A seismic hazard and risk scenario for Himalaya and Ganga plains due to a future great earthquake

Strong ground motion time histories are synthesized using the composite source model at a few sites for a prototype gap filling Mw 8.5 great earthquake in the western side of the central seismic gap in Himalaya which extends from the Bhagirathi valley in the west to the Kali valley in the east. The peak ground accelerations attain values around 1 g in the regions overlying the fault plane. In the Ganga plains the values vary from 0.32 g to 0.7 g depending on the distance from the fault plane. The damage potential of such an earthquake is extreme. The possibilities of its compounding due to failure civil works like high dams exist. The loss of human lives could be over several hundred thousand and economic loss of hundreds of billion Rupees. A further scenario was developed for an extentional type of earthquake (M-w 6) in the Ganga foredeep at a short epicentral distance. This showed that peak ground acceleration of about 0.32 g can be produced exposing the effected regions to considerable hazard.