Factors Affecting Occurrence of Landslides Induced by the M7.8 April 2015, Nepal Earthquake

Abstract

The M7.8 Nepal earthquake on 25 April 2015 and its aftershocks triggered thousands of landslides. Understanding correlations between the landslide occurrences and landslide conditioning factors is essential to generate a landslide susceptibility map. This study considers the two most reliable inventory data: landslide inventory 1 (LI-1) and landslide inventory 2 (LI-2). The LI-1 contains 1,352 landslide polygons, and the LI-2 contains 4,000 landslide points. The centroid locations of LI-1 were also considered as additional point inventory data for the statistical analyses. The landslide area percentage and landslide number density are computed for important factors such as slope angle, slope roughness, aspect, peak ground acceleration (PGA), distance to epicenter, distance to rivers and roads, Normalized Difference Vegetation Index (NDVI), land use and land cover, and mean annual precipitation. The cumulative percentage curves and the areas under the curve (AUC) are also compared for all the considered factors. PGAs of the main shock and two major aftershocks, distance to epicenter, slope angle, distance to river, and NDVI have relatively stronger correlations with the landslide occurrence than other factors. It is found that the LI-1 polygons have weaker correlations with the factors than LI-1 points and LI-2 points do because the LI-1 does not distinguish debris from scarps.