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Seismic Experiments in the Kumaon Himalaya: Do We Expect a Great Earthquake?

Description: 

The Kumaon segment is a part of the central Himalayan seismic gap that is thought to be capable of hosting a future great earthquake. A series of seismic experiments were performed based on data from a local seismic network to study the seismogenesis in the region. Initial receiver function (RF) studies identified a relatively shallow crust (~40 km). The Lesser Himalaya is the most widely spread lithology in the area and is divided into the Outer and Inner Lesser Himalaya (OLH and ILH respectively). Both stacked RFs and velocity models identify a double ramp structure on the decollement (or MHT) separating the Indian and Eurasian plates. This north-dipping MHT serves as the sole thrust to an overlying hinterland dipping duplex in the ILH. Seismotectonic study reveals steep-dip imbricate faults with coincident seismicity between shallow to mid-crustal (ramp) depth. Seismic imaging also reveals a lower crustal low-velocity zone with a high Poisson’s ratio (∼0.28) in the ILH. The ductile nature of the lower crust supports the decreasing events with depth. The number and correlation of gravity lineaments with the local anisotropy show the upper crust to be more brittle in the ILH. The region is anisotropic (delay time ~0.18 s) with fast polarization directions both along and orthogonal to the convergence direction. This indicates the combined effect of tectonic stress and local geological features in generating stress-aligned micro-cracks. Stress inversion of earthquakes shows a perturbed stress field and low friction coefficient in the ILH. These earthquakes also report low source parameters compared to that in other segments, showing incomplete dissipation of accumulated stress. The concentration of shallow-focus earthquakes is a result of the presence of a fluid-rich zone, strain localization, and large stress build-up due to locking in the ramp. The high seismicity with a low-stress drop (σ≤40.6 bar) and b-value (~0.64) makes this segment a seismically hazardous zone.

Session: Crustal Imaging of High Seismic Hazard Regions [Poster]

Type: Poster

Date: 4/20/2023

Presentation Time: 08:00 AM (local time)

Presenting Author: Somak Hazra

Student Presenter: No

Invited Presentation: 

Authors