Lg Attenuation Characteristics of the Jammu and Kashmir Himalaya

Pradhan, Kaushik Kumar (2021) Lg Attenuation Characteristics of the Jammu and Kashmir Himalaya. Masters thesis, Indian Institute of Science Education and Research Kolkata.

Text (MS Dissertation of Kaushik Kumar Pradhan (16MS169)) 16MS169_Thesis_file.pdf - Submitted Version Restricted to Repository staff only Download (13MB)

Abstract

The shear energy trapped in the crustal waveguide interferes with each other to produce the Lg phase in the seismogram. It carries the maximum energy from an earthquake and is the most destructive at regional distances. Lg waves excitation and propagation is used to characterise the attenuation structure of the crust in Jammu and Kashmir Himalaya as attenuation significantly modifies the ground shaking intensity resulting from an earthquake. The regional events recorded at Jammu and Kashmir Seismological NETwork (JAKSNET) stations have been used to study the propagation efficiency of Lg wave across the Indian, Himalaya, Tibetan Plateau, and Hindu Kush regions. The ratio Lg and Sn phases is computed to differentiate regions which allows the efficient Lg propagation from those Lg blockage. Tomography plot has been generated to observe the lateral variation in the propagation efficiency of Lg waves in the region. The efficient ray paths, having a good amount of Lg, were used in the two stations method to study the Lg wave quality factor (Q0) and its frequency dependence (η) for the Jammu and Kashmir Himalaya. The event, which was recorded at two stations of the network and where the stations were aligned within 15 degrees to the event, is used for further analysis. The amplitude ratio of Lg at different frequencies for the two stations have been used to calculate the interstation attenuation parameters. Q0 ranges from 16 to 669 and η ranges from 0.025 to 2.02 in the region, with an average Q0 of 156.27 ± 6.46 and average η of 0.875 ± 0.033. The lateral variation in Q0 is closely associated with the geology and tectonic setting of the Jammu and Kashmir Himalaya. iii

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