5. Crustal Structure of Seismically Active Regions by Non-seismic Methods

5.1 Himalaya

5.1.1  Seismotectonics of the Sikkim Himalaya

The occurrence of deep crustal strike-slip earthquakes in the Sikkim Himalaya is indicative of the ongoing transverse tectonic deformation of the Indian plate, in addition to the N-S convergence related deformation within the Himalayan wedge. The two dominant tectonic forces operating in this region could lead to a complex variable spatial deformation within the Indian lithosphere. Two-dimensional modeling of magnetotelluric data incorporating the NW-SE transverse tectonic trend within the Main Central Thrust zone (MCTZ) yields a lithospheric electrical resistivity structure of the region down to 100 km. By integration of these results with other geophysical information, seismological data and in conjunction with a kinematic wedge model, Pavankumar and Manglik (2021) proposed a comprehensive tectonic model for the Sikkim Himalaya that highlights the complex nature of the lithospheric structure (Fig.8). A major contact beneath the MCTZ separating two geologically and compositionally distinct blocks of the underthrusting Indian plate is suggested to be a NW-SE trending lithospheric-scale fault in this segment of the Himalaya. The tectonic model also demonstrates another crustal-scale tectonic feature beneath the Main Frontal Thrust that demarcates a transition zone of moderately conductive crust of the Ganga Foreland Basin and a resistive crustal block beneath the Sub-Himalaya.