ON THE POSSIBILITY OF RESERVOIR-INDUCED SEISMICITY IN THE GARHWAL HIMALAYA

It is argued from a brief review of available evidence that the possibility of reservoir-induced seismicity (RIS) in the Himalaya as a whole cannot be ruled out at the present time. On the other hand, a review of recent local investigations of small earthquakes (m(b) less than 5) and teleseismic investigations of moderate earthquakes (m(b) between 5 and 6, mainly) occurring in the Garhwal segment of the Alpide-Himalayan seismic belt provides evidence that RIS in the region can be anticipated. While their epicentral belts coincide geographically, the estimated focal depths of small and moderate earthquakes of the Garhwal Himalaya are in the ranges of 0-14 and 10-20 km, respectively. Small earthquakes occur by reactivation of strike-slip and reverse faults and moderate earthquakes occur on thrust faults. Elsewhere in the world, RIS has been observed most often in the crust at the depths where small earthquakes have been observed in the Garhwal Himalaya. In addition, RIS has been experienced during the impoundment of reservoirs in strike-slip and reverse fault environments, while theoretical analyses indicate that, if suitably located in relation to the reservoir, even a thrust fault may be destabilised by impoundment.