Campi Flegrei caldera is an Italian high risk volcano that, since the last two decades, is experiencing a progressively more intense long term uplift, accompained by increasing seismicity and geochemical emissions. Ground deformation shows an axisymmetric bell-shaped pattern, with maximum uplift of about 120 cm, from 2005, in the caldera central area. We analyzed Sentinel-1 and COSMO-SkyMed Multi Temporal DInSAR measurements and GNSS data to reveal and investigate a geodetic anomaly that clearly manifested since 2021, deviating from the typical bell-shaped deformation pattern. This anomaly is located east of the Pozzuoli town, in the Mt. Olibano-Accademia area, covers an area of about 1.3 km2 and shows, in comparison to surrounding areas, a maximum uplift deficit of about 9 cm between 2021 and 2023. To investigate the anomaly causes, we analyzed the caldera seismicity and inverted the DInSAR data to determine the primary source of the ground deformation pattern, which results consistent with a penny-shaped source, located approximately 3800 m beneath the Pozzuoli town, with a radius of about 1200 m. We also found that the time evolution of the uplift deficit in the geodetic anomaly area very well correlates with the earthquake occurrence, and the greater magnitude seismic events occurred in this area. These considerations suggest that the geodetic anomaly is connected to the primary deformation source tensile stress regime. This interpretation aligns with the concentration of earthquakes and hydrothermal fluid emissions in this area, which indicate the presence of faults, fractures and hydrothermal fluid circulation. This phenomenon can be elucidated by the influence of the Mt. Olibano-Accademia lava domes lithological heterogeneities, that can induce a localized reaction to ground deformation during the inflationary phase. For these reasons, the geodetic anomaly area represents a zone of crustal weakness amidst the ongoing unrest that requires careful monitoring and study.
