A clearer view of the current phase of unrest at Campi Flegrei caldera

We used a retrained machine learning workflow to enhance the performance of the seismic monitoring network at Campi Flegrei caldera (CFc) for improved tracking of the evolution of volcanic unrest. We analyzed the recent (21 January 2022 to 20 March 2025) continuous seismic data, which showed a sharp increase in seismicity at the highly populated CFc. Our analysis expanded the seismicity catalog from around 12,000 to more than 54,000 earthquakes. The more complete picture of seismicity revealed a sharply defined caldera ring fault system (RFS) featuring a very narrow depth range of seismicity, clearly illuminated shallow faults in the northern part of the caldera, and uncovered a source of very shallow hybrid earthquakes likely related to the hydrothermal system. To date, we have not observed any direct signature of upward migration of magma, nor have we observed seismic activity at depths below 3.7 kilometers on or inside the RFS.