Seismic potential of megathrust in the Kumaun-Garhwal region of NW Himalaya: implications from geodetic and seismic strain rates

We analysed the geodetic and seismic strain rates for composite analysis of seismic hazard potential of the Kumaun-Garhwal region of Northwest Himalaya. The principal geodetic strain rate is estimated using plate motion measurements at 144 Global Positioning System (GPS) sites reported in past similar to 20 years in the region. A modified least square inversion approach that utilizes a distance-based scale factor on the uncertainty in the velocity data is applied to get a reliable estimate of geodetic strain rate. Results indicate extensive compression in the region with a mean rate of - 113 nano strain/year towards NNE in the Higher Himalaya. The principal seismic strain rate is calculated from the focal mechanism solutions of the earthquakes in the region using the Kostrov formulation. We analysed the geodetic strain rate together with seismic strain rate using seismicity catalogue of 50, 220 and 700 years and found that the orientation of principal strain rates are consistent with each other. However, the seismic strain rate estimated from 700 years catalogue is comparable with geodetic strain rate indicating the high accumulation of elastic strain energy in this region. Analysis of strain budget using geodetic and seismic moment rates of this region, suggest a large amount of stored strain energy of similar to 5E + 21 Nm in the past 700 years which has a potential to generate a megathrust earthquake (Mw >= 8) in the present scenario.