Stress and deformation induced in layered media by cylindrical thermo-poro-elastic sources: An application to Campi Flegrei (Italy)

Abstract

In recent literature thermo-poro-elastic (TPE) inclusions are proposed to contribute to deformation and stress in volcanic and hydrothermal areas. With respect to previous works, the present study implements the modeling improvements requested for a more realistic description of a TPE source and the embedding medium. Firstly we propose a numerical method to represent inclusions with an arbitrary geometry. In the case of cylindrical-shaped sources, the proposed approach allows us to study the effects of the source thickness on both deformation and stress fields. Moreover, we are allowed to consider depth dependent pore pressure and temperature changes within the inclusion, as expected during the transient stage of hot fluid propagation. Secondly, we take into account elastic stratification of the crust, in order to perform unbiased inversion of ground deformation data. The inversion of geodetic data collected during the 1982–84 unrest episode in the Campi Flegrei caldera (Italy), performed in a layered elastic medium, leads to a lower misfit and a deeper deformation source with respect to the one obtained inverting data in a homogeneous half-space. Furthermore, the geometry and location of the thermo-poro-elastic inclusion retrieved from the inversion in the layered medium leads to a shear stress distribution in good agreement with the relocated seismicity observed at Campi Flegrei. Most hypocenters are found to be located near and inside the TPE inclusion boundaries, where the greatest shear stress is predicted. With respect to previous works we also found that vertical gradients of pore pressure and temperature and elastic layering can promote both normal and thrust earthquakes within the inclusion.