## 5 Discussion
### Geological Interpretation
#### 5.1.1 Coastal Land Subsidence at the Capo Colonna Promontory  
The vertical and horizontal displacement field at Capo Colonna in 2014-2020 unequivocally highlights that the promontory is affected by land subsidence (Figure 7). The spatial configuration (albeit due to different causative factors) is, indeed, not dissimilar to other subsidising areas in Calabria region (e.g., Gioia Tauro [88]). \(V_{U}\) increases from inland and from the promontory coastline toward the central agricultural area, which is bounded by the spatial distribution of the gas wells (Figure 7a). The full displacement history for a coherent target at the center of the bowl is shown in Figure 10a through its LOS time series at the nearly 300 dates composing the dataset. Despite the lower density of coherent targets across the rural landscape, the east-west horizontal field makes evident that the motions converge toward this agricultural area, and this is the location around which the subsidence bowl appears to be centered (Figure 7b), i.e., west of the Hera Lacinia 001 production well. The evidence of such an east-west deformation field at the promontory is similar to earlier observations based on COSMO-SkyMed 2011-2014 data [28]. These results highlight a spatial association between land subsidence and gas extraction infrastructure that has been observed in previous studies. In this regard, in chronological order of publication, Table 1 summarizes journal papers, proceedings, and technical reports that include InSAR analyses of land subsidence at Capo Colonna. Of these, the majority focused on InSAR datasets retrieved from one to two SAR sensor datasets. Whereas [46] provided not only the most recent assessment using COSMO-SkyMed ascending and descending (2011-2015) and Sentinel-1A ascending (2014-2016) data, but also a 25-year-long review of local land subsidence through the combination with other C- and X-band InSAR datasets from 1992 to 2010. Up to \(-2.0\) (2011-2014), \(-1.0\) (2014-2015) and \(-0.8\) (2014-2016) cm/year LOS rate; up to \(-20\) cm vertical displacement (1992-2016; stitched time series)  
Comparison of the Sentinel-1 P-SBAS outputs with past observations available in the literature allowed corroboration of the spatial patterns and the order of magnitude of the deformation rates affecting the study area. In particular, the present results corroborate the spatial patterns of land subsidence that were found with ERS-1/2 ascending and descending data processed with SBAS [38] and Permanent Scatterers InSAR (PS-InSAR) [39; 46], ENVISAT ascending data with SBAS [38] and Persistent Scatterers Pairs-DIFerential InSAR (PSP-DIFSAR) [39; 46], TerraSAR-X ascending and descending data with SBAS [45; 46], and COSMO-SkyMed ascending and descending data with PSP-DIFSAR and the Coherent Pixel Technique-Temporal Sublook Coherence (CPT-TSC) [46]. It is worth noting that a quantitative comparison of 2014-2020 deformation rates with those observed in these past studies is not viable due to their different time coverage. Figure 10: Examples of 2014–2020 time series of LOS displacement for coherent targets (**a**) at the center of the main subsidence bowl within the Capo Colonna promontory, (**b**) along the coast of the promontory, and (**c**) within the landslide-affected area south of Crotone, from the P-SBAS ascending mode dataset. Colors refer to the annual LOS velocity of each target, according to the legend in Figure 6. The target location is also indicated in Figure 6.  
Such corroboration is achieved through a significant improvement in terms of both InSAR processing and post-processing of coherent targets and their time series. In particular, most of the previous studies on Capo Colonna relied on LOS displacement values only [38; 39; 46] and, when the authors of those papers attempted the extraction of deformation components, they limited it to either the vertical [45; 46] or east-west [28] deformation field.