## 5 Discussion
### Geological Interpretation
#### 5.1.2 Landslides and Erosion Landforms  
South of the city of Crotone and northwest of the Capo Colonna promontory, the \(V_{U}\) map highlights two elongated patterns and a more circular one of vertical motions (Figure 9a) that cannot be attributed to land subsidence, given their shape and underlying topography, but instead to mass movement processes. As both ascending and descending mode data were exploited in the analysis, the directional variety of mass movements in this zone was taken into account. In turn, both east-facing and west-facing slopes were visible to the Sentinel-1 LOS and covered with targets from at least one P-SBAS output dataset. The first pattern of vertical motions, generally up to \(-0.75\) cm/year with a few peaks of \(-1.0\) to \(-1.4\) cm/year, covers the narrow coastline section where, according to the Hydrogeological Setting Plan (Piano Stralcio per l'Assetto Idrogeologico, PAI) updated in 2016 by the River Basin Authority of Calabria Region [86], a dormant landslide area with a medium hazard level (i.e., hazard index IP2) is mapped (i.e., polygon A in Figure 9a). Within the boundary of this polygon, the velocity along the steepest slope direction is generally lower than \(5\) cm/year, with some peaks at 30-50 cm/year. As per the simplified geology reported in Figure 1c [30], the bedrock lithology is made of Pliocene-Early Pleistocene clays, which are known for their susceptibility to local slope-wash processes, particularly in non-vegetated areas (Figure 2; [49]; see Section 2). According to the Copernicus Land Monitoring Service Coastal Zones dataset (Figure 5a; [85]), the land cover at the slope foot is mainly \"industrial, commercial, public and military units (other)\", \"continuous urban fabric\", and \"construction sites\". These classes match with the Google Earth satellite observation of residential buildings, leisure estates, and local commercial activities distributed along the SP49 road connecting Crotone with the Capo Colonna promontory and the southern part of the province. The second elongated pattern of vertical motions, up to nearly \(-3.0\) cm/year, is located on top of a superficial landslide zone (i.e., polygon B in Figure 9a) classified in PAI 2016 [86] as active with a high hazard level (i.e., hazard index IP3), and where calanchi landforms (Figure 9b) have been recognized [49]. The velocity along the steepest slope direction reaches 10-50 cm/year at several locations within the mapped landslide zone, though in this case this may not be the predominant deformation direction for the whole landslide body, given the existence of some accumulation zones, as well as some scarps. Displacement time series for the coherent targets within this zone show a clear trend reaching up to \(-15\) cm of total LOS displacement in the observation period (Figure 10c). More to the west, a third cluster of coherent targets moving vertically up to \(-2.4\) cm/year defines a nearly circular pattern indicating deformation at another calanchi landform (i.e., polygon C in Figure 9a) [49] that is classified in the PAI 2016 [86] as a dormant superficial landslide zone with a medium hazard level (IP2). Velocity values along the steepest slope direction are lower than \(5\) cm/year across most of the feature. Both the landslide areas exhibit a rural land cover ranging from sparse vegetation to scrubland grassland (Figure 5a). Since the P-SBAS results provide more recent information than the data used for the PAI 2016 classification, the above velocity values suggest the opportunity to update  
Figure 11: 1995–2020 vertical displacement time series of a target in the main subsidence bowl at Capo Colonna, obtained by stitching the Sentinel-1 displacement results from the present study with the ERS-1/2, ENVISAT, TerraSAR-X, and COSMO-SkyMed trend lines redrawn from [46]. the state of activity of these landslide and calanchi landforms, by applying the PSI-based matrix approach [84; 91] that was originally tested in northern and central Calabria.