Engineering geological mapping of earthquake-induced landslides in South Lefkada Island, Greece: evaluation of the type and characteristics of the slope failures

A moderate, shallow depth, earthquake (Mw = 6.5) occurred onshore Lefkada island on November 17, 2015 with the focal depth estimated at 11 km. The seismic fault is a near-vertical strike-slip fault running along the western coast, part of the Cephalonia Transform Fault. Landslides and ground cracks were mainly reported at the western part of the island, inducing structural damages. High severity slope failures occurred at Egremnoi and Gialos areas that both are located at coastal regions. This study aims to investigate the engineering geological conditions at these areas, and assess the characteristics and physical quantities (e.g., type, area—m², and volume—m³) of the instabilities. To achieve this, engineering geological mapping was implemented in Egremnoi and Gialos area aiming to; (a) classify the geological units mapped on the heavily damaged areas and (b) to correlate them with the type of slope failures. Furthermore, type and dimensions of slope failures were evaluated to estimate the total volume of the mass movement. All the data, originated from the engineering geological mapping, have been digitized and rasterized at 5 m grid spacing using the Arc/Info GIS software to perform a Newmark's sliding block analysis. The outcome arisen by this analysis is that the generated by the earthquake peak ground acceleration at these areas should be at least 0.45 g to trigger these kinds of slope failures.