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Seismic Structure, Lithospheric Deformation and Seismicity of the Indian Plate in Sikkim Himalaya

Description: 

Seismic structure, lithospheric deformation and seismogenic capacity of the Indian plate in Sikkim Himalaya is poorly understood amidst the well-explored regions of Bhutan, Nepal and Tibet. Study of this region is key to understanding the evolutionary past, on-going collisional dynamics and its implication on future seismic hazard potential. A well thought seismic experiment was planned in 2019 with the installation of 27 broadband seismic stations covering Sikkim Himalaya. The network was operational till May, 2023. Precious data gathered from this project have been crucial in providing high resolution crustal images using 12,288 receiver functions, robust earthquake catalouge of 1,496 earthquakes, and patterns of mantle deformation. The observations reveal an intermittent contrast in amplitudes related to Main Himalayan Thrust, contrary to prominent and continuous arrivals from this boundary from Nepal Himalaya. Prominent seismicity clusters in the upper crust follow this layer and are marked by the presence of low velocity zones. The seismic activity indicates active shearing along Main Himalayan Thrust in response to collision. Lower crust is observed to possess an imbricated Moho possibly resulting due to accumulation from crustal shortening, which is corroborated with seismicity exhibiting thrusting mechanism. The convergence in this segment of Himalaya can be thus stated to be partially accommodated by imbricate structures in the upper and lower crust. Sandwiched between upper and lower crust is the dextrally deforming mid-crustal Dhubri-Chungthang Fault Zone postulated to be segmenting the Himalayan arc. Seismicity studies delineate the northward discontinuation of the seismogenic extent of this fault beyond Chungthang in Sikkim. Distinct deformation is observed across Dhubri-Chungthang Fault Zone by the fast-axis orientations determined from core-refracted shear waves. Complex dynamics coupled with intricate geometry of the faults pose an intermediate risk of occurrence of a great earthquake in Sikkim Himalaya raising the cause of concern of seismic hazard potential in the region.

Session: Learning Across Geological, Geophysical & Model-Derived Observations to Constrain Earthquake Behavior [Poster Session]

Type: Poster

Date: 5/1/2024

Presentation Time: 08:00 AM (local time)

Presenting Author: Niptika

Student Presenter: No

Invited Presentation: 

Authors