Azimuthal anisotropy and mantle flow underneath the southeastern Tibetan Plateau and northern Indochina Peninsula revealed by shear wave splitting analyses

2018 ◽  
Vol 747-748 ◽  
pp. 68-78 ◽  
Author(s):  
Fansheng Kong ◽  
Jing Wu ◽  
Lin Liu ◽  
Kelly H. Liu ◽  
Jianguo Song ◽  
...  
Keyword(s):  
Tibetan Plateau ◽  
Shear Wave ◽  
Shear Wave Splitting ◽  
Azimuthal Anisotropy ◽  
Mantle Flow ◽  
Indochina Peninsula ◽  
Southeastern Tibetan Plateau ◽  
Wave Splitting

scholarly journals Characteristics of the Mantle Flow System Beneath the Indochina Peninsula Revealed by Teleseismic Shear Wave Splitting Analysis

2018 ◽  
Vol 19 (5) ◽  
pp. 1519-1532 ◽  
Author(s):  
Youqiang Yu ◽  
Stephen S. Gao ◽  
Kelly H. Liu ◽  
Ting Yang ◽  
Mei Xue ◽  
...  
Keyword(s):  
Shear Wave ◽  
Flow System ◽  
Shear Wave Splitting ◽  
Mantle Flow ◽  
Indochina Peninsula ◽  
Wave Splitting

scholarly journals Shear wave splitting and mantle flow beneath LA RISTRA

2003 ◽  
Vol 30 (12) ◽  
Author(s):  
Rengin Gök ◽  
James F. Ni ◽  
Michael West ◽  
Eric Sandvol ◽  
David Wilson ◽  
...  
Keyword(s):  
Shear Wave ◽  
Shear Wave Splitting ◽  
Mantle Flow ◽  
Wave Splitting

Seismic anisotropy and mantle flow constrained by shear wave splitting in central Myanmar

2021 ◽  
Author(s):  
Enbo Fan ◽  
Yumei He ◽  
Yinshuang Ai ◽  
Stephen S. Gao ◽  
Kelly H. Liu ◽  
...  
Keyword(s):  
Shear Wave ◽  
Seismic Anisotropy ◽  
Shear Wave Splitting ◽  
Mantle Flow ◽  
Wave Splitting

Seismic anisotropy of the Northeastern Tibetan Plateau from shear wave splitting analysis

2011 ◽  
Vol 304 (1-2) ◽  
pp. 147-157 ◽  
Author(s):  
Yonghua Li ◽  
Qingju Wu ◽  
Fengxue Zhang ◽  
Qiangqiang Feng ◽  
Ruiqing Zhang
Keyword(s):  
Tibetan Plateau ◽  
Shear Wave ◽  
Seismic Anisotropy ◽  
Shear Wave Splitting ◽  
Northeastern Tibetan Plateau ◽  
Wave Splitting

scholarly journals Crustal seismic anisotropy of the Northeastern Tibetan Plateau and the adjacent areas from shear-wave splitting measurements

2019 ◽  
Vol 220 (3) ◽  
pp. 1491-1503 ◽  
Author(s):  
Nan Hu ◽  
Yonghua Li ◽  
Liangxin Xu
Keyword(s):  
Tibetan Plateau ◽  
Shear Wave ◽  
Seismic Anisotropy ◽  
Active Faults ◽  
Shear Wave Splitting ◽  
Crustal Anisotropy ◽  
Western Qinling ◽  
Northeastern Tibetan Plateau ◽  
Wave Splitting ◽  
Mantle Anisotropy

SUMMARY The Northeastern Tibetan Plateau has thickened crust and is still undergoing strong active crustal shortening and deformation. Crustal anisotropy can provide clues to how the crust is currently deforming and evolving. We use an automatic method to analyse the upper-crustal anisotropy of the NE Tibetan Plateau and the adjacent region using local earthquakes recorded at 39 permanent seismic stations during the period 2009–2018. The majority of the dominant fast directions are consistent with the maximum horizontal stress orientation, suggesting that the upper-crustal anisotropy is mainly controlled by the regional or local stress field. Several fault-parallel measurements are observed for stations on or near to the main faults. These fault-parallel fast directions indicate that the main mechanism of upper-crustal anisotropy is associated with shear fabric caused by deformation. Fast directions neither fault-parallel nor stress-parallel are observed at stations lying several kilometres away from fault zones, likely reflecting the combined influence of stress-aligned microcracks and active faults. A comparison between our upper-crustal anisotropy parameters and those inferred from previous anisotropy studies that used receiver function and teleseismic shear wave splitting measurements suggests that the crust has the same deformation mechanisms as mantle anisotropy in the southern part of the Western Qinling Fault, whereas the upper-crustal anisotropic mechanism is different from those of lower crust and mantle anisotropy in the northern part of the Western Qinling Fault. These observations imply that the Western Qinling Fault may be an important boundary fault.

Fracture characterisation using frequency-dependent shear-wave splitting analysis of azimuthal anisotropy: application to fluid flow pathways at the Scanner Pockmark area, North Sea

2020 ◽  
Author(s):  
Adam Robinson ◽  
Gaye Bayracki ◽  
Calum MacDonald ◽  
Ben Callow ◽  
Giuseppe Provenzano ◽  
...  
Keyword(s):  
Shear Wave ◽  
North Sea ◽  
Seismic Anisotropy ◽  
Shear Wave Splitting ◽  
Azimuthal Anisotropy ◽  
Geophysical Data ◽  
Fluid Migration ◽  
Ocean Bottom ◽  
Air Gun ◽  
Wave Splitting

<p>Scanner pockmark, located in the Witch Ground Graben region of the North Sea, is a ~900 m by 450 m, ~22 m-deep elliptical seafloor depression at which vigorous and persistent methane venting is observed. Previous studies here have indicated the presence of chimney structures which extend to depths of several hundred meters, and which may represent the pathways along which upwards fluid migration occurs. A proposed geometry for the crack networks associated with such chimney structures comprises a background pattern outside the chimney with unconnected vertical fractures preferentially aligned with the regional stress field, and a more connected, possibly concentric fracture system within the chimney. The measurement of seismic anisotropy using shear-wave splitting (SWS) allows the presence, orientation and density of subsurface fracture networks to be determined. If the proposed model for the fracture structure of a chimney feature is correct, we would expect, therefore, to be able to observe variations in the anisotropy measured inside and outside of the chimney.</p><p>Here we test this hypothesis, using observations of SWS recorded on ocean bottom seismographs (OBS), with the arrivals generated using two different air gun seismic sources with a frequency range of ~10-200 Hz. We apply a layer-stripping approach based on observations of SWS events and shallow subsurface structures mapped using additional geophysical data to progressively determine and correct for the orientations of anisotropy for individual layers. The resulting patterns are then interpreted in the context of the chimney structure as mapped using other geophysical data. By comparing observations both at the Scanner pockmark and at a nearby reference site, we aim to further contribute to the understanding of the structures and their role in governing fluid migration. Our interpretation will additionally be informed by combining the field observations with analogue laboratory measurements and new and existing rock physics models.</p><p>This work has received funding from the NERC (CHIMNEY; NE/N016130/1) and EU Horizon 2020 programme (STEMM-CCS; No.654462).</p>

Mantle flow under the Central Alps: Constraints from non-vertical-ray SKS shear-wave splittting

2020 ◽  
Author(s):  
Eric Löberich ◽  
Götz Bokelmann
Keyword(s):  
Shear Wave ◽  
Upper Mantle ◽  
Seismic Anisotropy ◽  
Single Layer ◽  
Depth Resolution ◽  
Shear Wave Splitting ◽  
Mantle Flow ◽  
Central Alps ◽  
Upper Mantle Anisotropy ◽  
Wave Splitting

<p>The association of seismic anisotropy and deformation, as e.g. exploited by shear-wave splitting measurements, provides a unique opportunity to map the orientation of geodynamic processes in the upper mantle and to constraint their nature. However, due to the limited depth-resolution of steeply arriving core-phases, used for shear-wave splitting investigations, it appears difficult to differentiate between asthenospheric and lithospheric origins of observed seismic anisotropy. To change that, we take advantage of the different backazimuthal variations of fast orientation <em>φ</em> and delay time <em>Δt</em>, when considering the non-vertical incidence of phases passing through an olivine block with vertical b-axis as opposed to one with vertical c-axis. Both these alignments can occur depending on the type of deformation, e.g. a sub-horizontal foliation orientation in the case of a simple asthenospheric flow and a sub-vertical foliation when considering vertically-coherent deformation in the lithosphere. In this study we investigate the cause of seismic anisotropy in the Central Alps. Combining high-quality manual shear-wave splitting measurements of three datasets leads to a dense station coverage. Fast orientations <em>φ</em> show a spatially coherent and relatively simple mountain-chain-parallel pattern, likely related to a single-layer case of upper mantle anisotropy. Considering the measurements of the whole study area together, our non-vertical-ray shear-wave splitting procedure points towards a b-up olivine situation and thus favors an asthenospheric anisotropy source, with a horizontal flow plane of deformation. We also test the influence of position relative to the European slab, distinguishing a northern and southern subarea based on vertically-integrated travel times through a tomographic model. Differences in the statistical distribution of splitting parameters <em>φ</em> and <em>Δt</em>, and in the backazimuthal variation of <em>δφ</em> and <em>δΔt</em>, become apparent. While the observed seismic anisotropy in the northern subarea shows indications of asthenospheric flow, likely a depth-dependent plane Couette-Poiseuille flow around the Alps, the origin in the southern subarea remains more difficult to determine and may also contain effects from the slab itself.</p>

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