Seismic hazard maps of the eastern Himalaya syntaxis by integrating the surface topography and site effects

Abstract The complex tectonic position and the long history of the devastating earthquakes with massive casualties and socio-economic damages have highlighted the importance of proper seismic hazard assessment for the eastern Himalaya syntaxis region. Here, probabilistic seismic hazards are computed combining the area, linear and smooth grid seismogenic source models. The surface topography and the site effects are incorporated to thousands of 0.1° x 0.1° grid cells. Uniform moment magnitude of declustered catalogs are used. The mean seismicity rate, the b-value and the expected maximum magnitude are estimated using the maximum likelihood algorithm. Two sets of ground motion prediction equations for shallow crustal and subduction interface tectonic regime are assigned to every source model by utilizing a logic tree to reduce the epistemic uncertainties in hazard calculation. The peak ground acceleration and spectral acceleration are estimated at 0.2s and 1.0s for 2% and 10% probabilities of exceedance in 50 years. The hazard maps show a wide range of spatio-temporal variation of values. The topographic irregularities and site effects significantly amplified the seismic hazard values. High hazardous zones are associated with the continental plate collision beneath the Assam Syntaxis. Medium hazard is estimated at Namche Barwa syntaxis. This analysis suggests the integration of actual site conditions, well developed ground motion prediction equations and multiple source models through logic tree to evaluate the better seismic hazards for any complex region.