Seismic Hazard Maps of the Eastern Himalaya Syntaxis by Integrating the Surface Topography and Site Effects

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 degrees x 0.1 degrees grid cells. Uniform moment magnitude (MW) in declustered catalog is 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 regimes are assigned to every source model by utilizing a logic tree to reduce the epistemic uncertainties in hazard calculation. The peak ground acceleration (PGA) and spectral acceleration (SA) at 0.2 s and 1.0 s are estimated for 2% and 10% probabilities of exceedance in 50 years. The hazard maps show a wide range of spatio-temporal variation in PGA and SA values. The maximum and minimum PGA values are 0.18 g and 0.70 g, respectively for 10% probability of exceedance. 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 comprehensive seismic hazards for tectonically complex regions like the Himalaya orogen.

Automated summary

The importance of proper seismic hazard assessment for the eastern Himalaya syntaxis region, due to its complex tectonic position and long history of devastating earthquakes, has been highlighted. Probabilistic seismic hazards are computed, combining area, linear, and smooth grid seismogenic source models, and incorporating surface topography and site effects. The analysis estimates mean seismicity rate, b-value, and expected maximum magnitude using the Maximum Likelihood Algorithm. Ground motion prediction equations are assigned to each source model to reduce uncertainties in hazard calculation. Hazard maps show a wide range of spatio-temporal variation in peak ground acceleration and spectral acceleration.