Topographic Control on Ground Motions and Landslides From the 2015 Gorkha Earthquake

Landslides triggered by earthquake shaking pose a significant hazard in active mountain regions. Steep topography promotes gravitational instabilities and can amplify the seismic wavefield; however, the relationship between topographic amplification and landsliding is poorly understood. Here, we use numerical methods to investigate the link between low-frequency ground shaking, topographic amplification, and the landslide distribution from the 2015 Gorkha, Nepal earthquake. Results show that the largest landslides initiated where the highest topographic amplification, highest elevations, and steepest slopes converged, typically in glacially-sculpted terrain, with additional controls of rock strength and absolute ground motions. Additionally, the initiation of the largest and most fatal landslide was likely influenced by amplification throughout the rupture due the orientation of the ridge with respect to the propagating wavefield. These results indicate that topographic amplification is one of the key factors for understanding where large and potentially devastating landslides are likely to occur during future major earthquakes.