3D structure and dynamics of Campi Flegrei enhance multi-hazard assessment

Campi Flegrei is an active caldera in a populated area, currently experiencing significant ground uplift and seismicity. Leveraging seismicity relocations, here we obtain high resolution, 3D P- and S-wave seismic images which we combine with a tailored rock physics experiment to define key features of the caldera’s structure: gas-rich reservoir below 2 km depth, deformed caprock at 1–2 km depth, and basement below 3.5 km depth. Seismicity migrates downwards from the caprock and changes in stress loading trigger deeper, higher events along the inner-caldera boundary faults. The reservoir closely correlates the area of maximum uplift, where deformation acceleration due to pore- fluid pressure is corroborated by laboratory experiments using site-relevant rock. The interaction between the pressurized gas-reservoir and the confining caprock drives the ground uplift. Our results indicate that seismic activity and the potential for a phreatic explosion should be considered as plausible scenarios, prompting a re-evaluation of the hazard assessment.