Surface-wave Tomography from Earthquake, Crust and upper mantle structure

Behera, Pragyant Prada (2019) Surface-wave Tomography from Earthquake, Crust and upper mantle structure. Masters thesis, Indian Institute of Science Education and Research Kolkata.

PDF (MS dissertation of Pragyant Prada Behera (14MS160)) 14MS160.pdf - Submitted Version Restricted to Repository staff only Download (2MB)

Abstract

As the largest and highest and one of the most active orogenic plateau on our planet today, the Tibet plateau is an interesting region for investigating collision consequences and to know the evolution of the Tibetan Plateau, it’s essential to have knowledge of the crust beneath both the Tibetan and the Indian Plate. Result of a study of dispersion characteristics of high broadband fundamental Rayleigh waves propagation across Tibet is presented. Group velocities can be correlated with better-known geological and tectonic features and show an acceptable correlation with thickness of the sediments for short period waves. We present group velocity maps from 20 sec to 150 sec period for Rayleigh wave. Broadband waveform data from about 15000 events from 2007 through 2011, recorded at 31 individual seismic stations across Tibet, have produced ~8500 paths for which the individual dispersion curve is estimated. Resolution checking has been done from ”checker-board” test in 0:5⁰; 1⁰; 2⁰ by choosing appropriate regularization parameters. We have found that the southern east site of Tibet plateau has high group velocity(~3.7Km/s) of all time periods. For less than 80 sec time period, group velocity is decreasing in the south-west site of the plateau with the time period and for more than 80 sec there is increased group velocity with the time period. Except the group velocity for 20 sec , there is a very slight change in group velocity(~3.4Km/s) with the time period in north-east site. We have done inversion of the Rayleigh group speed maps to design s-wave velocity model till 300 km depth and then prepare a 3-D shear velocity structure of the Tibetan crust and uppermost mantle. We have used this 3-D picture to project the lateral variations of the crust of Tibet and nature of the Moho depth across the collision zone.

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