Source modelling of surface deformation and seismicity at the Campi Flegrei

Campi Flegrei, a restless caldera near Naples, Italy, has experienced significant ground uplift, elevated seismicity, and intense gas emissions over the past two decades. The physical source driving the observed deformation and seismicity remains debated, with proposed mechanisms including magmatic intrusion, hydrothermal pressurization, or hybrid processes. Recent seismic tomography images reveal a gas-rich reservoir at depths of ~2–3.5 km, coincident with concentrated seismicity, highlighting the potential dominant role of the shallow hydrothermal system.In this study, we investigate whether a shallow reservoir can jointly explain both surface deformation and seismicity during the ongoing unrest. We use geodetic observations to constrain time-dependent volume changes of the shallow reservoir, integrating multi-year InSAR data from Sentinel-1 with continuous GPS measurements. To isolate signals associated with distinct deformation sources, we apply variational Bayesian Independent Component Analysis (vbICA). The reconstructed reservoir volume-change history is then incorporated into the induced-seismicity framework Flow2Quake to compute Coulomb stress changes, which are assumed to modulate seismic activity.Our results show that volume changes within the shallow reservoir can consistently reproduce both the observed surface deformation and the spatial–temporal patterns of seismicity at Campi Flegrei. These findings place new constraints on the dominant source of unrest and improve our understanding of the coupled hydrothermal–mechanical processes governing the current state of the caldera.