Earthquake source dynamics and kinematics of the Eastern Indian Shield and adjoining regions

Abstract

The Eastern Indian Shield (EIS) consists of two cratonic nuclei, namely Singhbhum craton and Chhotanagpur Granitic Gneissic terrain. This area contains several crisscross faults, lineaments, shear zones, numerous hot springs and three major rivers (e.g., Ganga, Brahmaputra and Damodar). The area is regionally covered by 7 seismic stations and jointly recorded 16 events from the study area, and less noisy waveforms of 4 events were used for focal mechanism analysis using the Cut and Paste method. The focal parameters of these 4 events were compiled with results of 8 events computed by different workers for the study area. To understand the detailed tectonics, focal mechanisms of 21 events for the Himalayan segment were taken from CMT Harvard catalog of duration 1976–2017. Spatial variations of operative stress fields for major tectonic domains were analyzed in the present study based on stress inversion of focal mechanism parameters. We observed strike-slip-dominated movements in the EIS, which changes partially into extension in the northeast part between the Ganga and Brahmaputra Rivers. Thrust-dominated movements evidenced by focal mechanisms and the pure compression in the western segment of the Himalaya in the north might be promoting shear movements in the EIS and adjoining regions. The pure strike-slip in the eastern segment of the Himalaya and its deeper level account for lateral shearing and eastward movements of different tectonic blocks. The normal faulting earthquakes in the northeast part might be indicating stretching in the basement because of convergence of Indian lithosphere beneath the Myanmar plate.