Title: Researcher
Country/Region: India
Period: 2022/10/11-2022/12/17
Theme: Imaging the crustal and upper mantle structure beneath Western Himalaya subduction zone using Integrated seismological approaches
Host: Eiji Kurashimo
Introduction: My research interests are in understanding the seismotectonic architecture beneath a region using various passive seismic techniques such as shear wave splitting analysis, local earthquake tomography, ambient noise cross correlation, and receiver functions. I received my Ph.D. in “Seismic velocity structure, Anisotropy and Attenuation characteristics of NW Himalaya (India) region: Tectonic Implications” from the Indian Institute of Technology Kharagpur in 2021, where my doctoral work focused on studying the structural variations and rheology of continental lithosphere in the Himalaya collision zone. In addition to that, have also worked on seismic imaging of the earth’s upper and fluid trapped middle crust of Kinnaur Himalaya, Himachal Pradesh, India in collaboration with colleagues from University of Cambridge, UK. I also contributed to the microseismic source monitoring and characterization of the seismic behaviour in the western Himalaya, India.
Currently, I am involved with studying the shear wave velocity structure through surface wave dispersion analysis from ambient noise cross-correlation. My research goal with Professor Eiji Kurashimo at the Earthquake Research Institute (ERI) will be to investigate the medium characteristics of the upper Himalayan crust and its generic relation with the occurrence of the 25 April 2015 Gorkha Nepal earthquake of magnitude (Mw 7.8) in collaboration. The current proposal aims to provide significant constraints about the crustal deformation of this vulnerable seismic zone and its implications towards earthquake hazard mitigation for the Himalayan states.
Research Report:
Imaging the crustal structure beneath Western Himalaya
subduction zone using Local Earthquake Tomography
Summary
I collaborated with Professor Eiji Kurashimo’s lab during my time at the Earthquake Research
Institute (ERI) at the University of Tokyo. During my stay, I have developed an optimum 1D
velocity model for the Western Himalaya subduction zone. Using this velocity model as an input,
I have investigated the three dimensional velocity structure beneath the region. The result from
the present study help us to understand the earthquake source processes and the medium
characteristics in this section. The tomographic image shows a strong vertical heterogeneity
beneath the study domain. The study region exhibits high P-wave velocity (Vp) and low Vp /Vs
including a lower velocity zone (LVZ) at middle crust down to 40 km depth. The upper layer
heterogeneity may depend upon the deposited sediments due to the erosion phenomenon as well
as on the local crustal deformations. The lower layer crustal heterogeneity corresponds to
overpressure and other structural deformation due to the ongoing striking action of the northward
descending Indian plate below the Eurasian plate. The existence of LVZ indicates presence of
fluid or any partial melting strata in the middle crust of the lithosphere. This may be a
consequence of under thrusting of the Indian crust, which produces a frictional heat and cause
metamorphic dehydration reaction. This reaction causes the released fluid to percolate upwards
into the brittle portion of the crust that manifests the leucogranites, which marks the low-velocity
layer.
subduction zone using Local Earthquake Tomography
Summary
I collaborated with Professor Eiji Kurashimo’s lab during my time at the Earthquake Research
Institute (ERI) at the University of Tokyo. During my stay, I have developed an optimum 1D
velocity model for the Western Himalaya subduction zone. Using this velocity model as an input,
I have investigated the three dimensional velocity structure beneath the region. The result from
the present study help us to understand the earthquake source processes and the medium
characteristics in this section. The tomographic image shows a strong vertical heterogeneity
beneath the study domain. The study region exhibits high P-wave velocity (Vp) and low Vp /Vs
including a lower velocity zone (LVZ) at middle crust down to 40 km depth. The upper layer
heterogeneity may depend upon the deposited sediments due to the erosion phenomenon as well
as on the local crustal deformations. The lower layer crustal heterogeneity corresponds to
overpressure and other structural deformation due to the ongoing striking action of the northward
descending Indian plate below the Eurasian plate. The existence of LVZ indicates presence of
fluid or any partial melting strata in the middle crust of the lithosphere. This may be a
consequence of under thrusting of the Indian crust, which produces a frictional heat and cause
metamorphic dehydration reaction. This reaction causes the released fluid to percolate upwards
into the brittle portion of the crust that manifests the leucogranites, which marks the low-velocity
layer.