3D Structure and Dynamics of Campi Flegrei Enhance Multi-Hazard Assessment

Campi Flegrei is an active caldera in a densely populated area, currently experiencing significant ground uplift and seismicity. Leveraging precise relocations of extensive seismicity since 2014, we determined high resolution (250 m), 3D P- and S-wave seismic images of the inner caldera which we combine with a novel rock-physics experiment to characterize the primary features of the caldera’s 3D structure: a gas-rich reservoir below 2 km depth, a deformed caprock at 1 to 2 km depth, and a funnel-shaped, (thermo-metamorphic) basement below 3.5 km depth. Seismicity migrates downwards from the caprock to the reservoir, and, following reservoir depletion, stress loading triggers deeper, larger magnitude events along the inner-caldera boundary faults. The reservoir extent and the seismicity distribution closely correlate with the area of maximum uplift, where accelerating deformation due to pore-fluid pressure is corroborated by laboratory experiments using site-relevantin-situ rock samples. These findings suggest that coupling between gas-reservoir pressure and the fibrous microstructure of the confining caprock drives the ground uplift. This structural-dynamic reconstruction of interconnected seismic and ground deformation processes provides a framework for forecasting the evolution of unrest, which is crucial for enhancing medium- and short-term multi-hazard assessment and mitigation strategies. Our results indicate that seismic activity and the potential for a phreatic explosion should be considered as plausible scenarios, prompting a reevaluation of the hazard assessment for the area.