Landslide Susceptibility Mapping Based on Triggering Factors Using a multi-modal approach
With the absence of a landslide inventory for Lebanon, no regional scale landslide susceptibility assessment based on the modes of failure was conducted for the country. But rather, many researchers employed statistical and physical methods to assess landslides. In our paper, we present a multi-modal regional scale assessment for landslides based on geological and topographic settings, and on rainfall as the triggering factor. Under rainfall, Lebanese slopes were assumed to be prone to three different modes of failure, depending on their geology and topography: rock-slope failures, debris flows and coherent rotational slides. For each of these modes, a convenient geotechnical model was adopted and implemented in a geographic information system (GIS) to assess and visualize the susceptibility of slopes. Furthermore, a runout assessment approach was proposed in order to account for the full influence area of the landslide, rather than considering the initiation sources of landslides as the only hazard zones. The runout assessment was applied for the rainfall induced landslides that we predicted, and for the earthquake induced landslides predicted in Grant et al. (2016). Finally, the proposed model was validated during field assessment, since it was in good agreement with the actual slopes failures observed across the country. Therefore, the multi-modal approach can be used to assess rainfall induced landslide susceptibility, especially where landslide inventories are not available. Moreover, land use in the country can be assessed based on the proposed model, since it identifies high landslide hazard areas, and thus measures can be taken beforehand to reduce the impact of such events.
Figure 1: Landslide at Exit of Chekka Tunnel