Probabilistic seismic hazard assessment in the vicinity of MBT and MCT in western Himalaya

Abstract

Major seismic activity in India is concentrated along the Himalayan arc including the western Himalaya. A region in the vicinity of Main Boundary Thrust (MBT) and Main Central Thrust (MCT) bounded by latitude 29 N to 36 N and longitude 73 E to 80 E was considered for the study. Nine Seismogenic Source Zones (SSZ), were identified on the basis of seismicity and the tectonics around it. Seismic hazard parameters were computed for each source zone and return periods were calculated for different magnitude earthquakes. For validation of return periods, seven recent earthquakes were studied. Out of seven earthquakes three earthquakes of magnitude between 5.0 and 6.0 occurred in Kangra SSZ . Two Ground Motion Prediction Equations (GMPE’s) were used to estimate peak ground acceleration (PGA) in the region. PGA in the region was estimated to vary between 0.013 g to 0.315 g for 10% probability of exceedance in 50 years, and between 0.024 g to 0.68 g for 2% probability of exceedance in 50 years. Highest PGA values ≥ 0.31 g were observed in Kangra and Chamba district of Himachal Pradesh. For the Kangra SSZ, a return period of 141 years was estimated for magnitude Mw = 8.0, 44 years for Mw = 7 and 14 years for Mw = 6. Results obtained in the present study were compared with other studies. This hazard analysis study underlines the urgency for carrying out vulnerability analysis to estimate the populations that are at risk to this threat perception, so that appropriate mitigation measures can be put in place.