The distribution of landslides caused by the 2015 Mw7.8 Gorkha earthquake, Nepal

Coseismic landslides pose immediate and prolonged hazards to mountainous communities, and also serve as major contributors to erosion and sediment budgets in tectonically active mountain belts. We identify nearly 25,000 coseismic landslides triggered by the 25 April 2015 Mw7.8 Gorkha earthquake in central Nepal via a comparison of pre- and post-event satellite imagery of the Nepalese and Tibetan Himalaya. The high resolution of the imagery used enabled detailed mapping, including delineation of source and runout areas, a first, to our knowledge, for any inventory of coseismic landslides. Despite early reports estimating lower than expected landslide activity, we show that the total number, area, and volume of landslides associated with the Gorkha event are consistent with expectations, when compared to prior landslide-triggering earthquakes around the world. Landslides were concentrated in a region of the High Himalaya marked by steep slopes and high precipitation, and were also located near the source of high frequency energy released from the deepest portion of the slip patch. High-density landsliding is generally focused north-northeast from the highest modeled peak ground accelerations (PGA), and south-southeast from the region of highest-elevation and steepness of the glaciated High Himalaya. Landslide density increases eastward, mirroring the progression of fault rupture. We suggest that landslide density was determined by a combination of earthquake source characteristics, slope distributions, and the influence of precipitation on rock strength via increased weathering and vegetation cover.