Thermo-poro-elastic effects induced by fluid flow can explain the recent seismicity and deformation at Campi Flegrei (Italy)

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Abstract
Thermo-Poro-Elastic (TPE) inclusions are suitable to model the mechanical effects induced by hot and pressurized hydrothermal fluids pervading a closed volume of rocks. In fact, modeling of TPE deformation sources finds application in both geothermal and vulcanological fields. Some recent works showed that a cylindrical TPE inclusion located at about 2 km of depth contributed to the large and rapid soil uplift observed during the ‘82-’84 unrest phase in the Campi Flegrei caldera. In the present work, we demonstrate that such a source of deformation can be responsible for a significant contribution even in the current unrest phase, that started in 2005 and it is still in progress. We show that the time-series of soil uplift observed in the last years can be reproduced by assuming the rising of hot and pressurized fluids, possibly exsolved by a deep magmatic source, within the same deformation source responsible of the ‘82-’84 unrest. The existence of such a TPE inclusion at Campi Flegrei was supported by previous tomographic studies and it is reinforced by the new analysis of the b-values. In fact, we found a sharp variation of the b-value in correspondence of the depth of the modelled TPE inclusion. The decrease of the b-values is consistent with the fact that within the TPE inclusion the induced shear stress is maximum and the occurrence of larger earthquakes is favored. The results support the existence and the importance of the mechanical effects of fluids flow, during the unrest phases of the Campi Flegrei caldera.