Ambient Noise Tomography of Jammu And Kashmir Himalaya

Patra, Sai Raman (2023) Ambient Noise Tomography of Jammu And Kashmir Himalaya. Masters thesis, Indian Institute of Science Education and Research Kolkata.

Text (Ms dissertation of Sai Raman Patra (18MS172)) Thesis_18MS172.pdf - Submitted Version Restricted to Repository staff only Download (11MB)

Abstract

Jammu and Kashmir Himalaya lies in the meisoseismal zone of the 1555 (Mw 8.0) Kashmir earthquake and is a major “seismic gap” in the NW Himalaya. Therefore It is crucial to have a well-constrained velocity and attenuation structure in order to quantify the seismic hazard in the region. The Jammu And Kashmir Seismological NETwork (JAKSNET) was established in 2013 consisting of 25 broadband seismograph systems. These 25 stations’ ambient noise data were used to calculate high-frequency Rayleigh-wave dispersion. The analysis was conducted using continuous data spanning several years. The vertical component waveforms are cut into hour-long traces and corrected for instrument response. On these hour-long traces one-bit normalisation has been performed to suppress earthquake signals. This is followed by spectral whitening to eliminate the differential amplitudes of common noise sources. Finally common time traces from station-pairs are cross-correlated. Every station-pair’s hour-long correlograms are stacked to enhance the coherent signal. The stacked cross-correlograms are the empirical Green’s function between a station pair. From these the dispersed Rayleigh-wave signal is recovered at time periods between 5-30 s. This workflow is repeated for all station-pairs in order to obtain fundamental mode Rayleigh wave group velocity dispersion curves. A total of 140 station-pair dispersion curves have been obtained. In order to acquire lateral variation in group velocity across Jammu and Kashmir Himalaya, these dispersion data is combined with regional dispersion dataset obtained from earthquakes to perform a ray based tomography using variable grids. High frequency tomography maps reveal lateral variations in dispersion characteristics of the NW Himalaya.

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