Anomaly detection within the 2021-2023 deformation pattern of the Campi Flegrei (Italy) caldera through the analysis of DInSAR and GNSS data

The Campi Flegrei caldera (southern Italy) is an active volcano whose last eruption occurred in 1538. This caldera is characterized by ground displacements (subsidence or uplift), often referred to with the term "bradyseism". Over the last two decades the Campi Flegrei caldera was affected by a phase of uplift which became progressively more intense over time and was accompanied by increasing seismicity and geochemical anomalies. The Campi Flegrei deformation pattern generally shows a bell-like shape, with the zone of maximum uplift in the central area corresponding to Rione Terra, that is the historic district of Pozzuoli. In the 2021-2023 period the OV-INGV seismic network detected significant seismicity and the GNSS and DInSAR measurements highlighted a high uplift rate of the central area of the Caldera. In this period, seismicity was distinctly felt by the population several times (maximum magnitude Md = 4.2) and the uplift of the central sector of the caldera reached a level that made it difficult to enter the ancient fishermen's port of Pozzuoli (about 120 cm compared to the ground level in 2005). We have carried out a detailed analysis of the ground deformations relevant to the 2021-2023 time interval. Our study has highlighted a local anomaly of the caldera deformation pattern in the Solfatara-Pisciarelli-Olibano hydrothermal area. This anomaly became well recognizable in 2022 and it further developed during 2023. Moreover, it affects the area in which the earthquakes with greater magnitude occurred in the Campi Flegrei. We interpret this zone as a possible weakness area in the crustal structure of the Caldera and, therefore, we believe that a detailed monitoring of this zone is foreseen because it may provide some relevant insights on the caldera dynamics and the related hazard.