An insight into the unrest phenomena at the Campi Flegrei caldera from Vp and Vp/Vs tomography

Abstract

Abstract High resolution Vp and Vp/Vs tomography of the Campi Flegrei caldera is obtained using active and passive seismic data. We find a continuous ring of high Vp anomaly that defines the caldera rim associated to the last collapse. A sharp Vp/Vs decrease is observed between 2 and 4 km depth, suggesting the absence of magmatic fluids and the presence of rock volumes with over‐pressured gas within the source region of uplift. Atmospheric water penetrating within the caldera and deep CO 2 fluids are presumably heated by a magmatic body located at depth greater than 4 km nested within the limestone layer. Along the fractures bordering the shallow high Vp rim, deep gas and CO 2 fluids up‐raise and are released in the Pozzuoli solfatara. We hypothesize that the past unrest episode is more likely due to pressure changes within the shallow geothermal reservoir located at the top of the magma intrusion.