Inflating source imaging and stress/strain field analysis at campi flegrei caldera: The 2009-2013 unrest episode

In this study, we analyze the 2009-2013 uplift phenomenon at Campi Flegrei (CF) caldera in terms of temporal and spatial variations in the stress/strain field due to the effect of an inflating source. We start by performing a 3D stationary finite element (FE) modeling of X-band COSMO-SkyMed DInSAR and GPS mean velocities to retrieve the geometry and location of the deformation source. The modeling results suggest that the best-fit source is a three-axis oblate spheroid ~3 km deep, which is mostly elongated in the NE-SW direction. Furthermore, we verify the reliability of model results by calculating the total horizontal derivative (THD) of the modeled vertical velocity component; the findings emphasize that the THD maxima overlap with the projection of source boundaries at the surface. Then, we generate a 3D time-dependent FE model, comparing the spatial and temporal distribution of the shear stress and volumetric strain with the seismic swarms beneath the caldera. We found that low values of shear stress are observed corresponding with the shallow hydrothermal system where low-magnitude earthquakes occur, whereas high values of shear stress are found at depths of about 3 km, where high-magnitude earthquakes nucleate. Finally, the volumetric strain analysis highlights that the seismicity occurs mainly at the border between compression and dilatation modeled regions, and some seismic events occur within compression regions.