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  • 1
    Call number: M 20.93505
    Description / Table of Contents: Active and passive source data from two seismic experiments within the interdisciplinary project TIPTEQ (from The Incoming Plate to mega Thrust EarthQuake processes) were used to image and identify the structural and petrophysical properties (such as P- and S-velocities, Poisson's ratios, pore pressure, density and amount of fluids) within the Chilean seismogenic coupling zone at 38.25°S, where in 1960 the largest earthquake ever recorded (Mw 9.5) occurred. Two S-wave velocity models calculated using traveltime and noise tomography techniques were merged with an existing velocity model to obtain a 2D S-wave velocity model, which gathered the advantages of each individual model. In a following step, P- and S-reflectivity images of the subduction zone were obtained using different pre stack and post-stack depth migration techniques. Among them, the recent prestack line-drawing depth migration scheme yielded revealing results. Next, synthetic seismograms modelled using the reflectivity method allowed, through their input 1D synthetic P- and S-velocities, to infer the composition and rocks within the subduction zone. Finally, an image of the subduction zone is given, jointly interpreting the results from this work with results from other studies. The Chilean seismogenic coupling zone at 38.25°S shows a continental crust with highly reflective horizontal, as well as (steep) dipping events. Among them, the Lanalhue Fault Zone (LFZ), which is interpreted to be east-dipping, is imaged to very shallow depths. ...
    Type of Medium: Dissertations
    Pages: xvi, 111 Seiten , Illustrationen, Diagramme
    Language: English
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  • 2
    Publication Date: 2011-12-01
    Description: Tibetan plate overriding the Asian plate in central and northern Tibet Nature Geoscience 4, 870 (2011). doi:10.1038/ngeo1309 Authors: Wenjin Zhao, Prakash Kumar, James Mechie, Rainer Kind, Rolf Meissner, Zhenhan Wu, Danian Shi, Heping Su, Guangqi Xue, Marianne Karplus & Frederik Tilmann The southern boundary between India and the Tibetan Plateau represents a classical case of continental subduction, where the Indian continental lithosphere is subducted northwards beneath the Tibetan Plateau. At the northern boundary, southward subduction of Asian lithosphere beneath the Tibetan Plateau has also been proposed, but imaging has been hampered by inadequate data quality. Here we analyse the plate tectonic structure of the northern boundary between Tibet and Asia using the S receiver function technique. Our passive source seismic data build on, and extend further northwards, the existing geophysical data from the International Deep Profiling of Tibet and the Himalaya project. We detect, beneath central and northern Tibet, a relatively thin, but separate, Tibetan lithosphere overriding the flat, southward subducting Asian lithosphere. We suggest that this overriding Tibetan lithosphere helps to accommodate the convergence between India and Asia in central and northern Tibet. We conclude that the Tibetan–Himalayan system is composed of three major parts: the Indian, Asian and Tibetan lithospheres. In the south, the Indian lithosphere underthrusts Tibet. In central and northern Tibet a separate, thin Tibetan lithosphere exists, which is underthrust by the Asian lithosphere from the north.
    Print ISSN: 1752-0894
    Electronic ISSN: 1752-0908
    Topics: Geosciences
    Published by Springer Nature
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  • 3
    Publication Date: 2019
    Description: Abstract A series of conjugate strike‐slip faults is the most prominent geologic feature in central Tibet and is considered to accommodate east‐west extension and coeval north‐south contraction. The development mechanism of the conjugate strike‐slip fault system is under debate because of unclear crustal physical properties and compositional variations. P and S wave arrivals from 414 local earthquakes recorded by the temporary Seismic Array Integrated Detection for a Window of Indian Continental Head array and the permanent China National Seismic Network were used for the velocity tomography, with additional P and S wave arrivals from 12 shots of the International Deep Profiling of Tibet and the Himalaya III reflection/refraction profile. The local earthquakes were simultaneously relocated with the updated velocity models. We also inverted for a three‐dimensional upper crustal Qp model with the same earthquake data set. The Vp structure near the surface shows that low‐Vp anomalies generally correspond to sedimentary basins and high‐Vp anomalies are related to exhumed metamorphic blocks in the study area. Relatively low Vp/Vs ratios in the upper crust indicate widely distributed quartz‐rich rocks. The low‐Vp zone from 0‐ to 10‐km depth (resolving depth limit) is spatially correlated with the Bangong‐Nujiang suture, possibly reflecting the compositional difference along the ophiolitic mélange belt accompanied by twin volcanic arcs from a double‐sided subduction. This interpretation is supported by relatively heterogeneous Qp values. This low‐velocity zone also implies relatively uniform stress and continuous deformation in the upper crust of central Tibet. The relatively weak materials in at least the upper crust would result in strain concentration and help the development of the conjugate strike‐slip fault system along the Bangong‐Nujiang suture.
    Print ISSN: 2169-9313
    Electronic ISSN: 2169-9356
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 4
    Publication Date: 2014-07-17
    Description: Based on a two-year seismic record from a local network, we characterize the deformation of the seismogenic crust of the Pamir in the northwestern part of the India-Asia collision zone. We located more than 6000 upper crustal earthquakes in a regional 3D velocity model. For 132 of these events, we determined source mechanisms, mostly through full waveform moment-tensor inversion of locally and regionally recorded seismograms. We also produced a new and comprehensive neotectonic map of the Pamir, which we relate to the seismic deformation. Along Pamir's northern margin, where GPS measurements show significant shortening, we find thrust and dextral strike-slip faulting along west to northwest trending planes, indicating slip partitioning between northward thrusting and westward extrusion. An active, north-northeast trending, sinistral transtensional fault system dissects the Pamir's interior, connecting the Lakes Karakul and Sarez, and extends by distributed faulting into the Hindu Kush of Afghanistan. East of this lineament, the Pamir moves northward en bloc , showing little seismicity and internal deformation. The western Pamir exhibits a higher amount of seismic deformation; sinistral strike-slip faulting on northeast trending or conjugate planes and normal faulting indicate east-west extension and north-south shortening. We explain this deformation pattern by the gravitational collapse of the western Pamir Plateau margin and the lateral extrusion of Pamir rocks into the Tajik-Afghan depression, where it causes thin-skinned shortening of basin sediments above an evaporitic décollement. Superposition of Pamir's bulk northward movement and collapse and westward extrusion of its western flank causes the gradual change of surface velocity orientations from north-northwest to due west observed by GPS geodesy. The distributed shear deformation of the western Pamir and the activation of the Sarez-Karakul fault system may ultimately be caused by the northeastwards propagation of India's western transform margin into Asia, thereby linking deformation in the Pamir all the way to the Chaman fault in the south in Afghanistan.
    Print ISSN: 0278-7407
    Electronic ISSN: 1944-9194
    Topics: Geosciences
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 5
    Publication Date: 2019
    Description: Abstract We use local and teleseismic earthquakes to analyze shear wave splitting within the Pamir‐Hindu Kush region, north of the western syntaxis of the India‐Asia collision zone. These two data sets allowed us to map the distribution of azimuthal anisotropy, to put constraints on the depth range where it is accumulated, and to deduce characteristics of ongoing deformation. From 1,073 SKS (core‐mantle refracted phases) measurements at 107 stations, we derived time delays of 0.7–2.25 s and dominantly ENE‐WSW oriented fast polarization directions. Fast polarization directions only deviate adjacent to the subducting slabs and major strike‐slip faults, aligning parallel to these structures. From 461 direct S measurements along a transect perpendicular to the Pamir seismic zone, we obtain fast directions parallel to those from SKS measurements but smaller delay times (average 0.4 s), which vary depending on depth. Time delays exhibit 0.1–0.3 s crustal contribution and increase to 0.8 s in a narrow domain coinciding with the inferred subcrustal contact of the two colliding plates. We find measurements from the same event‐station paths at different filter frequencies to be frequency‐independent, allowing a comparison with SKS results along the studied profile. The smaller average time delays of local events imply that the crust and uppermost mantle only make a minor contribution to the SKS splitting. Thus, the coherent fast direction pattern suggests a strain field dominated by the indentation of India and the escape of sublithospheric material north of the indenter. Crustal anisotropy is likely also controlled by this regional deformation pattern with locally highest strain rates closest to the continental subduction front.
    Print ISSN: 2169-9313
    Electronic ISSN: 2169-9356
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 6
    Publication Date: 2022-11-29
    Description: Abstract
    Description: Raw-, SEG-Y and other supplementary data of the amphibious wide-angle seismic experiment carried out in south Turkey, Cyprus and south of Cyprus are presented. The aim of this project was to reveal the crustal structure of the Anatolian plateau, Cyprus and the Eratosthenes Seamount (ESM), south of Cyprus. Simultaneous data acquisition offshore with ocean bottom seismometers and airguns and onshore with seismic land stations and two land shots in south Turkey lead to a 650 km long amphibian seismic profile.
    Keywords: 201001-CyprusArc ; Wide-angle seismic ; crustal structure ; eastern Mediterranean ; Cyprus ; south Turkey ; Eratosthenes Seamount
    Type: Dataset
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  • 7
    Publication Date: 2020-08-26
    Description: SUMMARY We present an updated joint tomographic method to simultaneously invert receiver function waveforms and surface wave dispersions for a 3-D S-wave velocity (Vs) model. By applying this method to observations from ∼900 seismic stations and with a priori Moho constraints from previous studies, we construct a 3-D lithospheric S-wave velocity model and crustal-thickness map for the central–east Tibetan plateau. Data misfit/fitting shows that the inverted model can fit the receiver functions and surface wave dispersions reasonably well, and checkerboard tests show the model can retrieve major structural information. The results highlight several features. Within the plateau crustal thickness is 〉60 km and outwith the plateau it is ∼40 km. Obvious Moho offsets and lateral variations of crustal velocities exist beneath the eastern (Longmen Shan Fault), northern (central–east Kunlun Fault) and northeastern (east Kunlun Fault) boundaries of the plateau, but with decreasing intensity. Segmented high upper-mantle velocities have varied occurrences and depth extents from south/southwest to north/northeast in the plateau. A Z-shaped upper-mantle low-velocity channel, which was taken as Tibetan lithospheric mantle, reflecting deformable material lies along the northern and eastern periphery of the Tibetan plateau, seemingly separating two large high-velocity mantle areas that, respectively, correspond to the Indian and Asian lithospheres. Other small high-velocity mantle segments overlain by the Z-shaped channel are possibly remnants of cold microplates/slabs associated with subductions/collisions prior to the Indian–Eurasian collision during the accretion of the Tibetan region. By integrating the Vs structures with known tectonic information, we derive that the Indian slab generally underlies the plateau south of the Bangong–Nujiang suture in central Tibet and the Jinsha River suture in eastern Tibet and west of the Lanchangjiang suture in southeastern Tibet. The eastern, northern, northeastern and southeastern boundaries of the Tibetan plateau have undergone deformation with decreasing intensity. The weakly resisting northeast and southeast margins, bounded by a wider softer channel of uppermost mantle material, are two potential regions for plateau expansion in the future.
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
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  • 8
    Publication Date: 2012-05-01
    Description: INTRODUCTION As early as the 1920s, Gutenberg (1926) equated the low-viscosity asthenosphere with a seismic low-velocity zone. Regions of high and low velocity in the mantle are today usually determined with tomographic methods. These methods are, however, not very sensitive to sharp boundaries. Converted waves have been used for many years to study boundaries in the mantle. A velocity reduction with depth (possibly the lithosphere-asthenosphere boundary, LAB) was found with P-to-S converted waves (P-receiver functions) beneath North America at ∼100 km depth with a sharpness of about 10 km (Rychert and Shearer 2009). A comparison of the LAB depth from S-receiver functions (see, e.g., Yuan et al. 2006 and Kumar et al. 2006 for a description of the method and data examples) with that from surface-wave tomography found good agreement in the western United States (Li et al. 2007) and along the East Coast (Rychert et al. 2007). Our results from the California coast are also consistent with the P-to-S and S-to-P images earlier analyzed by Kumar and Kawakatsu (2011), along a profile spanning ocean to continent. A discrepancy exists in the central part of the craton, where the sharp velocity decrease at about 100 km in P-receiver functions (PRF) was confirmed with S-receiver functions (SRF) in contrast to the smooth velocity decrease around 200 km depth known from surface-wave data (Yuan and Romanowicz 2010; Abt et al. 2010; Yuan et al. 2011). The petrophysical nature of the LAB is still very much a subject of discussion (e.g., Eaton et al. 2009; Fischer et al. 2010). We think our results from USArray data significantly contribute to this discussion. The earlier results were obtained with relatively few, sparsely distributed seismic stations (Abt et al. 2010). We apply...
    Print ISSN: 0895-0695
    Electronic ISSN: 1938-2057
    Topics: Geosciences
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  • 9
    Publication Date: 2012-01-03
    Print ISSN: 1866-7511
    Electronic ISSN: 1866-7538
    Topics: Geosciences
    Published by Springer
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  • 10
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