## 3 Data, Methods and Results
### SAR Data Processing
We selected the SBAS technique because it works well in the vegetated and rural areas such as the mountainous Achaia region, due to the use of distributed scatterers. Figure 4: Perpendicular baseline configuration and network of the 346 small baseline interferograms formed from 99 Sentinel-1A images (ascending track, top panel) and network of the 317 SB interferograms formed from 120 Sentinel-1A images used in this study (descending track, bottom panel). Vertical lines indicate the network gaps. Figure 3: Correlation diagram showing standard deviation: (**a**), of unwrapped phases before and after the GACOS corrections and their reduction rates; (**b**), for descending track 80. The grey line denotes a 1:1. The STD decreased from 4.36 rad to 2.61 rad on average with a mean reduction rate 36.29%. We also used the percentile bootstrap method to calculate the LOS velocity's standard deviation from cumulative displacements. The next processing step was the masking of noisy pixels in the time series and the spatiotemporal filtering of time series. Finally, topography-correlated components (linear with elevation) were subtracted with deramping (see Figures S5 and S6), and we obtained the LOS velocity maps for each satellite track (Figure 5). After the main processing, we decomposed the LOS displacement data to east-west (E-W) and up-down (U-D) components assuming that the north-south (N-S) displacement is very small due to the track's imaging geometry of the Sentinel-1 satellite [62; 63]. In the area around the village of Krini (Figure 1), an active landslide is present (Figure 5a,b). More active landslides are also located near the villages of Graikas, Piittsa and Sella and to the monastery of Agia Eleoussa (Figure 5c,d). In those locations we measured LOS velocities up to \(-55\) mm/yr for the ascending track (Figure 5a). We obtained similar velocities, up to \(30\) mm/yr for the descending track (Figure 5b). Note that the values of LOS displacements are referenced to a local reference point which is located about \(30\) km south of the area of interest (see Figure S1 for location), and it is considered stable (free of gravitational or tectonic displacements). Then, we produced maps of the east-west and up-down components, assuming that the north-south component was neglected due to the track's geometry of the Sentinel-1  
Figure 5: Displacement maps in LOS direction for the broader areas of Krini (**a,b**) and Pititsa villages (**c,d**) for ascending track and descending track (**a**) shows the displacement map for ascending track; and (**b**), for descending track around the village of Krini, respectively. The Figure 5c,d corresponds to displacement map for ascending and descending track around the villages of Pititsa and Sella, respectively. satellite. We found that all active landslides were moving east and downward (subsidence, Figure 6a,b). All the affected areas are located on the east-facing slopes and in the foothills of Panachaiko mountain (Figure 1). We traced the boundaries of the active landslides using the InSAR motion data on the E-W component (Figure 6e,f). We note that our motion data refer to the period 2016-2021 (Figure 4), so it is possible that landslides mapped in previous studies in the same area [15; 20] have changed their motion patterns. In our study we measured the mean velocity of the larger landslides (Krini and Agia Ele  
Figure 6: Displacement-rate maps in mm/yr: Up (**a**,**c**) and E-W (**b**,**d**), component after the decomposition of InSAR data for the broader areas of Krini and Pititsa villages, respectively; (**e**), showing the landslides’ outlines for Krini and Griakos landslides; and (**f**), showing the landslides’ outlines for the monastery Agia Eleoussa and the villages of Pititsa and Sella. orange lines in Figure 6e,f)) by a statistical approach and not by referring to a single pixel. The mean velocity of the Krini landslide was found to be 6 mm/yr downward (nearly 0.6 cm/year) and 28.7 mm/yr (nearly 3 cm/year) eastward.