Seismotectonic and neotectonic investigations in a part of ‘Central Seismic Gap’ Uttarakhand, India

摘要

Summary. In the present paper an attempt has been made to understand the seismicity pattern in the unruptured part of the Central Seismic Gap. The seismic data from 1999–2008 used in the present investigation was acquired from a 5 station Digital Seismic Network in Kumaun Himalaya. The hypocentral parameters of the events used in the present investigation indicate low stress drop values and shallow focal depth. The clusters of the epicenters of the events are very close to the Main Central Thrust (MCT), in between Munsiari Thrust (MT) and Berinag Thrust (BT). The area between South Almora Thrust (SAT) and North Almora Thrust (NAT) and along Chaukhutia fault magnitude 3.0 or above events are frequently occurring. The Peak Ground Acceleration (PGA) and Peak Ground Velocity (PGV) values varies from 1.8 × 10~(–6) m/s~2 (E) for the earthquake of magnitude 2.6 to 2.0 × 10~(–3) m/s~2 (E) for earthquake of magnitude 4.8. Most of the earthquake events are also observed in Almora, Kausani, Bageshwar, Dhaulchhina, Kapkot regions between Munsiari and South Almora Thrust. The neotectonic investigations were carried out in the major river valleys of the Kumaun Himalaya. From the investigations some new faults are identified on the basis of geomorphological signatures. The morphotectonic development has been related to the prevalent seismicity of the region. It is evident that the major thrust and faults of the region are seismically as well as neotectonically active in some segments. From the ongoing seismic and neotectonic movements it is clear that some of the faults and thrusts are active at present. The results obtained would be significant in assessing the seismic hazards and planning and execution of various multipurpose developmental projects in Kumaun region.