Recent Trends in Seismicity of Uttaranchal

The seismic network in Kumaun Himalaya has recorded nearly three thousand earthquakes events since April 1999. The data has been analysed to study the seismicity pattern, seismicity rate, stress drop and focal depth pattern. The detailed analyses of 388 events have been carried out. The magnitude of the events is less than 4.2, the focal depth for most of the events lie between 10-25 km and the stress drop values are low. An attempt has been made to delineate seismically active zones and the seismicity pattern indicates that the strain energy is being released along NW-SE direction almost parallel to the regional thrust viz. Main Central Thrust/Munsiari Thrust/Berinag Thrust/North Almora Thrust and orthogonally along N-S/NNW-SSE directions. Considering the fact that the strain energy is continuously building up along the Himalayan front due to convergence of Indian and Eurasian Plates and the region lying between Bihar-Nepal border (1934 earthquake MS 8.4) and Kangra (1905, earthquake MS 8.6) has not experienced a major earthquake (M ≥8). The evaluated low value of seismicity rate and stress drop in the Kumaun Himalaya may be indicative of possible major earthquake in near future.