(ii) Slope inclination

Slope gradient influences on a high grade the slope proneness to failure due to a combination of reasons such as the weathering processes, the internal geometry of geological formations as well as the intensity of meteorological conditions [34]. Through the use of digital elevation model and geographical information systems processing, the slope layer was derived and classified into five classes, as follows: (1) 0◦–5◦, (2) 5◦–15◦, (3) 15◦–30◦, (4) 30◦–45◦, and (5) >45◦, with the higher rating (4) to be given to the slopes with the higher inclination (>45◦) [33].

#### (iii) Slope orientation (aspect)

Another morphological characteristic that influences landslide initiation is the slope orientation (i.e., aspect). Since vegetation and moisture retention depends on aspect, in their turn may affect soil strength and as a result the proneness to landslides. Furthermore, since specific orientations are associated with increased snow concentrations and consequently longer periods for freeze and thaw processes, (not to mention that significant amount of rainfall falling on a slope may vary depending on its orientation [40]),

make everybody accept that this is a very crucial parameter for the estimation of landslide susceptibility. The classification of the slope aspect is shown in Table 2 and its rating is based on Koukis and Ziourkas [37]. According to them, in statistical analysis for landslides in Greece took place in the period 1949–1991, the classes 0◦–45◦, 45◦–90◦, are associated more frequently with slope failures. Thus, in this study, the highest rating corresponds to rating 4.


**Table 2.** Parameters and their rating selected to be employed in the model.
