The effects of hot and pressurized fluid flow across a brittle layer on the recent seismicity and deformation in the Campi Flegrei caldera (Italy)

The influence of the hydrothermal circulation on seismicity and uplift observed at the Campi Flegrei caldera (Italy) is a topic of great interest to the scientific community. Recently, Thermo-Poro-Elastic (TPE) inclusions were proposed as likely deformation sources. They are suitable to explain the mechanical effects induced by hot and pressurized hydrothermal fluids, possibly exsolved from underlying magma, and pervading an overlying brittle layer. Recent works show that a TPE inclusion located at approximately 2 km depth below the Campi Flegrei caldera significantly contributed to the large and rapid soil uplift observed during the ‘82-’84 unrest phase. In the present work we demonstrate that such a source of deformation is likely playing a role even in the current unrest phase, which is characterized by a much lower uplift-rate with respect to the one occurred in the previous unrest phase. We will show that the time-series of soil uplift observed in the last 18 years can be reproduced by assuming the reactivation of the same deformation source responsible of the ‘82-’84 unrest located within a shallow brittle layer at about 2 km depth. The presence of a brittle layer has been evidenced in the past by tomographic studies and is confirmed by a sharp variation of the b-value at the corresponding depth. We believe that our results provide very important insights and evidences, supporting the existence and the importance of an active thermo-poro-elastic deformation source, which can be useful for understanding the unrest of the Campi Flegrei caldera, from both a scientific and geohazard perspective.