A Terrain classification system for coseismic landslide hazard analysis: Lebanon, a case study

Abstract

Coseismic landslides have caused vast amounts of damage throughout history, and are often responsible for more damage than all other seismic hazards combined (Kramer, 1996). To better assess coseismic landslide hazard on a regional scale a new terrain classification system is proposed. First, the landscape is divided into classes based on possible modes of failure, defining kinematically admissible regions, followed by mode-of-failure specific hazard analyses (strength admissibility) within each region. Terrain susceptible to rock failures, shallow and deep soil failures, and lateral spreading were identified and assessed. Terrain classification was modeled after the work of Iwahashi and Pike (2007), which has been shown to relate to engineering properties of the landscape (eg Vs 30, Yong et al., 2012) using slope, curvature, and roughness. In this work topographic slope, calculated using Ritter’s algorithm (1987) is used to demarcate landslide failure modes. Topographic roughness, calculated as the standard deviation of slope, and vegetation coverage, determined from NDVI values, are then applied to each slope class as a first order approximation of landslide susceptibility. Coseismic hazard is then calculated for each susceptible terrain class using a failure-mode-specific algorithm. Results from this method of hazard analysis are maps of terrain classes, coseismic hazard maps for individual mode of failure, and a composite hazard map.