Characteristics of Landslides Induced by the 25 April 2015 M7.8 Nepal Earthquake

The Mw 7.8 earthquake which struck the central part of Nepal on 25 April 2015 was the most devastating event since the Mw 8.0 Nepal-Bihar earthquake in 1934. Numerous landslides were triggered and these landslides were systematically mapped by various agencies using a combination of remote sensing, ground observations, and field reports. The purpose of this study is to characterize the distributions of large landslides induced by the main shock in relation to their predisposing parameters (i.e., slope angle, aspect, elevation, curvature, openness, and topographic position) as well as triggering factors. A study area was defined to encompass the majority of the slope failures. Instead of ground acceleration, a combination of source-to-site distances (i.e., epicentral and fault-line distances) as well as surficial soil lithology were used as proxies to examine the effects of seismic-induced ground motion on landslide initiation in this study. A weighted landslide concentration was used to quantify the distribution of landslides within soil lithological groups. It was observed that valley-sitting slopes facing southeast within elevations of 1600 to 2400 m had the highest landslide concentrations. The majority of the landslides were located within 80 to 100 km of the fault trace. Curvature, along with topographic openness and position analyses revealed that the articulated slopes situated on valleys were most prone to failure. A multivariate analysis using principal component analysis, parallel analysis, and binomial logistic regression was used to generate a landslide probability model while avoiding multicollinearity issues. Accuracy of the results was verified by a high area value under the receiver-operator-characteristic curve.