Attenuation Characteristics and Earthquakes: Northwestern Himalaya

Ghosh, Ayon (2022) Attenuation Characteristics and Earthquakes: Northwestern Himalaya. Masters thesis, Indian Institute of Science Education and Research Kolkata.

Text (MS dissertation of Ayon Ghosh (17MS077)) 17MS077_Thesis_file.pdf - Submitted Version Restricted to Repository staff only Download (11MB)

Abstract

A major seismic gap exists in the Kashmir Himalaya, which last ruptured in a megathrust earthquake in 1555. Significant stress has built up there, which can be released through a large megathrust earthquake in the future. A seismological network, JAKSNET was installed in the Kashmir Himalayas as a part of a collaborative experiment to better understand the crustal structure and earthquakes in this region. We study the attenuation characteristics of this region using Lg-coda waves to unravel the crustal structure and heterogeneities on a regional scale. We use the Stacked Spectral Ratio method to calculate the single trace Q₀ and η values. We obtain an average Q₀ and η value of 531 ± 151 and 0.72 ± 0.18 respectively. We also put these single trace measurements in a 2D backprojection tomography to look at the lateral variation of Q₀. We find high Q₀ values in the Indian Shield, intermediate Q₀ values in the Tarim Basin, and low Q₀ values in the highly deforming Pamir-Kohistan Block. Secondly, we use Matched Filter Detection to detect new earthquakes in the Kashmir Himalayas to look at the structure on a local scale and understand the evolution of seismicity. We use 189 events from the ISC-reviewed catalog as template events to detect a total of 977 events. We observe two clear bursts of seismicity in 2013 and 2016. We also relocate the events with a magnitude greater than 2 using probabilistic inversion to better understand the distribution of seismicity here. The relocated events clearly map the locked-to-creep transition beneath the Higher Himalayas and the locked zone beneath the Kashmir Basin.

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