LANDSLIDE HAZARD MAPPING IN THE SOUTH OF ISRAEL

Strong earthquakes (M >6) are expected in Israel once every 100 – 200 year or so. As part of the national earthquake preparedness in Israel and in order to mitigate the damage of such an event, studies of active and potentially active faults, as well as landslides, liquefaction and tsunami hazards, have been done in the last twenty years. The studies performed are in a regional scale (1:200,000 and 1: 50,000-25,000) usually targeting at once the whole country or large regions and thus are only general.

In early 2016, the Geological Survey of Israel launched a new project objecting a higher resolution (1:10,000 scale) mapping of the earthquake hazards in key sites chosen based on a high risk of damage, mainly due to the short distance to active faults and the existence of dense population. The first region chosen to be analyzed was the Elat region (S. Israel), situated on the Dead Sea faults line. The project included a detailed geological mapping of the quaternary units, a map of active and potentially active faults, a site response study of the area and maps of liquefaction and landslides hazards.

Here we illustrate the methodology and results of the landslides hazard evaluation. The process of producing the hazard map follows three steps: (1) mapping (creating GIS layers with grid cells of 25 m by 25 m) of the topographic slope; (2) grouping the exposed newly mapped geological units to five geotechnical units consisting of formations with decreasing rock strength; (3) hazard mapping; assigning susceptibility-grades, where the grade increases with decreasing rock strength and increasing slope steepness; calibration is performed using field-observations of slope instability within the studied area. The resultant hazard analysis highlighted section in the city of Elat with non-negligible landslide hazard as well as pointed out a few road sections that apparently will be blocked by landslides following an earthquake.