Earthquake scenario mapping reveals future earthquake hazards on a portion of the Himalayan Megathrust Fault, NW Himalaya

Abstract

The work presented here shows the earthquake scenario map of a portion of the Main Frontal Thrust (MHT) fault in the NW Himalaya. In our calculations, we have used the fault length for fault-rupture-length, which provides a simple way to estimate the overall earthquake potential of the region. The strike length of the fault was mapped based on the topographic expression on the 30 m spatial resolution imagery of the Shuttle Radar Topographic Mission dataset. The downdip width (W) was derived from estimates of the dips of the faults and the depth of the brittle-ductile transition, mainly available from the previously published structural and seismic sections and the data that show Moho depths. The dip of the fault zone was estimated based on the available centroid moment tensor (CMT) catalogue data and structural data; elsewhere, we use conventional dip angles of 30°, 60°, and 90° for reverse, normal and strike-slip faults, respectively. The seismogenic thickness of the continental lithosphere, which is the depth to the brittle-plastic transition boundary, is potentially limited to ~15-20 km depth in the studied area. The results show that the rupture zones on the fault could produce a moment magnitude (Mw) of 6.0 and above. These faults are mostly thrust faults and release the inter-seismic strain that develops over the geological past because of the continuous push of the Indian Plate, which moves ~3-5 cm/year, against the Eurasian Plate. Therefore, our earthquake scenario map is the first attempt to map the seismic potential of future rupture zones based on the structural parameters of the fault. The size of the expected earthquake is independent of the historical and contemporary earthquake rupturing information, which is valuable for predicting which fault zone will rupture first, which we have not covered here. The maps can be used to evaluate seismic risk and build earthquake-resistant structures.