Development of the coseismic landslide susceptibility map of the island of Lefkada, Greece

The island of Lefkada, Greece periodically suffered environmental and structural damages induced by earthquakes. During the twenty-first century, two moderate events of magnitude M > 6 occurred in 2003 and 2015 (M6.2 and M6.5, respectively). The dominant type of the earthquake-induced environmental failures was rock falls and slides that were widespread at the western part of the island. The goal of this study is to assess the earthquake-induced landslide susceptibility in the island of Lefkada and to compile a relevant susceptibility map. To achieve this, we took into account the inventories of coseismic slope failures, that were compiled for the 2003 and 2015 events. The spatial distribution of landslides in relation to the causal factors of geology and topography-oriented parameters were statistically analyzed based on the landslide susceptibility index LSI and the Likelihood ratio LR methods. In order to be able to validate the developed map, the dataset of slope failures was separated into two groups: training set (inventory of 2015 event) and testing one (inventory of 2003 earthquake). The outcome arisen by these analyses is that the geological formation of limestones of Paxos zone and the northwest-facing slopes are considered as the most causal factors for the triggering of slope failures. Considering the factor of slope angle, the LSI-based method shows that the highest frequency of slope failures is related to slope angles between 40° and 50° while the LR approach indicates the areas of high-angle slopes (60°–80°) as the most susceptible one. Taking into consideration that the susceptibility map is compiled based on the spatial distribution of coseismic slope failures triggered by earthquakes occurred both on the northern (2003 event) and southern part (2015 event) of the Lefkada segment of the Cephalonia Transform Fault (CTF), it can be characterized as a complete susceptibility map. Therefore, it is believed that can be used by public agencies and civil protection authorities since the locations of the slope failures triggered by future earthquakes are shown and consequently the elements of the manmade environment, e.g. road network that will be disrupted due to coseismic slope failures could be forecasted.