## 3 Methods  
InSAR (Interferometric Synthetic Aperture Radar [40; 41] can be considered one of the most powerful satellite remote sensing techniques used for the measurement of displacements of the Earth's surface. It is based on the comparison between RADAR images acquired in different times over the same area. The Advanced Differential SAR Interferometry (A-DInSAR) approach consists of the combination of many SAR images, allowing for the retrieval of the temporal evolution of displacements of objects on the ground during the investigated time period [42; 43]. The use of this Multi-Image technique allows for the identification of the deformation process, past or in progress, and to estimate its evolution over time and space, so it can be profitably exploited to investigate the spatial and temporal evolution of ground deformation processes with millimetric accuracy. In this study, 411 Sentinel-1 SAR scenes, in ascending and descending orbital geometries covering the study area, have been analyzed using a Multi-Image A-DInSAR technique. Sentinel-1 (European Space Agency, ESA) is a two-satellite constellation carrying onboard a C-band SAR sensor (5.40 GHz frequency and about 5.55 cm wavelength), operating since the second half of 2014. The acquired stacks cover a period of about 4 years and 7 months (from October 2014 to April 2019). We used Interferometric Wide beam mode in Single Polarization (IW) SAR images, characterized by a spatial resolution of approximately \(5\times 20\) m, a wavelength of 5.6 cm (C-band), and 250 km wide images (Table 1). Figure 2: Section XVIE of the Zelazny Most Tailings dam (eastern part of the dam; modified form [1], reprinted with permission from [1], 2014, ICE Publishing). Glacio-tectonic shear surfaces are represented in red. A-DInSAR analysis were performed to acquire information regarding past displacements that affected the ground surface over the entire investigated area since late 2014. The multi-temporal interferometric analyses have been carried out using Persistent Scatterers Interferometry (PSI) technique [41; 42; 43; 44; 45] and with proprietary procedures implemented in SARPROZ software [46]. The accuracy of the PSI results depends on many parameters, such as the number of SAR images, the spatial distribution of PSs, climatic and atmospheric conditions, distance from the reference point, and the quality of PSs within the area of interest. Specifically, to reduce the decorrelation effects, all images were related to a single master image, which was selected by considering the perpendicular and temporal baselines. After all images were co-registered to the master image, the maps of the radar parameter were generated: the reflectivity map (a multi-temporal amplitude value for each pixel) and the amplitude stability index map (the coefficient of variation of the amplitude). These maps were used as quality estimators for the selection of persistent scatter candidates (PSCs) in the PSI workflow. Then, the standard \"star\" graph (Figure 3; [43]) has been used to connect all slave images to a single master image and thus to generate interferograms. This graph represents all the SAR images according to their temporal baseline (X axis) and their normal baseline (Y axis), both for ascending and descending orbital geometries, and allows to generate a network by connecting all the images (slave images) to one (master image; Figure 3). A network of PSCs was created to estimate preliminary height and displacement parameters. This step is needed to detect and remove the atmospheric phase screen (APS), starting from the residual phase components. After APS estimation and removal, the final estimation of the velocity and residual height for the Persistent Scatterers (PS), was performed on a much larger set of points, as the final step of the PSI procedure. For each PS the velocity values along the Line of Sight (LOS), the displacement time series, and the height, were computed (relative to a reference point identified in a stable region).