LAUSR

Abstract The Kumaon Himalaya lies in the central seismic gap and therefore bears the potential to host a great Himalayan earthquake. The seismicity and seismotectonics of the Kumaon Himalaya and the adjacent region have been investigated based on local earthquake data recorded at 18 seismological stations. The seismically active zone of the eastern segment of the Kumaon Himalaya deviates from the usual pattern of seismicity in the Himalayan Seismic Belt of the NW Himalaya. Shallow-focus earthquakes in this region largely concentrate in the Chiplakot Crystalline Belt (CCB) immediately south of the Vaikrita Thrust. The Focal Mechanism Solutions of 41 earthquakes computed through waveform inversion technique along with the solutions of 12 earthquakes obtained from the Global Centroid Moment Tensor solution catalog are used to investigate the kinematics of the region. The study reveals a complex faulting pattern in the Inner Lesser Himalaya. The stress inversion results show a widely distributed stress pattern and low frictional coefficient which are attributed as one of the major causes of clustered seismicity observed in the CCB. Careful examination of the fault orientations indicates the presence of a hinterland dipping Lesser Himalayan Duplex over the ramp structure on the Main Himalayan Thrust. The high compressive stress and deformation rate in the CCB are partially accommodated by this duplex structure. The large concentration of shallow-focus earthquakes in the CCB is the result of the presence of fluid-rich zone as well as strain localization and large stress build-up due to locking in the ramp structure on the Main Himalayan Thrust beneath the CCB.