## 3 Results
### High-Resolution Remote Sensing Data
#### 3.2.1 Change Detection  
Specifically, we compared the orthophotos acquired by Pleiades before and after the November 2015 earthquake over four areas along the western coastline of Lefkada. At the same time, we also analyzed two DSMs. The first was dated back to 2008 and was obtained from the Greek cadastral, while the second was generated from Pleiades stereo pairs that were acquired in 2016. According to the cadastral official specifications, the DSM had a vertical accuracy ranging between 2 and 3 m. The respective accuracy of the Pleiades DSM was found to be considerably better than 1.5 m.  
The analysis of the aforementioned revealed that the 2015 earthquake provoked severe changes to the cliffs along the coastline. In further detail, Figure 8 depicts the coastal area of Egremmi as derived from Pleiades orthophoto before and after the earthquake. It is obvious that the cliff has totally changed; the inclination was increased (Figure 9) and there is a serious loss to the vegetation cover of the area (Figure 8). As can be observed in Figure 8, the road leading to the beach was totally destroyed. In the specific part of the coast, the length of the landslide was measured at 135 m. In the middle of the beach, there was a big rock outcrop lying next to the sea, while, on both sides of the rock, the cliff has impressively changed. In 2016, the cliff moved backwards, and the beach was covered through debris flow. The landslide length was found to have overpassed 185 m at the that point. Added to this, areas with a slope inclination greater than 45 degrees were increased along with the absolute value of the highest inclination (i.e., 84.6 degrees instead of 82.5 degrees in 2015). Generally speaking, all areas along the beach next to the sea presented higher inclination values in 2016 as a result of mass-wasting processes. The areas with the greatest vegetation losses, related to the 2015 earthquake, have been presented with red shades in Figure 10. NDVI indices for the years 2015 and 2016 have been calculated based on Pleiades multispectral data with a spatial resolution of 0.5 m. These  
Figure 7: NDVI results before (**a**) and after (**b**) the 2015 earthquake, as derived from the processing of Landsat imagery in the GEE. (**c**) NDVI difference between the years 2015 and 2016, as derived from the processing of Landsat imagery in the GEE. results verified the NDVI changes captured by the medium resolution data in the GEE. Red shades correspond to NDVI differences between 2015 and 2016, while the black dashed line indicates the landslide extent. A very high vegetation difference (loss) resulted from the 2015 earthquake was identified along the Egremni cliff. The width of the beach displaying the largest changes (change of inclination, vegetation loss, and mass movements) was measured to be about 1.5 km. The detected changes along the Okeanos cliff are presented in Figures 11 and 12. On the left of these figures, the Pleiades orthophoto of the Okeanos coast in 2016 is presented in both figures, while the right side depicts the same area in 2015. The yellow line indicates the landslide extent. The backwards movement of the cliff was evident on the left image. In fact, the pre-existing landslides were deemed to have been reactivated and enlarged both in their lengths and widths. The most characteristic example of such phenomenon is presented in Figure 12, which presents an enlarged part of Figure 11. As can be seen, the crown of the landslide reached the buildings on the top of the hill in 2016 (upper part of Figure 12), while the total length of the landslide body exceeded 237 m (upper part of Figure 12). Slope maps of the Okeanos coast before and after the occurrence of the 2015 earthquake are displayed in Figure 13. Large changes to the inclination were detected, especially at the south part of the coast. The lower inclination values (green shades) were replaced by red shades nearer to the sea, indicating that a large body of debris flow has moved from the cliff to the beach, altering the relief.