## 4 ETL Susceptibility Assessment in Cephalonia Based on GIS-Based Analytic Hierarchy Process
### ETL Susceptibility Model
The maps of slope, aspect and curvature (Figure 7a-c, respectively) were derived from the digital elevation model (DEM) of Cephalonia generated from the TanDEM-X mission, which was based on very high resolution (VHR) synthetic aperture radar (SAR) X-band data [94]. The TanDEM-X global DEM was initially introduced in 2016, based on the processing of SAR data, which were acquired within the years 2011 and 2012, succeeded a spatial DEM resolution of 0.4-arcsecond (ca. 12 m) with the aim of establishing a 2 m relative height accuracy [95; 96; 97]. Independently published comparisons prove an of TanDEM-X DEM smaller than \(\pm\)0.20 m, a root-mean-square error (RMSE) smaller than 1.4 m and an excellent absolute 90% linear height error below 2 m. The assessed accuracy of these data sets is rather excellent and are used quite often for geomorphological and hydrological modeling [98; 99]. Concerning the geological parameters used for the assessment of landslide susceptibility, the bedding of formations [100; 101], the presence of faults and especially the presence of active faults in seismic active areas [102; 103; 104; 105; 106] and local hydrogeological features [24; 107] are common in relevant models. The distance to tectonic structures and especially to faults is the most widespread parameter, derived from simple mapping of geo environmental and other data [108; 53; 109]. Consideration must be given to the fact that the faulted rock along the zone and the surrounding unfaulted rock behave differently during the occurrence of an earthquake, and each fault responds differently to each seismic event, even within the same fault zone. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Layer** & **Data Type** & **Data Source** \\ \hline Slope & Grid & \\ \hline Aspect & Grid & DEM of Cephalonia resulted from the TanDEM-X digital data \\ \hline Curvature & Grid & data \\ \hline Lithology & Polygon & Neootectonic Map of Gephalonia by [PERSON] [32] \\ \hline Tectonic Structures & Line & Neootectonic Map of Gephalonia by [PERSON] [32] \\ \hline NDVI & Grid & Sentinel (acquisition date 21.04.11) \\ \hline PGA & Grid & [PERSON] et al. [65] \\ \hline Rainfall & Grid & The Climate Atlas of Greece by the Hellenic National Meteorological Service [88] \\ \hline Rivers & Line & Topographic maps by the Hellenic Military Geographical Service [89; 90; 91; 92] \\ \hline Roads & Line & Topographic maps by the Hellenic Military Geographical Service [89; 90; 91; 92] \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Thematic layers used in the study and their sources. Regarding the geological parameters used for assessing landslide susceptibility, the presence of scree, talus cones and clastic formations of various age is an aggravating factor for the occurrence of slope failures by earthquakes. Alluvial deposits have little or no influence on the occurrence of these phenomena, while carbonate rocks are susceptible to slides and rockfalls in cases where a steep slope has been formed either by geological processes (e.g., fault zones, incision, erosion, etc.) or by human intervention (e.g., steep road slopes, etc.). Both geological parameters, lithology and tectonic structures, in the case of the landslide susceptibility in Cephalonia were derived from the Neotectonic Map of Cephalonia [32] (Figure 7d,e). Earthquakes are considered to be a main factor in landslide susceptibility, which is why they are taken into account in relevant studies worldwide, as in Greece [110, 111] and Central Asia [112]. In seismic hazard calculations related to landslide susceptibility studies, co-seismic strong ground motion, which is the cause of damage after the occurrence of large earthquakes, is most often expressed in terms of peak ground acceleration (PGA). PGA is often obtained from probabilistic seismic hazard assessment (PSHA). It is mainly preferred as an earthquake metric, as it refers to the overall seismicity of the study area [110].