Three Decades of Ground Deformation at Somma–Vesuvio (Italy) from Multi-Mission DInSAR Time Series (1993–2024): Insights from Time-Series Inspection and Variational Bayesian Independent Component Analysis

We analyse three decades of ground displacement time series at Somma–Vesuvio volcano (Italy), derived from a multi-mission Differential Interferometric Synthetic Aperture Radar (DInSAR) dataset combining ERS/ENVISAT (1993–2010), RADARSAT-2 (2010–2015), and Sentinel-1 (2015–2024) acquisitions. The DInSAR measurements are referenced to a site at Marigliano, approximately 12 km north of the summit, and are validated against continuous GNSS observations and analysed at representative sites spanning the summit area, the circum-Vesuvian ring, eastern Naples, and the volcanic apron. In addition, we apply Variational Bayesian Independent Component Analysis jointly to quasi-vertical and eastward displacements within 16 km of the summit. The results identify (i) a spatially confined, exponentially decaying subsidence transient along the circum-Vesuvian ring, previously identified from shorter ERS/ENVISAT time series; (ii) deformation in eastern Naples consistent with post-industrial groundwater rebound; (iii) a marked change in the regional deformation regime around 2001–2002, also previously identified from shorter ERS/ENVISAT time series; and (iv) a progressive subsidence slowdown after approximately 2014–2015, particularly along the southern flank. Together, the spatial and temporal coherence of these signals with published seismic, tilt, fumarolic, and groundwater–geochemical observations supports the interpretation of a persistent deep-seated contribution to the long-term deformation of the volcano, while the vbICA decomposition demonstrates that substantial shallow and anthropogenic contributions are superimposed on the volcanic signal. More generally, the results show that long-term multi-mission DInSAR combined with statistical source separation can help disentangle coexisting deformation processes in complex volcanic environments.