Fault geometries and histories in western Nepal and implications for seismic hazards
The 2015 Mw7.8 Gorkha earthquake, Nepal, was a reminder of the seismic hazard presented by the Himalayan fault system. However, the earthquake was small in the context of Himalayan events. From paleoseismic studies and historical data, we know that this fault system likely slips in much larger, surface-rupturing earthquakes with return periods on the order of 500-1000 years at various locations across the Himalaya.
Our research groups have spent several years working to understand the seismic hazards in central and eastern Nepal. Western Nepal, however, is much less well understood. Here, we propose to evaluate the active fault systems in western Nepal from two perspectives: (1) an overall tectonic reconstruction, in order to understand the geometry and possible segmentation of the Main Himalayan Thrust, and (2) a detailed paleoseismic survey of a surprising and active north-dipping normal fault that seems to roughly parallel the Main Boundary Thrust.
Through this study we hope not only to better understand the seismic hazard in western Nepal, but also to gain an understanding of the mechanics that have caused the formation and activation of this strange normal fault system. Similar normal faults have been identified in subduction zones, such as the Japan Trench and the Aleutians; this fault represents and opportunity to evaluate the slip history on a similar fault and to assess whether and how slip ties into larger events on the megathrust itself.
- Earth Observatory of Singapore
Paul Tapponnier, China Earthquake Administration
Rafael Almeida, Yachay Tech
Soma Nath Sapkota, DMG, Nepal