Evaluating Seismic Hazard based on Simulated Earthquake Strong Ground Motions in Himalaya

The importance of site-specific earthquake strong ground motions for the proper evaluation of seismic hazard of a region has now been well recognized.  It is useful to generate site-specific ground motions required for the designing of earthquake resistant buildings in seismic active regions as required number of observed records are not available at all the sites of interest.  The simulated time histories enhance the sparse data base of observed accelerograms which is useful for improving seismological understanding of an earthquake process.  Most of the earthquakes in Indian region occur in Himalaya which is the result of collision of northward drifting Indian plate with Eurasian plate.  The seismic hazard is severe in the region of Himalaya.  The first step to mitigate the seismic hazard is to evaluate the same.

In the present study, the seismic hazard has been estimated in the regions of Himalaya using simulated strong ground motions from earthquakes.  A modified hybrid technique has been used for the simulation of earthquake strong ground motions. In this technique a composite source model (Zeng et al, 1994) has been combined with semi-empirical envelope technique (Midorikawa, 1993).  In the technique, the envelope function of target earthquake is computed by summation of envelope functions that are generated from small size earthquakes distributed randomly on the fault plane. In order to simulate the ground motions at surface level, the high frequency decay parameter and site amplification functions have been taken into account.

The strong ground motions have been simulated at large number of points distributed spatially in the region.  The scenario hazard maps in the form of spatial distribution of peak ground acceleration values have been presented due to a great earthquake (M 8.5) in Central Seismic Gap of Himalaya and a major earthquake (M 6.9) in NE Himalaya.  The scenario hazard maps prepared in the present study may be useful to the local administrators for the mitigation of the earthquake hazard in the region.  These maps give the idea about the possible scenario in case of similar size future earthquake occurs in the region. The maps presented here are useful to mitigate the seismic hazard from the region.