scholarly journals Deformation of the upper crust in the Kumaon Himalaya analyzed from seismic anisotropy and gravity lineament studies

2021 ◽  
pp. 106827
Author(s):  
Somak Hajra ◽  
Devajit Hazarika ◽  
Subhendu Mondal ◽  
Sanjit K. Pal ◽  
P.N.S. Roy
Keyword(s):  
Seismic Anisotropy ◽  
Upper Crust ◽  
Kumaon Himalaya

scholarly journals Seismic anisotropy of the upper crust around Mount Fuji, Japan

2015 ◽  
Vol 120 (4) ◽  
pp. 2739-2751 ◽  
Author(s):  
Kohtaro R. Araragi ◽  
Martha K. Savage ◽  
Takao Ohminato ◽  
Yosuke Aoki
Keyword(s):  
Seismic Anisotropy ◽  
Upper Crust ◽  
Mount Fuji

Multilayered Crustal Anisotropy in Eastern Tibet Revealed by Receiver Function Data

2020 ◽  
Author(s):  
Shaohua Qi ◽  
Qiyuan Liu ◽  
Jiuhui Chen ◽  
Biao Guo
Keyword(s):  
Tibetan Plateau ◽  
Lower Crust ◽  
Seismic Anisotropy ◽  
Receiver Function ◽  
Azimuthal Anisotropy ◽  
Strain History ◽  
The Tibetan Plateau ◽  
Anisotropy Axis ◽  
Upper Crust ◽  
Western Sichuan

<p>It is widely accepted that the ongoing India-Asia collision since approximately 50 Ma ago has resulted in the uplift and eastward expansion of the Tibetan Plateau. Yet the interpretations of its dynamic process and deformation mechanism still remain controversial. Distinct models that emphasize particular aspects of the tectonic features have been proposed, including fault-controlled rigid blocks, continuous deformation of lithosphere and lower crust flow.</p><p>One possible way to reconcile these models is to investigate crustal deformation at multiple depths simultaneously, as well as crust-mantle interaction. Seismic anisotropy is considered as an effective tool to study the geometry and distribution of subsurface deformation, due to its direct connection to the stress state and strain history of anisotropic structures and fabrics. In the eastern margin of Tibetan plateau, previous studies of seismic anisotropy have already provided useful insights into the bulk anisotropic properties of the entire crust or upper mantle, based on shear wave splitting analyses of Moho Ps and XKS phases.</p><p>In this study, we went further to extract anisotropic parameters of multiple crustal layers by waveform inversion of teleseismic receiver function (RF) data from the western-Sichuan temporal seismic array using particle swarm optimization. Instead of directly fitting the backazimuthal stacking of RFs from each station, we translated the RF data into backazimuthal harmonic coefficients using harmonic decomposition technique, which separates the signals (of planar isotropic structure and anisotropy) from the scattering noise generated by non-planar lateral heterogeneity. The constant (k=0) and k=1, 2 terms of backazimuthal harmonic coefficients were used in our inversion. We also fixed the anisotropic model to slow-axis symmetry to avoid ambiguous interpretations.</p><p>Our results show that:</p><p>(1) Anisotropy with a titled anisotropy axis of symmetry is more commonly observed than pure azimuthal anisotropy in our data, which has been also reported by other RF studies across the surrounding areas of Tibetan plateau.</p><p>(2) The trends of slow symmetry axis vary from the upper to lower part of the crust in both Chuandian and Songpan units, indicating the deformation of the upper crust is decoupled from that of the lower crust in these two regions, while the trends are more consistent throughout the crust in the Sichuan basin.</p><p>(3) In the upper crust, the trends show a degree of tendency to lie parallel to the major geological features such as the Xianshuihe and Longmenshan faults, exhibiting a fault-controlled deformation or movement. In the middle and lower crust, the trends are NS or NW-SE in Chuandian unit and NE-SW in Songpan unit, which are coincident with the apparent extension directions of the ductile crustal flow.</p>

scholarly journals Earthquakes and crustal structure of Himalaya from Himalayan Nepal-Tibet seismic experiment (HIMNT)

2008 ◽  
Vol 38 ◽  
pp. 1-8
Author(s):  
Anne F. Sheehan ◽  
Thomas De La Torre ◽  
Gaspar Monsalve ◽  
Vera Schulte-Pelkum ◽  
Roger Bilham ◽  
...  
Keyword(s):  
Upper Mantle ◽  
Seismic Anisotropy ◽  
Velocity Structure ◽  
Receiver Functions ◽  
Moho Depth ◽  
Upper Crust ◽  
Southern Tibet ◽  
Seismic Experiment ◽  
3D Velocity Model ◽  
Mantle Earthquakes

The Himalayan Nepal - Tibet PASSCAL Seismic Experiment (HIMNT) included the deployment of 28 broadband seismometers throughout eastern Nepal and southern Tibet in 2001- 2002. The main goals of the project were to better understand the mountain building processes of this region through studies of seismicity and Earth structure determined from local and teleseismic earthquakes. The seismic deployment was in collaboration with the National Seismological Centre, Department of Mines and Geology, Nepal, and the Institute of Geology and Geophysics of the Chinese Academy of Sciences. Our new subsurface images from HIMNT teleseismic receiver functions and local earthquake tomography show evidence of the basal decollement of the Himalaya (Main Himalayan Thrust, MHT) and an increase in Moho depth from - 45 km beneath Nepal to -75 km beneath Tibet. We find strong seismic anisotropy above the decollement, likely developed in response to shear on the MHT. The shear may be taken up as slip in great earthquakes at shallower depths. Many local earthquakes were recorded during the deployment, and the large contrast in crustal thickness and velocity structure over a small lateral distance makes the use of a 3D velocity model important to determine accurate hypocentres. Large north-south variations are found in P and S wave velocity structure across the array. High Pn velocities are found beneath southern Tibet. Seismicity shows strong alignment of shallow (15-25 km depth) events beneath the region of highest relief along the Himalayan Front, and a cluster of upper mantle earthquakes beneath southern Tibet (70-90 km depth). Weak-mantle models do not expect the upper mantle earthquakes. Focal mechanisms of these upper mantle earthquakes beneath southern Tibet are mostly strike-slip, markedly different from the norm al faulting mechanisms observed for earthquakes in the mid and upper crust beneath Tibet. This change in the orientation of the major horizontal compression axis from vertical in the upper crust to horizontal in the upper mantle suggests a transition from deformation driven by body forces in the crust to plate boundary forces in the upper mantle. Several lines of evidence point to a decoupling zone in the Tibetan mid or lower crust, which may be related to the presence of a previously suggested flow channel in the Tibetan mid crust.

scholarly journals Seismic Anisotropy of the Upper Crust in the Mountain Ranges of Taiwan from the TAIGER Explosion Experiment

2013 ◽  
Vol 24 (6) ◽  
pp. 963 ◽  
Author(s):  
Hao Kuo-Chen ◽  
Piotr Środa ◽  
Francis Wu ◽  
Chien-Ying Wang ◽  
Yao-Wen Kuo
Keyword(s):  
Seismic Anisotropy ◽  
Upper Crust ◽  
Mountain Ranges ◽  
Explosion Experiment

scholarly journals Seismic anisotropy in the crystalline upper crust: observations and modelling from the Outokumpu scientific borehole, Finland

2012 ◽  
Vol 189 (1) ◽  
pp. 541-553 ◽  
Author(s):  
Heather Schijns ◽  
Douglas R. Schmitt ◽  
Pekka J. Heikkinen ◽  
Ilmo T. Kukkonen
Keyword(s):  
Seismic Anisotropy ◽  
Upper Crust

scholarly journals Preliminary seismic anisotropy in the upper crust of the south segment of Xiaojiang faults and its tectonic implications

2021 ◽  
Vol 34 (0) ◽  
pp. 1-13
Author(s):  
Ying Li ◽  
◽  
Yuan Gao ◽  
Yutao Shi ◽  
Peng Wu ◽  
...  
Keyword(s):  
Seismic Anisotropy ◽  
Upper Crust ◽  
The South ◽  
Tectonic Implications

Upper crust seismic anisotropy study and temporal variations of shear-wave splitting parameters in the western Gulf of Corinth (Greece) during 2013

2017 ◽  
Vol 269 ◽  
pp. 148-164 ◽  
Author(s):  
George Kaviris ◽  
Ioannis Spingos ◽  
Vasileios Kapetanidis ◽  
Panayotis Papadimitriou ◽  
Nicholas Voulgaris ◽  
...  
Keyword(s):  
Shear Wave ◽  
Seismic Anisotropy ◽  
Shear Wave Splitting ◽  
Temporal Variations ◽  
Upper Crust ◽  
Gulf Of Corinth ◽  
Wave Splitting
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