period of 2,475 yr, or a 2 percent probability of exceedance in 50 yr; and (3) shallow landslides for a PGA of 0.43 g, which has a return period of 475 yr, or a 10 percent probability of exceedance in 50 yr. Deep, translational landslide hazards were delineated based on previous studies of such landslides, with some modifications based on field observations of locations of deep landslides. Shallow-landslide hazards were delineated using a Newmark-type displacement analysis for the two probabilistic ground motions modeled.

Observation and Simulation of Microseisms Offshore Ireland

NASA Astrophysics Data System (ADS)

Le Pape, Florian; Bean, Chris; Craig, David; Jousset, Philippe; Donne, Sarah; Möllhoff, Martin

2017-04-01

Although more and more used in seismic imagery, ocean induced ambient seismic noise is still not so well understood, particularly how the signal propagates from ocean to land. Between January and September 2016, 10 broadband Ocean Bottom Seismometers (OBSs) stations, including acoustic sensors (hydrophone), were deployed across the shelf offshore Donegal and out into the Rockall Trough. The preliminary results show spatial and temporal variability in the ocean generated seismic noise which holds information about changes in the generation source process, including meteorological information, but also in the geological structure. In addition to the collected OBS data, numerical simulations of acoustic/seismic wave propagation are also considered in order to study the spatio-temporal variation of the broadband acoustic wavefield and its connection with the measured seismic wavefield in the region. Combination of observations and simulations appears significant to better understand what control the acoustic/seismic coupling at the sea floor as well as the effect of the water column and sediments thickness on signal propagation. Ocean generated seismic ambient noise recorded at the seafloor appears to behave differently in deep and shallow water and 3D simulations of acoustic/seismic wave propagation look particularly promising for reconciling deep ocean, shelf and land seismic observations.

A world-class target for ICDP drilling at Lake Nam Co, Tibetan Plateau, China: progresses and perspectives

NASA Astrophysics Data System (ADS)

Zhu, L.; Wang, J.; Daut, G.; Spiess, V.; Haberzettl, T.; Schulze, N.; Ju, J.; Lü, X.; Bergmann, F.; Haberkern, J.; Schwalb, A.; Mäusbacher, R.

2017-12-01

Lake Nam Co (ca. 2000 km2, 4718 m a.s.l., maximum depth: 100 m) is located at the interaction zone of the Westerlies and the Indian monsoon on the central Tibetan Plateau. It was part of a mega-lake during Marine Isotope Stage (MIS) 3 before the Last Glacial Maximum. A long term sedimentary record from Nam Co could therefore provide an excellent paleo-environmental sequence for regional and global comparative studies. This will to deepen our understanding of large scale atmospheric circulation shifts and the environmental links between the Tibetan Plateau at low latitudes and the North Atlantic region at high latitudes. A Nam Co deep drilling will fill the gap in two large scale ICDP/IODP drilling transects (N-S: Lake Baikal, Lake Qinghai, Bay of Bengal; W-E: Lake Van, Lake Issyk-Kul, South China Sea, Lake Towuti), which will show the great significance of monsoon dynamics on a long-term scale. Multidisciplinary researches have been conducted since 2005 by a Sino-German cooperative team. The progresses during the last decade are: 1) Detailed bathymetric surveying, including a shallow sediment profiler investigation (Innomar SES 2000 light, ca. 30 m sediment penetration); 2) Paleo-environmental reconstructions covering the past 24 ka; 3) Modern sediment distribution covering the entire lake; 4) Monitoring including water temperature profiles, sediment traps, seasonal airborne pollen collection; 5) Deep seismic survey penetrating up to 800 meters of lake sediments. Based on sediment rates from reference core NC08/01, seismic results show that an age of 500 ka may be reached at 500 m, and >1 Ma at the observed base. Faulting can be clearly detected in the seismic profiles, especially from MIS 5 to early Holocene, and shows the characteristics of normal faults or strike-slip faults. Both rotation of the layers and the close spacing, along with negative and positive offsets of the faults make a transtensional origin of the basin likely. An ICDP workshop proposal was approved this year (ID: ICDP-2017/10, http://www.icdp-online.org/projects/world/asia/lake-nam-co/). The workshop will likely be held in May 2018 in Beijing, where future scientific objectives, potential coring locations and logistics of a drilling campaign will be intensively discussed to ensure a successful drilling campaign in the near future.

Boundary current-controlled turbidite deposition: A sedimentation model for the Southern Nares Abyssal Plain, Western North Atlantic

NASA Astrophysics Data System (ADS)

Kuijpers, A.; Duin, E. J. Th.

1986-03-01

Examination of 38 sediment cores, bottom photographs, 7,000 km of 3.5 kHz reflection profiles and other seismic data from the southern part of the Nares Abyssal Plain suggests that complex sedimentary patterns and high sedimentation rates can be largely attributed to effects of a deep boundary current flowing eastward along the north flank of the Greater Antilles Outer Ridge. It is concluded that the areal dispersal pattern of turbidites on the plain results mainly from Quaternary climatically-induced fluctuations of the boundary current intensity.

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

NASA Astrophysics Data System (ADS)

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

2009-12-01

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

A quantitative analysis of global intermediate and deep seismicity

NASA Astrophysics Data System (ADS)

Ruscic, Marija; Becker, Dirk; Le Pourhiet, Laetitita; Agard, Philippe; Meier, Thomas

2017-04-01

The seismic activity in subduction zones around the world shows a large spatial variabilty with some regions exhibiting strong seismic activity down to depths of almost 700km while in other places seismicity terminates at depths of about 200 or 300 km. Also the decay of the number of seismic events or of the seismic moment with depth is more pronounced in some regions than in others. The same is true for the variability of the ratio of large to small events (the b-value of the Gutenberg-Richter relation) that is varying with depth. These observations are often linked to parameters of the downgoing plate like age or subduction velocity. In this study we investigate a subset of subduction zones utilizing the revised ISC catalogue of intermediate and deep seismicity to determine statistical parameters well suited to describe properties of intermediate deep and deep events. The seismicity is separated into three depth intervals from 50-175km, 175-400km and >400km based on the depth at which the plate contact decouples, the observed nearly exponential decay of the event rate with depth and the supposed depth of phase transition at 410 km depth where also an increase of the event number with depth is observed. For estimation of the b-value and the exponential decay with depth, a restriction of the investigated time interval to the period after 1997 produced significantly better results indicating a globally homogeneous magnitude scale with the magnitude of completeness of about Mw 5. On a global scale the b-value decreases with depth from values of about 1 at 50-175km to values of slightly below 0.8 for events below 400km. Also, there is a slight increase of the b-value with the age of the subducting plate. These changes in the b-value with depth and with age may indicate a varying fragmentation of the slab. With respect to the ratio of the seismic moment between deeper and shallower parts of the subduction zones a dependence on the age is apparent with older slabs exhibiting higher ratios indicating stronger hydration of older slabs and consequently stronger seismic activity at depth in older and thicker slabs. Furthermore, older slabs show the tendency to larger b-values. This indicates stronger fragmentation of older slabs favoring smaller events. Between 50 km and 300 km depth, seismicity in subduction zones decays nearly exponentially with depth. However, the majority of subduction zones show between about 60 km and 100 km lower seismic activity than expected by an exponential decay. This observation correlates well with findings from petrological studies that rocks are rarely scraped off from the downgoing plate at these depths indicating low seismic coupling and low stresses at the plate interface in a depth range below the seismogenic zone and above 100 km depth were dehydration reactions become virulent. Interestingly, the percentage of this deficit becomes larger with plate age for event frequency (reduced number of events), but decreases for moment release (events have larger magnitudes). It is observed that the forearc high is located above the plate interface with reduced seismic coupling. The forearc high is thus an indication of upward directed return flow along the seismically decoupled plate interface. In addition, it is found that the topography of the forearc high is larger above shallow dipping slabs. A correlation of the depth dependent seismic behavior with the subduction or trench velocity is not observed for the investigated subduction zones. Plate age seems to be the dominating factor for properties of intermediate deep and deep seismicity.

Crustal structure of Central Sicily

NASA Astrophysics Data System (ADS)

Giustiniani, Michela; Tinivella, Umberta; Nicolich, Rinaldo

2018-01-01

We processed crustal seismic profile SIRIPRO, acquired across Central Sicily. To improve the seismic image we utilized the wave equation datuming technique, a process of upward or downward continuation of the wave-field between two arbitrarily shaped surfaces. Wave equation datuming was applied to move shots and receivers to a given datum plane, removing time shifts related to topography and to near-surface velocity variations. The datuming procedure largely contributed to attenuate ground roll, enhance higher frequencies, increase resolution and improve the signal/noise ratio. Processed data allow recognizing geometries of crust structures differentiating seismic facies and offering a direct image of ongoing tectonic setting within variable lithologies characterizing the crust of Central Sicily. Migrated sections underline distinctive features of Hyblean Plateau foreland and above all a crustal thinning towards the Caltanissetta trough, to the contact with a likely deep Permo-Triassic rifted basin or rather a zone of a continent to oceanic transition. Inhomogeneity and fragmentation of Sicily crust, with a distinct separation of Central Sicily basin from western and eastern blocks, appear to have guided the tectonic transport inside the Caltanissetta crustal scale syncline and the accumulation of allochthonous terrains with south and north-verging thrusts. Major tectonic stack operated on the construction of a wide anticline of the Maghrebian chain in northern Sicily. Sequential south-verging imbrications of deep elements forming the anticline core denote a crust wedge indenting foreland structures. Deformation processes involved multiple detachment planes down to decoupling levels located near crust/mantle transition, supporting a presence of high-density lenses beneath the chain, interrelated to a southwards push of Tyrrhenian mantle and asthenosphere.

Oligo-Miocene reservoir sequence characterization and structuring in the Sisseb El Alem-Kalaa Kebira regions (Northeastern Tunisia)

NASA Astrophysics Data System (ADS)

Houatmia, Faten; Khomsi, Sami; Bédir, Mourad

2015-11-01

The Sisseb El Alem-Enfidha basin is located in the northeastern Tunisia, It is borded by Nadhour - Saouaf syncline to the north, Kairouan plain to the south, the Mediterranean Sea to the east and Tunisian Atlassic "dorsale" to the west. Oligocene and Miocene deltaic deposits present the main potential deep aquifers in this basin with high porosity (25%-30%). The interpretation of twenty seismic reflection profiles, calibrated by wire line logging data of twelve oil wells, hydraulic wells and geologic field sections highlighted the impact of tectonics on the structuring geometry of Oligo-Miocene sandstones reservoirs and their distribution in raised structures and subsurface depressions. Miocene seismostratigraphy analysis from Ain Ghrab Formation (Langhian) to the Segui Formation (Quaternary) showed five third-order seismic sequence deposits and nine extended lenticular sandy bodies reservoirs limited by toplap and downlap surfaces unconformities, Oligocene deposits presented also five third- order seismic sequences with five extended lenticular sandy bodies reservoirs. The Depth and the thickness maps of these sequence reservoir packages exhibited the structuring of this basin in sub-basins characterized by important lateral and vertical geometric and thichness variations. Petroleum wells wire line logging correlation with clay volume calculation showed an heterogeneous multilayer reservoirs of Oligocene and Miocene formed by the arrangement of fourteen sandstone bodies being able to be good reservoirs, separated by impermeable clay packages and affected by faults. Reservoirs levels correspond mainly to the lower system tract (LST) of sequences. Intensive fracturing by deep seated faults bounding the different sub-basins play a great role for water surface recharge and inter-layer circulations between affected reservoirs. The total pore volume of the Oligo-Miocene reservoir sandy bodies in the study area, is estimated to about 4 × 1012 m3 and equivalent to 4 × 109 m3 of deep water reserves.

Site-specific seismic ground motion analyses for transportation infrastructure in the New Madrid seismic zone.

DOT National Transportation Integrated Search

2012-11-01

Generic, code-based design procedures cannot account for the anticipated short-period attenuation and long-period amplification of earthquake ground motions in the deep, soft sediments of the Mississippi Embayment within the New Madrid Seismic Zone (...

Gas Reservoir Identification Basing on Deep Learning of Seismic-print Characteristics

NASA Astrophysics Data System (ADS)

Cao, J.; Wu, S.; He, X.

2016-12-01

Reservoir identification based on seismic data analysis is the core task in oil and gas geophysical exploration. The essence of reservoir identification is to identify the properties of rock pore fluid. We developed a novel gas reservoir identification method named seismic-print analysis by imitation of the vocal-print analysis techniques in speaker identification. The term "seismic-print" is referred to the characteristics of the seismic waveform which can identify determinedly the property of the geological objectives, for instance, a nature gas reservoir. Seismic-print can be characterized by one or a few parameters named as seismic-print parameters. It has been proven that gas reservoirs are of characteristics of negative 1-order cepstrum coefficient anomaly and Positive 2-order cepstrum coefficient anomaly, concurrently. The method is valid for sandstone gas reservoir, carbonate reservoir and shale gas reservoirs, and the accuracy rate may reach up to 90%. There are two main problems to deal with in the application of seismic-print analysis method. One is to identify the "ripple" of a reservoir on the seismogram, and another is to construct the mapping relationship between the seismic-print and the gas reservoirs. Deep learning developed in recent years is of the ability to reveal the complex non-linear relationship between the attribute and the data, and of ability to extract automatically the features of the objective from the data. Thus, deep learning could been used to deal with these two problems. There are lots of algorithms to carry out deep learning. The algorithms can be roughly divided into two categories: Belief Networks Network (DBNs) and Convolutional Neural Network (CNN). DBNs is a probabilistic generative model, which can establish a joint distribution of the observed data and tags. CNN is a feedforward neural network, which can be used to extract the 2D structure feature of the input data. Both DBNs and CNN can be used to deal with seismic data. We use an improved DBNs to identify carbonate rocks from log data, the accuracy rate can reach up to 83%. DBNs is used to deal with seismic waveform data, more information is obtained. The work was supported by NSFC under grant No. 41430323 and No. 41274128, and State Key Lab. of Oil and Gas Reservoir Geology and Exploration.

Seismic reflection and structuring characterization of deep aquifer system in the Dakhla syncline (Cap Bon, North-Eastern Tunisia)

NASA Astrophysics Data System (ADS)

Bellali, Abir; Jarraya Horriche, Faten; Gabtni, Hakim; Bédir, Mourad

2018-04-01

The Dakhla syncline is located in the North-Eastern Tunisia. It is bounded by Abd El Rahmene anticline to the North-West, El Haouaria Graben to the North-East, Grombalia Graben to the South-West and the Mediterranean Sea to the East. The main aquifer reservoirs of Dakhla syncline are constituted by stacks of fluvial to deltaic Neogene sequences and carbonates. The interpretation of eight seismic reflection profiles, calibrated by wire line logging data of three oil wells, hydraulic wells and geologic field sections highlighted the impact of tectonics on the structuring geometry of aquifers and their distribution in elevated structures and subsurface depressions. Lithostratigraphic correlations and seismic profiles analysis through the syncline show that the principal aquifers are thickest within the central and northern part of the study area and thinnest to the southern part of the syncline. Seismic sections shows that the fracture/fault pattern in this syncline is mainly concentrated along corridors with a major direction of NW-SE and secondary directions of N-S, E-W and NE-SW with different release. This is proved by the complexity structure of Eastern Tunisia, resulted from the interaction between the African and Eurasiatic plates. Isochron maps of aquifers systems exhibited the structuring of this syncline in sub-surface characterized by important lateral and vertical geometric and thickness variations. Seismic sections L1, L2, L3, L4, L5 and petroleum wells showed an heterogeneous multilayer aquifers of Miocene formed by the arrangement of ten sandstone bodies, separated by impermeable clay packages. Oligo-Miocene deposits correspond to the most great potential aquifers, with respectively an average transmissivity estimated: Somaa aquifer 6.5 10-4 m2/s, Sandstone level aquifer 2.6 10-3 m2/s, Beglia aquifer 1.1 10-3 m2/s, Ain Ghrab aquifer 1.3 10-4 m2/s and Oligocene aquifer 2 10-3 m2/s. The interpretation of spatial variations of seismic units and the recognition of tectonic structures and their development may reveal some new insights for hydrogeological aspects.

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

NASA Astrophysics Data System (ADS)

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

2009-12-01

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

Ancestral Structure of the Neuquén Basin, Supported by an Innovative Deep Seismic Reprocessing

NASA Astrophysics Data System (ADS)

Comínguez, A. H.; Franzese, J. R.

2007-05-01

Seismic-tracings comprising both the eastern and western sectors of Sierra de los Chihuidos, showed the deep structure of the Neuquén basin, Argentina. Deep reprocessing of historical industrial seismic-lines supplied interpretive information down to about 30-33 km. Consequently, seismic data reprocessed with "self-truncating extended correlation" confirmed an objective way for acquiring deep-seismic information where standard Vibroseis records are available. In addition, the FMED algorithm was an appreciated nonlinear mathematical tool to improve seismic resolution. Original results accomplished with the above emphasized techniques, revealed a list of concepts summarized along the subsequent comments. An acoustic contrast at about 24 km depth must be the top of the lower Crust. An oblique reflector between 16 and 18 km depth must be assumed as the local image of the master shear that controlled the extension system during the Late Triassic-Early Jurassic period. A sub-master fault dipping about 8° W, surely have been controlling the evolution of `Las Cárceles' area. An important inversion event initiated during the Bathonian-Callovian, sensibly affected the western sector of `Las Cárceles' (that is the site contiguous to the Neuquén river). Significant deposition of synrift sediments (Precuyo Group) originated in contiguous scarp degradation was detected on the western side of `Los Chihuidos' arch, at about 7 km depth. A Pliensbachian-Toarcian bipolar inversion developed during the transition to the Cuyo Group was evidenced in the western area. In the same sector, a middle Jurassic postrift episode is characterized by a deltaic depositional system prograding to the west with accentuate high energy. A deep discontinuity was related with the ancestral origin of the Basin, its seismic tracing permitted to match field results with a scale tank experiment simulating orogenic collapse. Bulk extension of the ancestral thickened crust could be only justified if a relative free boundary is adjacent to the ancestral orogenic domain. In such case, the idea of rollback of the western subducting slab would emerge as the most credible hypothesis.

An investigation into the bedrock depth in the Eskisehir Quaternary Basin (Turkey) using the microtremor method

NASA Astrophysics Data System (ADS)

Tün, M.; Pekkan, E.; Özel, O.; Guney, Y.

2016-10-01

Amplification can occur in a graben as a result of strong earthquake-induced ground motion. Thus, in seismic hazard and seismic site response studies, it is of the utmost importance to determine the geometry of the bedrock depth. The main objectives of this study were to determine the bedrock depth and map the depth-to-bedrock ratio for use in land use planning in regard to the mitigation of earthquake hazards in the Eskişehir Basin. The fundamental resonance frequencies (fr) of 318 investigation sites in the Eskişehir Basin were determined through case studies, and the 2-D S-wave velocity structure down to the bedrock depth was explored. Single-station microtremor data were collected from the 318 sites, as well as microtremor array data from nine sites, seismic reflection data from six sites, deep-drilling log data from three sites and shallow drilling log data from ten sites in the Eskişehir Graben. The fundamental resonance frequencies of the Eskişehir Basin sites were obtained from the microtremor data using the horizontal-to vertical (H/V) spectral ratio (HVSR) method. The phase velocities of the Rayleigh waves were estimated from the microtremor data using the spatial autocorrelation (SPAC) method. The fundamental resonance frequency range at the deepest point of the Eskişehir Basin was found to be 0.23-0.35 Hz. Based on the microtremor array measurements and the 2-D S-wave velocity profiles obtained using the SPAC method, a bedrock level with an average velocity of 1300 m s-1 was accepted as the bedrock depth limit in the region. The log data from a deep borehole and a seismic reflection cross-section of the basement rocks of the Eskişehir Basin were obtained and permitted a comparison of bedrock levels. Tests carried out using a multichannel walk-away technique permitted a seismic reflection cross-section to be obtained up to a depth of 1500-2000 m using an explosive energy source. The relationship between the fundamental resonance frequency in the Eskişehir Basin and the results of deep drilling, shallow drilling, shear wave velocity measurement and sedimentary cover depth measurement obtained from the seismic reflection section was expressed in the form of a nonlinear regression equation. An empirical relationship between fr, the thickness of sediments and the bedrock depth is suggested for use in future microzonation studies of sites in the region. The results revealed a maximum basin depth of 1000 m, located in the northeast of the Eskişehir Basin, and the SPAC and HVSR results indicated that within the study area the basin is characterized by a thin local sedimentary cover with low shear wave velocity overlying stiff materials, resulting in a sharp velocity contrast. The thicknesses of the old Quaternary and Tertiary fluvial sediments within the basin serve as the primary data sources in seismic hazard and seismic site response studies, and these results add to the body of available seismic hazard data contributing to a seismic microzonation of the Eskişehir Graben in advance of the severe earthquakes expected in the Anatolian Region.

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

NASA Astrophysics Data System (ADS)

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

2016-12-01

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

Development of Vertical Cable Seismic System (3)

NASA Astrophysics Data System (ADS)

Asakawa, E.; Murakami, F.; Tsukahara, H.; Mizohata, S.; Ishikawa, K.

2013-12-01

The VCS (Vertical Cable Seismic) is one of the reflection seismic methods. It uses hydrophone arrays vertically moored from the seafloor to record acoustic waves generated by surface, deep-towed or ocean bottom sources. Analyzing the reflections from the sub-seabed, we could look into the subsurface structure. Because VCS is an efficient high-resolution 3D seismic survey method for a spatially-bounded area, we proposed the method for the hydrothermal deposit survey tool development program that the Ministry of Education, Culture, Sports, Science and Technology (MEXT) started in 2009. We are now developing a VCS system, including not only data acquisition hardware but data processing and analysis technique. We carried out several VCS surveys combining with surface towed source, deep towed source and ocean bottom source. The water depths of the survey are from 100m up to 2100m. The target of the survey includes not only hydrothermal deposit but oil and gas exploration. Through these experiments, our VCS data acquisition system has been completed. But the data processing techniques are still on the way. One of the most critical issues is the positioning in the water. The uncertainty in the positions of the source and of the hydrophones in water degraded the quality of subsurface image. GPS navigation system are available on sea surface, but in case of deep-towed source or ocean bottom source, the accuracy of shot position with SSBL/USBL is not sufficient for the very high-resolution imaging. We have developed another approach to determine the positions in water using the travel time data from the source to VCS hydrophones. In the data acquisition stage, we estimate the position of VCS location with slant ranging method from the sea surface. The deep-towed source or ocean bottom source is estimated by SSBL/USBL. The water velocity profile is measured by XCTD. After the data acquisition, we pick the first break times of the VCS recorded data. The estimated positions of shot points and receiver points in the field include the errors. We use these data as initial guesses, we invert iteratively shot and receiver positions to match the travel time data. After several iterations we could finally estimate the most probable positions. Integration of the constraint of VCS hydrophone positions, such as the spacing is 10m, can accelerate the convergence of the iterative inversion and improve results. The accuracy of the estimated positions from the travel time date is enough for the VCS data processing.

Relationships between the geometry of seismogenic faults and observed seismicty: a contribute from reflection seismic

NASA Astrophysics Data System (ADS)

Ciaccio, M. G.; Mirabella, F.; Stucchi, E.

2003-04-01

We analyze the seismogenic structures of the the Colfiorito area (central Italy), strucked by the 1997-98 relevant seismic sequence. This area has been used as a test site to investigate the possible interactions between earthquake seismology, reflection seismology and structural geology. Here we show the results obtained from the interpretation of the re-processed seismic reflection profile, acquired in the 80' for hydrocarbon exploration by ENI-Agip, crossing the epicentral area and the relationships between relating hypocentral locations and geological features derived from surface and from seismic data. The dense distribution of seismic stations connected to a temporary network installed after the occurrence of the first two large shocks (Mw=5.7 and Mw=6.0) provided high quality data showing earthquakes located at depth varying from 3 to 9 km and characterised by normal faulting mechanisms, with a NE-SW tension axis oriented about N55^o. The non conventional reprocessing sequence adopted was aimed to the early removal of the coherent and random noise and to the optimal definition of fault systems. The obtained profile shows an outstanding increase in the resolution of the geological structures with a better evidence of the faults and allows a much better correlation of surface geology features with the reflectors and the banning of parts of the profiles which run along the strike of the geological structures. The profile also shows a good image of the deep structure which has been interpreted as the depth image of the major fault of the Colfiorito fault system. A first attempt of projection of the earthquakes of the 1997-98 sequence shows a basic consistence with the inferred extensional structures at depth. The study also evidences that at least the upper part of the basement is involved in the thrust sheets, with a stepping and deepening of the basement from west to east from 5.5, to 9 km depth. The average dip at depth of the active faults is about 40^o fitting with the slip plane inferred from the focal mechanism of the main shocks and with the aftershocks distribution alignment in cross section of the aftershock sequence. At a depth of about 8 km, the trace of the active normal fault corresponds to the position of a Basement step, hence suggesting that the position of the Basement steps, generated by Miocene-Pliocene thrust tectonics, may have controlled the location of the subsequent normal faults.

Miscellaneous High-Resolution Seismic Imaging Investigations in Salt Lake and Utah Valleys for Earthquake Hazards

USGS Publications Warehouse

Stephenson, W.J.; Williams, R.A.; Odum, J.K.; Worley, D.M.

2007-01-01

Introduction In support of earthquake hazards and ground motion studies by researchers at the Utah Geological Survey, University of Utah, Utah State University, Brigham Young University, and San Diego State University, the U.S. Geological Survey Geologic Hazards Team Intermountain West Project conducted three high-resolution seismic imaging investigations along the Wasatch Front between September 2003 and September 2005. These three investigations include: (1) a proof-of-concept P-wave minivib reflection imaging profile in south-central Salt Lake Valley, (2) a series of seven deep (as deep as 400 m) S-wave reflection/refraction soundings using an S-wave minivib in both Salt Lake and Utah Valleys, and (3) an S-wave (and P-wave) investigation to 30 m at four sites in Utah Valley and at two previously investigated S-wave (Vs) minivib sites. In addition, we present results from a previously unpublished downhole S-wave investigation conducted at four sites in Utah Valley. The locations for each of these investigations are shown in figure 1. Coordinates for the investigation sites are listed in Table 1. With the exception of the P-wave common mid-point (CMP) reflection profile, whose end points are listed, these coordinates are for the midpoint of each velocity sounding. Vs30 and Vs100, also shown in Table 1, are defined as the average shear-wave velocities to depths of 30 and 100 m, respectively, and details of their calculation can be found in Stephenson and others (2005). The information from these studies will be incorporated into components of the urban hazards maps along the Wasatch Front being developed by the U.S. Geological Survey, Utah Geological Survey, and numerous collaborating research institutions.

Structure of the San Bernardino Basin Along Two Seismic Transects: Rialto-Colton Fault to the San Andreas Fault and Along the I-215 Freeway (I-10 to SR30)

USGS Publications Warehouse

Catchings, R.D.; Rymer, M.J.; Goldman, M.R.; Gandhok, G.; Steedman, C.E.

2008-01-01

In this report, we present seismic data and acquisition parameters for two seismic profiles acquired in the San Bernardino, California area in May and October 2003. We refer to these seismic profiles as the San Bernardino Regional (SBR) and San Bernardino High-Resolution (SBHR) seismic profiles. We present both un-interpreted and interpreted seismic images so that the structure of the area can independently interpreted by others. We explain the rationale for our interpretations within the text of this report, and in addition, we provide a large body of supporting evidence. The SBR seismic profile extended across the San Bernardino Basin approximately N30?E from the town of Colton to the town of Highland. The data were acquired at night when the signal-to-noise ratios were reasonably good, and for the larger shots, seismic energy propagated across the ~20-km-long array. Tomographic velocity data are available to depths of about 4 km, and low-fold reflection data are available to depths in excess of 5 km. The SBR seismic data reveal an asymmetric, fault-bound basin to about 5 km depth. The SBHR seismic profile trended along the I-215 freeway from its intersection with the Santa Ana River to approximately State Road 30 in San Bernardino. Seismic data acquired along the I-215 freeway provide detailed images, with CDP spacing of approximately 2.5 m along an approximately 8.2-km-long profile; shot and geophone spacing was 5 m. For logistical reasons, the high-resolution (SBHR) seismic data were acquired during daylight hours on the shoulder of the I-215 freeway and within 5 to 10 m of high-traffic volumes, resulting in low signal-to-noise ratios. The limited offset at which refracted first-arrivals could be measured along the SBHR seismic profile limited our measurements of tomographic refraction velocities to relatively shallow (< 150 m) depths. The SBHR reflection data reveal a basin with complex structural details within the upper kilometer. The two seismic profiles show internal consistency and consistency with other existing geophysical data. Collectively, the data suggest that the I-215 freeway trends along the faulted edge of a pull-apart basin, within a zone where the principal slip of the San Jacinto Fault is transferred to the San Andreas Fault. Because the I-215 freeway trends at low angles to these flower-structure faults, both primary and numerous secondary faults are apparent between the I-10 exchange and State Road-30, suggesting that much of the 8-km-long segment of the I-215 freeway could experience movement along primary or secondary faults.

The lithospheric Structure of the Sahara Metacraton From Joint Analysis of Satellite Gravity Gradients and Seismological Data

NASA Astrophysics Data System (ADS)

Sobh, M.; Ebbing, J.; Goetze, H. J.; Abdelsalam, M. G.

2016-12-01

For the Saharan Metacraton in northern Africa only a few geophysical results exists, which can be used to characterize its deep structure. We combine recent seismological models with satellite gravity gradients to build a 3D lithospheric density model of the metacraton and its surrounding regions. Due to the sparse distribution of seismic data, we estimate the Moho boundary by non-linear gravity inversion in spherical coordinates. The model is constrained by some wide angle refraction seismic profiles and receiver function Moho depths. Despite the high topography of the Darfur and Tibisti Cenozoic volcanic provinces, we estimate thin crust which indicates an upper mantle contribution to the isostatic balance. In combination with seismic tomography models, we found that the lithospheric thickness in the western part of the Metacraton is thicker than in the eastern part. This indicates that the western resembles the remnants of the pre-Neoproterozoic Sahara craton (e.g. the Marzuk craton which escaped the metacratonization process). In order to explain the partial loss of the expected cratonic root beneath the Metacraton, we present different petrological-geophysical scenario testing for different upper mantle compositions.

Seismology in the United States, 1983-1986 (Paper 7R0264)

NASA Astrophysics Data System (ADS)

Hanks, Thomas C.

1987-07-01

Any seismologist trying even to carry, let alone read, the EOS abstract volumes for recent AGU Meetings knows full well of the substantial growth in seismological research during this reporting period, the four years of 1983 through 1986. Indeed, the number of Seismology Section abstracts has grown from 188 (Fall, 1982) to about 320 (Fall, 1986), to be more or less precise. At a time when research monies seem to be no better than stable (and declining in real terms) and when job opportunities for seismologists seem to have never been worse, at least in the professional lifetimes of most of us, something must be amiss, but certainly this is not the great vitality and diversity in seismological research during the past four years. The current reporting period saw the consortium approach brought to full flower in several fields of seismology, and these include CALCRUST, a consortium of California universities to investigate the crustal structure of the southwestern United States with seismic reflection data; DOSECC (Deep Observation and Sampling of the Earth's Continental Crust), a consortium to drill and make measurements within scientifically dedicated deep holes to sample active processes that make and remake the continents; EDGE, a consortium of university, government, and private industry scientists intent on exploring the oceanic/continental transitions along U.S. continental margins, using seismic and potential field methods; and IRIS (Incorporated Research Institutions for Seismology), whose prospectus includes a major upgrading of the global seismic network, an advanced portable array of 1000 seismic units for a host of active and passive experiments, and a data management center to store and utilize the vast quantities of data forthcoming from the first two activities. Each of these fledglings can trace their basic nature and motivation, if not their specific scientific agendas, to COCORP (Consortium for Continental Reflection Profiling), now a teenager, whose activities were summarized by Phinney and Odom[1983] for the last reporting period and by W. D. Mooney for the current one.

Seismic investigation on the Littoral Faults Zone in the northern continental margin of South China Sea

NASA Astrophysics Data System (ADS)

Sun, J.; Xu, H.; Xia, S.; Cao, J.; Wan, K.

2017-12-01

The continental margin of the northern South China Sea (SCS) had experienced continuous evolution from an active continental margin in the late Mesozoic to a passive continental margin in the Cenozoic. The 1200km-long Littoral Faults Zone (LFZ) off the mainland South China was suggested to represent one of the sub-plate boundaries and play a key role during the evolution. Besides, four devastating earthquakes with magnitude over 7 and another 11 destructive events with M>6 were documented to have occurred along the LFZ. However, its approximity to the shoreline, the shallow water depth, and the heavy fishing activities make it hard to conduct a marine seismic investigation. As a result, understandings about the LFZ before 2000 were relatively poor and mostly descriptive. After two experiments of joint onshore-offshore wide-angle seismic surveys in the 1st decade of this century, several cruses aiming to unveil the deep structure of the LFZ were performed in the past few years, with five joint onshore-offshore wide-angle seismic survey profiles completed. Each of these profiles is perpendicular to the shoreline, with four to five seismometers of campaign mode deployed on the landside and over ten Ocean Bottom Seismometers (OBSs) spacing at 20km deployed on the seaside. Meanwhile, multi-channel seismic (MCS) data along these profiles were obtained simultaneously. Based on these data, velocity models from both forward modeling and inversion were obtained. According to these models, the LFZ was imaged to be a low-velocity fractured zone dipping to the SSE-SE at a high-angle and cutting through the thinned continental crust at some locations. Width of the fractured zone varies from 6km to more than 10km from site to site. With these results, it is suggested that the LFZ accommodates the stresses from both the east side, where the Eurasia/Philippine Sea plate converging and mountain building is ongoing, and the west side, where a strike-slip between the Indochina peninsular and the South China is occurring. Moreover, a low-velocity layer on the top of the lower-crust was also modeled, and its intersection with the fractured zone formed a weak zone where stresses concentrated, and led to those abovementioned earthquakes along the LFZ.

Heat Flow, Regional Geophysics and Lithosphere Structure In The Czech Republic

NASA Astrophysics Data System (ADS)

Safanda, J.; Cermak, V.; Kresl, M.; Dedecek, P.

Paper summarises and critically revises heat flow data that have been collected in the Czech Republic to date. The regional heat flow density map was prepared in view of all existing heat flow data completed with the similar in the surrounding countries and taking into consideration also temperature measurements in deep boreholes. Crustal temperature profiles were calculated by using the available geological information, results of deep seismic sounding and the laboratory data on radiogenic heat produc- tion and thermal conductivity. Special attention was paid to numerous temperature logs in two sedimentary basins, namely in the Cheb and Ostrava-Karvina coal basins, for which detailed heat flow patterns were proposed. Relationships between heat flow distribution and the crustal/lithosphere evolution, between heat flow and the heat pro- duction of the crustal rocks, heat flow and crustal thickness and the steady-state vs. transient heat transport are discussed.

Deep structure of the continental margin and basin off Greater Kabylia, Algeria - New insights from wide-angle seismic data modeling and multichannel seismic interpretation

NASA Astrophysics Data System (ADS)

Aïdi, Chafik; Beslier, Marie-Odile; Yelles-Chaouche, Abdel Karim; Klingelhoefer, Frauke; Bracene, Rabah; Galve, Audrey; Bounif, Abdallah; Schenini, Laure; Hamai, Lamine; Schnurle, Philippe; Djellit, Hamou; Sage, Françoise; Charvis, Philippe; Déverchère, Jacques

2018-03-01

During the Algerian-French SPIRAL survey aimed at investigating the deep structure of the Algerian margin and basin, two coincident wide-angle and reflection seismic profiles were acquired in central Algeria, offshore Greater Kabylia, together with gravimetric, bathymetric and magnetic data. This 260 km-long offshore-onshore profile spans the Balearic basin, the central Algerian margin and the Greater Kabylia block up to the southward limit of the internal zones onshore. Results are obtained from modeling and interpretation of the combined data sets. The Algerian basin offshore Greater Kabylia is floored by a thin oceanic crust ( 4 km) with P-wave velocities ranging between 5.2 and 6.8 km/s. In the northern Hannibal High region, the atypical 3-layer crustal structure is interpreted as volcanic products stacked over a thin crust similar to that bordering the margin and related to Miocene post-accretion volcanism. These results support a two-step back-arc opening of the west-Algerian basin, comprising oceanic crust accretion during the first southward stage, and a magmatic and probably tectonic reworking of this young oceanic basement during the second, westward, opening phase. The structure of the central Algerian margin is that of a narrow ( 70 km), magma-poor rifted margin, with a wider zone of distal thinned continental crust than on the other margin segments. There is no evidence for mantle exhumation in the sharp ocean-continent transition, but transcurrent movements during the second opening phase may have changed its initial geometry. The Plio-Quaternary inversion of the margin related to ongoing convergence between Africa and Eurasia is expressed by a blind thrust system under the margin rising toward the surface at the slope toe, and by an isostatic disequilibrium resulting from opposite flexures of two plates decoupled at the continental slope. This disequilibrium is likely responsible for the peculiar asymmetrical shape of the crustal neck that may thus be a characteristic feature of inverted rifted margins.

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

NASA Astrophysics Data System (ADS)

Ahmadi, Omid; Juhlin, Christopher

2014-05-01

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

Mermaid floating seismometer : A versatile Oceanographic profiler dedicated to the Earthscope Ocean Program.

NASA Astrophysics Data System (ADS)

Hello, Y.; Nolet, G.; Bonnieux, S.; Yegikyan, M.; Chao, Y.; Chen, J.

2016-12-01

Mermaids have been developed to improve seismic data coverage in the oceanic domain for imaging of the Earth's interior. The first generation of Mermaids was housed in conventional Argo-type floats, while hardware and software was developed to analyze acoustic signals, determine whether an earthquake has been recorded, and whether the Mermaid should to come up to the surface and transmit to the satellite. Since 2012, we have deployed small test networks of Mermaids in the Indian Ocean, and in the Mediterranean sea, and we present at this meeting the result from a main network of 9 Mermaids deployed since mid 2014 in the Galapagos archipelago to image the deep plume structure. Since then, we have moved from typical cylinder container, which equips most of the Argo Floats, to a more suitable spherical design, which allows for a larger power supply and more versatile payload. The life time of the new Mermaids is 6 years if sampling continuously for seismic signals, e.g. for seismic tomography by providing worldwide coverage of P wave arrival times. The passband can be widened to allow for monitoring of whale and dolphin sounds. An interface board allows to connect up to 8 external sensors to serve other goals (bio-Argo, geochemical, meteorological). This year we have started collaboration with Sea-Trec to equip the Mermaids with an optional new green renewable power source to guaranty its 6 years lifetime even with a full payload. The Mermaids monitor continuously during the parking phase when drifting freely at a depth down to 3000m, but also provide Argo profiles during the descent. We are collaborating with Sea-Bird to customize an SBE37 to equip the Mermaid for salinity measurements. The new Mermaid has all the features to answer many scientific goals, and a project to develop a user-friendly, adaptable, software system has begun in collaboration with i3s. The first stage of a global network, EarthScope-Oceans, will be launched in 2017, and is planned to grow to 500 units to image the deep interior of the Earth.

Asteroseismology of Red-Giant Stars: Mixed Modes, Differential Rotation, and Eccentric Binaries

NASA Astrophysics Data System (ADS)

Beck, Paul G.

2013-12-01

Astronomers are aware of rotation in stars since Galileo Galilei attributed the movement of sunspots to rotation of the Sun in 1613. In contrast to the Sun, whose surface can be resolved by small telescopes or even the (protected) eye, we detect stars as point sources with no spatial information. Numerous techniques have been developed to derive information about stellar rotation. Unfortunately, most observational data allow only for the surface rotational rate to be inferred. The internal rotational profile, which has a great effect on the stellar structure and evolution, remains hidden below the top layers of the star - the essential is hidden to the eyes. Asteroseismology allows us to "sense" indirectly deep below the stellar surface. Oscillations that propagate through the star provide information about the deep stellar interiors while they also distort the stellar surface in characteristic patterns leading to detectable brightness or velocity variations. Also, certain oscillation modes are sensitive to internal rotation and carry information on how the star is spinning deep inside. Thanks to the unprecedented quality of NASA's space telescope Kepler, numerous detailed observations of stars in various evolutionary stages are available. Such high quality data allow that for many stars, rotation can not only be constrained from surface rotation, but also investigated through seismic studies. The work presented in this thesis focuses on the oscillations and internal rotational gradient of evolved single and binary stars. It is shown that the seismic analysis can reach the cores of oscillating red-giant stars and that these cores are rapidly rotating, while nested in a slowly rotating convective envelope.

Integrated Geophysical Monitoring Program to Study Flood Performance and Incidental CO2 Storage Associated with a CO2 EOR Project in the Bell Creek Oil Field

NASA Astrophysics Data System (ADS)

Burnison, S. A.; Ditty, P.; Gorecki, C. D.; Hamling, J. A.; Steadman, E. N.; Harju, J. A.

2013-12-01

The Plains CO2 Reduction (PCOR) Partnership, led by the Energy & Environmental Research Center, is working with Denbury Onshore LLC to determine the effect of a large-scale injection of carbon dioxide (CO2) into a deep clastic reservoir for the purpose of simultaneous CO2 enhanced oil recovery (EOR) and to study incidental CO2 storage at the Bell Creek oil field located in southeastern Montana. This project will reduce CO2 emissions by more than 1 million tons a year while simultaneously recovering an anticipated 30 million barrels of incremental oil. The Bell Creek project provides a unique opportunity to use and evaluate a comprehensive suite of technologies for monitoring, verification, and accounting (MVA) of CO2 on a large-scale. The plan incorporates multiple geophysical technologies in the presence of complementary and sometimes overlapping data to create a comprehensive data set that will facilitate evaluation and comparison. The MVA plan has been divided into shallow and deep subsurface monitoring. The deep subsurface monitoring plan includes 4-D surface seismic, time-lapse 3-D vertical seismic profile (VSP) surveys incorporating a permanent borehole array, and baseline and subsequent carbon-oxygen logging and other well-based measurements. The goal is to track the movement of CO2 in the reservoir, evaluate the recovery/storage efficiency of the CO2 EOR program, identify fluid migration pathways, and determine the ultimate fate of injected CO2. CO2 injection at Bell Creek began in late May 2013. Prior to injection, a monitoring and characterization well near the field center was drilled and outfitted with a distributed temperature-monitoring system and three down-hole pressure gauges to provide continuous real-time data of the reservoir and overlying strata. The monitoring well allows on-demand access for time-lapse well-based measurements and borehole seismic instrumentation. A 50-level permanent borehole array of 3-component geophones was installed in a second monitoring well. A pre-injection series of carbon-oxygen logging across the reservoir was acquired in 35 wells. The baseline 3-D surface seismic survey was acquired in September 2012. A 3-D VSP incorporating two wells and 2 square miles of overlapping seismic coverage in the middle of the field was acquired in May 2013. Initial iterations of geologic modeling and reservoir simulation of the field have been completed. Currently, passive seismic monitoring with the permanent borehole array is being conducted during injection. Interpretation results from the baseline surface 3-D survey and preliminary results from the baseline 3-D VSP are being evaluated and integrated into the reservoir model. The PCOR Partnership's philosophy is to combine site characterization, modeling, and monitoring strategies into an iterative process to produce descriptive integrated results. The comprehensive effort at Bell Creek will allow a comparison of the effectiveness of several complementary geophysical and well-based methods in meeting the goals of the deep subsurface monitoring effort.

The Flemish Cap - Goban Spur conjugate margins: New evidence of asymmetry

NASA Astrophysics Data System (ADS)

Gerlings, J.; Louden, K. E.; Minshull, T. A.; Nedimović, M. R.

2011-12-01

The combined results of deep multichannel seismic (MCS) and refraction/wide-angle reflection seismic (R/WAR) profiles across the Flemish Cap-Goban Spur conjugate margin pair will be presented to help constrain rifting and breakup processes. Both profiles cross magnetic anomaly 34 and extend into oceanic crust, which makes it possible to observe the complete extensional history from continental rifting through the formation of initial oceanic crust. Kirchhoff poststack time and prestack time and depth migration images of the Flemish Cap MCS data are produced using a velocity model constructed from the MCS and R/WAR data. These new images show improved continuity of the Moho under the thick continental crust of Flemish Cap. The basement morphology image is sharper and reflections observed in the thin crust of the transition zone are more coherent. A basement high at the seaward-most end of the transition zone now displays clear diapiric features. To compare the two margins, the existing migrated MCS data across Goban Spur has been time-to-depth converted using the R/WAR velocity model of the margin. These reimaged seismic profiles demonstrate asymmetries in continental rifting and breakup with a complex transition to oceanic spreading: (1) During initial phases of rifting, the Flemish Cap margin displays a sharper necking profile than that of the Goban Spur margin. (2) Within the ocean-continent-transition zone, constraints from S-wave velocities on both margins indentifies previously interpreted oceanic crust as thinned continental crust offshore Flemish Cap in contrast with primarily serpentinized mantle offshore Goban Spur. (3) Continental breakup and initial seafloor spreading occur in a complex, asymmetric manner where the initial ~50 km of oceanic crust appears different on the two margins. Offshore Flemish Cap, both R/WAR and MCS results indicate a sharp boundary immediately seaward of a ridge feature, where the basement morphology becomes typical of slow seafloor spreading. There are no significant changes in either reflectivity or velocity seaward toward magnetic anomaly 34. On the Goban Spur margin in marked contrast, the basement morphology landward of magnetic anomaly 34 is shallower and has lower relief, and the velocity model indicates a diffuse change between the transitional crust and seafloor spreading. The results from these two very different conjugate margins emphasize the importance of having both types of seismic data from both conjugate margins when interpreting the geodynamic processes.

Fault creep and persistent asperities on the western section of the North Anatolian Fault, Turkey

NASA Astrophysics Data System (ADS)

Floyd, M.; Reilinger, R. E.; Ergintav, S.; Karabulut, H.; Vernant, P.; Konca, A. O.; Dogan, U.; Cetin, S.; Cakir, Z.; Mencin, D.; Bilham, R. G.; King, R. W.

2017-12-01

We interpret new geodetic and seismic observations along the western section of the North Anatolian Fault (NAF) in Turkey as evidence for persistent asperities on the fault surface. Analysis of geodetic and seismic observations of seven segments of the fault at different stages of the earthquake cycle suggest that areas of the fault surface that are accumulating strain (i.e. asperities) are deficient in interseismic seismicity and earthquake aftershocks compared to areas between asperities that are failing at least in part by fault creep. From west to east, these segments include the 2014 M6.9 Gokceada earthquake and 1912 M7.4 Ganos earthquake segments, the Sea of Marmara and Princes' Islands seismic "gaps", the 1999 M7.6/7.2 Izmit/Duzce earthquake segments, and the 1944 M7.4 Ismetpasa segment, which remains actively creeping. Aspects of each segment contribute to our interpretation of overall fault behavior. The most well-defined distribution of coseismic slip in relation to pre- and post-earthquake seismicity is for the 2014 Gokceada event. The most complete set of geodetic observations (pre-, co-, and short- and long-term post-seismic) come from the 1999 Izmit and Duzce events. Simple three-layer elastic models including a middle layer that is fully locked between earthquakes, and shallow and deeper layers that are allowed to creep, can account for these observations of the deformation cycle. Recent observations from InSAR, creepmeters and small-aperture GPS profiles indicate ongoing surface and shallow fault creep rates, as allowed by the upper layer of the three-layer model. Conceptually, creep in the deeper layer represents the deep healing of the fault following the earthquake. For the Izmit and Duzce earthquake segments, healing from prior earthquakes was complete before the 1999 sequence. More generally, the consistent pattern of strain accumulation along the full length of the NAF, including the long eastern segments that ruptured in major earthquakes in 1939, 1942 and 1943, suggests that deep fault healing is complete over time scales much shorter than the earthquake repeat time. Given their similarities, these results may be applicable and provide insights into the mechanics of strain accumulation and earthquake potential along other continental strike-slip faults such as the San Andreas Fault.

Preliminary stratigraphic and hydrogeologic cross sections and seismic profile of the Floridan aquifer system of Broward County, Florida

USGS Publications Warehouse

Reese, Ronald S.; Cunningham, Kevin J.

2013-01-01

To help water-resource managers evaluate the Floridan aquifer system (FAS) as an alternative water supply, the U.S. Geological Survey initiated a study, in cooperation with the Broward County Environmental Protection and Growth Management Department, to refine the hydrogeologic framework of the FAS in the eastern part of Broward County. This report presents three preliminary cross sections illustrating stratigraphy and hydrogeology in eastern Broward County as well as an interpreted seismic profile along one of the cross sections. Marker horizons were identified using borehole geophysical data and were initially used to perform well-to-well correlation. Core sample data were integrated with the borehole geophysical data to support stratigraphic and hydrogeologic interpretations of marker horizons. Stratigraphic and hydrogeologic units were correlated across the county using borehole geophysical data from multiple wells. Seismic-reflection data were collected along the Hillsboro Canal. Borehole geophysical data were used to identify and correlate hydrogeologic units in the seismic-reflection profile. Faults and collapse structures that intersect hydrogeologic units were also identified in the seismic profile. The information provided in the cross sections and the seismic profile is preliminary and subject to revision.

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).

2008 Joint United States-Canadian program to explore the limits of the Extended Continental Shelf aboard the U.S. Coast Guard cutter Healy--Cruise HLY0806

USGS Publications Warehouse

Childs, Jonathan R.; Triezenberg, Peter J.; Danforth, William W.

2012-01-01

In September 2008, the U.S. Geological Survey (USGS), in cooperation with Natural Resources Canada, Geological Survey of Canada (GSC), conducted bathymetric and geophysical surveys in the Arctic Beaufort Sea aboard the U.S. Coast Guard cutter USCGC Healy. The principal objective of this mission to the high Arctic was to acquire data in support of delineation of the outer limits of the U.S. and Canadian Extended Continental Shelf (ECS) in the Arctic Ocean in accordance with the provisions of Article 76 of the Law of the Sea Convention. The Healy was accompanied by the Canadian Coast Guard icebreaker Louis S. St- Laurent. The science parties on the two vessels consisted principally of staff from the USGS (Healy), and the GSC and the Canadian Hydrographic Service (Louis). The crew included marine mammal and Native-community observers, ice observers, and biologists conducting research of opportunity in the Arctic Ocean. The joint survey proved an unqualified success. The Healy collected 5,528 km of swath (multibeam) bathymetry (38,806 km2) and CHIRP subbottom profile data, with accompanying marine gravity measurements. The Louis acquired 2,817 km of multichannel seismic (airgun) deep-penetration reflection-profile data along 12 continuous lines, as well as 35 sonobuoy refraction stations and accompanying single-beam bathymetry. The coordinated efforts of the two vessels resulted in seismic-reflection profile data of much higher quality and continuity than if the data had been acquired with a single vessel alone. Equipment failure rate of the seismic equipment gear aboard the Louis was greatly improved with the advantage of having a leading icebreaker. When ice conditions proved too severe to deploy the seismic system, the Louis led the Healy, resulting in much improved quality of the swath bathymetry and CHIRP sub-bottom data in comparison with data collected by the Healy in the lead or working alone. Ancillary science objectives, including ice observations, deployment of ice-monitoring buoys and water-column sampling for biologic (phytoplankton) studies, were also successfully accomplished.

Multidisciplinary approach for the characterization of landslides in volcanic areas - a case study from the Palma Sola-Chiconquiaco Mountain Range, Mexico

NASA Astrophysics Data System (ADS)

Wilde, Martina; Rodríguez Elizarrarás, Sergio R.; Morales Barrera, Wendy V.; Schwindt, Daniel; Bücker, Matthias; Flores Orozco, Adrián; García García, Emilio; Pita de la Paz, Carlos; Terhorst, Birgit

2017-04-01

The Palma Sola-Chiconquiaco mountain range, situated in the State of Veracruz, Mexico, is highly susceptible to landslides, which is evidenced by the high frequency of landslide events of different sizes. The study area is located near the Gulf of Mexico coastline in the eastern sector of the Trans Mexican Volcanic Belt. There, landslide triggers are intense rainfalls related to tropical storms and hurricanes. Steeper slopes are commonly affected by rockfalls, whereas moderate slopes, covered by massive slope deposits, are affected by shallow as well as deep seated landslides. Some of the landslides in the slope deposits reach dimensions of more than 1000 m in length and depths of over 30 m. The heterogeneous parent material as well as older slide masses hamper the detailed characterization of the involved materials. Therefore, in this study, a multidisciplinary approach is applied that integrates geomorphological, geological, and geophysical data. The aim is the reconstruction of process dynamics by analyzing the geomorphological situation and subsurface conditions before and after the event. The focus lies on the identification of past landslide areas, which represent areas with high susceptibility for the reactivation of old slide masses. Furthermore, the analysis of digital terrain models, generated before the landslide event, indicate initial movements like extension cracks, which are located close to the current scarp area. In order to characterize the subsurface of slide masses geophysical investigations are applied. The geophysical survey consists of a total of nine profiles covering relevant key features of the large affected area. Along these profiles, electrical resistivity tomography (ERT) and seismic refraction tomography (SRT) data were collected. Both, electrical and seismic images reveal a sharp contrast between relatively loose and dry material of the slide mass (high resistivities and low seismic velocities) and the former land surface that is characterized by significantly reduced resistivities and higher seismic velocities. This contrast allows to establish the thicknesses of slope deposits and geological layers along all geophysical profiles. Furthermore, the investigations are complemented by a high resolution digital terrain model of the landslide and its surroundings, which was reconstructed from orthophotos derived from unmanned aerial vehicle photogrammetry.

Multi-azimuth Anisotropic Velocity Measurements in Fractured Crystalline Rock From the International Continental Drilling Program Outokumpu Borehole, Finland

NASA Astrophysics Data System (ADS)

Schijns, H.; Duo, X.; Heinonen, S.; Schmitt, D. R.; Kukkonen, I. T.; Heikkinen, P.

2008-12-01

A high resolution seismic survey consisting of a multi-depth multi-azimuth VSP, a zero-offset VSP and a reflection/refraction survey was conducting in May, 2006, near the town of Outokumpu, Finland, using the International Continental Scientific Drilling Program 2.5 km deep fully cored scientific borehole. The survey was undertaken in order to create an anisotropic velocity model for future micro-seism studies as well as to provide a higher resolution reflection profile through the area than was previously available. The seismic survey high frequency seismic vibrator as a source, employing 8 s linear taper sweeps from 15-250 Hz at 20 m shot spacing. Receivers were 14 Hz single component geophones on the surface and a three component geophone downhole. The walk-away VSP included measurements over two azimuths with the receiver at depths of 1000, 1750 and 2500 m, while the zero-offset VSP used a 2 m depth increment. Surface geophones were located along the same seismic lines as employed in the walk-away VSP and were nominally 4 m apart. The survey area is located on the Fennoscandian shield, and the glacial history of the area required significant static corrections to account for the variable overburden overlying the mica-rich schist and pegmatitic granite composing the bedrock. These were calculated using travel-time inversion of the refraction data and were applied to the walk-away VSP and reflection profiles, significantly improving the quality of both. Anisotropic velocity analysis was performed using a plane-wave decomposition of the processed walk-away VSP. The maximum anisotropy was observed in the walk-away VSPs along the Southeastern azimuth, with the P-wave phase velocity ranging from 5330-5950 m/s between 50-1000 m in depth, and up to 6150 m/s between 1000-1750 m in depth. Shear wave splitting was observed in the Northeastern direction. Preliminary analysis of the zero-offset VSP has revealed shown good agreement with the relevant portions of the anisotropic velocity measurements and the reflection profile.

Seismic Tomography and the Development of a State Velocity Profile

NASA Astrophysics Data System (ADS)

Marsh, S. J.; Nakata, N.

2017-12-01

Earthquakes have been a growing concern in the State of Oklahoma in the last few years and as a result, accurate earthquake location is of utmost importance. This means using a high resolution velocity model with both lateral and vertical variations. Velocity data is determined using ambient noise seismic interferometry and tomography. Passive seismic data was acquired from multiple IRIS networks over the span of eight years (2009-2016) and filtered for earthquake removal to obtain the background ambient noise profile for the state. Seismic Interferometry is applied to simulate ray paths between stations, this is done with each possible station pair for highest resolution. Finally the method of seismic tomography is used to extract the velocity data and develop the state velocity map. The final velocity profile will be a compilation of different network analyses due to changing station availability from year to year. North-Central Oklahoma has a dense seismic network and has been operating for the past few years. The seismic stations are located here because this is the most seismically active region. Other parts of the state have not had consistent coverage from year to year, and as such a reliable and high resolution velocity profile cannot be determined from this network. However, the Transportable Array (TA) passed through Oklahoma in 2014 and provided a much wider and evenly spaced coverage. The goal of this study is to ultimately combine these two arrays over time, and provide a high quality velocity profile for the State of Oklahoma.

Two Generations of Detachment System in an Aborted Hyper-extended Rift Basin: A Case in the Baiyun Sag, northern South China Sea

NASA Astrophysics Data System (ADS)

Zhou, Z.; Mei, L.; Liu, J.; Chen, L.; Zheng, J.

2016-12-01

Three episodes of rifting started from the latest Cretaceous and contributed to final breakup of the South China Sea in Early Oligocene. The Baiyun Sag developed in the continental slope of northern South China Sea was supposed to be only affected by the second and third rifting events and defined as a hyper-extended rift basin with extremely thinned crust through a deep seismic reflection profile by former researchers. In this paper, 19 supplementary deep seismic images were used to investigate the deep crustal structure. The results suggest that only 4-km-thick continental crust is preserved in the middle of the Baiyun Sag, whereas about 26-km-thick in the adjacent relatively unextended regions, such as Panyu Low Uplift in the north and Shunhe Uplift in the southwest. Furthermore, recently gathered 2D/3D offshore seismic data almost cover the whole research region, allowing us to recognize a Cenozoic detachment system which consists of six major detachment faults. In contrast to the performance of the distal domains in the Iberia and Mid-Norway rifted margins, all of these detachment faults dipped toward the continent and thinned the crust effectively, indicating that the extension of the Baiyun Sag was independent of the future lithospheric breakup zone. Consequently, we define the Baiyun Sag as an aborted hyper-extended rift basin formed during Paleocene to Early Oligocene. The inherited basement structures will clearly influence the evolution process of new born rift basin. Under the top basement, a pre-Cenozoic detachment system is also well described in our research area and act as a series of surface with strong amplitude in seismic imaging. We argue that the Cenozoic detachment system was built on the basis of the pre-rift detachment system which is speculated to have formed in the Late Cretaceous. Extensional style of a conveyor belt is recognized in this sediment-rich, aborted hyper-extended supra-detachment basin, showing that the breakaway blocks or extensional allochthons move gradually away from the footwall upon the major detachment surface. This study provides valuable insights into the processes that are related to the evolution of extremely crustal thinning under the constraint of pre-existing fabrics.

Enhanced Geothermal Systems in Urban Areas - Lessons Learned from the 2006 Basel ML3.4 Earthquake

NASA Astrophysics Data System (ADS)

Kraft, T.; Mai, P. M.; Wiemer, S.; Deichmann, N.; Ripperger, J.; Kästli, P.; Bachmann, C. E.; Fäh, D.; Woessner, J.; Giardini, D.

2009-12-01

We report on a recent deep-heat mining experiment carried out in 2006/2007 in the city of Basel (Switzerland). This pilot project was designed to produce renewable geothermal energy using the Enhanced Geothermal System (EGS) methodology. For developing the geothermal reservoir, a deep borehole was brought down to 5 km depth. Then, in December 2006, the deep-heat-mining project entered the first critical phase when the water injections started for generating micro-fracturing of the rock. These fractures increase the permeability of the host rock, needed for efficient heat exchange between the rock and the cold water; however, these fracture are also source of micro-seismicity - small earthquakes that are continuously recorded and monitored by dedicated local seismic networks. In this stimulation phase, the seismic activity increased rapidly above the usual background seismicity, and culminated in a widely felt ML 3.4 earthquake, which caused some damage in the city of Basel. Due to the higher-than-expected seismic activity, and the reaction of the population, the media, and the politicians, the experiment was stalled only 6 days after the stimulations began. Although the injected water was allowed to escape immediately after the mainshock and pressure at the wellhead dropped rapidly, the seismic activity declined only slowly, with three ML > 3 events occurring one to two months later. Although the EGS technology has been applied and studied at various sites since the 1970s, the physical processes and parameters that control injection-induced seismicity - in terms of earthquake rate, size distribution and maximum magnitude - are still poorly understood. Consequently, the seismic hazard and risk associated with the creation and operation of EGS are difficult to estimate. The very well monitored Basel seismic sequence provides an excellent opportunity to advance the understanding of the physics of EGS. The Swiss Seismological Service (SED) is investigating the Basel dataset in the framework of the multidisciplinary research project GEOTHERM (www.geotherm.ethz.ch) Left) Seismic network in Basel, Switzerland. An epicenter map of the fluid injection-induced seismicity recorded by the seismic network, indicating high event densities in hot colors, is shown in the inset. Right) Fluid injection-induced seismicity recorded by the seismic network.

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

NASA Astrophysics Data System (ADS)

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

2017-12-01

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

Basin Analysis and Petroleum System Characterisation of Western Bredasdorp Basin, Southern Offshore of South Africa: Insights from a 3d Crust-Scale Basin Model - (Phase 1)

NASA Astrophysics Data System (ADS)

Sonibare, W. A.; Scheck-Wenderoth, M.; Sippel, J.; Mikeš, D.

2012-04-01

In recent years, construction of 3D geological models and their subsequent upscaling for reservoir simulation has become an important tool within the oil industry for managing hydrocarbon reservoirs and increasing recovery rate. Incorporating petroleum system elements (i.e. source, reservoir and trap) into these models is a relatively new concept that seems very promising to play/prospect risk assessment and reservoir characterisation alike. However, yet to be fully integrated into this multi-disciplinary modelling approach are the qualitative and quantitative impacts of crust-scale basin dynamics on the observed basin-fill architecture and geometries. The focus of this study i.e. Western Bredasdorp Basin constitutes the extreme western section of the larger Bredasdorp sub-basin, which is the westernmost depocentre of the four southern Africa offshore sub-basins (others being Pletmos, Gamtoos and Algoa). These basins, which appear to be initiated by volcanically influenced continental rifting and break-up related to passive margin evolution (during the Mid-Late Jurassic to latest Valanginian), remain previously unstudied for crust-scale basin margin evolution, and particularly in terms of relating deep crustal processes to depo-system reconstruction and petroleum system evolution. Seismic interpretation of 42 2D seismic-reflection profiles forms the basis for maps of 6 stratigraphic horizons which record the syn-rift to post-rift (i.e. early drift and late drift to present-day seafloor) successions. In addition to this established seismic markers, high quality seismic profiles have shown evidence for a pre-rift sequence (i.e. older than Late Jurassic >130 Ma). The first goal of this study is the construction of a 3D gravity-constrained, crust-scale basin model from integration of seismics, well data and cores. This basin model is constructed using GMS (in-house GFZ Geo-Modelling Software) while testing its consistency with the gravity field is performed using IGMAS+ (Interactive Gravity and Magnetic Assistant System; Götze et al., 2010 and Schmidt et al., 2011). The ensuing model will be applied to predict the present-day deep crustal configuration and thermal field characteristics of the basin. Thereafter, 3D volumetric backstripping analysis will be performed to predict basin subsidence mechanisms (i.e. tectonic, thermal and sediment load) through time as well as to estimate paleo-water depths for paleogeographic reconstruction. The information gathered from crust-scale basin dynamics will be subsequently used at the petroleum system modelling stage to holistically assess the hydrocarbon potential of the basin in terms of source rock maturity and hydrocarbon generation, migration, timing and accumulation.

Constraining the crustal root geometry beneath the Rif Cordillera (North Morocco)

NASA Astrophysics Data System (ADS)

Diaz, Jordi; Gil, Alba; Carbonell, Ramon; Gallart, Josep; Harnafi, Mimoun

2016-04-01

The analyses of wide-angle reflections of controlled source experiments and receiver functions calculated from teleseismic events provide consistent constraints of an over-thickened crust beneath the Rif Cordillera (North Morocco). Regarding active source data, we investigate now offline arrivals of Moho-reflected phases recorded in RIFSIS project to get new estimations of 3D crustal thickness variations beneath North Morocco. Additional constrains on the onshore-offshore transition are derived from onland recording of marine airgun shots from the coeval Gassis-Topomed profiles. A regional crustal thickness map is computed from all these results. In parallel, we use natural seismicity data collected throughout TopoIberia and PICASSO experiments, and from a new RIFSIS deployment, to obtain teleseismic receiver functions and explore the crustal thickness variations with a H-κ grid-search approach. The use of a larger dataset including new stations covering the complex areas beneath the Rif Cordillera allow us to improve the resolution of previous contributions, revealing abrupt crustal changes beneath the region. A gridded surface is built up by interpolating the Moho depths inferred for each seismic station, then compared with the map from controlled source experiments. A remarkably consistent image is observed in both maps, derived from completely independent data and methods. Both approaches document a large modest root, exceeding 50 km depth in the central part of the Rif, in contrast with the rather small topographic elevations. This large crustal thickness, consistent with the available Bouguer anomaly data, favor models proposing that the high velocity slab imaged by seismic tomography beneath the Alboran Sea is still attached to the lithosphere beneath the Rif, hence pulling down the lithosphere and thickening the crust. The thickened area corresponds to a quiet seismic zone located between the western Morocco arcuate seismic zone, the deep seismicity area beneath western Alboran Sea and the superficial seismicity in Alhoceima area. Therefore, the presence of a crustal root seems to play also a major role in the seismicity distribution in northern Morocco.

Detailed seismic velocity structure of the ultra-slow spread crust at the Mid-Cayman Spreading Center from travel-time tomography and synthetic seismograms

NASA Astrophysics Data System (ADS)

Harding, J.; Van Avendonk, H. J.; Hayman, N. W.; Grevemeyer, I.; Peirce, C.

2017-12-01

The Mid-Cayman Spreading Center (MCSC), an ultraslow-spreading center in the Caribbean Sea, has formed highly variable oceanic crust. Seafloor dredges have recovered extrusive basalts in the axial deeps as well as gabbro on bathymetric highs and exhumed mantle peridotite along the only 110 km MCSC. Wide-angle refraction data were collected with active-source ocean bottom seismometers in April, 2015, along lines parallel and across the MCSC. Travel-time tomography produces relatively smooth 2-D tomographic models of compressional wave velocity. These velocity models reveal large along- and across-axis variations in seismic velocity, indicating possible changes in crustal thickness, composition, faulting, and magmatism. It is difficult, however, to differentiate between competing interpretations of seismic velocity using these tomographic models alone. For example, in some areas the seismic velocities may be explained by either thin igneous crust or exhumed, serpentinized mantle. Distinguishing between these two interpretations is important as we explore the relationships between magmatism, faulting, and hydrothermal venting at ultraslow-spreading centers. We therefore improved our constraints on the shallow seismic velocity structure of the MCSC by modeling the amplitude of seismic refractions in the wide-angle data set. Synthetic seismograms were calculated with a finite-difference method for a range of models with different vertical velocity gradients. Small-scale features in the velocity models, such as steep velocity gradients and Moho boundaries, were explored systematically to best fit the real data. With this approach, we have improved our understanding of the compressional velocity structure of the MCSC along with the geological interpretations that are consistent with three seismic refraction profiles. Line P01 shows a variation in the thinness of lower seismic velocities along the axis, indicating two segment centers, while across-axis lines P02 and P03 show variations in igneous crustal thickness and exhumed mantle in some areas.

Seismic measurements of the internal properties of fault zones

USGS Publications Warehouse

Mooney, W.D.; Ginzburg, A.

1986-01-01

The internal properties within and adjacent to fault zones are reviewed, principally on the basis of laboratory, borehole, and seismic refraction and reflection data. The deformation of rocks by faulting ranges from intragrain microcracking to severe alteration. Saturated microcracked and mildly fractured rocks do not exhibit a significant reduction in velocity, but, from borehole measurements, densely fractured rocks do show significantly reduced velocities, the amount of reduction generally proportional to the fracture density. Highly fractured rock and thick fault gouge along the creeping portion of the San Andreas fault are evidenced by a pronounced seismic low-velocity zone (LVZ), which is either very thin or absent along locked portions of the fault. Thus there is a correlation between fault slip behavior and seismic velocity structure within the fault zone; high pore pressure within the pronounced LVZ may be conductive to fault creep. Deep seismic reflection data indicate that crustal faults sometimes extend through the entire crust. Models of these data and geologic evidence are consistent with a composition of deep faults consisting of highly foliated, seismically anisotropic mylonites. ?? 1986 Birkha??user Verlag, Basel.

Kinematics of Active Deformation Across the Western Kunlun Mountain Range (Xinjiang, China), and Potential Seismic Hazards Within the Southern Tarim Basin

NASA Astrophysics Data System (ADS)

Guilbaud, C.; Simoes, M.; Barrier, L.; Laborde, A.; van der Woerd, J.; Li, H.; Tapponnier, P.; Coudroy, T.; Murray, A. S.

2017-12-01

The Western Kunlun mountain range (Xinjiang, north-west China) is a slowly deforming intra-continental orogen where deformation rates are too low to be quantified from geodetic techniques. This region has recorded little historical seismicity, but the recent July 2015 (Mw 6.4) Pishan earthquake shows that this mountain range remains seismic. To quantify the rate of active deformation and the potential for major earthquakes in this region, we combine a structural and quantitative morphological analysis of the Yecheng-Pishan fold along the topographic mountain front in the epicentral area. Using field observations and a seismic profile, we derive a structural cross-section in which we identify the fault that broke during the Pishan earthquake, an 8-12 km deep blind ramp beneath the Yecheng-Pishan fold. Combining satellite images and DEMs, we achieve a detailed morphological analysis of the Yecheng-Pishan fold, where we find nine levels of incised fluvial terraces and alluvial fans. From their incision pattern and using age constraints retrieved on some of these terraces, we quantify the slip rate on the underlying blind ramp to 0.5 to 2.5 mm/yr over the last 400 kyr, with a most probable long-term value of 2 to 2.5 mm/yr. The evolution of the Yecheng-Pishan fold is then proposed by combining all structural, morphological and chronological observations. Finally, we compare the seismotectonic context of the Western Kunlun to what has been proposed for the Himalayas of Central Nepal. This allows for discussing the possibility of major M ≥ 8-8.5 earthquakes in the case that the whole decollement is presently seismically locked and fully ruptures in one single seismic event.

Model identification and control of development of deeply buried paleokarst reservoir in the central Tarim Basin, northwest China

NASA Astrophysics Data System (ADS)

Yu, Jingbo; Li, Zhong; Yang, Liu; Han, Yinxue

2018-04-01

The paleokarst reservoirs of the Ordovician Yingshan formation, rich in oil and gas, are deeply buried in the central Tarim Basin, northwest China. Dozens of imaging well-logs in this region reveal five typical paleokarst features, including solution vugs, solution-enlarged fractures, filled caves, unfilled caves and collapsed caves, as well as two typical paleokarst structures located in different paleotopographic sites, including paleokarst vadose and phreatic zones. For seismic data, the large wave impedance contrast between the paleocave system and the surrounding rocks leads to a strong seismic reflection, which is highlighted as a bead-like ‘bright spot’ in a seismic section. By quantitatively estimating the seismic resolution limits of deep seismic reflections, a single paleocave cannot be identified from a seismic profile, and the bead-like reflection represents an entire paleocave complex. The spectral decomposition technique was employed to depict the planar shape and semi-quantitatively measure the size of the paleocave complexes. The results indicate that the sizes of the paleokarst caves are all small, and most of the karst caves are nearly completely filled by clay and calcite. The small cave size and the effective support of cave fills for the overlying strata mean that some individual paleocaves in a paleocave complex are preserved at a burial depth of more than 6000 m. Paleotopography and faults strongly impact the distribution of paleokarst reservoirs. Well-developed paleokarst reservoirs are generally located in paleotopographic highlands and on slopes, and for a specific paleotopographic site, the distribution of paleokarst reservoirs is obviously controlled by NW-SE trending faults. The most favorable area for paleokarst development is the Tazhong No. 10 fault zone, a faulted anticline bounded by two NW-SE trending back thrusts.

Revealing the deep structure and rupture plane of the 2010 Maule, Chile earthquake (Mw = 8.8) using wide angle seismic data

NASA Astrophysics Data System (ADS)

Moscoso, Eduardo; Grevemeyer, Ingo; Contreras-Reyes, Eduardo; Flueh, Ernst R.; Dzierma, Yvonne; Rabbel, Wolfgang; Thorwart, Martin

2011-07-01

The 27 February, 2010 Maule earthquake (Mw = 8.8) ruptured ~ 400 km of the Nazca-South America plate boundary and caused hundreds of fatalities and billions of dollars in material losses. Here we present constraints on the fore-arc structure and subduction zone of the rupture area derived from seismic refraction and wide-angle data. The results show a wedge shaped body ~ 40 km wide with typical sedimentary velocities interpreted as a frontal accretionary prism (FAP). Landward of the imaged FAP, the velocity model shows an abrupt velocity-contrast, suggesting a lithological change which is interpreted as the contact between the FAP and the paleo accretionary prism (backstop). The backstop location is coincident with the seaward limit of the aftershocks, defining the updip limit of the co-seismic rupture and seismogenic zone. Furthermore, the seaward limit of the aftershocks coincides with the location of the shelf break in the entire earthquake rupture area (33°S-38.5°S), which is interpreted as the location of the backstop along the margin. Published seismic profiles at the northern and southern limit of the rupture area also show the presence of a strong horizontal velocity gradient seismic backstop at a distance of ~ 30 km from the deformation front. The seismic wide-angle reflections from the top of the subducting oceanic crust constrain the location of the plate boundary offshore, dipping at ~ 10°. The projection of the epicenter of the Maule earthquake onto our derived interplate boundary yielded a hypocenter around 20 km depth, this implies that this earthquake nucleated somewhere in the middle of the seismogenic zone, neither at its updip nor at its downdip limit.

Newly discovered abundant fluid seep indicators off southern Costa Rica, imaged from overlapping multibeam swaths and 3D seismic data

NASA Astrophysics Data System (ADS)

Kluesner, J. W.; Silver, E. A.; Gibson, J. C.; Bangs, N. L.; McIntosh, K.; von Huene, R.; Orange, D.; Ranero, C. R.

2012-12-01

Offshore southern Costa Rica we have identified 161 potential fluid seepage sites on the shelf and slope regions within an 11 x 55 km strip where no fluid indicators had been reported previously using conventional deep-water mutlibeam bathymetry (100 m grid cell size) and deep towed side scan sonar. Evidence includes large and small pockmarks, mounds, ridges, and slope failure features with localized anomalous high-amplitude backscatter strength. The majority of seepage indicators are associated with shallow sub-bottom reversed polarity bright spots and flat spots imaged within the CRISP 3D seismic grid. Data were collected ~50 km west of Osa Peninsula, Costa Rica onboard the R/V Marcus G. Langseth during the spring of 2011. We obtained EM122 multibeam data using fixed, closely spaced receiver beams and 9-10 times swath overlap, which greatly improved the signal-to-noise ratio and sounding density and allowed for very small grid and mosaic cell sizes (2-10 m). A gas plume in the water column, seen on a 3.5 kHz profile, is located along a fault trace and above surface and subsurface seep indicators. Fluid indicators on the outer shelf occur largely on a dense array of faults, some of which cut through the reflective basement. Seismic flat spots commonly underlie axes of large anticlines on the shelf and slope. Pockmarks are also located at the foot of mid-slope canyons, very near to the upper end of the BSR. These pockmarks appear to be associated with canyon abandonment and folded beds that channel fluids upward, causing hydrate instability. Our findings suggest that significant amounts of methane are venting into ocean and potentially into the atmosphere across the heavily deformed shelf and slope of Costa Rica.

Deep crustal electromagnetic structure of central India tectonic zone and its implications

NASA Astrophysics Data System (ADS)

Naganjaneyulu, K.; Naidu, G. Dhanunjaya; Rao, M. Someswara; Shankar, K. Ravi; Kishore, S. R. K.; Murthy, D. N.; Veeraswamy, K.; Harinarayana, T.

2010-07-01

Magnetotelluric data at 45 locations along the Mahan-Khajuria Kalan profile in the central India tectonic zone are analysed. This 290 km long profile yields data in the period range 0.001-1000 s across the tectonic elements of the study region bounded by Purna fault, Gavligarh fault, Tapti fault, Narmada South fault and Narmada North fault. Multi-site, multi-frequency analysis suggests N70°E as the geo-electric strike direction. Data rotated into the N70°E strike direction are modelled using a non-linear conjugate gradient scheme with error floors of 10% for both apparent resistivity and phase components. Two-dimensional magnetotelluric model yields conductors that correlate with known faults in the study region and regional seismicity. Presence of a -30 mgal gravity high together with the observed conductive bodies (less than 20 ohm m) in the deep crust beneath the Purna graben and Tapti valley is explained by the process of magmatic underplating. The conductive bodies beneath the Mahakoshal rift belt and Vindhyans accompanied by regional gravity lows of the order -70 mgal are attributed to the presence of deep crustal fluids. Following the re-activation model proposed for the entire region, the conductors (20 ohm m) at various depth levels correspond to mafic magmatic and/or fluid intrusions controlled by deep-seated faults that seem to tap reservoirs beyond the crust-mantle boundary. The shallow depth localized faults also seem to have facilitated further upward movement of these underplated material and fluids release during this process.

Geophysical evidence for a transform margin in Northwestern Algeria: possible vestige of a Subduction-Transform Edge Propagator

NASA Astrophysics Data System (ADS)

Badji, R.; Charvis, P.; Bracene, R.; Galve, A.; Badsi, M.; Ribodetti, A.; Benaissa, Z.; Klingelhoefer, F.; Medaouri, M.; Beslier, M.

2013-12-01

This work is part of the Algerian-French SPIRAL program (Sismique Profonde et Investigation Régionale du Nord de l'Algérie) which provides unprecedented images of the deep structure of the western Algerian Margin based on several wide-angle and multichannel seismic data shot across the Algerian Margin. One of the different hypotheses for the opening of the western Mediterranean Sea, we are testing is that the western part of the Algerian margin was possibly part of the southern edge of the Alboran continental block during its westward migration related to the rollback of the Betic-Rif-Alboran subduction zone. A tomographic inversion of the first arrival traveltimes along a 100-km long wide-angle seismic profile shot over 40 Ocean Bottom Seismometers, across the Margin offshore Mostaganem (Northwestern Algerian Margin) was conducted. The final model reveals striking feature in the deep structure of the margin from north to south: 1- the oceanic crust is as thin as 4-km, with velocities ranging from 5.0 to 7.1 km/s, covered by a 3.3 km thick sedimentary pile (seismic velocities from 1.5 to 5.0 km/s) characterized by an intense diapiric activity of the Messinian salt layer. 2- a sharp transition zone, less than 10 km wide, with seismic velocities intermediate between oceanic seismic velocities (observed northward) and continental seismic velocities (observed southward). This zone coincides with narrow and elongated pull apart basins imaged by multichannel seismic data. No evidence of volcanism nor of exhumed serpentinized upper mantle as described along many extensional continental margins are observed along this segment of the margin. 3- a thinned continental crust coincident with a rapid variation of the Moho depth imaged from 12 to ~20 km with a dip up to 50%. The seafloor bathymetry is showing a steep continental slope (>20%). Either normal or inverse faults are observed along MCS lines shot in the dip direction but they do not present large vertical displacement and could be related primarily to strike slip motion. These results support the hypothesis, that the margin offshore Mostaganem is not an extensional margin but rather a transform margin. There is little evidence of tectonic inversion as described eastward along the Kabylian Margin. Possibly strike slip motion affected the thinned continental crust and the transition zone suggesting that this margin is a vestige of the Subduction-Transform Edge Propagator (STEP) related to the westward migration of the Alboran block.

Advanced Gas Hydrate Reservoir Modeling Using Rock Physics

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

McConnell, Daniel

Prospecting for high saturation gas hydrate deposits can be greatly aided with improved approaches to seismic interpretation and especially if sets of seismic attributes can be shown as diagnostic or direct hydrocarbon indicators for high saturation gas hydrates in sands that would be of most interest for gas hydrate production. A large 3D seismic data set in the deep water Eastern Gulf of Mexico was screened for gas hydrates using a set of techniques and seismic signatures that were developed and proven in the Central deepwater Gulf of Mexico in the DOE Gulf of Mexico Joint Industry Project JIP Legmore » II in 2009 and recently confirmed with coring in 2017. A large gas hydrate deposit is interpreted in the data where gas has migrated from one of the few deep seated faults plumbing the Jurassic hydrocarbon source into the gas hydrate stability zone. The gas hydrate deposit lies within a flat-lying within Pliocene Mississippi Fan channel that was deposited outboard in a deep abyssal environment. The uniform architecture of the channel aided the evaluation of a set of seismic attributes that relate to attenuation and thin-bed energy that could be diagnostic of gas hydrates. Frequency attributes derived from spectral decomposition also proved to be direct hydrocarbon indicators by pseudo-thickness that could be only be reconciled by substituting gas hydrate in the pore space. The study emphasizes that gas hydrate exploration and reservoir characterization benefits from a seismic thin bed approach.« less

Seismic signature of crustal magma and fluid from deep seismic sounding data across Tengchong volcanic area

NASA Astrophysics Data System (ADS)

Bai, Z. M.; Zhang, Z. Z.; Wang, C. Y.; Klemperer, S. L.

2012-04-01

The weakened lithosphere around eastern syntax of Tibet plateau has been revealed by the Average Pn and Sn velocities, the 3D upper mantle velocity variations of P wave and S wave, and the iimaging results of magnetotelluric data. Tengchong volcanic area is neighboring to core of eastern syntax and famous for its springs, volcanic-geothermal activities and remarkable seismicity in mainland China. To probe the deep environment for the Tengchong volcanic-geothermal activity a deep seismic sounding (DSS) project was carried out across the this area in 1999. In this paper the seismic signature of crustal magma and fluid is explored from the DSS data with the seismic attribute fusion (SAF) technique, hence four possible positions for magma generation together with some locations for porous and fractured fluid beneath the Tengchong volcanic area were disclosed from the final fusion image of multi seismic attributes. The adopted attributes include the Vp, Vs and Vp/Vs results derived from a new inversion method based on the No-Ray-Tomography technique, and the migrated instantaneous attributes of central frequency, bandwidth and high frequency energy of pressure wave. Moreover, the back-projected ones which are mainly consisted by the attenuation factor Qp , the delay-time of shear wave splitting, and the amplitude ratio between S wave and P wave + S wave were also considered in this fusion process. Our fusion image indicates such a mechanism for the surface springs: a large amount of heat and the fluid released by the crystallization of magma were transmitted upward into the fluid-filled rock, and the fluid upwells along some pipeline since the high pressure in deep, thus the widespread springs of Tengchong volcanic area were developed. Moreover, the fusion image, regional volcanic and geothermal activities, and the seismicity suggest that the main risk of volcanic eruption was concentrated to the south of Tengchong city, especially around the shot point (SP) Tuantian. There are typical tectonic and deep origin mechanisms for the moderate-strong earthquakes nearby SP Tuantian, and precaution should be added on this area in case of the potential earthquake. Our fusion image also clearly revealed that there exist two remarkable positions on the Moho discontinuity through which the heat from the upper mantle was transmitted upward, and this is attributed to the widely distributed hot material within the crust and upper mantle. We acknowledge the financial support of the Ministry of Land and Resources of China (SinoProbe-02-02), and the National Nature Science Foundation of China (No. 41074033 and No. 40830315). Key Words: Seismic Signature, Magma, Tengchong Volcanic Area, Deep Seismic Sounding, Seismic Attribute Fusion Li, Chang, van der Hilst, D., Meltzer, A.S., Engdahl, E.R., 2008. Subduction of the Indian lithosphere beneath the Tibetan Plateau and Burma. Earth Planet. Sci. Lett. 274. doi:10.1016/j.epsl.2008.07.016. Lebedev, S., van der Hilst, R.D., 2008. Global upper-mantle tomography with the automated multi-mode surface and S waveforms. Geophys. J. Int. 173 (2), 505-518. Wang C.Y. and Huangfu G.. 2004. Crustal structure in Tengchong Volcano-Geothermal Area, western Yunnan, China. Tectonophysics, 380: 69-87.

Depth-Dependent Earthquake Properties Beneath Long-Beach, CA: Implications for the Rheology at the Brittle-Ductile Transition Zone

NASA Astrophysics Data System (ADS)

Inbal, A.; Clayton, R. W.; Ampuero, J. P.

2015-12-01

Except for a few localities, seismicity along faults in southern California is generally confined to depths shallower than 15 km. Among faults hosting deep seismicity, the Newport-Inglewood Fault (NIF), which traverses the Los-Angeles basin, has an exceptionally mild surface expression and low deformation rates. Moreover, the NIF structure is not as well resolved as other, less well instrumented faults because of poor signal-to-noise ratio. Here we use data from three temporary dense seismic arrays, which were deployed for exploration purposes and contain up to several thousands of vertical geophones, to investigate the properties of deep seismicity beneath Long-Beach (LB), Compton and Santa-Fe Springs (SFS). The latter is located 15 km northeast of the NIF, presumably above a major detachment fault underthrusting the basin.Event detection is carried out using a new approach for microseismic multi-channel picking, in which downward-continued data are back-projected onto the volume beneath the arrays, and locations are derived from statistical analysis of back-projection images. Our technique reveals numerous, previously undetected events along the NIF, and confirms the presence of an active shallow structure gently dipping to the north beneath SFS. Seismicity characteristics vary along the NIF strike and dip. While LB seismicity is uncorrelated with the mapped trace of the NIF, Compton seismicity illuminates a sub-vertical fault that extends down to about 20 km. This result, along with the reported high flux of mantle Helium along the NIF (Boles et al., 2015), suggests that the NIF is deeply rooted and acts as a major conduit for mantle fluids. We find that the LB size distribution obeys the typical power-law at shallow depths, but falls off exponentially for events occurring below 20 km. Because deep seismicity occurs uniformly beneath LB, this transition is attributed to a reduction in seismic asperity density with increasing depth, consistent with a transition to a diffuse deformation regime.

Application of normal mode theory to seismic source and structure problems: Seismic investigations of upper mantle lateral heterogeneity. Ph.D. Thesis

NASA Technical Reports Server (NTRS)

Okal, E. A.

1978-01-01

The theory of the normal modes of the earth is investigated and used to build synthetic seismograms in order to solve source and structural problems. A study is made of the physical properties of spheroidal modes leading to a rational classification. Two problems addressed are the observability of deep isotropic seismic sources and the investigation of the physical properties of the earth in the neighborhood of the Core-Mantle boundary, using SH waves diffracted at the core's surface. Data sets of seismic body and surface waves are used in a search for possible deep lateral heterogeneities in the mantle. In both cases, it is found that seismic data do not require structural differences between oceans and continents to extend deeper than 250 km. In general, differences between oceans and continents are found to be on the same order of magnitude as the intrinsic lateral heterogeneity in the oceanic plate brought about by the aging of the oceanic lithosphere.

Analysis of the geological structure and tectonic evolution of Xingning-Jinghai sag in deep water area, northern South China Sea

NASA Astrophysics Data System (ADS)

Han, Xiaoying; Ren, Jianye; Lin, Zi; Yang, Linlong

2015-04-01

Recent years, oil and gas exploration of the Pearl River Mouth Basin in the northern margin of South China Sea continuously achieved historic breakthroughs. The Xingning-Jinghai sag, which is located in southeast of the Pearl River Mouth Basin, is a deep-water sag with a great exploration potential. Its tectonic evolution is extremely complex. It experienced Mesozoic subduction to Cenozoic intra-continental rifting background, and finally evolved into a deep-water sag of the northern continental margin of South China Sea. The geological characteristics and the tectonic evolution of Xingning-Jinghai sag was closely related to the process of formation and evolution of the passive continental margin of the northern South China Sea. It is confirmed by many geophysical data that compared with adjacent Chaoshan depression, the crustal thickness of Xingning-Jinghai sag was rapidly thinning, and it developed detachment faults with later magmatic intrusion. The development of detachment faults have dynamic significance for the spreading of the South China Sea. Based on the seismic geological interpretation of 2D seismic data in the study area, the characteristics of detachment fault and supra-detachment basin have been proposed in this study. The characteristics of the detachment fault are low angle and high ratio between heave and throw. The geometry of the detachment fault is a typical lisric shape, with the dip of fault decreasing generally from the seismic profile. The detachment basin where sediments are not deposited over a tilting hanging-wall block but onto a tectonically exhumed footwall which is different from the typical half graben basin. Seismic profiles indicate two different structural styles in the east and west part of Xingning-Jinghai sag. In the west of the sag, there developed two large detachment faults, which control their detachment basin systems and the typical H block, and the two detachment faults are dipping landward and seaward, respectively. In the east, affected by the later volcanic activities, Xingning-Jinghai sag deformed complicatedly and developed a series of landward dipping faults, showing the compound graben structure. Combined with the fault activity quantitative calculation, basin subsidence history and other advanced technology, the basin tectonic evolution has been divided into rift stage and post-rift stage. Considering the extension development evolution of Xingning-Jinghai sag and the extension and thinning of lithosphere under the background of spreading of the South China Sea, we argue that the northern margin of the South China lithosphere experienced an intense stretching and thinning stage. At this period, the subsidence of the Xingning-Jinghai sag was controlled by the detachment faults, indicating a rifting stage. With the development of the detachment faults, the thickness of crust was extremely thinned. After the spreading of the South China Sea the whole sag entered into the depression period which was characterized by thermal subsidence.

The 3-D aftershock distribution of three recent M5~5.5 earthquakes in the Anza region,California

NASA Astrophysics Data System (ADS)

Zhang, Q.; Wdowinski, S.; Lin, G.

2011-12-01

The San Jacinto fault zone (SJFZ) exhibits the highest level of seismicity compared to other regions in southern California. On average, it produces four earthquakes per day, most of them at depth of 10-17 km. Over the past decade, an increasing seismic activity occurred in the Anza region, which included three M5~5.5 events and their aftershock sequences. These events occurred in 2001, 2005, and 2010. In this research we map the 3-D distribution of these three events to evaluate their rupture geometry and better understand the unusual deep seismic pattern along the SJFZ, which was termed "deep creep" (Wdowinski, 2009). We relocated 97,562 events from 1981 to 2011 in Anza region by applying the Source-Specific Station Term (SSST) method (Lin et al., 2006) and used an accurate 1-D velocity model derived from 3-D model of Lin et al (2007) and used In order to separate the aftershock sequence from background seismicity, we characterized each of the three aftershock sequences using Omori's law. Preliminary results show that all three sequences had a similar geometry of deep elongated aftershock distribution. Most aftershocks occurred at depth of 10-17 km and extended over a 70 km long segments of the SJFZ, centered at the mainshock hypocenters. A comparative study of other M5~5.5 mainshocks and their aftershock sequences in southern California reveals very different geometrical pattern, suggesting that the three Anza M5~5.5 events are unique and can be indicative of "deep creep" deformation processes. Reference 1.Lin, G.and Shearer,P.M.,2006, The COMPLOC earthquake location package,Seism. Res. Lett.77, pp.440-444. 2.Lin, G. and Shearer, P.M., Hauksson, E., and Thurber C.H.,2007, A three-dimensional crustal seismic velocity model for southern California from a composite event method,J. Geophys.Res.112, B12306, doi: 10.1029/ 2007JB004977. 3.Wdowinski, S. ,2009, Deep creep as a cause for the excess seismicity along the San Jacinto fault, Nat. Geosci.,doi:10.1038/NGEO684.

Deep-focus earthquakes and recycling of water into the earth's mantle

NASA Technical Reports Server (NTRS)

Meade, Charles; Jeanloz, Raymond

1991-01-01

For more than 50 years, observations of earthquakes to depths of 100 to 650 kilometers inside earth have been enigmatic: at these depths, rocks are expected to deform by ductile flow rather than brittle fracturing or frictional sliding on fault surfaces. Laboratory experiments and detailed calculations of the pressures and temperatures in seismically active subduction zones indicate that this deep-focus seismicity could originate from dehydration and high-pressure structural instabilities occurring in the hydrated part of the lithosphere that sinks into the upper mantle. Thus, seismologists may be mapping the recirculation of water from the oceans back into the deep interior of the planet.

Deep Stimulation at Newberry Volcano EGS Demonstration

NASA Astrophysics Data System (ADS)

Grasso, K.; Cladouhos, T. T.; Petty, S.; Garrison, G. H.; Nordin, Y.; Uddenberg, M.; Swyer, M.

2014-12-01

The Newberry Volcano EGS Demonstration is a 5 year field project designed to demonstrate recent technological advances for engineered geothermal systems (EGS) development. Advances in reservoir stimulation, diverter, and monitoring are being tested in a hot (>300 C), dry well (NWG 55-29) drilled in 2008. These technologies could reduce the cost of electrical power generation. The project began in 2010 with two years of permitting, technical planning, and development of a project-specific Induced Seismicity Mitigation Plan (ISMP), and is funded in part by the Department of Energy. In 2012, the well was hydraulically stimulated with water at pressures below the principle stress for 7 weeks, resulting in hydroshearing. The depth of stimulation was successfully shifted by injection of two pills of Thermally-degradable Zonal Isolation Materials (TZIMs). Injectivity changes, thermal profiles and seismicity indicate that fracture permeability in well NWG 55-29 was enhanced during stimulation. This work successfully demonstrated the viability of large-volume (40,000 m3), low-pressure stimulation coupled with non-mechanical diverter technology, and microseismic monitoring for reservoir mapping. Further analysis and field testing in 2013 indicates further stimulation will be required in order to develop an economically viable reservoir, and is scheduled in 2014. The 2014 stimulation will use improved stimulation and monitoring equipment, better knowledge based on 2012 outcomes, and create a deep EGS reservoir in the hottest part of the wellbore.

The Crustal Structure of the North-South Earthquake Belt in China Revealed from Deep Seismic Soundings and Gravity Data

NASA Astrophysics Data System (ADS)

Zhao, Yang; Guo, Lianghui; Shi, Lei; Li, Yonghua

2018-01-01

The North-South earthquake belt (NSEB) is one of the major earthquake regions in China. The studies of crustal structure play a great role in understanding tectonic evolution and in evaluating earthquake hazards in this region. However, some fundamental crustal parameters, especially crustal interface structure, are not clear in this region. In this paper, we reconstructed the crustal interface structure around the NSEB based on both the deep seismic sounding (DSS) data and the gravity data. We firstly reconstructed the crustal structure of crystalline basement (interface G), interface between upper and lower crusts (interface C) and Moho in the study area by compiling the results of 38 DSS profiles published previously. Then, we forwardly calculated the gravity anomalies caused by the interfaces G and C, and then subtracted them from the complete Bouguer gravity anomalies, yielding the regional gravity anomalies mainly due to the Moho interface. We then utilized a lateral-variable density interface inversion technique with constraints of the DSS data to invert the regional anomalies for the Moho depth model in the study area. The reliability of our Moho depth model was evaluated by comparing with other Moho depth models derived from other gravity inversion technique and receiver function analysis. Based on our Moho depth model, we mapped the crustal apparent density distribution in the study area for better understanding the geodynamics around the NSEB.

Geographical coincidence of high heat flow, high seismicity, and upwelling, with hydrocarbon deposits, phosphorites, evaporites, and uranium ores.

PubMed

Libby, L M; Libby, W F

1974-10-01

Oil deposits occur in deep sediments, and appear to be organic matter that has been transformed through the action of geothermal heat and pressure. Deep sediments, rich in biological remains, are created by ocean upwelling, caused in part by high geothermal heat flow through the sea bottom. Such regions correlate with enhanced seismic activity. We look for correlations of seismicity, high heat flux, petroleum, uranium, phosphates, and salts, deposited from abundant plant life. These may be useful in discovering more petroleum and coal. We estimate that the known world reserves of petroleum and coal are about 10(-4) of the total of buried biogenic carbon.

Geographical Coincidence of High Heat Flow, High Seismicity, and Upwelling, with Hydrocarbon Deposits, Phosphorites, Evaporites, and Uranium Ores

PubMed Central

Libby, L. M.; Libby, W. F.

1974-01-01

Oil deposits occur in deep sediments, and appear to be organic matter that has been transformed through the action of geothermal heat and pressure. Deep sediments, rich in biological remains, are created by ocean upwelling, caused in part by high geothermal heat flow through the sea bottom. Such regions correlate with enhanced seismic activity. We look for correlations of seismicity, high heat flux, petroleum, uranium, phosphates, and salts, deposited from abundant plant life. These may be useful in discovering more petroleum and coal. We estimate that the known world reserves of petroleum and coal are about 10-4 of the total of buried biogenic carbon. Images PMID:16592185

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

USGS Publications Warehouse

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

1982-01-01

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

Plate boundary and major fault system in the overriding plate within the Shumagin gap at the Alaska-Aleutian subduction zone

NASA Astrophysics Data System (ADS)

Becel, A.; Shillington, D. J.; Nedimovic, M. R.; Keranen, K. M.; Li, J.; Webb, S. C.; Kuehn, H.

2013-12-01

Structure in the overriding plate is one of the parameters that may increase the tsunamigenic potential of a subduction zone but also influence the seismogenic behavior and segmentation of great earthquake rupture. The Alaska-Aleutian margin is characterized by along-strike changes in plate interface coupling over relatively small distances. Here, we present trench normal multichannel seismic (MCS) profiles acquired across the Shumagin gap that has not broken in many decades and appears to be weakly coupled. The high fold, deep penetration (636 channel, 8-km long streamer, 6600 cu.in airgun source) MCS data were acquired as part of the ALEUT project. This dataset gives us critical new constraints on the interplate boundary that can be traced over ~100 km distance beneath the forearc with high variation in its reflection response with depth. These profiles also reveal the detailed upper plate fault structure and forearc morphology. Clear reflections in the overriding plate appear to delineate one or more large faults that cross the shelf and the upper slope. These faults are observed 75 km back from the trench and seem to branch at depth and connect to the plate interface within this gap at ~11 s twtt. We compare the reflective structure of these faults to that of the plate boundary and examine where it intersects the megathrust with respect of the expected downdip limit of coupling. We also compare this major structure with the seismicity recorded in this sector. The imaged fault system is associated with a large deep basin (~6s twt) that is an inherited structure formed during the pre-Aleutian period. Basins faults appear to have accommodated primarily normal motion, although folding of sediments near the fault and complicated fault geometries in the shallow section may indicate that this fault has accommodated other types of motion during its history that may reflect the stress-state at the megathrust over time. The deformation within the youngest sediment also suggests also that this fault system might be still active. The coincident wide-angle seismic data coincident with one MCS profile allow the addition of more information about the deep P-wave velocity structure whereas the streamer tomography (Michaelson-Rotermund et al., this session) around the fault system add more detailed view into the complex structure in the shallow portions (upper 2km) of these structures showing a low velocity zone along one large fault suggesting that this fault is still active. These large-scale structures imaged in the overriding plate within the Shumagin gap are probably sufficiently profound to play a major role in the behavior of the megathrust in this area, segmentation of great earthquake rupture area, tsunami generation and may influence the frictional properties of the seismogenic zone at depth.

Seismic characteristics of central Brazil crust and upper mantle: A deep seismic refraction study

USGS Publications Warehouse

Soares, J.E.; Berrocal, J.; Fuck, R.A.; Mooney, W.D.; Ventura, D.B.R.

2006-01-01

A two-dimensional model of the Brazilian central crust and upper mantle was obtained from the traveltime interpretation of deep seismic refraction data from the Porangatu and Cavalcante lines, each approximately 300 km long. When the lines were deployed, they overlapped by 50 km, forming an E-W transect approximately 530 km long across the Tocantins Province and western Sa??o Francisco Craton. The Tocantins Province formed during the Neoproterozoic when the Sa??o Francisco, the Paranapanema, and the Amazon cratons collided, following the subduction of the former Goia??s ocean basin. Average crustal VP and VP/VS ratios, Moho topography, and lateral discontinuities within crustal layers suggest that the crust beneath central Brazil can be associated with major geological domains recognized at the surface. The Moho is an irregular interface, between 36 and 44 km deep, that shows evidences of first-order tectonic structures. The 8.05 and 8.23 km s-1 P wave velocities identify the upper mantle beneath the Porangatu and Cavalcante lines, respectively. The observed seismic features allow for the identification of (1) the crust has largely felsic composition in the studied region, (2) the absence of the mafic-ultramafic root beneath the Goia??s magmatic arc, and (3) block tectonics in the foreland fold-and-thrust belt of the northern Brasi??lia Belt during the Neoproterozoic. Seismic data also suggested that the Bouguer gravimetric discontinuities are mainly compensated by differences in mass distribution within the lithospheric mantle. Finally, the Goia??s-Tocantins seismic belt can be interpreted as a natural seismic alignment related to the Neoproterozoic mantle domain. Copyright 2006 by the American Geophysical Union.

Correlation of offshore seismic profiles with onshore New Jersey Miocene sediments

USGS Publications Warehouse

Monteverde, D.H.; Miller, K.G.; Mountain, Gregory S.

2000-01-01

The New Jersey passive continental margin records the interaction of sequences and sea-level, although previous studies linking seismically defined sequences, borehole control, and global ??18O records were hindered by a seismic data gap on the inner-shelf. We describe new seismic data from the innermost New Jersey shelf that tie offshore seismic stratigraphy directly to onshore boreholes. These data link the onshore boreholes to existing seismic grids across the outer margin and to boreholes on the continental slope. Surfaces defined by age; facies, and log signature in the onshore boreholes at the base of sequences Kw2b, Kw2a, Kw1c, and Kw0 are now tied to seismic sequence boundaries m5s, m5.2s, m5.4s, and m6s, respectively, defined beneath the inner shelf. Sequence boundaries recognized in onshore boreholes and inner shelf seismic profiles apparently correlate with reflections m5, m5.2, m5.4, and m6, respectively, that were dated at slope boreholes during ODP Leg 150. We now recognize an additional sequence boundary beneath the shelf that we name m5.5s and correlate to the base of the onshore sequence Kw1b. The new seismic data image prograding Oligocene clinoforms beneath the inner shelf, consistent with the results from onshore boreholes. A land-based seismic profile crossing the Island Beach borehole reveals reflector geometries that we tie to Lower Miocene litho- and bio-facies in this borehole. These land-based seismic profiles image well-defined sequence boundaries, onlap and downlap truncations that correlate to Transgressive Systems Tracts (TST) and Highstand Systems Tracts (HST) identified in boreholes. Preliminary analysis of CH0698 data continues these system tract delineations across the inner shelf The CH0698 seismic profiles tie seismically defined sequence boundaries with sequences identified by lithiologic and paleontologic criteria. Both can now be related to global ??18O increases and attendant glacioeustatic lowerings. This integration of core, log, and seismic character of mid-Tertiary sediments across the width of the New Jersey margin is a major step in the long-standing effort to evaluate the impact of glaciouestasy on siliciclastic sediments of a passive continental margin. (C) 2000 Elsevier Science B.V. All rights reserved.

Window into the Caledonian orogen: Structure of the crust beneath the East Shetland platform, United Kingdom

USGS Publications Warehouse

McBride, J.H.; England, R.W.

1999-01-01

Reprocessing and interpretation of commercial and deep seismic reflection data across the East Shetland platform and its North Sea margin provide a new view of crustal subbasement structure beneath a poorly known region of the British Caledonian orogen. The East Shetland platform, east of the Great Glen strike-slip fault system, is one of the few areas of the offshore British Caledonides that remained relatively insulated from the Mesozoic and later rifting that involved much of the area around the British Isles, thus providing an "acoustic window" into the deep structure of the orogen. Interpretation of the reflection data suggests that the crust beneath the platform retains a significant amount of its original Caledonian and older architecture. The upper to middle crust is typically poorly reflective except for individual prominent dipping reflectors with complex orientations that decrease in dip with depth and merge with a lower crustal layer of high reflectivity. The three-dimensional structural orientation of the reflectors beneath the East Shetland platform is at variance with Caledonian reflector trends observed elsewhere in the Caledonian orogen (e.g., north of the Scottish mainland), emphasizing the unique tectonic character of this part of the orogen. Upper to middle crustal reflectors are interpreted as Caledonian or older thrust surfaces that were possibly reactivated by Devonian extension associated with post-Caledonian orogenic collapse. The appearance of two levels of uneven and diffractive (i.e., corrugated) reflectivity in the lower crust, best developed on east-west-oriented profiles, is characteristic of the East Shetland platform. However, a north-south-oriented profile reveals an interpreted south-vergent folded and imbricated thrust structure in the lower crust that appears to be tied to the two levels of corrugated reflectivity on the east-west profiles. A thrust-belt origin for lower crustal reflectivity would explain its corrugated appearance. Regional seismic velocity models derived from refraction data suggest that this reflectivity correlates with a continuous lower crustal layer that has an intermediate seismic velocity. The lower crustal reflectivity is determined to be older than Mesozoic age by the bending down and truncation of the two reflectivity levels at the western margin of the North Sea Viking graben by a major mantle reflector inferred to be associated with Mesozoic rifting. The results of this study are thus in contrast with orthodox interpretations of the reflective layered lower crust as being caused by mantle-derived igneous intrusion or by deformation fabrics associated with stretching in response to continental rifting.

Acoustic Velocity Of The Sediments Offshore Southwestern Taiwan

NASA Astrophysics Data System (ADS)

Tsai, C.; Liu, C.; Huang, P.

2004-12-01

Along the Manila Trench south of 21øXN, deep-sea sediments are being underthrusted beneath the Taiwan accretionary prism which is composed of the Kaoping Slope and Hengchun Ridge. Offshore southwestern Taiwan, foreland sediments and Late Miocene strata of the Tainan Basin are being accreted onto the fold-and thrust belt of the syn-collision accretionary wedge of the Kaoping Slope. The Kaoping Slope consists of thick Neogene to Recent siliciclastics deformed by fold-and-thrust structures and mud diapers. These Pliocene-Quaternary sediments deposited in the Kaoping Shelf and upper slope area are considered to be paleo-channel deposits confined by NNE-SSW trend mud diapiric structure. Seismic P-wave velocities of the sediment deposited in the Kaoping Shelf and Kaoping Slope area are derived from mutichannel seismic reflection data and wide-angle reflection and refraction profiles collected by sonobuoys. Sediment velocity structures constrained from mutichannel seismic reflection data using velocity spectrum analysis method and that derived from sonobuoy data using tau-sum inversion method are compared, and they both provide consistent velocity structures. Seismic velocities were analyzed along the seismic profile from the surface to maximum depths of about 2.0 km below the seafloor. Our model features a sediment layer1 with 400 ms in thickness and a sediment layer2 with 600 ms in thickness. For the shelf sediments, we observe a linear interval velocity trend of V=1.53+1.91T in layer1, and V=1.86+0.87T in layer2, where T is the one way travel time within the layer. For the slop sediment, the trend of V=1.47+1.93T in layer1, and V=1.70+1.55T in layer2. The layer1¡¦s velocities gradients are similar between the shelf (1.91 km/sec2) and the slope(1.93 km/sec2). It means layer1 distributes over the slope and shelf widely. The result of the sediment velocity gradients in this area are in good agreement with that reported for the south Atlantic continental margins.

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

NASA Astrophysics Data System (ADS)

Alp, H.

2015-12-01

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

Preparing for InSight - using the continuous seismic data flow to investigate the deep interior of Mars

NASA Astrophysics Data System (ADS)

Hempel, S.; Garcia, R.; Weber, R. C.; Schmerr, N. C.; Panning, M. P.; Lognonne, P. H.; Banerdt, W. B.

2016-12-01

Complementary to investigating ray theoretically predictable parameters to explore the deep interior of Mars (see AGU contribution by R. Weber et al.), this paper presents the waveform approach to illuminate the lowermost mantle and core-mantle boundary of Mars. In preparation to the NASA discovery mission InSight, scheduled for launch in May, 2018, we produce synthetic waveforms considering realistic combinations of sources and a single receiver, as well as noise models. Due to a lack of constraints on the scattering properties of the Martian crust and mantle, we assume Earth-like scattering as a minimum and Moon-like scattering as a maximum possibility. Various seismic attenuation models are also investigated. InSight is set up to deliver event data as well as a continuous data flow. Where ray theoretical approaches will investigate the event data, the continuous data flow may contain signals reflected multiple times off the same reflector, e.g. the underside of the lithosphere, or the core-mantle boundary. It may also contain signals of individual events not detected or interfering wavefields radiated off multiple undetected events creating 'seismic noise'. We will use AxiSEM to simulate a continuous data flow for these cases for various 1D and 2D Mars models, and explore the possibilities of seismic interferometry to use seismic information hidden in the coda to investigate the deep interior of Mars.

Crustal Structure and Deformation of the Yakutat Microplate: New Insights From STEEP Marine Seismic Reflection Data

NASA Astrophysics Data System (ADS)

Lowe, L. A.; Gulick, S. P.; Christeson, G.; van Avendonk, H.; Reece, R.; Elmore, R.; Pavlis, T.

2008-12-01

In fall 2008, we will conduct an active source marine seismic experiment of the offshore Yakutat microplate in the northern Gulf of Alaska. The survey will be conducted aboard the academic research vessel, R/V Marcus Langseth, collecting deep-penetrating multi-channel seismic reflection survey using an 8-km, 640 channel hydrophone streamer and a 6600 cu. in., 36 airgun array. The survey is the concluding data acquisition phase for the ST. Elias Erosion and tectonics Project (STEEP), a multi-institution NSF-Continental Dynamics project investigating the interplay of climate and tectonics in the Chugach-St. Elias Mountains in southern Alaska. The experiment will also provide important site survey information for possible future Integrated Ocean Drilling Program investigations. Two profiles coincident with wide-angle refraction data (see Christeson, et al., this session) will image structural changes across the Dangerous River Zone from east to west and the Transition Fault from south to north. We will also image the western portion of the Transition Fault to determine the nature of faulting along this boundary including whether or not the Pacific Plate is underthrusting beneath the Yakutat microplate as part of this collision. Our westernmost profile will image the Kayak Island Zone, typically described as the northern extension of the Aleutian megathrust but which may be a forming suture acting as a deformation backstop for the converging Yakutat and North American plates. Profiles across the Pamplona Zone, the current Yakutat-North America deformation front, will further constrain relative timing of structural development and the depth of deformation on the broad folds and thrust faults that comprise the area. This new dataset will allow further insight into regional tectonics of the St. Elias region as well as provide more detail regarding the development of the south Alaskan margin during major Plio-Pleistocene glacial- interglacial periods.

Analysis shear wave velocity structure obtained from surface wave methods in Bornova, Izmir

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

Pamuk, Eren, E-mail: eren.pamuk@deu.edu.tr; Akgün, Mustafa, E-mail: mustafa.akgun@deu.edu.tr; Özdağ, Özkan Cevdet, E-mail: cevdet.ozdag@deu.edu.tr

2016-04-18

Properties of the soil from the bedrock is necessary to describe accurately and reliably for the reduction of earthquake damage. Because seismic waves change their amplitude and frequency content owing to acoustic impedance difference between soil and bedrock. Firstly, shear wave velocity and depth information of layers on bedrock is needed to detect this changing. Shear wave velocity can be obtained using inversion of Rayleigh wave dispersion curves obtained from surface wave methods (MASW- the Multichannel Analysis of Surface Waves, ReMi-Refraction Microtremor, SPAC-Spatial Autocorrelation). While research depth is limeted in active source study, a passive source methods are utilized formore » deep depth which is not reached using active source methods. ReMi method is used to determine layer thickness and velocity up to 100 m using seismic refraction measurement systems.The research carried out up to desired depth depending on radius using SPAC which is utilized easily in conditions that district using of seismic studies in the city. Vs profiles which are required to calculate deformations in under static and dynamic loads can be obtained with high resolution using combining rayleigh wave dispersion curve obtained from active and passive source methods. In the this study, Surface waves data were collected using the measurements of MASW, ReMi and SPAC at the İzmir Bornova region. Dispersion curves obtained from surface wave methods were combined in wide frequency band and Vs-depth profiles were obtained using inversion. Reliability of the resulting soil profiles were provided by comparison with theoretical transfer function obtained from soil paremeters and observed soil transfer function from Nakamura technique and by examination of fitting between these functions. Vs values are changed between 200-830 m/s and engineering bedrock (Vs>760 m/s) depth is approximately 150 m.« less

The Late Pleistocene Contourites on Ceara Rise: Stratigraphy, Sedimentology and Paleoceanography

NASA Astrophysics Data System (ADS)

Ivanova, E. V.; Murdmaa, I.; Borisov, D.; Seitkalieva, E.; Ovsepyan, E.

2016-12-01

The study of sediment cores obtained during the cruises 35 (2012) and 50 (2015) of RV Akademic Ioffe from the Ceara Rise in the western tropical Atlantic strongly supports a significant influence of bottom (contour) currents on the Late Quaternary sedimentation. Seismic evidence of contourites in the study area (migrating contourite sediment waves, furrows) was previously described by Kumar and Embley (1977) and Curry et al. (1995). Widespread distribution of seismic waves on the rise and adjacent areas was suggested by Murdmaa et al (2014) based on the results of high-resolution seismic profiling with SES-2000 deep (4-5 kHz) in 2012. Our sediment cores recovered intercalation of bioturbated clays and silty clays with thin linear or wavy sand and silt layers and lenses implying strong bottom current control on sedimentation. The stratigraphic frame of the reference core AI-3426 retrieved near the summit of the Ceara Rise, at the water depth of 3046 m is based on the foraminiferal (Globorotalia menardii zones), oxygen isotope and AMS-14C data. The core recovered sediments of the last 140 ka with very rich and well-preserved tropical planktic foraminiferal assemblages. G. menardii is common within MIS 1 and 5 and is almost absent in MIS 2-4 and upper MIS 6. The abundance of benthic foraminifers is rather low. However, dominance of Globocassidulina subglobosa in benthic assemblages likely indicates a moderate bottom-current activity on the Ceara Rise during the last glacial. The other 4-5m long sediment cores collected along the seismic profile from the northern and southern slopes demonstrate the similar contourite sedimentological features and insignificant reworking of the Neogene foraminiferal species as inferred from the core AI-3426 along with the significant variations in foraminiferal preservation during the Pleistocene. The study is supported by the projects RSF 14-50-00095, RFBR 14-05-00744 and RFBR 16-35-60111, and Program I3P by RAS.

Earthquakes - on the moon

NASA Technical Reports Server (NTRS)

Nakamura, Y.

1981-01-01

Information obtained with the Apollo lunar seismic stations is discussed. The four types of natural seismic sources that have been identified are described, viz., thermal moonquakes, deep moonquakes, meteoroid impacts, and shallow moonquakes. It is suggested that: (1) the thermal quakes represent the slow cracking and movement of surface rocks; (2) the deep quakes are induced by the tide-generating force of the earth's gravity; (3) the meteoroids responsible for most of the observed impacts are in the mass range from 1 to 100 kg and are clustered in groups near the earth's orbit; and (4) the shallow quakes are similar to intraplate earthquakes and indicate that the moon is as seismically active as the interior regions of the earth's tectonic plates. The structure of the lunar interior as inferred from seismic signals due to both the last three natural sources and 'artificial' impacts of used spacecraft is examined in detail.

Blueschist- and Eclogite facies Pseudotachylytes: Products of Earthquakes in Collision- and Subduction zones

NASA Astrophysics Data System (ADS)

Andersen, T. B.; Austrheim, H.; John, T.; Medvedev, S.; Mair, K.

2009-04-01

Pseudotachylytes are the products of violent geological processes such as metorite impacts and seismic faulting. The fault-rock weakening processes leading to release of earthquakes are commonly related to phenomena such as grain size reduction and gouge formation, pressurization of pore-fluids and in some cases to melting by frictional heating. Explaining the frequently observed intermediate and deep earthquakes by brittle failure is, however, inherently difficult to reconcile because of extremely high normal stresses occuring at depth. In recent years several mechanisms for seismic events on deep faults have been suggested. These include: a) The most commonly accepted mechanism, dehydration embrittlement coupled to prograde metamorphic dehydration of wet rocks, such as serpentinites, at depth. b) Grain-size dependent flow-laws coupled with shear heating instability has been suggested as an alternative to explain repeated seismic faulting in Wadati-Benioff zones. c) Self-localized-thermal-runaway (SLTR) has been forwarded as a mechanism for ultimate failure of visco-elastic materials and as mechanism to explain the co-existence of shear zones and pseudotachylyte fault veins formed at eclogite facies conditions. All these mechanism point to the importance of metamorphism and/or metasomatism in understanding the mechanism(s) of intermediate- and deep earthquakes. Exhumed high to ultra-high pressure [(U)HP] metamorphic rocks are recognized in many orogenic belts. These complexes provide avenues to study a number of important products of geological processes including earthquakes with hypocentres at great depths. (U)HP co-seismic fault rocks are difficult to find in the field; nevertheless, a number of occurrences of co-seismic fault rocks from such complexes have been described after the initial discovery of such rocks in Norway (see: Austrheim and Boundy, Science 1994). In this talk we review some observations and interpretations based on these hitherto rarely observed but important co-seismic fault rocks from deep-crust and mantle complexes.

Geodynamic models of the deep structure of the natural disaster regions of the Earth

NASA Astrophysics Data System (ADS)

Rodnikov, A. G.; Sergeyeva, N. A.; Zabarinskaya, L. P.

2012-04-01

Investigation of the deep structure and creation of geodynamic models of natural disaster regions are important for understanding of the nature of such phenomena as earthquakes, eruptions of volcanoes, tsunami and others. Carrying out of such researches is necessary for definition of areas of potential risk, forecasting and the prevention of negative consequences of acts of nature. Research region is active continental margins of the Sea of Okhotsk, and especially the area of Neftegorsk earthquake which has occurred on May, 28th 1995 in the North Sakhalin and caused many victims and destructions. The geodynamic model of the lithosphere in the region of Neftegorsk earthquake has been constructed along the profile crossing the North Sakhalin Basin, Deryugin Basin and ophiolite complex between them. The Deryugin Basin was formed at the site of an ancient deep trench after the subduction of the Okhotsk Sea Plate under Sakhalin. The basin is located above a hot plume in the mantle at a depth of 25 km. The ophiolite belt of ultramafic magmatic rocks is an ancient (K2-Pg) paleosubduction zone separating the Deryugin basin from the North Sakhalin Basin. The thickness of the ancient seismic focal zone is 80 km. It is probably that the structures of the North Sakhalin have been formed in the following way. In the Late Cretaceous the oceanic Okhotsk Sea Plate subducted under Sakhalin, the eastern part of which was an andesite island arc. Approximately in Miocene the subduction of the plate apparently ceased. In that time the Tatar Rift Strait was formed. Ophiolite rocks of the subduction zones as a result of compression have been squeezed out on a surface. The ophiolite complex combined by the ultrabasic rocks, fixes position of ancient subduction zone. It is probable that the manifestation of the Neftegorsk earthquake was a result of activization of this ancient subduction zone. On a surface the subduction zone manifests itself as deep faults running along Sakhalin. The center of the Neftegorsk earthquake was directly formed by burst of activity of this ancient subduction zone. From a position of the ancient subduction zone under Sakhalin, which is a cause of strong earthquakes here, it follows that the region is one of seismic dangerous in Russia. Constructed on the basis of complex interpretation of the geologic-geophysical data the geodynamic models of natural disaster regions give the chance: to study a deep structure under seismic dangerous zones; to investigate a role of deep processes in the upper mantle in formation of structures of earth crust; to relate the geological features, tectonomagmatic, hydrothermal activity with the processes in the upper mantle; to plot maps in detail with zones of increasing risks to prevent active building or other economic activities in such dangerous regions.

Saudi Arabian refraction profile: Crustal structure of the Red Sea-Arabian shield transition

NASA Astrophysics Data System (ADS)

Milkereit, B.; Flüh, E. R.

1985-02-01

An interpretation of deep seismic sounding measurements across the ocean-continent transition of the Red Sea-Saudi Arabian Shield is presented. Using synthetic seismograms based on ray tracing we achieve a good fit to observed traveltimes and some of the characteristic amplitudes of the record sections. Crustal thickness varies along the profile from 15 km in the Red Sea Shelf to 40-45 km beneath the Asir Mountains and the Saudi Arabian Shield. Based on the computation of synthetic seismograms our model requires a velocity inversion in the Red Sea-Arabian Shield transition. High-velocity oceanic mantle material is observed above continental crust and mantle, thereby forming a double-layered Moho. Our results indicate a thick sedimentary basin in the shelf area, and zone of high velocities within the Asir Mountains (probably uplifted lower crust). Prominent secondary low-frequency arrivals are interpreted as multiples.

Hydro-mechanical modelling of induced seismicity during the deep geothermal project in St. Gallen, Switzerland

NASA Astrophysics Data System (ADS)

Zbinden, Dominik; Rinaldi, Antonio Pio; Kraft, Toni; Diehl, Tobias; Wiemer, Stefan

2017-04-01

The St. Gallen deep geothermal project in 2013 was the second geothermal project in Switzerland with the objective of power production after the Enhanced Geothermal System in Basel in 2006. In St. Gallen, the seismic risk was expected to be smaller than in Basel, since the hydrothermal resource was an aquifer at a depth of about 4 km, not expected to require permeability enhancement and associated hydroshearing of the rock. However, after an injectivity test and two acid stimulations, unexpected gas release from an unidentified source forced the operators to inject drilling mud into the well to fight the gas kick. Subsequently, several seismic events were induced, the largest one having a local magnitude of 3.5, which was distinctly felt by the nearby living population. Even though the induced seismicity could not be handled properly, the community still strongly supported the geothermal project. The project was however halted because the target formation was not as permeable as required to deliver sufficient power. Still, controlling induced seismicity during deep geothermal projects is a key factor to successfully operate future geothermal projects. Hence, it is crucial to understand the physical relations of fluid injection, pressure and stress response at reservoir depth as well as associated induced seismicity. To date, these processes are yet not fully understood. In this study, we aim at developing a hydro-mechanical model reproducing the main features of the induced seismic sequence at the St. Gallen geothermal site. Here, we present the conceptual model and preliminary results accounting for hydraulic and mechanical parameters from the geothermal well, geological information from a seismic survey conducted in the St. Gallen region, and actual fluid injection rates from the injectivity tests. In a future step, we are going to use this model to simulate the physical interaction of injected fluid, gas release, hydraulic response of the rock, and induced seismicity during the St. Gallen project. The results will then allow us to more accurately estimate the seismic hazard for future geothermal projects.

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

NASA Astrophysics Data System (ADS)

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

2009-05-01

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

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

NASA Astrophysics Data System (ADS)

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

2018-04-01

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

Geomorphology of the Eastern North American Continental Margin: the role of deep sea sedimentation processes

NASA Astrophysics Data System (ADS)

Mosher, D. C.; Campbell, C.; Piper, D.; Chaytor, J. D.; Gardner, J. V.; Rebesco, M.

2016-12-01

Deep-sea sedimentation processes impart a fundamental control on the morphology of the western North Atlantic continental margin from Blake Spur to Hudson Strait. This fact is illustrated by the variable patterns of cross-margin gradients that are based on extensive new multibeam echo-sounder data in concert with subbottom profiler and seismic reflection data. Most of the continental margin has a steep (>3o) upper slope down to 1500 to 2500 m and then a gradual middle and lower slope with a general concave upward shape There is a constant interplay of deep sea sedimentation processes, but the general morphology is dictated by the dominant one. Erosion by off-shelf sediment transport in turbidity currents creating channels, gullies and canyons creates the steep upper slope. These gullies and canyons amalgamate to form singular channels that are conduits to the abyssal plain. This process results in a general seaward flattening of gradients, producing an exponentially decaying slope profile. Comparatively, sediment mass failure produces steeper upper slopes due to head scarp development and a wedging architecture to the lower slope as deposits thin in the downslope direction. This process results in either a two-segment slope, and/or a significant downslope gradient change where MTDs pinch out. Large sediment bodies deposited by contour-following currents are developed all along the margin. Blake Ridge, Sackville Spur, and Hamilton Spur are large detached drifts on disparate parts of the margin. Along their crests, they form a linear profile from the shelf to abyssal plain. Deeper portions of the US continental margin are dominated by the Chesapeake Drift and Hatteras Outer Ridge; both plastered elongate mounded drifts. Farther north, particularly on the Grand Banks margin, are plastered and separated drifts. These drifts tend to form bathymetric steps in profile, where they onlap the margin. Stacked drifts create several steps. Turbidites of the abyssal plain onlap the lowermost drift creating a significant gradient change at this juncture. Understanding the geomorphological consequences of deep sea sedimentation processes is important to extended continental shelf mapping, for example, in which gradient change is a critical metric.

Seismic profile analysis of the Kangra and Dehradun re-entrant of NW Himalayan Foreland thrust belt, India: A new approach to delineate subsurface geometry

NASA Astrophysics Data System (ADS)

Dey, Joyjit; Perumal, R. Jayangonda; Sarkar, Subham; Bhowmik, Anamitra

2017-08-01

In the NW Sub-Himalayan frontal thrust belt in India, seismic interpretation of subsurface geometry of the Kangra and Dehradun re-entrant mismatch with the previously proposed models. These procedures lack direct quantitative measurement on the seismic profile required for subsurface structural architecture. Here we use a predictive angular function for establishing quantitative geometric relationships between fault and fold shapes with `Distance-displacement method' (D-d method). It is a prognostic straightforward mechanism to probe the possible structural network from a seismic profile. Two seismic profiles Kangra-2 and Kangra-4 of Kangra re-entrant, Himachal Pradesh (India), are investigated for the fault-related folds associated with the Balh and Paror anticlines. For Paror anticline, the final cut-off angle β =35{°} was obtained by transforming the seismic time profile into depth profile to corroborate the interpreted structures. Also, the estimated shortening along the Jawalamukhi Thrust and Jhor Fault, lying between the Himalayan Frontal Thrust (HFT) and the Main Boundary Thrust (MBT) in the frontal fold-thrust belt, were found to be 6.06 and 0.25 km, respectively. Lastly, the geometric method of fold-fault relationship has been exercised to document the existence of a fault-bend fold above the Himalayan Frontal Thrust (HFT). Measurement of shortening along the fault plane is employed as an ancillary tool to prove the multi-bending geometry of the blind thrust of the Dehradun re-entrant.

Stratigraphic and structural evolution of the Selenga Delta Accommodation Zone, Lake Baikal Rift, Siberia

NASA Astrophysics Data System (ADS)

Scholz, C. A.; Hutchinson, D. R.

Seismic reflection profiles from the Lake Baikal Rift reveal extensive details about the sediment thickness, structural geometry and history of extensional deformation and syn-rift sedimentation in this classic continental rift. The Selenga River is the largest single source of terrigenous input into Lake Baikal, and its large delta sits astride the major accommodation zone between the Central and South basins of the lake. Incorporating one of the world's largest lacustrine deltas, this depositional system is a classic example of the influence of rift basin structural segmentation on a major continental drainage. More than 3700km of deep basin-scale multi-channel seismic reflection (MCS) data were acquired during the 1989 Russian and the 1992 Russian-American field programs. The seismic data image most of the sedimentary section, including pre-rift basement in several localities. The MCS data reveal that the broad bathymetric saddle between these two major half-graben basins is underlain by a complex of severely deformed basement blocks, and is not simply a consequence of long-term deltaic deposition. Maximum sediment thickness is estimated to be more than 9km in some areas around the Selenga Delta. Detailed stratigraphic analyses of the Selenga area MCS data suggest that modes of deposition have shifted markedly during the history of the delta. The present mode of gravity- and mass-flow sedimentation that dominates the northern and southern parts of the modern delta, as well as the pronounced bathymetric relief in the area, are relatively recent developments in the history of the Lake Baikal Rift. Several episodes of major delta progradation, each extending far across the modern rift, can be documented in the MCS data. The stratigraphic framework defined by these prograding deltaic sequences can be used to constrain the structural as well as depositional evolution of this part of the Baikal Rift. An age model has been established for this stratigraphy, by tying the delta sequences to the site of the Baikal Drilling Project 1993 Drill Hole. Although the drill hole is only 100m deep, and the base of the cores is only 670ka in age, ages were extrapolated to deeper stratigraphic intervals using the Reflection-Seismic-Radiocarbon method of Cohen et al. (1993). The deep prograding delta sequences now observed in the MCS data probably formed in response to major fluctuations in sediment supply, rather than in response to shifts in lake level. This stratigraphic framework and age model suggest that the deep delta packages developed at intervals of approximately 400ka and may have formed as a consequence of climate changes affiliated with the northern hemisphere glaciations. The stratigraphic analysis also suggests that the Selenga Basin and Syncline developed as a distinct depocentre only during the past 2-3Ma.

Seismic swarms and diffuse fracturing within Triassic evaporites fed by deep degassing along the low-angle Alto Tiberina normal fault (central Apennines, Italy)

NASA Astrophysics Data System (ADS)

Piana Agostinetti, Nicola; Giacomuzzi, Genny; Chiarabba, Claudio

2017-01-01

We present high-resolution elastic models and relocated seismicity of a very active segment of the Apennines normal faulting system, computed via transdimensional local earthquake tomography (trans-D LET). Trans-D LET, a fully nonlinear approach to seismic tomography, robustly constrains high-velocity anomalies and inversions of P wave velocity, i.e., decreases of VP with depth, without introducing bias due to, e.g., a starting model, and giving the possibility to investigate the relation between fault structure, seismicity, and fluids. Changes in seismicity rate and recurring seismic swarms are frequent in the Apennines extensional belt. Deep fluids, upwelling from the delaminating continental lithosphere, are thought to be responsible for seismicity clustering in the upper crust and lubrication of normal faults during swarms and large earthquakes. We focus on the tectonic role played by the Alto Tiberina low-angle normal fault (ATF), finding displacements across the fault consistent with long-term accommodation of deformation. Our results show that recent seismic swarms affecting the area occur within a 3 km thick, high VP/VS, densely cracked, and overpressurized evaporitic layer, composed of dolostones and anhydrites. A persistent low VP, low VP/VS volume, present on top of and along the ATF low-angle detachment, traces the location of mantle-derived CO2, the upward flux of which contributes to cracking within the evaporitic layer.

Early Opening of Seychelles and India: the Gop Basin Revisited

NASA Astrophysics Data System (ADS)

Dyment, J.; Vadakkeyakath, Y.; Bhattacharya, G.

2012-12-01

The deep offshore region located between the India-Pakistan continental margin and the Laxmi Ridge continental sliver contains valuable imprints of the early oceanic opening phase between India and the Seychelles. The acquisition of wide-angle deep seismic data by British scientists in 2003 provided new information about the deep structure and nature of the crust [1,2]. These data complement the large amount of seismic reflection profiles, altimetry-derived gravity and marine magnetic data which allow mapping the structure and determining the age of the oceanic crust [3,4,5]. Although these authors all agree on the oceanic nature of the Gop Basin, they surprisingly differ on the extent of the oceanic crust, the location of the extinct spreading center and the age of the basin. Here we re-evaluate published interpretations of the Gop Basin in light of all available data. The major discrepancy between [1,2,4] and [5] is the location of the extinct spreading center. [1,2,4] place it on an unnamed basement high located at 19°55'N, whereas [5] identify it with the Palitana Ridge at 19°25'N. Checking the location of the basement high of [1,2,4] on the basement isobath map of [3], based on many seismic reflection profiles, reveals that this basement high actually is an isolated feature of limited extent, which at best can be considered as part of a NE-SW trending basement high zone. This basement high locally coincides with a strong positive magnetic anomaly and a narrow gravity anomaly low but the trend of these anomalies is E-W, in contrast to the NE-SW trend of the basement in this area. For these reasons, this basement high probably is not the location of the Gop Basin extinct spreading center. Conversely, on the basement isobath map of [3], the Palitana Ridge appears as a prominent E-W high, located in the middle of a broad E-W graben, the Gop Basin. It extends over 200 km and is flanked on both sides by basement 2000 m deeper. On free air gravity anomaly maps, the Palitana Ridge lies in the center of the broad gravity high that delineates the Gop Basin. It corresponds, to the west, to a narrow gravity low, a typical signature of fossil spreading centers. The crustal structure determined by the wide angle seismic data of [1,2] shows that the base of the lower crust, the best seismically constrained interface (according to the ray diagram of [1]), is flat in the Arabian Basin, deeper under the Laxmi Ridge, shallower in the Gop Basin under the Palitana Ridge, and deeper again further north. For these reasons, the Palitana Ridge probably is the location of the Gop Basin extinct spreading centre. Further, the Gop Basin, being narrow, does not exhibit long sequences of magnetic anomalies, thereby making their interpretation difficult. Many models may fit the observed anomalies, so [4] and [5] each proposed different hypotheses. We note, however, that [4] consider a plausible (and preferred) model with "initial" spreading rates, i.e. just after break up, as fast as 68 mm/yr half-rate, which implies the Gop Basin to form in 1 Myr. Such a fast initial rate appears unrealistic, considering that initial spreading rates are usually much slower, about one fourth of that rate. [1] Minshull et al., Nature Geo., 2008 [2] Collier et al., JGR, 2009 [3] Malod et al., Tectonophys., 1997 [4] Collier et al., EPSL, 2008 [5] Yatheesh et al., EPSL, 2009

Pre-stack depth Migration imaging of the Hellenic Subduction Zone

NASA Astrophysics Data System (ADS)

Hussni, S. G.; Becel, A.; Schenini, L.; Laigle, M.; Dessa, J. X.; Galve, A.; Vitard, C.

2017-12-01

In 365 AD, a major M>8-tsunamignic earthquake occurred along the southwestern segment of the Hellenic subduction zone. Although this is the largest seismic event ever reported in Europe, some fundamental questions remain regarding the deep geometry of the interplate megathrust, as well as other faults within the overriding plate potentially connected to it. The main objective here is to image those deep structures, whose depths range between 15 and 45 km, using leading edge seismic reflection equipment. To this end, a 210-km-long multichannel seismic profile was acquired with the 8 km-long streamer and the 6600 cu.in source of R/V Marcus Langseth. This was realized at the end of 2015, during the SISMED cruise. This survey was made possible through a collective effort gathering labs (Géoazur, LDEO, ISTEP, ENS-Paris, EOST, LDO, Dpt. Geosciences of Pau Univ). A preliminary processing sequence has first been applied using Geovation software of CGG, which yielded a post-stack time migration of collected data, as well as pre-stack time migration obtained with a model derived from velocity analyses. Using Paradigm software, a pre-stack depth migration was subsequently carried out. This step required some tuning in the pre-processing sequence in order to improve multiple removal, noise suppression and to better reveal the true geometry of reflectors in depth. This iteration of pre-processing included, the use of parabolic Radon transform, FK filtering and time variant band pass filtering. An initial velocity model was built using depth-converted RMS velocities obtained from SISMED data for the sedimentary layer, complemented at depth with a smooth version of the tomographic velocities derived from coincident wide-angle data acquired during the 2012-ULYSSE survey. Then, we performed a Kirchhoff Pre-stack depth migration with traveltimes calculated using the Eikonal equation. Velocity model were then tuned through residual velocity analyses to flatten reflections in common reflection point gathers. These new results improve the imaging of deep reflectors and even reveal some new features. We will present this work, a comparison with our previously obtained post-stack time migration, as well as some insights into the new geological structures revealed by the depth imaging.

Modeling Wide-Angle Seismic Data from the Hi-CLIMB Experiment in Tibet

NASA Astrophysics Data System (ADS)

Nowack, R. L.; Griffin, J. D.; Tseng, T.; Chen, W.

2009-12-01

Using data from local and regional events recorded by the Hi-CLIMB array in Tibet, we utilize seismic attributes, including arrival times, Hilbert amplitudes and pulse frequencies, to constrain structures of seismic wave speed and attenuation in the crust and the upper mantle in western China. We construct more than 30 high-quality, regional seismic profiles, and select 14 of these, which show excellent crustal and Pn arrivals, for further analysis. Travel-times from events at regional distances constrain large-scale velocity structures, and four close-in events provide further details on crustal structure. We use the 3-D ray tracer, CRT, to model the travel-times. Initial results indicate that the Moho beneath the Lhasa terrane of southern Tibet is over 73 km deep with a high Pn speed of about 8.2 km/s. In contrast, the Qiangtang terrane farther north shows a thinner crust, by up to 10 km, and a low Pn speed of 7.8-7.9 km/s. Preliminary estimates of upper mantle velocity gradients are between .003 and .004 km/s per km, consistent with previous results by Phillips et al. (2007). We also use P to SV conversions from teleseismic earthquakes to independently constrain variations in speeds of Pn and depths of the Moho. For instance, amplitudes of the SsPmP phase, when its last reflection off the Moho is near-critical, are particularly sensitive to the contrast in seismic wave speeds across the crust-mantle interface; and results from these additional data are consistent with those from modeling of travel-times. Additional seismic attributes, extracted from wave-trains containing Pn and major crustal phases, are being compared with results of numerical modeling based on the spectral element method and asymptotic calculations in laterally varying media, where both lateral and vertical gradients in seismic wave speeds can strongly affect Pn amplitudes and pulse frequencies.

In-situ Planetary Subsurface Imaging System

NASA Astrophysics Data System (ADS)

Song, W.; Weber, R. C.; Dimech, J. L.; Kedar, S.; Neal, C. R.; Siegler, M.

2017-12-01

Geophysical and seismic instruments are considered the most effective tools for studying the detailed global structures of planetary interiors. A planet's interior bears the geochemical markers of its evolutionary history, as well as its present state of activity, which has direct implications to habitability. On Earth, subsurface imaging often involves massive data collection from hundreds to thousands of geophysical sensors (seismic, acoustic, etc) followed by transfer by hard links or wirelessly to a central location for post processing and computing, which will not be possible in planetary environments due to imposed mission constraints on mass, power, and bandwidth. Emerging opportunities for geophysical exploration of the solar system from Venus to the icy Ocean Worlds of Jupiter and Saturn dictate that subsurface imaging of the deep interior will require substantial data reduction and processing in-situ. The Real-time In-situ Subsurface Imaging (RISI) technology is a mesh network that senses and processes geophysical signals. Instead of data collection then post processing, the mesh network performs the distributed data processing and computing in-situ, and generates an evolving 3D subsurface image in real-time that can be transmitted under bandwidth and resource constraints. Seismic imaging algorithms (including traveltime tomography, ambient noise imaging, and microseismic imaging) have been successfully developed and validated using both synthetic and real-world terrestrial seismic data sets. The prototype hardware system has been implemented and can be extended as a general field instrumentation platform tailored specifically for a wide variety of planetary uses, including crustal mapping, ice and ocean structure, and geothermal systems. The team is applying the RISI technology to real off-world seismic datasets. For example, the Lunar Seismic Profiling Experiment (LSPE) deployed during the Apollo 17 Moon mission consisted of four geophone instruments spaced up to 100 meters apart, which in essence forms a small aperture seismic network. A pattern recognition technique based on Hidden Markov Models was able to characterize this dataset, and we are exploring how the RISI technology can be adapted for this dataset.

Fault zone characterization using P- and S-waves

NASA Astrophysics Data System (ADS)

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

2014-05-01

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

Extraction of Pn seismic signals from air-gun shots recorded by the Cascadia Amphibious seismic experiment

NASA Astrophysics Data System (ADS)

Rathnayaka, S.; Gao, H.

2017-12-01

The goal of this study is to extract Pn (head wave) seismic waveforms recorded by both offshore and onshore (broadband and short period) seismic stations and evaluate the data quality. Two offshore active-source seismic experiments, MGL 1211 and MGL 1212, were conducted from 13th June to 24th July 2012, during the first year deployment of the Cascadia Initiative Amphibious Array. In total, we choose 110 ocean bottom seismometers and 209 inland stations that are located along the entire Cascadia subduction zone. We first remove the instrument response, and then explore the potential frequency ranges and the diurnal effect. We make the common receiver gathering for each seismic station and filter the seismic waveforms at multiple frequency bands, ranging from 3-5 Hz, 5-10 Hz, 10-20 Hz, to 20-40 Hz, respectively. To quantitatively evaluate the data quality, we calculate the signal-to-noise ratio (SNR) of the waveforms for usable stations that record clear Pn arrivals at multiple frequency bands. Our results show that most offshore stations located at deep water (>1.5 km) record clear air-gun shot signals at frequencies higher than 3 Hz and up to 550 km away from the source. For most stations located on the shallow continental shelf, the seismic recordings appear much noisier at all the frequencies compared to stations at deep water. Three general trends are observed for the SNR distribution; First, the SNR ratio increases from lower to higher frequency bands; Second, the ratio decreases with the increasing source-to-receiver distance; And third, the ratio increases from shallow to deep water. We also observe a rough negative relationship of the signal-to-noise ratio with the thickness of the marine sediment. Only 5 inland stations record clear air-gun shot arrivals up to 200 km away from the source. More detailed data quality analysis with more results will also be present.

Application of seismic interferometric migration for shallow seismic high precision data processing: A case study in the Shenhu area

NASA Astrophysics Data System (ADS)

Wei, Jia; Liu, Huaishan; Xing, Lei; Du, Dong

2018-02-01

The stability of submarine geological structures has a crucial influence on the construction of offshore engineering projects and the exploitation of seabed resources. Marine geologists should possess a detailed understanding of common submarine geological hazards. Current marine seismic exploration methods are based on the most effective detection technologies. Therefore, current research focuses on improving the resolution and precision of shallow stratum structure detection methods. In this article, the feasibility of shallow seismic structure imaging is assessed by building a complex model, and differences between the seismic interferometry imaging method and the traditional imaging method are discussed. The imaging effect of the model is better for shallow layers than for deep layers because coherent noise produced by this method can result in an unsatisfactory imaging effect for deep layers. The seismic interference method has certain advantages for geological structural imaging of shallow submarine strata, which indicates continuous horizontal events, a high resolution, a clear fault, and an obvious structure boundary. The effects of the actual data applied to the Shenhu area can fully illustrate the advantages of the method. Thus, this method has the potential to provide new insights for shallow submarine strata imaging in the area.

From rifting to spreading - seismic structure of the rifted western Mariana extinct arc and the ParceVela back-arc basin

NASA Astrophysics Data System (ADS)

Grevemeyer, Ingo; Kodaira, Shuichi; Fujie, Gou; Takahashi, Narumi

2017-04-01

The proto Izu-Ogasawara (Bonin)-Mariana (IBM) Island arc was created when subduction of the Pacific plate began during the Eocene. Today, the Kyushu-Palau Ridge (KPR) at the centre of the Philippine Sea and the western Mariana Ridge (WMR) are considered to be a remnant of the proto IBM Island arc. The KPR and WMR were separated when back-arc spreading began at 30 to 29 Ma in the Shikoku Basin and ParceVela Basin (PVB). Volcanic activity along the arcs diminished at 27 Ma and there is little evidence of volcanic activity between 23-17 Ma. Arc volcanism was reactivated at 15 Ma, when the opening of the Shikoku Basin and PVB ceased. At about 5 Ma the Mariana Basin opened, rifting the WMR from the Mariana arc. Here, we report results from the seismic refraction and wide-angle profile MR101c shot in summer of 2003 by the Japan Agency for Marine-Earth Science and Technology (JAMSTEC) aboard the RV KAIYO during the cruise KY03-06, extending from the PVB across the WMR and terminating just to the east of the WMR. Along MR101c 46 OBS recorded shots from an airgun array of 12,000 cubic inches (197 litres); 44 OBS provided excellent P-wave data, including arrivals sampling the crust (Pg), the crust/mantle boundary (PmP), the uppermost mantle (Pn) and a deep reflection (PnP) under the WMR. To yield the seismic velocity structure, we used a joint reflection and refraction tomography, revealing the crustal and mantle P-wave velocity structure, the seismic Moho, and a deep-seated reflector. Distinct features are a 14 km thick crust forming the WMR, a high-velocity lower crust in both transition zones to the ParceVela Basin and Mariana Basin, and a reflector at 24 km depth, which shallows to 18 km in the transition zone to the Mariana Basin, perhaps reflecting rifting-related thinning of the entire lithosphere. The deep-reflector, however, did not occur under the PVB. Upper mantle velocity below the WMR is <7.5 km/s. High velocities of the lower crust of the WMR flanking the adjacent basins mimic the structure found in the Lau Basin - Tonga Arc system, perhaps indicating entrainment of hydrous melts from the adjacent arc governing early seafloor spreading when the spreading centre was at close distant to the volcanic arc. Upper mantle below the PVB shows typical mantle properties, supporting a P-wave velocity of >8 km/s. However, with respect to oceanic crust sampled in the Pacific Basin, PVB crust is with 5 km thinner and seismic velocities in the lower crust are with 6.7 km/s much lower.

Fallon, Nevada FORGE Seismic Reflection Profiles

DOE Data Explorer

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

2018-02-01

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

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

NASA Astrophysics Data System (ADS)

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

2017-12-01

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

Resolving the fine-scale velocity structure of continental hyperextension at the Deep Galicia Margin using full-waveform inversion

NASA Astrophysics Data System (ADS)

Davy, R. G.; Morgan, J. V.; Minshull, T. A.; Bayrakci, G.; Bull, J. M.; Klaeschen, D.; Reston, T. J.; Sawyer, D. S.; Lymer, G.; Cresswell, D.

2018-01-01

Continental hyperextension during magma-poor rifting at the Deep Galicia Margin is characterized by a complex pattern of faulting, thin continental fault blocks and the serpentinization, with local exhumation, of mantle peridotites along the S-reflector, interpreted as a detachment surface. In order to understand fully the evolution of these features, it is important to image seismically the structure and to model the velocity structure to the greatest resolution possible. Traveltime tomography models have revealed the long-wavelength velocity structure of this hyperextended domain, but are often insufficient to match accurately the short-wavelength structure observed in reflection seismic imaging. Here, we demonstrate the application of 2-D time-domain acoustic full-waveform inversion (FWI) to deep-water seismic data collected at the Deep Galicia Margin, in order to attain a high-resolution velocity model of continental hyperextension. We have used several quality assurance procedures to assess the velocity model, including comparison of the observed and modeled waveforms, checkerboard tests, testing of parameter and inversion strategy and comparison with the migrated reflection image. Our final model exhibits an increase in the resolution of subsurface velocities, with particular improvement observed in the westernmost continental fault blocks, with a clear rotation of the velocity field to match steeply dipping reflectors. Across the S-reflector, there is a sharpening in the velocity contrast, with lower velocities beneath S indicative of preferential mantle serpentinization. This study supports the hypothesis that normal faulting acts to hydrate the upper-mantle peridotite, observed as a systematic decrease in seismic velocities, consistent with increased serpentinization. Our results confirm the feasibility of applying the FWI method to sparse, deep-water crustal data sets.

Sequence stratigraphy, seismic stratigraphy, and seismic structures of the lower intermediate confining unit and most of the Floridan aquifer system, Broward County, Florida

USGS Publications Warehouse

Cunningham, Kevin J.; Kluesner, Jared W.; Westcott, Richard L.; Robinson, Edward; Walker, Cameron; Khan, Shakira A.

2017-12-08

Deep well injection and disposal of treated wastewater into the highly transmissive saline Boulder Zone in the lower part of the Floridan aquifer system began in 1971. The zone of injection is a highly transmissive hydrogeologic unit, the Boulder Zone, in the lower part of the Floridan aquifer system. Since the 1990s, however, treated wastewater injection into the Boulder Zone in southeastern Florida has been detected at three treated wastewater injection utilities in the brackish upper part of the Floridan aquifer system designated for potential use as drinking water. At a time when usage of the Boulder Zone for treated wastewater disposal is increasing and the utilization of the upper part of the Floridan aquifer system for drinking water is intensifying, there is an urgency to understand the nature of cross-formational fluid flow and identify possible fluid pathways from the lower to upper zones of the Floridan aquifer system. To better understand the hydrogeologic controls on groundwater movement through the Floridan aquifer system in southeastern Florida, the U.S. Geological Survey and the Broward County Environmental Planning and Community Resilience Division conducted a 3.5-year cooperative study from July 2012 to December 2015. The study characterizes the sequence stratigraphy, seismic stratigraphy, and seismic structures of the lower part of the intermediate confining unit aquifer and most of the Floridan aquifer system.Data obtained to meet the study objective include 80 miles of high-resolution, two-dimensional (2D), seismic-reflection profiles acquired from canals in eastern Broward County. These profiles have been used to characterize the sequence stratigraphy, seismic stratigraphy, and seismic structures in a 425-square-mile study area. Horizon mapping of the seismic-reflection profiles and additional data collection from well logs and cores or cuttings from 44 wells were focused on construction of three-dimensional (3D) visualizations of eight sequence stratigraphic cycles that compose the Eocene to Miocene Oldsmar, Avon Park, and Arcadia Formations. The mapping of these seismic-reflection and well data has produced a refined Cenozoic sequence stratigraphic, seismic stratigraphic, and hydrogeologic framework of southeastern Florida. The upward transition from the Oldsmar Formation to the Avon Park Formation and the Arcadia Formation embodies the evolution from (1) a tropical to subtropical, shallow-marine, carbonate platform, represented by the Oldsmar and Avon Park Formations, to (2) a broad, temperate, mixed carbonate-siliciclastic shallow marine shelf, represented by the lower part of the Arcadia Formation, and to (3) a temperate, distally steepened carbonate ramp represented by the upper part of the Arcadia Formation.In the study area, the depositional sequences and seismic sequences have a direct correlation with hydrogeologic units. The approximate upper boundary of four principal permeable units of the Floridan aquifer system (Upper Floridan aquifer, Avon Park permeable zone, uppermost major permeable zone of the Lower Floridan aquifer, and Boulder Zone) have sequence stratigraphic and seismic-reflection signatures that were identified on cross sections, mapped, or both, and therefore the sequence stratigraphy and seismic stratigraphy were used to guide the development of a refined spatial representation of these hydrogeologic units. In all cases, the permeability of the four permeable units is related to stratiform megaporosity generated by ancient dissolution of carbonate rock associated with subaerial exposure and unconformities at the upper surfaces of carbonate depositional cycles of several hierarchical scales ranging from high-frequency cycles to depositional sequences. Additionally, interparticle porosity also contributes substantially to the stratiform permeability in much of the Upper Floridan aquifer. Information from seismic stratigraphy allowed 3D geomodeling of hydrogeologic units—an approach never before applied to this area. Notably, the 3D geomodeling provided 3D visualizations and geocellular models of the depositional sequences, hydrostratigraphy, and structural features. The geocellular data could be used to update the hydrogeologic structure inherent to groundwater flow simulations that are designed to address the sustainability of the water resources of the Floridan aquifer system.Two kinds of pathways that could enable upward cross-formational flow of injected treated wastewater from the Boulder Zone have been identified in the 80 miles of high-resolution seismic data collected for this study: a near-vertical reverse fault and karst collapse structures. The single reverse fault, inferred to be of tectonic origin, is in extreme northeastern Broward County and has an offset of about 19 feet at the level of the Arcadia Formation. Most of the 17 karst collapse structures identified manifest as columniform, vertically stacked sagging seismic reflections that span early Eocene to Miocene age rocks equivalent to much of the Floridan aquifer system and the lower part of the overlying intermediate confining unit. In some cases, the seismic-sag structures extend upward into strata of Pliocene age. The seismic-sag structures are interpreted to have a semicircular shape in plan view on the basis of comparison to (1) other seismic-sag structures in southeastern Florida mapped with two 2D seismic cross lines or 3D data, (2) comparison to these structures located in other carbonate provinces, and (3) plausible extensional ring faults detected with multi-attribute analysis. The seismic-sag structures in the study area have heights as great as 2,500 vertical feet, though importantly, one spans about 7,800 feet. Both multi-attribute analysis and visual detection of offset of seismic reflections within the seismic-sag structures indicate faults and fractures are associated with many of the structures. Multi-attribute analysis highlighting chimney fluid pathways also indicates that the seismic-sag structures have a high probability for potential vertical cross-formational fluid flow along the faulted and fractured structures. A collapse of the seismic-sag structures within a deep burial setting evokes an origin related to hypogenic karst processes by ascending flow of subsurface fluids. In addition, paleo-epigenic karst related to major regional subaerial unconformities within the Florida Platform generated collapse structures (paleo-sinkholes) that are much smaller in scale than the cross-formational seismic-sag structures.

Deep Structures of The Angola Margin

NASA Astrophysics Data System (ADS)

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

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

Depressions and other lake-floor morphologic features in deep water, southern Lake Michigan

USGS Publications Warehouse

Colman, Steven M.; Foster, D.S.; Harrison, D.W.

1992-01-01

The most common features are subcircular depressions, commonly compound, that are irregularly distributed across the lake floor. The depressions are most common in the southern basin of the lake where lacustrine sediments are more than a few meters thick, corresponding to water depths greater than about 90 m. We have divided the depressions into three types on the basis of their internal structure seen in seismic-reflection profiles. The depressions show varying degrees of muting, ranging from fresh to completely buried, suggesting a range in the time of their formation. The origin of the depressions is problematic, but their structure suggests collapse and(or) subsidence. -from Authors

Mountain building processes during continent continent collision in the Uralides

NASA Astrophysics Data System (ADS)

Brown, D.; Juhlin, C.; Ayala, C.; Tryggvason, A.; Bea, F.; Alvarez-Marron, J.; Carbonell, R.; Seward, D.; Glasmacher, U.; Puchkov, V.; Perez-Estaun, A.

2008-08-01

Since the early 1990's the Paleozoic Uralide Orogen of Russia has been the target of a significant research initiative as part of EUROPROBE and GEODE, both European Science Foundation programmes. One of the main objectives of these research programmes was the determination of the tectonic processes that went into the formation of the orogen. In this review paper we focus on the Late Paleozoic continent-continent collision that took place between Laurussia and Kazakhstania. Research in the Uralides was concentrated around two deep seismic profiles crossing the orogen. These were accompanied by geological, geophysical, geochronological, geochemical, and low-temperature thermochronological studies. The seismic profiles demonstrate that the Uralides has an overall bivergent structural architecture, but with significantly different reflectivity characteristics from one tectonic zone to another. The integration of other types of data sets with the seismic data allows us to interpret what tectonic processes where responsible for the formation of the structural architecture, and when they were active. On the basis of these data, we suggest that the changes in the crustal-scale structural architecture indicate that there was significant partitioning of tectonothermal conditions and deformation from zone to zone across major fault systems, and between the lower and upper crust. Also, a number of the structural features revealed in the bivergent architecture of the orogen formed either in the Neoproterozoic or in the Paleozoic, prior to continent-continent collision. From the end of continent-continent collision to the present, low-temperature thermochronology suggests that the evolution of the Uralides has been dominated by erosion and slow exhumation. Despite some evidence for more recent topographic uplift, it has so far proven difficult to quantify it.

Magnetotelluric Investigation of Melt Storage Beneath Okmok Caldera, Alaska

NASA Astrophysics Data System (ADS)

Bennington, N. L.; Bedrosian, P.; Key, K.; Zelenak, G.

2015-12-01

Alaska accounts for nearly 99% of the seismic moment release within the US. Much of this is associated with the Aleutian volcanic arc, the most tectonically active region in North America, and an ideal location for studying arc magmatism. Okmok is an active volcano located in the central Aleutian arc, defined by a pair of nested, 10 km diameter calderas. The subdued topography of Okmok, relative to other Aleutian volcanoes, improves access and permits dense sampling within the caldera closer to the underlying magmatic system. Okmok volcano was selected as the site of study for this project due to frequent volcanic activity and the presence of a crustal magma reservoir as inferred from previous coarse resolution seismic studies. In June-July 2015, we carried out an amphibious geophysical field deployment at Okmok. Onshore work in and around the volcano included collection of an array of magnetotelluric (MT) stations and installation of a temporary, year-long seismic array. A ring of 3D offshore MT deployments made around the island augments the onshore array. An additional 2D tectonic-scale profile spans the trench, volcanic arc, and backarc. This new geophysical data will be used to gain a greater understanding of Aleutian arc melt generation, migration, and storage beneath an active caldera. We present results from the analysis of the newly collected amphibious 3D MT data. This data will be used to model the distribution and migration of melt within Okmok's crustal magma reservoir. Initial processing of the data shows strong MT signal levels, in particular from a geomagnetic storm that occurred from June 21-23, 2015. A companion abstract discussing the 2D tectonic scale MT profile, which constrains the mantle and deep crust beneath Okmok volcano, is discussed by Zelenak et al.

Archive of digital boomer seismic reflection data collected offshore east-central Florida during USGS cruise 00FGS01, July 14-22, 2000

USGS Publications Warehouse

Subino, Janice A.; Dadisman, Shawn V.; Wiese, Dana S.; Calderon, Karynna; Phelps, Daniel C.

2009-01-01

In July of 2000, the U.S. Geological Survey (USGS), in cooperation with the Florida Geological Survey (FGS), conducted a geophysical survey of the Atlantic Ocean offshore Florida's east coast from Brevard County to northern Martin County. This report serves as an archive of unprocessed digital boomer seismic reflection data, trackline maps, navigation files, Geographic Information System (GIS) information, digital and handwritten Field Activity Collection System (FACS) logs, and Federal Geographic Data Committee (FGDC) metadata. A filtered and gained (a relative increase in signal amplitude) digital image of each seismic profile is also provided. Refer to the Acronyms page for expansions of all acronyms and abbreviations used in this report. The archived trace data are in standard Society of Exploration Geophysicists (SEG) SEG-Y format (Barry and others, 1975) and may be downloaded and processed with commercial or public domain software such as Seismic Unix (SU) (Cohen and Stockwell, 2005). Example SU processing scripts and USGS Software for viewing the SEG-Y files (Zihlman, 1992) are also provided. The USGS St. Petersburg Coastal and Marine Science Center assigns a unique identifier to each cruise or field activity. For example, 00FGS01 tells us the data were collected in 2000 for cooperative work with the Florida Geological Survey (FGS) and the data were collected during the first field activity for that study in that calendar year. Refer to http://walrus.wr.usgs.gov/infobank/programs/html/definition/activity.html for a detailed description of the method used to assign the field activity ID. The boomer plate is an acoustic energy source that consists of capacitors charged to a high voltage and discharged through a transducer in the water. The transducer is towed on a sled floating on the water surface and when discharged, emits a short acoustic pulse, or shot, which propagates through the water, sediment column, or rock beneath. The acoustic energy is reflected at density boundaries (such as the seafloor, sediment, or rock layers beneath the seafloor), detected by the receiver, and recorded by a PC-based seismic acquisition system. This process is repeated at timed intervals (for example, 0.5 s) and recorded for specific intervals of time (for example, 100 ms). In this way, a two-dimensional (2D) vertical profile of the shallow geologic structure beneath the ship track is produced. Figure 1 displays the acquisition geometry. Refer to table 1 for a summary of acquisition parameters. The unprocessed seismic data are stored in SEG-Y format (Barry and others, 1975). For a detailed description of the data format, refer to the SEG-Y Format page. See the How To Download SEG-Y Data page for download instructions. The printable profiles provided are GIF images that were filtered and gained using Seismic Unix software. Refer to the Software page for details about the processing and examples of the processing scripts. The printable profiles can be viewed from the Profiles page or from links located on the trackline maps. To view the trackline maps and navigation files, and for more information about these items, see the Navigation page. Detailed information about the navigation system used can be found in table 1. Of a total record length of 200 ms, only the upper 100 ms of each profile are displayed because no useful information was observed deeper in the sections. A 10 ms deep water delay appears on lines b57-b63 and sl2-sl28. No digital data were collected for line sl6. However, line sl6r is a second attempt to collect digital data for this line. Digital data and 500-shot-interval location navigation are not available for the last 1,161 shots of line sl26 due to an equipment malfunction.

The Sunda-Banda Arc Transition: New Insights from Marine Multichannel Seismic Data

NASA Astrophysics Data System (ADS)

Mueller, C.; Kopp, H.; Djajadihardja, Y.; Engels, M.; Flueh, E.; Gaedicke, C.; Lueschen, E.; Lutz, R.; Planert, L.; Shulgin, A.; Soemantri, D. D.

2007-12-01

After the Indian Ocean Mw 9.3 earthquake and tsunami on December 26, 2004, intensive research activities focussed on the Sunda Arc subduction system offshore Sumatra. For this area a broad database is now available interpreted in terms of plate segmentation and outer arc high evolution. In contrast, the highly active easternmost part of this subduction system, as indicated by the south of Java Mw 7.7 earthquake and tsunami on July 17, 2006, has remained almost unexplored until recently. During RV SONNE cruise SO190 from October until December 2006 almost 5000 km of marine geophysical profiles have been acquired at the eastern Sunda Arc and the transition to the Banda Arc. The SINDBAD project (Seismic and Geoacoustic Investigations along the Sunda-Banda Arc Transition) comprises 30-fold multichannel reflection seismics with a 3-km streamer, wide-angle OBH/OBS refraction seismics for deep velocity control (see poster of Planert et al. in this session), swath bathymetry, sediment echosounder, gravimetric and geomagnetic measurements. We present data and interpretations of several 250-380 km long, prestack depth-migrated seismic sections, perpendicular to the deformation front, based on velocity models from focussing analysis and inversion of OBH/OBS refraction data. We focus on the variability of the lower plate and the tectonic response of the overriding plate in terms of outer arc high formation and evolution, forearc basin development, accretion and erosion processes at the base of the overriding plate. The subducting Indo-Australian Plate is characterized by three segments: i) the Roo Rise with rough topography offshore eastern Java ii) the Argo Abyssal Plain with smooth oceanic crust offshore Bali, Lombok, and Sumbawa, and iii) the Scott Plateau with continental crust colliding with the Banda island arc. The forearc responds to differences in the incoming oceanic plate with the absence of a pronounced forearc basin offshore eastern Java and with development of the 4000 m deep forearc Lombok Basin offshore Bali, Lombok, and Sumbawa. The eastern termination of the Lombok Basin is formed by Sumba Island, which shows evidence for recent uplift, probably associated with the collision of the island arc with the continental Scott Plateau. The Sumba area represents the transition from subduction to collision. Our seismic profiles image the bending of the oceanic crust seaward of the trench and associated normal faulting. Landward of the trench, they image the subducting slab beneath the outer arc high, where the former bending-related normal faults appear to be reactivated as reverse faults introducing vertical displacements in the subducting slab. The accretionary prism and the outer arc high are characterized by an ocean-verging system of imbricate thrust sheets with major thrust faults connecting seafloor and detachment. Compression results in shortening and steepening of the imbricated thrust sheets building up the outer arc high. Tilted piggy-back basins and downlaps of tilted sediments in the southern Lombok forearc basin indicate ongoing uplift of the entire outer arc high, abrupt displacements, and recent tectonic activity.

Deep Crustal Structure beneath Large Igneous Provinces and the Petrologic Evolution of Flood Basalts

NASA Astrophysics Data System (ADS)

Richards, Mark; Ridley, Victoria

2010-05-01

We present a review of seismological constraints on deep crustal structures underlying large igneous provinces (LIPs), largely from wide-angle seismic refraction surveys. The main purpose of this review is to ascertain whether this seismic evidence is consistent with, or contrary to, petrological models for the genesis of flood basalt lavas. Where high-quality data are available beneath continental flood basalt (CFB) provinces (Emeishan, Columbia River, Deccan, Siberia), high-velocity structures (Vp ~6.9-7.5 km/sec) are typically found immediately overlying the Moho in layers of order ~5-15 km thick. Oceanic plateau (OP) LIPs exhibit similar layers, with a conspicuous layer of very high crustal velocity (Vp~7.7 km/sec) beneath the enormous Ontong-Java plateau. These structures are similar to inferred ultramafic underplating structures seen beneath active hotspots such as Hawaii, the Marqueses, and La Reunion. Petrogenetic models for flood basalt volcanism based on hot plume melting beneath mature lithosphere suggest that these deep seismic structures may consist in large part of cumulate bodies of olivine and clinopyroxene which result from ponding and deep-crustal fractionation of ultramafic primary melts. Such fractionation is necessary to produce basalts with typical MgO contents of ~6-8%, as observed for the vast bulk of observed flood basalts, from primary melts with MgO contents of order ~15-18% (or greater) such as result from hot, deep melting beneath the lithosphere. The volumes of cumulate bodies and ultramafic intrusions in the lowermost crust, often described in the literature as "underplating," are comparable to those of the overlying basaltic formations, also consistent with petrological models. Further definition of the deep seismic structure beneath such prominent LIPs as the Ontong-Java Plateau could place better constraints on flood basalt petrogenesis by determining the relative volumes of ultramafic bodies and basaltic lavas, thereby better constraining the overall process of LIP emplacement.

Deep crustal structure beneath large igneous provinces and the petrologic evolution of flood basalts

NASA Astrophysics Data System (ADS)

Ridley, Victoria A.; Richards, Mark A.

2010-09-01

We present a review of seismological constraints on deep crustal structures underlying large igneous provinces (LIPs), largely from wide-angle seismic refraction surveys. The main purpose of this review is to ascertain whether this seismic evidence is consistent with, or contrary to, petrological models for the genesis of flood basalt lavas. Where high-quality data are available beneath continental flood basalt (CFB) provinces (Emeishan, Columbia River, Deccan, Siberia), high-velocity structures (Vp ˜ 6.9-7.5 km/sec) are typically found immediately overlying the Moho in layers of order ˜5-15 km thick. Oceanic plateau (OP) LIPs exhibit similar layers, with a conspicuous layer of very high crustal velocity (Vp ˜ 7.7 km/sec) beneath the enormous Ontong-Java plateau. These structures are similar to inferred ultramafic underplating structures seen beneath active hot spots such as Hawaii, the Marquesas, and La Reunion. Petrogenetic models for flood basalt volcanism based on hot plume melting beneath mature lithosphere suggest that these deep seismic structures may consist in large part of cumulate bodies of olivine and clinopyroxene which result from ponding and deep-crustal fractionation of ultramafic primary melts. Such fractionation is necessary to produce basalts with typical MgO contents of ˜6-8%, as observed for the vast bulk of observed flood basalts, from primary melts with MgO contents of order ˜15-18% (or greater) such as result from hot, deep melting beneath the lithosphere. The volumes of cumulate bodies and ultramafic intrusions in the lowermost crust, often described in the literature as "underplating," are comparable to those of the overlying basaltic formations, also consistent with petrological models. Further definition of the deep seismic structure beneath such prominent LIPs as the Ontong-Java Plateau could place better constraints on flood basalt petrogenesis by determining the relative volumes of ultramafic bodies and basaltic lavas, thereby better constraining the overall process of LIP emplacement.

Deep Crustal Structure beneath Large Igneous Provinces and the Petrologic Evolution of Flood Basalts

NASA Astrophysics Data System (ADS)

Richards, M. A.; Ridley, V. A.

2010-12-01

We present a review of seismological constraints on deep crustal structures underlying large igneous provinces (LIPs), largely from wide-angle seismic refraction surveys. The main purpose of this review is to ascertain whether this seismic evidence is consistent with, or contrary to, petrological models for the genesis of flood basalt lavas. Where high-quality data are available beneath continental flood basalt (CFB) provinces (Emeishan, Columbia River, Deccan, Siberia), high-velocity structures (Vp ~6.9-7.5 km/sec) are typically found immediately overlying the Moho in layers of order ~5-15 km thick. Oceanic plateau (OP) LIPs exhibit similar layers, with a conspicuous layer of very high crustal velocity (Vp~7.7 km/sec) beneath the enormous Ontong-Java plateau. These structures are similar to inferred ultramafic underplating structures seen beneath active hotspots such as Hawaii, the Marquesas, and La Reunion. Petrogenetic models for flood basalt volcanism based on hot plume melting beneath mature lithosphere suggest that these deep seismic structures may consist in large part of cumulate bodies of olivine and clinopyroxene which result from ponding and deep-crustal fractionation of ultramafic primary melts. Such fractionation is necessary to produce basalts with typical MgO contents of ~6-8%, as observed for the vast bulk of observed flood basalts, from primary melts with MgO contents of order ~15-18% (or greater) such as result from hot, deep melting beneath the lithosphere. The volumes of cumulate bodies and ultramafic intrusions in the lowermost crust, often described in the literature as “underplating,” are comparable to those of the overlying basaltic formations, also consistent with petrological models. Further definition of the deep seismic structure beneath such prominent LIPs as the Ontong-Java Plateau could place better constraints on flood basalt petrogenesis by determining the relative volumes of ultramafic bodies and basaltic lavas, thereby better constraining the overall process of LIP emplacement.

ON-SITE CAVITY LOCATION-SEISMIC PROFILING AT NEVADA TEST SITE

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

Forbes, C.B.; Peterson, R.A.; Heald, C.L.

1961-10-25

Experimental seismic studies were conducted at the Nevada Test Site for the purpose of designing and evaluating the most promising seismic techniques for on-site inspection. Post-explosion seismic profiling was done in volcanic tuff in the vicinity of the Rainier and Blanca underground explosions. Pre-explosion seismic profiling was done over granitic rock outcrops in the Climax Stock area, and over tuff at proposed location for Linen and Orchid. Near surface velocity profiling techniques based on measurements of seismic time-distance curves gave evidence of disturbances in near surface rock velocities over the Rainier and Refer als0 to abstract 30187. Blanca sites. Thesemore » disturbances appear to be related to near surface fracturing and spallation effects resulting from the reflection of the original intense compression wave pulse at the near surface as a tension pulse. Large tuned seismometer arrays were used for horizontal seismic ranging in an attempt to record back-scattered'' or reflected seismic waves from subsurface cavities or zones of rock fracturing around the underground explosions. Some possible seismic events were recorded from the near vicinities of the Rainier and Blanca sites. However, many more similar events were recorded from numerous other locations, presumably originating from naturally occurring underground geological features. No means was found for discriminating between artificial and natural events recorded by horizontal seismic ranging, and the results were, therefore, not immediately useful for inspection purposes. It is concluded that in some instances near surface velocity profiling methods may provide a useful tool in verifying the presence of spalled zones above underground nuclear explosion sites. In the case of horizontal seismic ranging it appears that successful application would require development of satisfactory means for recognition of and discrimination against seismic responses to naturally occurring geological features. It is further concluded that, although more sophisticated instrumentation systems can be conceived, the most promising returns for effort expended can be expected to come from increased experience, skill, and human ingenuity in applying existing techniques. The basic problem is in large part a geological one of differentiating seismic response to man made irregularities from that of natural features which are of a similar or greater size and universally proved. It would not appear realistic to consider the seismic tool as a proven routine device for giving clear answers in on-site inspection operations. Application must still be considered largely experimental. (auth)« less

Automated classification of seismic sources in a large database: a comparison of Random Forests and Deep Neural Networks.

NASA Astrophysics Data System (ADS)

Hibert, Clement; Stumpf, André; Provost, Floriane; Malet, Jean-Philippe

2017-04-01

In the past decades, the increasing quality of seismic sensors and capability to transfer remotely large quantity of data led to a fast densification of local, regional and global seismic networks for near real-time monitoring of crustal and surface processes. This technological advance permits the use of seismology to document geological and natural/anthropogenic processes (volcanoes, ice-calving, landslides, snow and rock avalanches, geothermal fields), but also led to an ever-growing quantity of seismic data. This wealth of seismic data makes the construction of complete seismicity catalogs, which include earthquakes but also other sources of seismic waves, more challenging and very time-consuming as this critical pre-processing stage is classically done by human operators and because hundreds of thousands of seismic signals have to be processed. To overcome this issue, the development of automatic methods for the processing of continuous seismic data appears to be a necessity. The classification algorithm should satisfy the need of a method that is robust, precise and versatile enough to be deployed to monitor the seismicity in very different contexts. In this study, we evaluate the ability of machine learning algorithms for the analysis of seismic sources at the Piton de la Fournaise volcano being Random Forest and Deep Neural Network classifiers. We gather a catalog of more than 20,000 events, belonging to 8 classes of seismic sources. We define 60 attributes, based on the waveform, the frequency content and the polarization of the seismic waves, to parameterize the seismic signals recorded. We show that both algorithms provide similar positive classification rates, with values exceeding 90% of the events. When trained with a sufficient number of events, the rate of positive identification can reach 99%. These very high rates of positive identification open the perspective of an operational implementation of these algorithms for near-real time monitoring of mass movements and other environmental sources at the local, regional and even global scale.

Frequency power analyses of seismic sources on firn

NASA Astrophysics Data System (ADS)

Sanz, Christopher; Diez, Anja; Coen, Hofstede; Kristoffersen, Yngve; Mayer, Christoph; Lambrecht, Astrid; Miller, Heinz; Eisen, Olaf

2013-04-01

A great obstacle for seismic surveys on firn-covered ice masses is the ability of firn to strongly attenuate seismic energy and divert downward ray paths away from the vertical because of the velocity gradient. The standard way to overcome these limitations is the drilling of shotholes about 10-30 m deep. However, drilling of shotholes is a time and energy consuming task. Another possibility is to use vibroseismic sources at the surface and increase the signal-to-noise ratio by repeated stacking. However, compared to explosive charges, vibroseismic signals are bandlimited per se. As a third variant, we investigate the usage of ordered patterns of surface charges consisting of detonation cord. Previous applications of detonation cord only explored their general comparison to bulk explosives when deployed in a linear fashion, i.e. a single line. Our approach extends these results to other geometries, like fan- or comb-shaped patterns. These have two advantages: first, over the pattern area a locally plane wave is generated, limiting the spherical and velocity-gradient induced spreading of energy during propagation; second, the ratio between seismic wave speed of the firn and the detonation cord of typically about 1:5 causes the wave to propagate in an angle downward. When using large offsets like a snow streamer, it is possible to direct the refected energy towards the streamer, depending on offset range and reflector depth. We compare the different source types for several surveys conducted in Antarctica in terms of frequency spectra. Our results show that ordered patterns of detonation cord serve as suitable seismic surface charges, avoiding the need to drill shotholes. Moreover, an example of a short profile with patterned surface charges is presented. The technique can be of advantage for surveys in remote areas, which can only be accessed by aircrafts.

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

USGS Publications Warehouse

Cunningham, Kevin J.

2014-01-01

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

Kinematics of Active Deformation Across the Western Kunlun Mountain Range (Xinjiang, China) and Potential Seismic Hazards Within the Southern Tarim Basin

NASA Astrophysics Data System (ADS)

Guilbaud, Christelle; Simoes, Martine; Barrier, Laurie; Laborde, Amandine; Van der Woerd, Jérôme; Li, Haibing; Tapponnier, Paul; Coudroy, Thomas; Murray, Andrew

2017-12-01

The Western Kunlun mountain range is a slowly converging intracontinental orogen where deformation rates are too low to be properly quantified from geodetic techniques. This region has recorded little seismicity, but the recent July 2015 (Mw 6.4) Pishan earthquake shows that this mountain range remains seismic. To quantify the rate of active deformation and the potential for major earthquakes in this region, we combine a structural and quantitative morphological analysis of the Yecheng-Pishan fold, along the topographic mountain front in the epicentral area. Using a seismic profile, we derive a structural cross section in which we identify the fault that broke during the Pishan earthquake, an 8-12 km deep blind ramp beneath the Yecheng-Pishan fold. Combining satellite images and DEMs, we achieve a detailed morphological analysis of the Yecheng-Pishan fold, where we find nine levels of incised fluvial terraces and alluvial fans. From their incision pattern and using age constraints retrieved on some of these terraces from field sampling, we quantify the slip rate on the underlying blind ramp to 0.5 to 2.5 mm/yr, with a most probable long-term value of 2 to 2.5 mm/yr. The evolution of the Yecheng-Pishan fold is proposed by combining all structural, morphological, and chronological observations. Finally, we compare the seismotectonic context of the Western Kunlun to what has been proposed for the Himalayas of Central Nepal. This allows for discussing the possibility of M ≥ 8 earthquakes if the whole decollement across the southern Tarim Basin is seismically locked and ruptures in one single event.

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

NASA Astrophysics Data System (ADS)

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

2017-04-01

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

Further Constraints and Uncertainties on the Deep Seismic Structure of the Moon

NASA Technical Reports Server (NTRS)

Lin, Pei-Ying Patty; Weber, Renee C.; Garnero, Ed J.; Schmerr, Nicholas C.

2011-01-01

The Apollo Passive Seismic Experiment (APSE) consisted of four 3-component seismometers deployed between 1969 and 1972, that continuously recorded lunar ground motion until late 1977. The APSE data provide a unique opportunity for investigating the interior of a planet other than Earth, generating the most direct constraints on the elastic structure, and hence the thermal and compositional evolution of the Moon. Owing to the lack of far side moonquakes, past seismic models of the lunar interior were unable to constrain the lowermost 500 km of the interior. Recently, array methodologies aimed at detecting deep lunar seismic reflections found evidence for a lunar core, providing an elastic model of the deepest lunar interior consistent with geodetic parameters. Here we study the uncertainties in these models associated with the double array stacking of deep moonquakes for imaging deep reflectors in the Moon. We investigate the dependency of the array stacking results on a suite of parameters, including amplitude normalization assumptions, polarization filters, assumed velocity structure, and seismic phases that interfere with our desired target phases. These efforts are facilitated by the generation of synthetic seismograms at high frequencies (approx. 1Hz), allowing us to directly study the trade-offs between different parameters. We also investigate expected amplitudes of deep reflections relative to direct P and S arrivals, including predictions from arbitrarily oriented focal mechanisms in our synthetics. Results from separate versus combined station stacking help to establish the robustness of stacks. Synthetics for every path geometry of data were processed identically to that done with data. Different experiments were aimed at examining various processing assumptions, such as adding random noise to synthetics and mixing 3 components to some degree. The principal stacked energy peaks put forth in recent work persist, but their amplitude (which maps into reflector impedance contrast) and timing (which maps into reflector depth) depend on factors that are not well constrained -- most notably, the velocity structure of the overlying lunar interior. Thus, while evidence for the lunar core remains strong, the depths of imaged reflectors have associated uncertainties that will require new seismic data and observations to constrain. These results strongly advocate further investigations on the Moon to better resolve the interior (e.g., Selene missions), for the Moon apparently has a rich history of construction and evolution that is inextricably tied to that of Earth.

Plate and Plume Flux: Constraints for paleomagnetic reference frames and interpretation of deep mantle seismic heterogeneity. (Invited)

NASA Astrophysics Data System (ADS)

Bunge, H.; Schuberth, B. S.; Shephard, G. E.; Müller, D.

2010-12-01

Plate and plume flow are dominant modes of mantle convection, as pointed out by Geoff Davies early on. Driven, respectively, from a cold upper and a hot lower thermal boundary layer these modes are now sufficiently well imaged by seismic tomographers to exploit the thermal boundary layer concept as an effective tool in exploring two long standing geodynamic problems. One relates to the choice of an absolute reference frame in plate tectonic reconstructions. Several absolute reference frames have been proposed over the last decade, including those based on hotspot tracks displaying age progression and assuming either fixity or motion, as well as palaeomagnetically-based reference frames, a subduction reference frame and hybrid versions. Each reference frame implies a particular history of the location of subduction zones through time and thus the evolution of mantle heterogeneity via mixing of subducted slab material in the mantle. Here we compare five alternative absolute plate motion models in terms of their consequences for deep mantle structure. Taking global paleo-plate boundaries and plate velocities back to 140 Ma derived from the new plate tectonic reconstruction software GPlates and assimilating them into vigorous 3-D spherical mantle circulation models, we infer geodynamic mantle heterogeneity and compare it to seismic tomography for each absolute rotation model. We also focus on the challenging problem of interpreting deep mantle seismic heterogeneity in terms of thermal and compositional variations. Using published thermodynamically self-consistent mantle mineralogy models in the pyrolite composition, we find strong plume flux from the CMB, with a high temperature contrast (on the order of 1000 K) across the lower thermal boundary layer is entirely sufficient to explain elastic heterogeneity in the deep mantle for a number of quantitative measures. A high excess temperatures of +1000--1500 K for plumes in the lowermost mantle is particularly important in understanding the strong seismic velocity reduction mapped by tomography in low-velocity bodies of the deep mantle, as this produces significant negative anomalies of shear wave velocity of up to -4%. We note, however, that our results do not account for the curious observation of seismic anti-correlation, which appears difficult to explain in any case. Our results provide important constraints for the integration of plate tectonics and mantle dynamics and their use in forward and inverse geodynamic mantle models.

Proposed Drill Sites

DOE Data Explorer

Lane, Michael

2013-06-28

Proposed drill sites for intermediate depth temperature gradient holes and/or deep resource confirmation wells. Temperature gradient contours based on shallow TG program and faults interpreted from seismic reflection survey are shown, as are two faults interpreted by seismic contractor Optim but not by Oski Energy, LLC.

Complex local Moho topography in the Western Carpathians: Indication of the ALCAPA and the European Plate contact

NASA Astrophysics Data System (ADS)

Hrubcová, Pavla; Środa, Piotr

2015-01-01

Seismic data from deep refraction and wide-angle reflection profiles intersecting the Western Carpathians show distinct upper-mantle Pn phases with anomalous apparent velocities identified in the first and later arrivals. Their systematic analysis indicates that such phases are present in numerous seismic sections both for in-line and off-line shots. They are observed in data from profiles intersecting the Carpathians in the west at the contact with the Bohemian Massif; similar feature was also found in data at the northern edge of the Carpathians at the contact with the North European Platform. Modelling of these anomalous Pn phases shows that they originate due to local structural anomalies of the Moho discontinuity detected in several places along the Western Carpathian arc. Such anomalies are located in close lateral proximity of the Pieniny Klippen Belt representing the contact between the stable European Plate in the north and the ALCAPA (Alpine-Carpathian-Pannonian) microplate in the south. Thus, the complex local Moho topography modelled from the Pn phases suggests tectonic relation to the formation of the Carpathian orogen. The result is supported by correlation with the large-scale Carpathian conductivity anomaly modelled in the Carpathians at a mid-crustal level. Relative lateral position of these two structures together with the Pieniny Klippen Belt at the surface delineates a zone affected by deformations at various depths along the whole Western Carpathian arc.

The Mesozoic-Cenozoic igneous intrusions and related sediment-dominated hydrothermal activities in the South Yellow Sea Basin, the Western Pacific continental margin

NASA Astrophysics Data System (ADS)

Yumao, Pang; Xunhua, Zhang; Guolin, Xiao; Luning, Shang; Xingwei, Guo; Zhenhe, Wen

2018-04-01

Various igneous complexes were identified in multi-channel seismic reflection profiles from the South Yellow Sea Basin. It is not rare that magmatic intrusions in sedimentary basins cause strong thermal perturbations and hydrothermal activities. Some intrusion-related hydrothermal vent complexes have been identified and they are considered to originate from the deep sedimentary contact aureole around igneous intrusions and terminate in upper vents structures, and are linked by a vertical conduit system. The upper vent complexes are usually eye-shaped, dome-shaped, fault-related, crater-shaped or pock-shaped in seismic profiles. A schematic model was proposed to illustrate the structures of different types of hydrothermal vent complexes. A conceptual conduit model composed of an upper pipe-like part and a lower branching part was also derived. Hydrothermal vent complexes mainly developed during the Middle-Late Cretaceous, which is coeval with, or shortly after the intrusion. The back-arc basin evolution of the area which is related to the subduction of the Paleo-Pacific plate during the Mesozoic-Cenozoic may be the principal factor for voluminous igneous complexes and vent complexes in this area. It is significant to study the characteristics of igneous complexes and related hydrothermal vent complexes, which will have implications for the future study of this area.

Crustal structure in Tengchong Volcano-Geothermal Area, western Yunnan, China

NASA Astrophysics Data System (ADS)

Wang, Chun-Yong; Huangfu, Gang

2004-02-01

Based upon the deep seismic sounding profiles carried out in the Tengchong Volcano-Geothermal Area (TVGA), western Yunnan Province of China, a 2-D crustal P velocity structure is obtained by use of finite-difference inversion and forward travel-time fitting method. The crustal model shows that a low-velocity anomaly zone exists in the upper crust, which is related to geothermal activity. Two faults, the Longling-Ruili Fault and Tengchong Fault, on the profile extend from surface to the lower crust and the Tengchong Fault likely penetrates the Moho. Moreover, based on teleseismic receiver functions on a temporary seismic network, S-wave velocity structures beneath the geothermal field show low S-wave velocity in the upper crust. From results of geophysical survey, the crust of TVGA is characterized by low P-wave and S-wave velocities, low resistivity, high heat-flow value and low Q. The upper mantle P-wave velocity is also low. This suggests presence of magma in the crust derived from the upper mantle. The low-velocity anomaly in upper crust may be related to the magma differentiation. The Tengchong volcanic area is located on the northeast edge of the Indian-Eurasian plate collision zone, away from the eastern boundary of the Indian plate by about 450 km. Based on the results of this paper and related studies, the Tengchong volcanoes can be classified as plate boundary volcanoes.

Dominant seismic sources for the cities in South Sumatra

NASA Astrophysics Data System (ADS)

Sunardi, Bambang; Sakya, Andi Eka; Masturyono, Murjaya, Jaya; Rohadi, Supriyanto; Sulastri, Putra, Ade Surya

2017-07-01

Subduction zone along west of Sumatra and Sumatran fault zone are active seismic sources. Seismotectonically, South Sumatra could be affected by earthquakes triggered by these seismic sources. This paper discussed contribution of each seismic source to earthquake hazards for cities of Palembang, Prabumulih, Banyuasin, OganIlir, Ogan Komering Ilir, South Oku, Musi Rawas and Empat Lawang. These hazards are presented in form of seismic hazard curves. The study was conducted by using Probabilistic Seismic Hazard Analysis (PSHA) of 2% probability of exceedance in 50 years. Seismic sources used in analysis included megathrust zone M2 of Sumatra and South Sumatra, background seismic sources and shallow crustal seismic sources consist of Ketaun, Musi, Manna and Kumering faults. The results of the study showed that for cities relatively far from the seismic sources, subduction / megathrust seismic source with a depth ≤ 50 km greatly contributed to the seismic hazard and the other areas showed deep background seismic sources with a depth of more than 100 km dominate to seismic hazard respectively.

Seismic structure and activity of the north-central Lesser Antilles subduction zone from an integrated approach: Similarities with the Tohoku forearc

NASA Astrophysics Data System (ADS)

Laigle, M.; Hirn, A.; Sapin, M.; Bécel, A.; Charvis, P.; Flueh, E.; Diaz, J.; Lebrun, J.-F.; Gesret, A.; Raffaele, R.; Galvé, A.; Evain, M.; Ruiz, M.; Kopp, H.; Bayrakci, G.; Weinzierl, W.; Hello, Y.; Lépine, J.-C.; Viodé, J.-P.; Sachpazi, M.; Gallart, J.; Kissling, E.; Nicolich, R.

2013-09-01

The 300-km-long north-central segment of the Lesser Antilles subduction zone, including Martinique and Guadeloupe islands has been the target of a specific approach to the seismic structure and activity by a cluster of active and passive offshore-onshore seismic experiments. The top of the subducting plate can be followed under the wide accretionary wedge by multichannel reflection seismics. This reveals the hidden updip limit of the contact of the upper plate crustal backstop onto the slab. Two OBS refraction seismic profiles from the volcanic arc throughout the forearc domain constrain a 26-km-large crustal thickness all along. In the common assumption that the upper plate Moho contact on the slab is a proxy of its downdip limit these new observations imply a three times larger width of the potential interplate seismogenic zone under the marine domain of the Caribbean plate with respect to a regular intra-oceanic subduction zone. Towards larger depth under the mantle corner, the top of the slab imaged from the conversions of teleseismic body-waves and the locations of earthquakes appears with kinks which increase the dip to 10-20° under the forearc domain, and then to 60° from 70 km depth. At 145 km depth under the volcanic arc just north of Martinique, the 2007 M 7.4 earthquake, largest for half a century in the region, allows to document a deep slab deformation consistent with segmentation into slab panels. In relation with this occurrence, an increased seismic activity over the whole depth range provides a new focussed image thanks to the OBS and land deployments. A double-planed dipping slab seismicity is thus now resolved, as originally discovered in Tohoku (NE Japan) and since in other subduction zones. Two other types of seismic activity uniquely observed in Tohoku, are now resolved here: "supraslab" earthquakes with normal-faulting focal mechanisms reliably located in the mantle corner and "deep flat-thrust" earthquakes at 45 km depth on the interplate fault under the Caribbean plate forearc mantle. None such types of seismicity should occur under the paradigm of a regular peridotitic mantle of the upper plate which is expected to be serpentinized by the fluids provided from the dehydrating slab beneath. This process is commonly considered as limiting the downward extent of the interplate coupling. Interpretations are not readily available either for the large crustal thickness of this shallow water marine upper plate, except when remarking its likeness to oceanic plateaus formed above hotspots. The Caribbean Oceanic Plateau of the upper plate has been formed earlier by the material advection from a mantle plume. It could then be underlain by a correspondingly modified, heterogeneous mantle, which may include pyroxenitic material among peridotites. Such heterogeneity in the mantle corner of the present subduction zone may account for the notable peculiarities in seismic structure and activity and impose regions of stick-slip behavior on the interplate among stable-gliding areas.

A recent deep earthquake doublet in light of long-term evolution of Nazca subduction

NASA Astrophysics Data System (ADS)

Zahradník, J.; Čížková, H.; Bina, C. R.; Sokos, E.; Janský, J.; Tavera, H.; Carvalho, J.

2017-03-01

Earthquake faulting at ~600 km depth remains puzzling. Here we present a new kinematic interpretation of two Mw7.6 earthquakes of November 24, 2015. In contrast to teleseismic analysis of this doublet, we use regional seismic data providing robust two-point source models, further validated by regional back-projection and rupture-stop analysis. The doublet represents segmented rupture of a ˜30-year gap in a narrow, deep fault zone, fully consistent with the stress field derived from neighbouring 1976-2015 earthquakes. Seismic observations are interpreted using a geodynamic model of regional subduction, incorporating realistic rheology and major phase transitions, yielding a model slab that is nearly vertical in the deep-earthquake zone but stagnant below 660 km, consistent with tomographic imaging. Geodynamically modelled stresses match the seismically inferred stress field, where the steeply down-dip orientation of compressive stress axes at ˜600 km arises from combined viscous and buoyant forces resisting slab penetration into the lower mantle and deformation associated with slab buckling and stagnation. Observed fault-rupture geometry, demonstrated likelihood of seismic triggering, and high model temperatures in young subducted lithosphere, together favour nanometric crystallisation (and associated grain-boundary sliding) attending high-pressure dehydration as a likely seismogenic mechanism, unless a segment of much older lithosphere is present at depth.

Analysis and Modeling of the Shear Waves Generated by Explosions at the San Andreas Fault Observatory at Depth

DTIC Science & Technology

2012-09-01

09NA29328 Proposal No. BAA09-69 ABSTRACT Using a deep deployment of an 80-element, 3-component borehole seismic array stretching from 1.5 to 2.3...Administration (NNSA). 14. ABSTRACT Using a deep deployment of an 80-element, 3-component borehole seismic array stretching from 1.5 to 2.3 kilometer (km) depth...in the lower half of the borehole array . The strong velocity discontinuity at 2.0 km depth gives rise to another converted S wave, best seen in

Combined seismic and radar investigation to define ice properties and structure of a cold alpine site

NASA Astrophysics Data System (ADS)

Eisen, O.; Bohleber, P.; Drews, R.; Heilig, A.; Hofstede, C.

2009-04-01

The cold alpine saddle Colle Gnifetti, Monte Rosa, Swiss-Italian Alps resembles very much polar and subpolar ice masses in terms of glaciological conditions. It has been the site for several ice-core drilling campaigns over more than 20 years to determine paleoclimatological and glaciological conditions. To investigate the feasibility of geophysical methods for improved characterization of ice masses surrounding borehole and ice-core sites, a combined active reflection seismic and ground-penetrating radar pilot study has been carried out in summer 2008. Aims are the characterization of density, internal layering, seismic and radar wave speed and attenuation, identification of anisotropic features (like crystal orientation or bubble content and shape). Here we present the overall setup and first results. Seismic and GPR profiles were centered on an existing borehole location covering the full ice thickness of 62 m. Active seismics was carried out with 24-channel 3-m spacing recording, using a Seismic Impulse Source System (SISSY) along two profiles parallel and perpendicular to the ice-flow direction. The same profiles were complemented with GPR measurements utilizing 250, 500 MHz frequencies. Additionally, circular profiles with 250, 500 and 800 MHz were carried out circumferencing the borehole to detect anisotropic features.

New seismic observation on the lithosphere and slab subduction beneath the Indo-Myanmar block: Implications for continent oblique subduction and transition to oceanic slab subduction

NASA Astrophysics Data System (ADS)

Jiang, M.; He, Y.; Zheng, T.; Mon, C. T.; Thant, M.; Hou, G.; Ai, Y.; Chen, Q. F.; Sein, K.

2017-12-01

The Indo-Myanmar block locates to the southern and southeastern of the Eastern Himalayan Syntax (EHS) and marks a torsional boundary of the collision between the Indian and Eurasian plates. There are two fundamental questions concerned on the tectonics of Indo-Myanmar block since the Cenozoic time. One is whether and how the oblique subduction is active in the deep; the other is where and how the transition from oceanic subduction and continental subduction operates. However, the two problems are still under heated debate mainly because the image of deep structure beneath this region is still blurring. Since June, 2016, we have executed the China-Myanmar Geophysical Survey in the Myanmar Orogen (CMGSMO) and deployed the first portable seismic array in Myanmar in cooperation with Myanmar Geosciences Society (MGS). This array contains 70 stations with a dense-deployed main profile across the Indo-Myanmar Range, Central Basin and Shan State Plateau along latitude of 22° and a 2-D network covering the Indo-Myanmar Range and the western part of the Central Basin. Based on the seismic data collected by the new array, we conducted the studies on the lithospheric structure using the routine surface wave tomography and receiver function CCP stacking. The preliminary results of surface wave tomography displayed a remarkable high seismic velocity fabric in the uppermost of mantle beneath the Indo-Myanmar Range and Central Basin, which was interpreted as the subducted slab eastward. Particularly, we found a low velocity bulk within the high-velocity slab, which was likely to be a slab window due to the slab tearing. The preliminary results of receiver function CCP stacking showed the obvious variations of the lithospheric structures from the Indo-Myanmar Range to the Central Basin and Shan State Plateau. The lithospheric structure beneath the Indo-Myanmar Range is more complex than that beneath the Central Basin and Shan State Plateau. Our resultant high-resolution images will provide important constrains for establishing the tectonic framework of Indian plate eastward subduction. This study is supported by the National Natural Science Foundation of China (grants 41490612, 41274002).

Large-scale Mass Transport Deposits in the Valencia Basin (Western Mediterranean): slope instability induced by rapid sea-level drawdown?

NASA Astrophysics Data System (ADS)

Cameselle, Alejandra L.; Urgeles, Roger; Llopart, Jaume

2014-05-01

The Messinian Salinity Crisis (MSC) strongly affected the physiography of the Mediterranean margins at the end of the Miocene. The sharp sea-level fall gave a new configuration to the Mediterranean basin and created dramatic morphological and sedimentological changes: margins have been largely eroded whereas the deep basins accumulated thick evaporitic and detrital units. Amongst these detrital units, there are evidences on seismic reflection data for major large-scale slope failure of the Mediterranean continental margins. About 2700 km of seismic reflection profiles in the southwestern part of the Valencia Basin (Western Mediterranean) have enabled us the detailed mapping of distinctive Messinian erosional surfaces, evaporites and deep detrital deposits. The detrital deposits occur in a distinct unit that is made of chaotic, roughly-bedded or transparent seismic bodies, which have been mainly mapped in the basin domain. Locally, the seismic unit shows discontinuous high-amplitude reflections and/or an imbricate internal structure. This unit is interpreted to be formed by a series of Mass Transport Deposits (MTDs). Rapid drawdown has long been recognized as one of the most severe loadings conditions that a slope can be subjected to. Several large historical slope failures have been documented to occur due to rapid drawdown in dams, riverbanks and slopes. During drawdown, the stabilizing effect of the water on the upstream face is lost, but the pore-water pressures within the slope may remain high. The dissipation of these pore pressures in the slope is controlled by the permeability and the storage characteristics of the slope sediments. We hypothesize that the MTDs observed in our data formed under similar conditions and represent a large-scale equivalent of this phenomenon. Therefore, these MTDs can be used to put some constraints on the duration of the drawdown phase of the MSC. We have performed a series of slope stability analysis under rapid Messinian sea-level drawdown using slope geotechnical properties and pre-conditioning factors related to the geological setting of the Valencia Basin. Using several sea-level fall ratios, the variation of the safety factor with respect to successive positions of the sea-level during drawdown has been evaluated.

A wave equation migration method for receiver function imaging: 2. Application to the Japan subduction zone

NASA Astrophysics Data System (ADS)

Chen, Ling; Wen, Lianxing; Zheng, Tianyu

2005-11-01

The newly developed wave equation poststack depth migration method for receiver function imaging is applied to study the subsurface structures of the Japan subduction zone using the Fundamental Research on Earthquakes and Earth's Interior Anomalies (FREESIA) broadband data. Three profiles are chosen in the subsurface imaging, two in northeast (NE) Japan to study the subducting Pacific plate and one in southwest (SW) Japan to study the Philippine Sea plate. The descending Pacific plate in NE Japan is well imaged within a depth range of 50-150 km. The slab image exhibits a little more steeply dipping angle (˜32°) in the south than in the north (˜27°), although the general characteristics between the two profiles in NE Japan are similar. The imaged Philippine Sea plate in eastern SW Japan, in contrast, exhibits a much shallower subduction angle (˜19°) and is only identifiable at the uppermost depths of no more than 60 km. Synthetic tests indicate that the top 150 km of the migrated images of the Pacific plate is well resolved by our seismic data, but the resolution of deep part of the slab images becomes poor due to the limited data coverage. Synthetic tests also suggest that the breakdown of the Philippine Sea plate at shallow depths reflects the real structural features of the subduction zone, rather than caused by insufficient coverage of data. Comparative studies on both synthetics and real data images show the possibility of retrieval of fine-scale structures from high-frequency contributions if high-frequency noise can be effectively suppressed and a small bin size can be used in future studies. The derived slab geometry and image feature also appear to have relatively weak dependence on overlying velocity structure. The observed seismicity in the region confirms the geometries inferred from the migrated images for both subducting plates. Moreover, the deep extent of the Pacific plate image and the shallow breakdown of the Philippine Sea plate image are observed to correlate well with the depth extent of the seismicity beneath NE and SW Japan. Such a correlation supports the inference that the specific appearance of slabs and intermediate-depth earthquakes are a consequence of temperature-dependent dehydration induced metamorphism occurring in the hydrated descending oceanic crust.

Along-axis variability in crustal accretion at the Mid-Atlantic Ridge: Results from the OCEAN study

USGS Publications Warehouse

Henstock, T.J.; White, Robert S.; McBride, J.H.

1996-01-01

The OCEAN experiment is an integrated geophysical study of a region of the Cape Verde abyssal plain that formed at 140 Ma. Deep seismic reflection and ocean bottom hydrophone (OBH) refraction data were acquired along lines parallel and perpendicular to the paleoridge axis trend identified from a detailed magnetic anomaly survey. The igneous basement is overlain by about 1.3 km of sediment which enables improved imaging of intracrustal structure beyond that possible near the Mid-Atlantic Ridge axis. We describe the results of a 150-km long profile oriented parallel to magnetic anomalies M15 and M16, along which deep seismic reflection data collected by the British Institutions Reflection Profiling Syndicate are complemented by refraction data constrained by four OBHs. The line spans an entire spreading segment between two fracture zones; the northern of which has an offset of 40 km and the other (central) has an offset of only 10 km. Away from the fracture zones, the mean igneous crustal thickness is 7.2 km; near both fracture zones, thinning of up to 4 km is observed, giving a mean igneous crustal thickness over the whole segment of approximately 6.5 km. Differences are seen between the two fracture zones in their seismic velocity structure, in the associated basement topography, and in the presence of a strong reflection extending into the mantle beneath the northern fracture zone. The boundary between oceanic layers 2 and 3 correlates with variably coherent normal incidence reflections and a change in the character of the reflectivity. A number of planar reflections up to 10 km in length are present within the middle and lower crust, dipping outward from beneath low-amplitude basement highs at ??? 15??; these appear to be present only within layer 3. The Moho has several expressions in the reflection data, including isolated reflection events, a local increase in reflected amplitudes, and a downward decrease in coherent reflections. At the center of the segment there is a zone at the base of the crust within which both high- and low-velocity materials are present. This zone shows an enhanced level of discontinuous normal incidence reflectivity and may represent an initial fractionation event as melt was emplaced at the spreading ridge.

Constraints on Lunar Structure from Combined Geochemical, Mineralogical, and Geophysical modeling

NASA Astrophysics Data System (ADS)

Bremner, P. M.; Fuqua, H.; Mallik, A.; Diamond, M. R.; Lock, S. J.; Panovska, S.; Nishikawa, Y.; Jiménez-Pérez, H.; Shahar, A.; Panero, W. R.; Lognonne, P. H.; Faul, U.

2016-12-01

The internal physical and geochemical structure of the Moon is still poorly constrained. Here, we take a multidisciplinary approach to attempt to constrain key parameters of the lunar structure. We use an ensemble of 1-D lunar compositional models with chemically and mineralogically distinct layers, and forward calculated physical parameters, in order to constrain the internal structure. We consider both a chemically well-mixed model with uniform bulk composition, and a chemically stratified model that includes a mantle with preserved mineralogical stratigraphy from magma ocean crystallization. Additionally, we use four different lunar temperature profiles that span the range of proposed selenotherms, giving eight separate sets of lunar models. In each set, we employed a grid search and a differential evolution genetic search algorithm to extensively explore model space, where the thickness of individual compositional layers was varied. In total, we forward calculated over one hundred thousand lunar models. It has been proposed that a dense, partially molten layer exists at the CMB to explain the lack of observed far-side deep moonquakes, the observation of reflected seismic phases from deep moonquakes, and enhanced tidal dissipation. However, subsequent models have proposed that these observables can be explained in other ways. In this study, using a variety of modeling techniques, we find that such a layer may have been formed by overturn of an ilmenite-rich layer, formed after the crystallization of a magma ocean. We therefore include a denser layer (modeled as an ilmenite-rich layer) at both the top and bottom of the lunar mantle in our models. For each set of models, we find models that explain the observed lunar mass and moment of inertia. We find that only a narrow range of core radii are consistent with the mass and moment of inertia constraints. Furthermore, in the chemically well-mixed models, we find that a dense layer is required in the upper mantle to meet the moment of inertia requirement. In no set of models is the mass of the lower dense layer well constrained. For the models that fit the observed mass and moment of inertia, we calculated 1-D seismic velocity profiles, the majority of which compare well with those determined by inverting the Apollo seismic data (Garcia et al., 2011 and Weber et al., 2011).

Lithology of the long sediment record recovered by the ICDP Dead Sea Deep Drilling Project (DSDDP)

NASA Astrophysics Data System (ADS)

Neugebauer, Ina; Brauer, Achim; Schwab, Markus J.; Waldmann, Nicolas D.; Enzel, Yehouda; Kitagawa, Hiroyuki; Torfstein, Adi; Frank, Ute; Dulski, Peter; Agnon, Amotz; Ariztegui, Daniel; Ben-Avraham, Zvi; Goldstein, Steven L.; Stein, Mordechai

2014-10-01

The sedimentary sections that were deposited from the Holocene Dead Sea and its Pleistocene precursors are excellent archives of the climatic, environmental and seismic history of the Levant region. Yet, most of the previous work has been carried out on sequences of lacustrine sediments exposed at the margins of the present-day Dead Sea, which were deposited only when the lake surface level rose above these terraces (e.g. during the Last Glacial period) and typically are discontinuous due to major lake level variations in the past. Continuous sedimentation can only be expected in the deepest part of the basin and, therefore, a deep drilling has been accomplished in the northern basin of the Dead Sea during winter of 2010-2011 within the Dead Sea Deep Drilling Project (DSDDP) in the framework of the ICDP program. Approximately 720 m of sediment cores have been retrieved from two deep and several short boreholes. The longest profile (5017-1), revealed at a water depth of ˜300 m, reaches 455 m below the lake floor (blf, i.e. to ˜1175 m below global mean sea level) and comprises approximately the last 220-240 ka. The record covers the upper part of the Amora (penultimate glacial), the Last Interglacial Samra, the Last Glacial Lisan and the Holocene Ze'elim Formations and, therewith, two entire glacial-interglacial cycles. Thereby, for the first time, consecutive sediments deposited during the MIS 6/5, 5/4 and 2/1 transitions were recovered from the Dead Sea basin, which are not represented in sediments outcropping on the present-day lake shores. In this paper, we present essential lithological data including continuous magnetic susceptibility and geochemical scanning data and the basic stratigraphy including first chronological data of the long profile (5017-1) from the deep basin. The results presented here (a) focus on the correlation of the deep basin deposits with main on-shore stratigraphic units, thus providing a unique comprehensive stratigraphic framework for regional paleoenvironmental reconstruction, and (b) highlight the outstanding potential of the Dead Sea deep sedimentary archive to record hydrological changes during interglacial, glacial and transitional intervals.

3-D architecture modeling using high-resolution seismic data and sparse well control: Example from the Mars {open_quotes}Pink{close_quotes} reservoir, Mississippi Canyon Area, Gulf of Mexico

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

Chapin, M.A.; Tiller, G.M.; Mahaffie, M.J.

1996-12-31

Economic considerations of the deep-water turbidite play, in the Gulf of Mexico and elsewhere, require large reservoir volumes to be drained by relatively few, very expensive wells. Deep-water development projects to date have been planned on the basis of high-quality 3-D seismic data and sparse well control. The link between 3-D seismic, well control, and the 3-D geological and reservoir architecture model are demonstrated here for Pliocene turbidite sands of the {open_quotes}Pink{close_quotes} reservoir, Prospect Mars, Mississippi Canyon Areas 763 and 807, Gulf of Mexico. This information was used to better understand potential reservoir compartments for development well planning.

Deep crustal structure of the northeastern margin of the Arabian plate from seismic and gravity data

NASA Astrophysics Data System (ADS)

Pilia, Simone; Ali, Mohammed; Watts, Anthony; Keats, Brook; Searle, Mike

2017-04-01

The United Arab Emirates-Oman mountains constitute a 700 km long, 50 km wide compressional orogenic belt that developed during the Cainozoic on an underlying extensional Tethyan rifted margin. It contains the world's largest and best-exposed thrust sheet of oceanic crust and upper mantle (Semail Ophiolite), which was obducted onto the Arabian rifted continental margin during the Late Cretaceous. Although the shallow structure of the UAE-Oman mountain belt is reasonably well known through the exploitation of a diverse range of techniques, information on deeper structure remains little. Moreover, the mechanisms by which dense oceanic crustal and mantle rocks are emplaced onto less dense and more buoyant continental crust are still controversial and remain poorly understood. The focus here is on an active-source seismic and gravity E-W transect extending from the UAE-mountain belt to the offshore. Seismic refraction data were acquired using the survey ship M/V Hawk Explorer, which was equipped with a large-volume airgun array (7060 cubic inches, 116 liters). About 400 air gun shots at 50-second time interval were recorded on land by eight broadband seismometers. In addition, reflection data were acquired at 20 seconds interval and recorded by a 5-km-long multichannel streamer. Results presented here include an approximately 85 km long (stretching about 35 km onshore and 50 km offshore) P-wave velocity crustal profile derived by a combination of forward modelling and inversion of both diving and reflected wave traveltimes using RAYINVR software. We employ a new robust algorithm based on a Monte Carlo approach (VMONTECARLO) to address the velocity model uncertainties. We find ophiolite seismic velocities of about 5.5 km/s and a thick sedimentary package in the offshore. Furthermore, the velocity model reveals a highly stretched crust with the Moho discontinuity lying at about 20 km. A prestack depth-migrated profile (about 50 km long) coincident with the offshore part of the refraction profile shows a thick sequence (up to about 10 km) of seaward dipping sediments that are offset by a number of listric (normal) faults, some of which intersect the seabed and so reflect recent tectonic activity. The trend of the Bouguer anomaly provides further constraints on the deeper structure of the margin and appears to confirm the presence of a stretched crust.

Deep crustal structure of the UAE-Oman mountain belt from seismic and gravity data

NASA Astrophysics Data System (ADS)

Pilia, S.; Tanveer, M.; Ali, M.; Watts, A. B.; Searle, M. P.; Keats, B. S.

2016-12-01

The UAE-Oman mountains constitute a 700 km long, 50 km wide compressional orogenic belt that developed during the Cenozoic on an underlying extensional Tethyan rifted margin. It contains the world's largest and best-exposed thrust sheet of oceanic crust and upper mantle (Semail Ophiolite), which was obducted onto the Arabian rifted continental margin during the Late Cretaceous. Although the shallow structure of the UAE-Oman mountain belt is reasonably well known through the exploitation of a diverse range of techniques, information on deeper structure remains little. Moreover, the mechanisms by which dense oceanic crustal and mantle rocks are emplaced onto less dense and more buoyant continental crust are still controversial and remain poorly understood. The focus here is on an active-source seismic and gravity E-W transect extending from the UAE-mountain belt to the offshore. Seismic refraction data were acquired using the survey ship M/V Hawk Explorer, which was equipped with a large-volume airgun array (116 liters). About 400 air gun shots at 50-second time interval were recorded on land by eight broadband seismometers. In addition, reflection data were acquired at 20 seconds interval and recorded by a 5-km-long multichannel streamer. Results presented here include an approximately 85 km long (stretching about 35 km onshore and 50 km offshore) P-wave velocity crustal profile derived by a combination of forward modelling and inversion of both diving and reflected wave traveltimes using RAYINVR software. We employ a new robust algorithm based on a Monte Carlo approach (VMONTECARLO) to address the velocity model uncertainties. We find ophiolite seismic velocities of about 5.5 km/s, underlain by a thin layer of slower material (about 4.5 km/s). Furthermore, the velocity model reveals a Moho depth that rises from ca 30 km in the west to ca 20 km in the east. A poststack depth-migrated profile (about 50 km long) coincident with the offshore part of the refraction profile shows a thick sequence (up to 6 km) of seaward dipping sediments that are offset by a number of listric (normal) faults, some of which intersect the seabed and so reflect recent tectonic activity. The trend of the Bouguer anomaly provides further constraints on the deeper structure of the margin and appears to confirm the presence of a stretched crust.

Mantle wedge structure beneath the Yamato Basin, southern part of the Japan Sea, revealed by long-term seafloor seismic observations

NASA Astrophysics Data System (ADS)

Shinohara, M.; Nakahigashi, K.; Yamashita, Y.; Yamada, T.; Mochizuki, K.; Shiobara, H.

2016-12-01

The Japanese Islands are located at subduction zones where Philippine Sea (PHS) plate subducts from the southeast beneath the Eurasian plate and the Pacific plate descends from the east beneath the PHS and Eurasian plates and have a high density of seismic stations. Many seismic tomography studies using land seismic station data were conducted to reveal the seismic structure. These studies discussed the relationship between heterogeneous structures and the release of fluids from the subducting slab, magma generation and movement in the subduction zone. However, regional tomography using the land station data did not have a sufficient resolution to image a deep structure beneath the Japan Sea.To obtain the deep structure, observations of natural earthquakes within the Japan Sea are essential. Therefore, we started the repeating long-term seismic observations using ocean bottom seismometers(OBSs) in the Yamato Basin from 2013 to 2016. We apply travel-time tomography method to the regional earthquake and teleseismic arrival-data recorded by OBSs and land stations. In this presentation, we will report the P and S wave tomographic images down to a depth of 300 km beneath the southern part of the Japan Sea. This study was supported by "Integrated Research Project on Seismic and Tsunami Hazards around the Sea of Japan" conducted by the Ministry of Education, Culture, Sports, Science, and Technology (MEXT) of Japan.

Broadband calibration of the R/V Marcus G. Langseth four-string seismic sources

NASA Astrophysics Data System (ADS)

Tolstoy, M.; Diebold, J.; Doermann, L.; Nooner, S.; Webb, S. C.; Bohnenstiehl, D. R.; Crone, T. J.; Holmes, R. C.

2009-08-01

The R/V Marcus G. Langseth is the first 3-D seismic vessel operated by the U.S. academic community. With up to a four-string, 36-element source and four 6-km-long solid state hydrophone arrays, this vessel promises significant new insights into Earth science processes. The potential impact of anthropogenic sound sources on marine life is an important topic to the marine seismic community. To ensure that operations fully comply with existing and future marine mammal permitting requirements, a calibration experiment was conducted in the Gulf of Mexico in 2007-2008. Results are presented from deep (˜1.6 km) and shallow (˜50 m) water sites, obtained using the full 36-element (6600 cubic inches) seismic source. This array configuration will require the largest safety radii, and the deep and shallow sites provide two contrasting operational environments. Results show that safety radii and the offset between root-mean-square and sound exposure level measurements were highly dependent on water depth.

Multi-scale mass movements: example of the Nile deep-sea fan (NDSF)

NASA Astrophysics Data System (ADS)

Loncke, L.; Droz, L.; Bellaiche, G.; Gaullier, V.; Mascle, J.; Migeon, S.

2003-04-01

The almost 90 000 km2 NDSF, fed by one of the major river in the world, has been nearly entirely surveyed by swath bathymetry and back-scatter imagery during the last four years. Seismic-reflection and 3-5 kHz profiles, and in some places, high resolution data were collected. Some profiles have been provided by BP-Egypt. Using this set of data, we have conducted a multi-scale regional synthesis which stresses the importance of gravity processes in the edification and evolution of this major deep turbidite system. Gravity processes range from regional gravity-driven spreading and gliding of the Plio-Pleistocene sediments above the Messinian mobile evaporites, to huge collapses of large areas of the upper continental slope as well as very localized levee destabilizations and related avulsion mechanisms. The Eastern - tectonized - area of the NDSF is characterized by lens-shaped transparent bodies, likely indicating debris-flow deposits, settled at crestal graben flanks, themselves generated by reactive diapir rise. Debris flows are probably triggered by local readjustments of salt-related tectonic features destabilizing their sedimentary cover. In contrast, within the poorly deformed Western part of the NDSF, we mainly observe recent slumping and gliding phenomenons, incising the upper slope where salt layers are absent. These slumps and glidings evolved downslope to large debris flows. Some of them exhibit volumes up to 1900 km3 and are covered by recent stacked channel-levees units. Smaller scale debris-flows are inter-fingered within these constructional units and led to numerous channel migrations and avulsions, characterized by typical HARP's seismic facies. Recent sedimentary destabilizations seem to be associated with gas seeping or under-compacted mud ascents: in the Central NDSF, the association between pock-marks (or mounds) and destabilizated masses suggest the existence of gas hydrates. Given the variety of processes (either triggered by tectonics, sedimentary overloading, sea-level fluctations, or fluids) and scales of the identified destabilizations, the NDSF appears as an excellent natural laboratory to study mass movement processes.

Magnetic signature of the Sicily Channel volcanism

NASA Astrophysics Data System (ADS)

Lodolo, E.; Civile, D.; Zanolla, C.; Geletti, R.

2012-03-01

Widespread Late Miocene to Quaternary volcanic activity is know to have occurred in the Sicily Channel continuing up to historical time. New magnetic anomaly data acquired in the Pantelleria Graben, one of the three main tectonic depressions forming the WNW-trending Sicily Channel rift system, integrated with available profiles, are used to identify and map volcanic bodies in this sector of the northern African margin. Some of these manifestations, both outcropping at the sea-floor or buried beneath a variable thickness of Plio-Quaternary sedimentary cover, have been imaged by seismic reflection profiles. Three main positive magnetic anomalies have been found: to the S-E of the Pantelleria Island, the largest emerged caldera of the Sicily Channel, along the eastern margin of the Nameless Bank, and at the north-western termination of the Linosa Graben. Only the anomaly located off the south-eastern coast of the Pantelleria Island, associated with a large outcropping body gradually buried beneath a substantially undisturbed Upper Pliocene-Quaternary sediments, aligns with the trend of the tectonic depression. 2-D geophysical models produced along seismic transects perpendicularly crossing the Pantelleria Graben have allowed to derive its deep crustal structure, and detect the presence of buried magmatic bodies which generate the anomalies. Marginal faults seem to have played a major role in focussing magma emplacement in this sector of the Sicily Channel. The other anomalies represent off-axis volcanic episodes and generally do not show evident magmatic manifestations at the sea-floor. These magnetic maxima seem to follow a NNE-SSW-trending belt extending from Linosa Island to the Nameless Bank, where pre-existing crustal anisotropies may have conditioned magma emplacement both at deep and shallow crustal levels. In general, data analysis has shown that there is a structural control on magma emplacement, with the major magmatic features located in specific locations like boundary faults and transfer zones, in a manner similar to that found along several segments of the East African Rift system.

Oligocene to Holocene sediment drifts and bottom currents on the slope of Gabon continental margin (west Africa). Consequences for sedimentation and southeast Atlantic upwelling

NASA Astrophysics Data System (ADS)

Séranne, Michel; Nzé Abeigne, César-Rostand

1999-10-01

Seismic reflection profiles on the slope of the south Gabon continental margin display furrows 2 km wide and some 200 m deep, that develop normal to the margin in 500-1500 m water depth. Furrows are characterised by an aggradation/progradation pattern which leads to margin-parallel, northwestward migration of their axes through time. These structures, previously interpreted as turbidity current channels, display the distinctive seismic image and internal organisation of sediment drifts, constructed by the activity of bottom currents. Sediment drifts were initiated above a major Oligocene unconformity, and they developed within a Oligocene to Present megasequence of general progradation of the margin, whilst they are markedly absent from the underlying Late Cretaceous-Eocene aggradation megasequence. The presence of upslope migrating sediment waves, and the northwest migration of the sediment drifts indicate deposition by bottom current flowing upslope, under the influence of the Coriolis force. Such landwards-directed bottom currents on the slope probably represent coastal upwelling, which has been active along the west Africa margin throughout the Neogene.

Electrical conductivity structure of the mantle derived from inversion of geomagnetic observatory data: implications for lateral variations in temperature, composition and water content.

NASA Astrophysics Data System (ADS)

Munch, Federico; Grayver, Alexander; Khan, Amir; Kuvshinov, Alexey

2017-04-01

As most of Earth's interior remains geochemically unsampled, geophysical techniques based on seismology, geodesy, gravimetry, and electromagnetic studies play prominent roles because of their ability to sense structure at depth. Although seismic tomography maps show a variety of structures, separating thermal and compositional contributions from seismic velocities alone still remains a challenging task. Alternatively, as electrical conductivity is sensitive to temperature, chemical composition, oxygen fugacity, water content, and the presence of melt, it can serve for determining chemistry, mineralogy, and physical structure of the deep mantle. In this work we estimate and invert local C-responses (period range 3-100 days) for a number of worldwide geomagnetic observatories to map lateral variations of electrical conductivity in Earth's mantle (400-1600 km depth). The obtained conductivity profiles are interpreted in terms of basalt fraction in a basalt-harzburgite mixture, temperature structure, and water content variations. Interpretation is based on a self-consistent thermodynamic calculation of mineral phase equilibria, electrical conductivity databases, and probabilistic inverse methods.

Humboldt slide - A large shear-dominated retrogressive slope failure

USGS Publications Warehouse

Gardner, J.V.; Prior, D.B.; Field, M.E.

1999-01-01

Humboldt Slide is a large, complex slide zone located on the northern California continental margin. Its three-dimensional architecture has been imaged by a combination of multibeam bathymetry, Huntec Deep-Tow seismic profiling, and sidescan sonar. The slide is interpreted to be Late Pleistocene to early Holocene in age and was caused by a combination of factors. The area of the slide is a local depocenter with high accumulation rates of organic-rich sediment; there has been local steepening of slopes by tectonic uplifts; and the entire area is one of high seismicity. Overall, the failure occurred by retrogressive, shear-dominated, minimum movement apparently as a sequence of events. Failure initially occurred by subsidence extension at the middle of the feature, followed by upslope retrogressive failure and downslope compression, and finally by translational sliding at the top of the slide. Degassing, as evidenced by abundant pockmarks, may have inhibited downslope translation. The slide may still be active, as suggested by offsets in Holocene hemipelagic sediment draped over some of the shear surfaces. Crown cracks occur above the present head of the failure and may represent the next generation of failure.

An Amphibious Seismic Study of the Crustal Structure of the Adriatic Microplate

NASA Astrophysics Data System (ADS)

Dannowski, A.; Kopp, H.; Schurr, B.; Improta, L.; Papenberg, C. A.; Krabbenhoeft, A.; Argnani, A.; Ustaszewski, K. M.; Handy, M.; Glavatovic, B.

2016-12-01

The present-day structure of the southern Adriatic area is controlled by two oppositely-vergent fold-and-thrust belt systems (Apennines and Dinarides). The Adriatic continental domain is one of the most enigmatic segments of the Alpine-Mediterranean collision zone. It separated from the African plate during the Mesozoic extensional phase that led to the opening of the Ionian Sea. Basin widening and deepening peaked during Late Triassic-Liassic extension, resulting in the formation of the southern Adriatic basin, bounded on either side by the Dinaric and Apulian shallow water carbonate platforms. Because of its present foreland position with respect to the Dinaric part of orogenic belt, the southern Adriatic basin represents the only remnant of the Neotethyan margin and offers the unique opportunity to image a segment of Mesozoic passive margin in the Mediterranean. To study the deep crustal structure, the upper mantle and the shape of the plate margin, the German research vessel Meteor acquired 2D seismic refraction and wide-angle reflection data during an onshore-offshore experiment (cruise M86-3). We present two profiles: Profile P03 crossed Adria from the Gargano Promontory into Albania. A second profile (P01) was shot parallel to the coastlines, extending from the southern Adriatic basin to a possible mid-Adriatic strike-slip fault that purportedly segments the Adriatic microplate. Two different approaches of travel time tomography are applied to the data set: A non-linear approach is used for the shorter profile P01. A linear approach is applied to profile P03 (360 km length) and allows for the integration of the 36 ocean bottom stations and 19 land stations. First results show a good resolution of the sedimentary part of the Adriatic region. The depth of the basement as well as the depth of the Moho discontinuity vary laterally and deepen towards the North-East, consistent with the notion of flexural loading of the externally propagating orogenic wedge of the Dinarides.

The isolated ˜680 km deep 30 May 2015 MW 7.9 Ogasawara (Bonin) Islands earthquake

NASA Astrophysics Data System (ADS)

Ye, Lingling; Lay, Thorne; Zhan, Zhongwen; Kanamori, Hiroo; Hao, Jin-Lai

2016-01-01

Deep-focus earthquakes, located in very high-pressure conditions 300 to 700 km below the Earth's surface within sinking slabs of relatively cold oceanic lithosphere, are mysterious phenomena. The largest recorded deep-focus earthquake (MW 7.9) in the Izu-Bonin slab struck on 30 May 2015 beneath the Ogasawara (Bonin) Islands, isolated from prior seismicity by over 100 km in depth, and followed by only a few small aftershocks. Globally, this is the deepest (680 km centroid depth) event with MW ≥ 7.8 in the seismological record. Seismicity indicates along-strike contortion of the Izu-Bonin slab, with horizontal flattening near a depth of 550 km in the Izu region and rapid steepening to near-vertical toward the south above the location of the 2015 event. This event was exceptionally well-recorded by seismic stations around the world, allowing detailed constraints to be placed on the source process. Analyses of a large global data set of P, SH and pP seismic phases using short-period back-projection, subevent directivity, and broadband finite-fault inversion indicate that the mainshock ruptured a shallowly-dipping fault plane with patchy slip that spread over a distance of ∼40 km with a multi-stage expansion rate (∼ 5 + km /s down-dip initially, ∼3 km/s up-dip later). During the 17 s total rupture duration the radiated energy was ∼ 3.3 ×1016 J and the stress drop was ∼38 MPa. The radiation efficiency is moderate (0.34), intermediate to that of the 1994 Bolivia and 2013 Sea of Okhotsk MW 8.3 deep earthquakes, indicating that source processes of very large deep earthquakes sample a wide range of behavior from dissipative, more viscous failure to very brittle failure. The isolated occurrence of the event, much deeper than the apparently thermally-bounded distribution of Bonin-slab seismicity above 600 km depth, suggests that localized stress concentration associated with the pronounced deformation of the Izu-Bonin slab and proximity to the 660-km phase transition likely played a dominant role in generating this major earthquake.

Source and Aftershock Analysis of a Large Deep Earthquake in the Tonga Flat Slab

NASA Astrophysics Data System (ADS)

Cai, C.; Wiens, D. A.; Warren, L. M.

2013-12-01

The 9 November 2009 (Mw 7.3) deep focus earthquake (depth = 591 km) occurred in the Tonga flat slab region, which is characterized by limited seismicity but has been imaged as a flat slab in tomographic imaging studies. In addition, this earthquake occurred immediately beneath the largest of the Fiji Islands and was well recorded by a temporary array of 16 broadband seismographs installed in Fiji and Tonga, providing an excellent opportunity to study the source mechanism of a deep earthquake in a partially aseismic flat slab region. We determine the positions of main shock hypocenter, its aftershocks and moment release subevents relative to the background seismicity using a hypocentroidal decomposition relative relocation method. We also investigate the rupture directivity by measuring the variation of rupture durations at different azimuth [e.g., Warren and Silver, 2006]. Arrival times picked from the local seismic stations together with teleseismic arrival times from the International Seismological Centre (ISC) are used for the relocation. Teleseismic waveforms are used for directivity study. Preliminary results show this entire region is relatively aseismic, with diffuse background seismicity distributed between 550-670 km. The main shock happened in a previously aseismic region, with only 1 small earthquake within 50 km during 1980-2012. 11 aftershocks large enough for good locations all occurred within the first 24 hours following the earthquake. The aftershock zone extends about 80 km from NW to SE, covering a much larger area than the mainshock rupture. The aftershock distribution does not correspond to the main shock fault plane, unlike the 1994 March 9 (Mw 7.6) Fiji-Tonga earthquake in the steeply dipping, highly seismic part of the Tonga slab. Mainshock subevent locations suggest a sub-horizontal SE-NW rupture direction. However, the directivity study shows a complicated rupture process which could not be solved with simple rupture assumption. We will present the result of this example earthquake and some other deep earthquakes at the fall meeting. Warren, L. M., and P. G. Silver (2006), Measurement of differential rupture durations as constraints on the source finiteness of deep earthquakes, J. Geophys. Res., 111, B06304, doi:10.1029/2005JB004001.

A Closer Look at Recent Deep Mauna Loa Seismicity

NASA Astrophysics Data System (ADS)

Okubo, P. G.; Wolfe, C. J.; Nakata, J. S.; Koyanagi, S. K.; Uribe, J. O.

2005-12-01

In 2002, Mauna Loa Volcano showed signs of reawakening, some 18 years since its last eruption in 1984. First, in April, a brief flurry of microearthquakes occurred at cataloged depths from 25 to 55 km beneath Mauna Loa's summit caldera. Then in May 2002, after the microearthquake swarm had ended, geodetic monitors across Mauna Loa's summit caldera registered a change, from line-length shortening to extension, interpreted as reinflation of a magma body approximately 4 km beneath the volcano's summit. Accordingly, the Hawaiian Volcano Observatory issued advisories related to Mauna Loa's stirring. In July 2004, HVO began to record deep long-period (LP) earthquakes beneath Mauna Loa. Historically, interpretations of such seismicity patterns have associated LP source volumes with magma chambers and magma pathways. Over a few weeks, this seismicity dramatically jumped to levels of several dozen per day. Between the months of July and December 2004, nearly 2000 Mauna Loa LPs were located between roughly 25 km and greater than 60 km depths by HVO seismic analysts. In late December, these earthquakes rather abruptly ceased, and their levels have remained low ever since. We seek a more detailed understanding of how these earthquakes may factor into Mauna Loa's eruptive framework. Given that their first arrivals are typically emergent, hypocentral estimates using only P-wave first-arrival times of LP earthquakes are often marginally constrained. With such hypocentral estimates, it is difficult to establish clear relationships among the earthquake locations themselves, or between the earthquakes and other processes like crustal extension or magma accumulation or withdrawl. Building on earlier applications to deep earthquakes in Hawaii and LP earthquakes beneath Kilauea, we are reexamining this unprecedented Mauna Loa deep seismicity with waveform correlation and precise earthquake relocation techniques. Work to date reveals that, although the waveform correlation coefficients are low, a significant subset of the deep Mauna Loa LPs can be relocated to improve our understanding of the remarkable 2004 swarm. We are currently seeking stronger resolution to determine whether the waveform data are consistent with the vertically extended, conduit-like source distributions suggested by the catalog locations or, alternatively, whether the events are consistent with one or more narrowly extended point sources.

Seismic Prediction While Drilling (SPWD): Seismic exploration ahead of the drill bit using phased array sources

NASA Astrophysics Data System (ADS)

Jaksch, Katrin; Giese, Rüdiger; Kopf, Matthias

2010-05-01

In the case of drilling for deep reservoirs previous exploration is indispensable. In recent years the focus shifted more on geological structures like small layers or hydrothermal fault systems. Beside 2D- or 3D-seismics from the surface and seismic measurements like Vertical Seismic Profile (VSP) or Seismic While Drilling (SWD) within a borehole these methods cannot always resolute this structures. The resolution is worsen the deeper and smaller the sought-after structures are. So, potential horizons like small layers in oil exploration or fault zones usable for geothermal energy production could be failed or not identified while drilling. The application of a device to explore the geology with a high resolution ahead of the drill bit in direction of drilling would be of high importance. Such a device would allow adjusting the drilling path according to the real geology and would minimize the risk of discovery and hence the costs for drilling. Within the project SPWD a device for seismic exploration ahead of the drill bit will be developed. This device should allow the seismic exploration to predict areas about 50 to 100 meters ahead of the drill bit with a resolution of one meter. At the GFZ a first prototype consisting of different units for seismic sources, receivers and data loggers has been designed and manufactured. As seismic sources four standard magnetostrictive actuators and as receivers four 3-component-geophones are used. Every unit, actuator or geophone, can be rotated in steps of 15° around the longitudinal axis of the prototype to test different measurement configurations. The SPWD prototype emits signal frequencies of about 500 up to 5000 Hz which are significant higher than in VSP and SWD. An increased radiation of seismic wave energy in the direction of the borehole axis allows the view in areas to be drilled. Therefore, every actuator must be controlled independently of each other regarding to amplitude and phase of the source signal to maximize the energy of the seismic source in order to reach a sufficient exploration range. The next step for focusing is to use the method of phased array. Dependent of the seismic wave velocities of the surrounding rock, the distance of the actuators to each other and the used frequencies the signal phases for each actuator can be determined. Since one year several measurements with the prototype have been realized under defined conditions at a test site in a mine. The test site consists of a rock block surrounded from three galleries with a dimension of about 100 by 200 meters. For testing the prototype two horizontal boreholes were drilled. They are directed to one of the gallery to get a strong reflector. The quality of the data of the borehole seismics in amplitude and frequency spectra show overall a good signal-to-noise ratio and correlate strongly with the fracture density along the borehole and are associated with a lower signal-to-noise ratio. Additionally, the geophones of the prototype show reflections from ahead and rearward in the seismic data. In particular, the reflections from the gallery ahead are used for the calibration of focusing. The direct seismic wave field indicates distinct compression and shear waves. The analysis of several seismic measurements with a focus on the direct seismic waves shows that the phased array technology explicit can influence the directional characteristics of the radiated seimic waves. The amplitudes of the seismic waves can be enhanced up to three times more in the desired direction and simultaneously be attenuated in the reverse direction. A major step for the directional investigation in boreholes has accomplished. But the focusing of the seismic waves has to be improved to maximize the energy in the desired direction in more measurements by calibrating the initiating seismic signals of the sources. A next step this year is the development of a wireline prototype for application in vertical boreholes with depths not more than 2000 meters are planned. The prototype must be modified and adapted to the conditions in deep boreholes with respect to pressure and temperature. This project is funded by the German Federal Environment Ministry.

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

NASA Astrophysics Data System (ADS)

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

2017-11-01

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

A Methodology to Seperate and Analyze a Seismic Wide Angle Profile

NASA Astrophysics Data System (ADS)

Weinzierl, Wolfgang; Kopp, Heidrun

2010-05-01

General solutions of inverse problems can often be obtained through the introduction of probability distributions to sample the model space. We present a simple approach of defining an a priori space in a tomographic study and retrieve the velocity-depth posterior distribution by a Monte Carlo method. Utilizing a fitting routine designed for very low statistics to setup and analyze the obtained tomography results, it is possible to statistically separate the velocity-depth model space derived from the inversion of seismic refraction data. An example of a profile acquired in the Lesser Antilles subduction zone reveals the effectiveness of this approach. The resolution analysis of the structural heterogeneity includes a divergence analysis which proves to be capable of dissecting long wide-angle profiles for deep crust and upper mantle studies. The complete information of any parameterised physical system is contained in the a posteriori distribution. Methods for analyzing and displaying key properties of the a posteriori distributions of highly nonlinear inverse problems are therefore essential in the scope of any interpretation. From this study we infer several conclusions concerning the interpretation of the tomographic approach. By calculating a global as well as singular misfits of velocities we are able to map different geological units along a profile. Comparing velocity distributions with the result of a tomographic inversion along the profile we can mimic the subsurface structures in their extent and composition. The possibility of gaining a priori information for seismic refraction analysis by a simple solution to an inverse problem and subsequent resolution of structural heterogeneities through a divergence analysis is a new and simple way of defining a priori space and estimating the a posteriori mean and covariance in singular and general form. The major advantage of a Monte Carlo based approach in our case study is the obtained knowledge of velocity depth distributions. Certainly the decision of where to extract velocity information on the profile for setting up a Monte Carlo ensemble is limiting the a priori space. However, the general conclusion of analyzing the velocity field according to distinct reference distributions gives us the possibility to define the covariance according to any geological unit if we have a priori information on the velocity depth distributions. Using the wide angle data recorded across the Lesser Antilles arc, we are able to resolve a shallow feature like the backstop by a robust and simple divergence analysis. We demonstrate the effectiveness of the new methodology to extract some key features and properties from the inversion results by including information concerning the confidence level of results.

Orbital- to Sub-Orbital-Scale Cyclicity in Seismic Reflections and Sediment Character in Early to Middle Pleistocene Mudstone, Santa Barbara Basin, California

NASA Astrophysics Data System (ADS)

Peterson, C. D.; Behl, R. J.; Nicholson, C.; Lisiecki, L. E.; Sorlien, C. C.

2009-12-01

High-resolution seismic reflection records and well logs from the Santa Barbara Channel suggest that large parts of the Pleistocene succession records climate variability on orbital to sub-orbital scales with remarkable sensitivity, much like the well-studied sediments of the last glacial cycle (ODP Site 893). Spectral analysis of seismic reflection data and gamma ray logs from stratigraphically similar Pleistocene sections finds similar cyclic character and shifts through the section. This correlation suggests that acoustic impedance and physical properties of sediment are linked by basin-scale, likely climatically-driven, oscillations in lithologic composition and fabric during deposition, and that seismic profiling can provide a method for remote identification and correlation of orbital- and sub-orbital-scale sedimentary cyclicity. Where it crops out along the northern shelf of the central Santa Barbara Channel, the early to middle Pleistocene succession (~1.8-1.2 Ma) is a bathyal hemipelagic mudstone with remarkably rhythmic planar bedding, finely laminated fabric, and well-preserved foraminifera, none of which have been significantly altered, or obscured by post-depositional diagenesis or tectonic deformation. Unlike the coarser, turbiditic successions in the central Ventura and Los Angeles basins, this sequence has the potential to record Quaternary global climate change at high resolution. Seismic reflection data (towed chirp) collected on the R/V Melville 2008 Cruise (MV08) penetrate 10's of meters below seafloor into a ~1 km-long sequence of south-dipping seismic reflectors. Sampling parallel to the seafloor permits acquisition of consistent signal amplitude for similar reflectors without spreading loss. Based on established age ranges for this section, sedimentation rates may range from 0.4 to 1.4 meters/kyr, therefore suggesting that the most powerful cycles are orbital- to sub-orbital-scale. Discrete sets of cycles with high power show an abrupt shift to shorter wavelengths midway through the section. Deep in the section, the strongest cycles indicated by spectral analysis are 50 and 16 meters thick, whereas up section, the strongest cycles are 20 and 12 meters thick. Nearby industry boreholes that penetrate a stratigraphically similar, 1500-meter-thick mudstone section, provide logs of natural gamma ray intensity with a higher sample interval (15 cm), allowing resolution and analysis of even higher frequency lithologic cycles. The strongest cycle deep in the section is 100 meters thick, and up section, the strongest cycle is 12 meters thick. This abrupt decrease in dominant cycle thickness midway through both the seismic and gamma ray records perhaps indicates a basin-wide shift in sedimentation. With improved chronostratigraphy based on Sr-isotope ratios and biostratigraphy, and comparison with paleoclimate proxy data, we will test if seismically resolved lithologic oscillations can be reliably interpreted as representing climatically driven Milankovitch cycles. This method may be used to evaluate the age and paleoceanographic potential of sedimentary strata before a coring vessel is deployed.

Analysis of Deep Long-Period Subglacial Seismicity in Marie Byrd Land, Antarctica

NASA Astrophysics Data System (ADS)

McMahon, N. D.; Aster, R. C.; Myers, E. K.; Lough, A. C.

2017-12-01

We utilize subspace detection methodology to extend the detection and analysis of deep, long-period seismic activity associated with the subglacial and lower crust magmatic complex beneath the Executive Committee Range volcanoes of Marie Byrd Land (Lough et al., 2013). The Marie Byrd Land (MBL) volcanic province is a remote continental region that is almost completely covered by the West Antarctic Ice Sheet (WAIS). The southern extent of Marie Byrd Land lies within the West Antarctic Rift System (WARS), which includes the volcanic Executive Committee Range. Lough et al. noted that seismic stations in the POLENET/ANET seismic network detected two swarms of seismic activity during 2010 and 2011. These events have been interpreted as deep, long-period (DLP) earthquakes based on their depth (25-40 km), tectonic context, and low frequency spectra. The DLP events in MBL lie beneath an inferred volcanic edifice that is visible in ice penetrating radar images via subglacial topography and intraglacial ash deposits, and have been interpreted as a present location of Moho-proximal magmatic activity. The magmatic swarm activity in MBL provides a promising target for advanced subspace detection, and for the temporal, spatial, and event size analysis of an extensive deep long period earthquake swarm using a remote and sparse seismographic network. We utilized a catalog of 1370 traditionally identified DLP events to construct subspace detectors for the nine nearest stations using two years of data spanning 2010-2011. Via subspace detection we increase the number of observable detections more than 70 times at the highest signal to noise station while decreasing the overall minimum magnitude of completeness. In addition to the two previously identified swarms during early 2010 and early 2011, we find sustained activity throughout the two years of study that includes several previously unidentified periods of heightened activity. These events have a very high Gutenberg-Richter b-value (>2.0). We also note evidence of continuing seismicity through 2015 examining data from the small number of longer-running POLENET stations in the region.

Investigating Deep-Marine Sediment Waves in the Northern Gulf of Mexico Using 3D Seismic Data

NASA Astrophysics Data System (ADS)

Wang, Z.; Gani, M. R.

2016-12-01

Deep-water depositional elements have been studied for decades using outcrop, flume tank, sidescan sonar, and seismic data. Even though they have been well recognized by researchers, the improvements in the quality of 3D seismic data with increasingly larger dimension allow detailed analysis of deep-water depositional elements with new insights. This study focuses on the deep-marine sediment waves in the northern Gulf of Mexico. By interpreting a 3D seismic dataset covering 635 km2 at Mississippi Canyon and Viosca Knoll areas, large sediment waves, generated by sediment gravity flows, were mapped and analyzed with various seismic attributes. A succession of sediment waves, approximately 100 m in thickness, is observed on the marine slope that tapers out at the toe of the slope. The individual sediment wave exhibits up to 500 m in wavelength and up to 20 m in height. The wave crests oriented northeast-southwest are broadly aligned parallel to the regional slope-strike, indicating their sediment gravity flow origin. The crestlines are straight or slightly sinuous, with sinuosity increasing downslope. Their anti-dune patterns likely imply the presence of supercritical flows. The sediment waves have a retrogradational stacking pattern. Seismic amplitude maps of each sediment wave revealed that after depositing the majority of sheet-like sands on the upper slope, sediment gravity flows started to form large sediment waves on the lower slope. The steep and narrow upcurrent flanks of the sediment waves always display higher amplitudes than the gentle and wide downcurrent flanks, indicating that the sands were likely preferentially trapped along the upcurrent flanks, whereas the muds spread along the downcurrent flanks. The formation of sediment waves likely requires a moderate sand-mud ratio, as suggested by these observations: (1) absence of sediment waves on the upper slope where the sands were mainly deposited as unconfined sheets with a high sand-mud ratio; (2) absence of sediment waves on the basin floor, which is covered mainly by muds and hemipelagic sediments with a low sand-mud ratio; and (3) presence of sediment waves on the lower slope with a moderate sand-mud ratio.

Progressive reactivation of the volcanic plumbing system beneath Tolbachik volcano (Kamchatka, Russia) revealed by long-period seismicity

NASA Astrophysics Data System (ADS)

Frank, William B.; Shapiro, Nikolaï M.; Gusev, Alexander A.

2018-07-01

After lying dormant for 36 yr, the Tolbachik volcano of the Klyuchevskoy group started to erupt on 27 November 2012. We investigate the preparatory phase of this eruption via a statistical analysis of the temporal behavior of long-period (LP) earthquakes that occurred beneath this volcanic system. The LP seismicity occurs close to the surface beneath the main volcanic edifices and at 30 km depth in the vicinity of a deep magmatic reservoir. The deep LP earthquakes and those beneath the Klyuchevskoy volcano occur quasi-periodically, while the LP earthquakes beneath Tolbachik are clustered in time. As the seismicity rate increased beneath Tolbachik days before the eruption, the level of the time clustering decreased. We interpret this as a manifestation of the evolution of the volcano plumbing system. We suggest that when a plumbing system awakes after quiescence, multiple cracks and channels are reactivated simultaneously and their interaction results in the strong time clustering of LP earthquakes. With time, this network of channels and cracks evolves into a more stable state with an overall increased permeability, where fluids flow uninhibited throughout the plumbing system except for a few remaining impediments that continue to generate seismic radiation. The inter-seismic source interaction and the level of earthquake time clustering in this latter state is weak. This scenario suggests that the observed evolution of the statistical behavior of the shallow LP seismicity beneath Tolbachik is an indicator of the reactivation and consolidation of the near-surface plumbing system prior to the Tolbachik eruption. The parts of the plumbing system above the deep magmatic reservoir and beneath the Klyuchevskoy volcano remain in nearly permanent activity, as demonstrated by the continuous occurrence of the deep LP earthquakes and very frequent Klyuchevskoy eruptions. This implies that these parts of the plumbing system remain in a stable permeable state and contain a few weakly interacting seismogenic sources. Our results provide new constraints on future mechanical models of the magmatic plumbing systems and demonstrate that the level of time clustering of LP earthquakes can be a useful parameter to infer information about the state of the plumbing system.

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.

Yearly report, Yucca Mountain project

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

Brune, J.N.

1992-09-30

We proposed to (1) Develop our data logging and analysis equipment and techniques for analyzing seismic data from the Southern Great Basin Seismic Network (SGBSN), (2) Investigate the SGBSN data for evidence of seismicity patterns, depth distribution patterns, and correlations with geologic features (3) Repair and maintain our three broad band downhole digital seismograph stations at Nelson, nevada, Troy Canyon, Nevada, and Deep Springs, California (4) Install, operate, and log data from a super sensitive microearthquake array at Yucca Mountain (5) Analyze data from micro-earthquakes relative to seismic hazard at Yucca Mountain.

Rethinking turbidite paleoseismology along the Cascadia subduction zone

USGS Publications Warehouse

Atwater, Brian F.; Carson, Bobb; Griggs, Gary B.; Johnson, H. Paul; Salmi, Marie

2014-01-01

A stratigraphic synthesis of dozens of deep-sea cores, most of them overlooked in recent decades, provides new insights into deep-sea turbidites as guides to earthquake and tsunami hazards along the Cascadia subduction zone, which extends 1100 km along the Pacific coast of North America. The synthesis shows greater variability in Holocene stratigraphy and facies off the Washington coast than was recognized a quarter century ago in a confluence test for seismic triggering of sediment gravity flows. That test compared counts of Holocene turbidites upstream and downstream of a deep-sea channel junction. Similarity in the turbidite counts among seven core sites provided evidence that turbidity currents from different submarine canyons usually reached the junction around the same time, as expected of widespread seismic triggering. The fuller synthesis, however, shows distinct differences between tributaries, and these differences suggest sediment routing for which the confluence test was not designed. The synthesis also bears on recent estimates of Cascadia earthquake magnitudes and recurrence intervals. The magnitude estimates hinge on stratigraphic correlations that discount variability in turbidite facies. The recurrence estimates require turbidites to represent megathrust earthquakes more dependably than they do along a flow path where turbidite frequency appears limited less by seismic shaking than by sediment supply. These concerns underscore the complexity of extracting earthquake history from deep-sea turbidites at Cascadia.

Structure of the San Fernando Valley region, California: implications for seismic hazard and tectonic history

USGS Publications Warehouse

Langenheim, V.E.; Wright, T.L.; Okaya, D.A.; Yeats, R.S.; Fuis, G.S.; Thygesen, K.; Thybo, H.

2011-01-01

Industry seismic reflection data, oil test well data, interpretation of gravity and magnetic data, and seismic refraction deep-crustal profiles provide new perspectives on the subsurface geology of San Fernando Valley, home of two of the most recent damaging earthquakes in southern California. Seismic reflection data provide depths to Miocene–Quaternary horizons; beneath the base of the Late Miocene Modelo Formation are largely nonreflective rocks of the Middle Miocene Topanga and older formations. Gravity and seismic reflection data reveal the North Leadwell fault zone, a set of down-to-the-north faults that does not offset the top of the Modelo Formation; the zone strikes northwest across the valley, and may be part of the Oak Ridge fault system to the west. In the southeast part of the valley, the fault zone bounds a concealed basement high that influenced deposition of the Late Miocene Tarzana fan and may have localized damage from the 1994 Northridge earthquake. Gravity and seismic refraction data indicate that the basin underlying San Fernando Valley is asymmetric, the north part of the basin (Sylmar subbasin) reaching depths of 5–8 km. Magnetic data suggest a major boundary at or near the Verdugo fault, which likely started as a Miocene transtensional fault, and show a change in the dip sense of the fault along strike. The northwest projection of the Verdugo fault separates the Sylmar subbasin from the main San Fernando Valley and coincides with the abrupt change in structural style from the Santa Susana fault to the Sierra Madre fault. The Simi Hills bound the basin on the west and, as defined by gravity data, the boundary is linear and strikes ~N45°E. That northeast-trending gravity gradient follows both the part of the 1971 San Fernando aftershock distribution called the Chatsworth trend and the aftershock trends of the 1994 Northridge earthquake. These data suggest that the 1971 San Fernando and 1994 Northridge earthquakes reactivated portions of Miocene normal faults.

From underplating to delamination-retreat in the northern Apennines

NASA Astrophysics Data System (ADS)

Chiarabba, C.; Giacomuzzi, G.; Bianchi, I.; Agostinetti, N. P.; Park, J.

2014-10-01

Recordings of teleseismic earthquakes from a dense set of temporary and permanent broadband seismic stations reveal the lithospheric structure of the northern Apennines and support the scenario of a retreating detachment within the mid-crust. Lithospheric delamination appears crucial to the formation and evolution of the Apennines orogen. Receiver-function (RF) stacks outline a continuous west-dipping Ps converted phase from a positive velocity jump that we interpret as the top of the lower crust and mantle of the Adria continental lithosphere, which is descending into the shallow mantle. The correlation of seismicity with two RF profiles across the northern Apennines suggests distinct stages of lithospheric delamination. Active penetration of the detachment into the Adria lithosphere seems evident in the south/east, with induced shallow-mantle flow facilitated by slab dehydration. Penetration of the detachment in the north/west seems to have arrested, and is possibly marked by crustal underplating. This layer atop the Apennines slab is visible only down to 80 km depth and suspends above an oppositely-dipping paired positive/negative Ps converted phase in stacked receiver functions. The break in the west-dipping Adria lithosphere conflicts with a westward-subduction scenario continuous from the Oligocene. Lateral changes of deep structure and seismicity along the northern Apennines suggest that underplating of crustal material and delamination-retreat are distinct mechanisms active today in the western and eastern sectors, respectively, of the northern Apennines. Negative Ps-pulses at 100-120 km depth help to define a seismic lithosphere-asthenosphere boundary (LAB), but cross-cut a volume of high-velocity mantle rock, as inferred from tomographic models. We hypothesize that this seismic LAB is a rheological discontinuity that affects the frequency band of seismic body waves, but not the long-term viscous response that governs the evolution and eventual detachment of the continental slab.

Evidence of a modern deep water magmatic hydrothermal system in the Canary Basin (eastern central Atlantic Ocean)

NASA Astrophysics Data System (ADS)

Medialdea, T.; Somoza, L.; González, F. J.; Vázquez, J. T.; de Ignacio, C.; Sumino, H.; Sánchez-Guillamón, O.; Orihashi, Y.; León, R.; Palomino, D.

2017-08-01

New seismic profiles, bathymetric data, and sediment-rock sampling document for the first time the discovery of hydrothermal vent complexes and volcanic cones at 4800-5200 m depth related to recent volcanic and intrusive activity in an unexplored area of the Canary Basin (Eastern Atlantic Ocean, 500 km west of the Canary Islands). A complex of sill intrusions is imaged on seismic profiles showing saucer-shaped, parallel, or inclined geometries. Three main types of structures are related to these intrusions. Type I consists of cone-shaped depressions developed above inclined sills interpreted as hydrothermal vents. Type II is the most abundant and is represented by isolated or clustered hydrothermal domes bounded by faults rooted at the tips of saucer-shaped sills. Domes are interpreted as seabed expressions of reservoirs of CH4 and CO2-rich fluids formed by degassing and contact metamorphism of organic-rich sediments around sill intrusions. Type III are hydrothermal-volcanic complexes originated above stratified or branched inclined sills connected by a chimney to the seabed volcanic edifice. Parallel sills sourced from the magmatic chimney formed also domes surrounding the volcanic cones. Core and dredges revealed that these volcanoes, which must be among the deepest in the world, are constituted by OIB-type, basanites with an outer ring of blue-green hydrothermal Al-rich smectite muds. Magmatic activity is dated, based on lava samples, at 0.78 ± 0.05 and 1.61 ± 0.09 Ma (K/Ar methods) and on tephra layers within cores at 25-237 ky. The Subvent hydrothermal-volcanic complex constitutes the first modern system reported in deep water oceanic basins related to intraplate hotspot activity.