Upper mantle anisotropy beneath northeast India–Asia collision zone from shear-wave splitting analysis

2013 ◽  
Vol 102 (7) ◽  
pp. 2061-2076 ◽  
Author(s):  
Devajit Hazarika ◽  
Dilip Kumar Yadav ◽  
V. Sriram ◽  
Abhishek Rai
Keyword(s):  
Shear Wave ◽  
Upper Mantle ◽  
Shear Wave Splitting ◽  
Northeast India ◽  
Upper Mantle Anisotropy ◽  
Collision Zone ◽  
Wave Splitting ◽  
Mantle Anisotropy

scholarly journals Insight into NE Tibetan Plateau expansion from crustal and upper mantle anisotropy revealed by shear-wave splitting

2017 ◽  
Vol 478 ◽  
pp. 66-75 ◽  
Author(s):  
Zhouchuan Huang ◽  
Frederik Tilmann ◽  
Mingjie Xu ◽  
Liangshu Wang ◽  
Zhifeng Ding ◽  
...  
Keyword(s):  
Tibetan Plateau ◽  
Shear Wave ◽  
Upper Mantle ◽  
Shear Wave Splitting ◽  
Upper Mantle Anisotropy ◽  
Wave Splitting ◽  
Mantle Anisotropy ◽  
Insight Into ◽  
Ne Tibetan Plateau

Upper mantle anisotropy beneath North China from shear wave splitting measurements

2012 ◽  
Vol 522-523 ◽  
pp. 235-242 ◽  
Author(s):  
Lijun Chang ◽  
Chun-Yong Wang ◽  
Zhifeng Ding
Keyword(s):  
Shear Wave ◽  
Upper Mantle ◽  
North China ◽  
Shear Wave Splitting ◽  
Upper Mantle Anisotropy ◽  
Wave Splitting ◽  
Mantle Anisotropy

Upper mantle anisotropy beneath Sudetes from shear wave splitting - passive seismic experiment AniMaLS

2020 ◽  
Author(s):  
Julia Rewers ◽  
Piotr Środa ◽  
AniMaLS Working Group
Keyword(s):  
Shear Wave ◽  
Bohemian Massif ◽  
Upper Mantle ◽  
Shear Wave Splitting ◽  
Upper Mantle Anisotropy ◽  
Seismic Experiment ◽  
Wave Splitting ◽  
Passive Seismic ◽  
Mantle Anisotropy ◽  
Passive Seismic Experiment

<p>The passive seismic experiment AniMaLS was organized in 2017 in the Sudetes in Poland. One of the objectives was to study the anisotropy of the sub-crustal lithosphere and asthenosphere beneath the NE termination of the Bohemian Massif. Temporary seismic network of 23 broadband stations was operating in the area of Sudetes mountains and Fore-Sudetic Block, covering a ~200 x 100 km large area, with ~30 km spacing between stations. Obtained recordings were supplemented with data from permanent stations of Czech and Polish seismological networks located in the study area.</p><p>The Sudetes belong to internal zone of Variscan Orogen and are located in the NE part of the Bohemian Massif, between the Elbe Fault in SW and the Odra Fault in NE. The sudetic lithosphere represents a complex mosaic of several units with distinct histories of tectonic evolution and with consolidation ages ranging from the upper Proterozoic to the Quaternary. The aim of the project is to study seismic structure and anisotropy of the lithosphere-asthenosphere system based on broadband seismograms of local, regional and teleseismic events. The obtained data will be analysed using several interpretation methods. The poster presents the results of analysis by shear wave splitting method.</p><p>The analysis was done based on SKS and SKKS phases recorded during a ~2 years observation period. For analysis, three single-station methods were used: cross-correlation, eigenvalue minimization and transverse energy minimization. The dependence of resulting splitting parameters on the backazimuth of the event was also analysed. The results show that time delays between slow and fast S-wave components are typically in the range of ~0.5-1.6 sec, with average 1.2 sec. The splitting is interpreted as a result of lattice-preferred orientation (LPO) of mantle olivine. The azimuths of fast velocity axis are mostly consistent and showed largely WNW-ESE direction. They correlate well with trends of tectonic units observed at the surface and with strike directions of major fault zones. This suggests vertically coherent deformation throughout the lithosphere and frozen-in LPO, reflecting last tectonic episode which shaped Sudetic area. Obtained results were also compared with previous seismic studies of the upper mantle anisotropy in the neighboring areas by various methods.</p>

Upper mantle anisotropy and it's geodynamical implications in Sri Lanka region

2020 ◽  
Author(s):  
shivam chandra
Keyword(s):  
Sri Lanka ◽  
Shear Wave ◽  
Upper Mantle ◽  
Delay Time ◽  
Lower Layer ◽  
Shear Wave Splitting ◽  
Anisotropic Layer ◽  
Upper Mantle Anisotropy ◽  
Wave Splitting ◽  
Mantle Anisotropy

<p>Anisotropy in the Earth’s upper mantle is a signature of past and present deformation. Sri Lanka comprises four main lithological units, viz. the Highland Complex (HC), the Wanni Complex (WC), the Vijayan complex (VC) and the Kadugannawa complex (KC). To calculate the upper mantle anisotropy, we have collected the earthquake data from IRIS (Incorporated Research Institutions for Seismology) network. The upper mantle anisotropy beneath Sri Lanka is measured in the frequency band 0.01–0.15 Hz, with magnitude (Mw) of six or more and within the epicentral distance of 90°-140°. We have analyzed (the fast direction and delay time) shear wave splitting of SKS/SKKS phases at 3 stations, namely, MALK (WC), HALK (HC) and PALK (KC) in Sri Lanka. In this study, shear wave splitting measurements were done using high-quality seismograms (~30) of many earthquakes occurring in the region. We have used rotational correlation (RC) , minimum energy (SC) and eigenvalue techniques. The result of the shear-wave splitting measurement shows the presence of two anisotropic layers in the upper mantle. The upper and lower layer’s fast-polarization direction is found to be NE-SW and NW-SE, has the delay time varies from 0.4-0.5s in the upper layer, and 0.6-0.8s in the lower layer. We found two major fast directions in the upper and lower layers, viz. NE-SW in the upper layer of MALK and PALK and NW-SE for the HALK stations, and NNE-SSW in the lower layer beneath MALK and HALK stations and NW-SE in the PALK station. Overall, Fast direction for Sri Lanka region is found to be NE-SW in the lower layer and NW-SE in the upper layer. Our study suggests that fast axis direction of lower layer with an average delay time of 0.6 s depicts a ~67 km thick anisotropic layer with 4% anisotropy (from previous studies) beneath Sri Lanka region. However, if we assume an anisotropy range of 3–5%, then the calculated delay time of 0.6 s would correspond to thickness variation of 89.3 to 53.59 km, respectively, for the inferred anisotropic layer. Comparing from APM (Absolute Plate Motion) direction with our fast directions, we infer that the SAF(Simple Asthenospheric Flow) model prevails in this region and secondly, when S<sub>hmax </sub>(Maximum Horizontal stress) and the GPS (Global Positioning System) data compared with the fast direction we infer that there is partial contribution from lithospheric mantle. So, we confirmed that anisotropy in the region is mainly governed by asthenospheric flow and partially due to lithospheric mantle.</p>

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