Possibility of Induced Seismicity in Pancheshwar Dam Site on Kali River, Uttarakhand

Abstract

The geomorphological and seismic evidence near NW of proposed Pancheshwar dam site on Kali River in Kumaun Lesser Himalaya suggests influence of neotectonics along imbricated zone of high-angle North Almora Thrust (NAT) dipping towards SW. The NAT zone represents the deformed northern margin of Almora nappe. It separates the granite gneisses of Almora crystallines from the quartzites and slates of Lesser Himalayan sequence. The region shows earthquakes swarm with strongest event of M=6-7.5 in the years of 1966 and 1974. The seismisity of M≥ 3.5 is being continuously recorded till very recently. The region has not experienced any major earthquake since 1974. A prominent seismically active linear segment is noticed near NW of study area. The mass of 315m high water column of the future dam-reservoir may transmit the stress into the subsurface rocks that are characerized by occurrence of duplex structures bounded by multiple discrete shears. The chlrorite-sericite schist developed within shear zones may accommodate the ongoing convergence of Indian plate towards Himalaya in the form of shear strain in the subsurface region. This accumulated strain may cause gravity collapse along steeply dipping shear planes. Thus the reservoir-induced seismicity may be one of the consequences of active deformation prevailing in the region.