An MT-InSAR-Based Procedure for Detecting and Interpreting Vertical Ground Deformation Anomalies During Phases of Unrest at Campi Flegrei Caldera, Italy

Active volcanic calderas often experience significant ground deformation, characterized by uplift and subsidence, typically with a radial or elliptical pattern centered on the caldera. However, the detection of small second-order anomalies within the main deformation pattern can provide critical insight into impending eruptions and/or hazardous structural and volcano-tectonic features. In this study, we present a simple but novel method for detecting and interpreting second-order deformation anomalies at Campi Flegrei caldera by filtering the primary, radial deformation signal observed during volcanic unrest phases. For this purpose, we used a procedure based on the polynomial fit of vertical displacement data, assuming that they depend only on the distance from the deformation center. By subtracting the best fitting radial deformation from the observed vertical displacement, we generated an anomaly map that highlights sectors with unexpected deformation patterns. We applied the proposed procedure to analyze the ground deformation at the Campi Flegrei caldera (Italy) that occurred from 2016 to 2021, by using MT-InSAR data from Sentinel-1. Coeval GPS datasets were also used for cross-checking the obtained results. The results of this analysis show a pronounced NE-SW alignment that separates sectors with different uplift trends. It highlights a primary volcano-tectonic structure potentially linked to high seismic hazard. This method, after further investigation, can provide a valuable tool for improving hazard assessment and understanding the structural dynamics of calderas during unrest phases, with implications for improving preparedness in densely populated volcanic regions.