## 3 Material and Methods
### InSAR Technique and Data  
Since the 1990s, the Synthetic Aperture Radar Interferometry (InSAR) technique allowed the detection and measurements of crustal movements from space with unprecedented accuracy and spatial coverage [89; 90]. The InSAR is a non-invasive technique [91], suitable to monitor large areas of the Earth's surface, measuring the projection of the deformation vector onto the Line of Sight (LoS) direction. In the last 20 years, the increased availability of new SAR instruments and satellite constellations, has stimulated a steady improvement of processing algorithms. Several multi-temporal InSAR techniques have been proposed, exploiting the redundancy offered by hundreds of image pairs, i.e., hundreds of interferograms, to retrieve mean ground velocity and time-series of relative ground displacements. The existing algorithms fall into two broad categories, based on the Permanent Scatterer (PS) [92] and the Small Baseline (SB) [93] approaches, although more recently algorithms exploiting the basic principles of both methodologies have also been proposed [94]. In this study, we adopted the SBAS methodology applied along both the ascending and descending orbit of the Sentinel-1A satellites (C-Band SAR sensor wavelength=5.6 cm) operated by the European Space Agency (ESA) in the TOPSAR acquisition mode (VV polarization) and free-distributed ([[https://sentinel.esa.int/web/sentinel/missions/sentinel-1](https://sentinel.esa.int/web/sentinel/missions/sentinel-1)]([https://sentinel.esa.int/web/sentinel/missions/sentinel-1](https://sentinel.esa.int/web/sentinel/missions/sentinel-1)), accessed on 6 January 2021 [95]). Both the ascending and descending SAR datasets have been processed using the Geohazard Exploitation Platform (GEP, [[https://geohazards-tep.eu/](https://geohazards-tep.eu/)]([https://geohazards-tep.eu/](https://geohazards-tep.eu/)), accessed on 6 January 2021 [96]) and the P-SBAS service, implemented therein. An initial multi-looking operation was applied to the Single Look Complex images equal to 20 and 5 looks along the range and azimuth direction, respectively, resulting in a ground pixel resolution of 90 meters. The main processing steps of the SBAS approach consist of differential interferograms generation from the formed SAR image pairs with a small orbital separation (spatial baseline) to reduce the spatial decorrelation and topographic effects. The Shuttle Radar Topography Mission (SRTM) [97] with 1 arc-second (\(\sim\)30 m pixel size) DEM from NASA and precise orbits from the European Space Agency (ESA) were used for the co-registration and for topographic phase removal from the interferometric phase on each of the compute interferograms. Then, a filtering operation is performed to improve the obtained interferogram's quality and make easier the following phase unwrapping step according to a fixed coherence threshold (equal to 0.7 for both the ascending and descending processing). Then, an inversion step is performed to put together the ground displacement time series in the time interval covered by the considered SAR acquisitions. At this stage, the atmospheric artifacts are also estimated and removed through a double filtering in the spatial and temporal domain (high and low pass filtering equal to 1200 meters and 365 days, respectively) [93; 98]. Finally, the geocoding step is applied by means of the adopted DEM, obtaining a 90m ground pixel in the WGS84 datum to reference the displacements estimated for both the orbits. In detail, we considered 60 images along the descending orbit (track 124) covering the time interval from 6 July 2017 to 8 March 2020 with a revisiting time of 12 days, enough to detect the movement in the investigated area, and resulting in 163 pairs. The same procedure was considered for the ascending case (track 44) selecting 103 images relative to the 3 October 2016-28 March 2020 temporal span and forming 290 interferograms.