Clues on the ongoing unrest at Campi Flegrei from the high-definition seismic 2022-2025 catalogue

The statistical analysis of the recently published high-resolution seismic catalogue for Campi Flegrei (January 2022–March 2025, Tan et al. 2025) reveals that deep-sourced degassing controls Campi Flegrei seismicity, illuminating pathways to the surface along a subset of permeable structures and generating seismicity only in specific volumes. Analysing the catalogue using machine learning cluster analysis to identify objective volumetric seismicity sources, two main seismogenic volumes emerge: a deep ring of cigar-shaped 1D source volumes, and a cloud of shallower 1D/3D source volumes connecting the ring's northern sector to the surface. The found clusters were compared with other existing information about the caldera structure (e.g. known faults, deep and surficial tomography studies of different nature, geochemical data), showing that ring seismicity encircles a potential primary volcanic source (main degassing zone) and occurs at the intersection between pre-existing faults and a sub-horizontal south-dipping rheological interface, while the cloud track the main gas plumes detaching from the ring and infiltrating through faults into the shallowest seismic volumes below Accademia, Solfatara-Piscarelli and Rione Terra. Interesting spatio-temporal variations in the rate of activity of the different sources seem to track pressurization cycles, leading to the activation of new volumes during high activity periods.

 

Xing Tan, A. Tramelli, S. Gammaldi, G.C. Beroza, W.L. Ellsworth, W. Marzocchi, A clearer view of the current phase of unrest at Campi Flegrei caldera. Science 390, 70-75 (2025). doi:10.1126/science.adw9038