Source investigation at Campi Flegrei caldera through the analysis of the 2015-2019 GPS and InSAR time series

Observations from satellites provide spatial and temporal high-resolution images of ground deformation; in particular, the joint use of InSAR and GPS measurements allow to better characterize the ongoing geological phenomena by analysing the three components (i.e., horizontal and vertical) of the deformation pattern.

Here, we take into account the 2015-2019 Sentinel-1 SBAS InSAR time series and the overlapped GPS measurements to study the active deformation source at Campi Flegrei caldera (CFc). The availability of SAR images acquired along the ascending and descending orbits allows discriminating the Vertical and East-West deformation components; we combine these measurements with GPS ones, recorded at 21 permanent stations, retrieving additional information about the displacement along the North-South direction and improving the examined dataset.

Starting from this retrieved measurements, we apply the Total Horizontal Derivative (THD) as preliminary analysis to investigate the spatial distribution of the active deformation source and its temporal evolution; indeed, this technique allows rapidly mapping the projection to the ground surface of the source boundaries and/or the shallow caldera structures modulating the observed deformation. The findings appear to be consistent with the 2015-2019 seismicity distribution of the nucleated earthquakes, mostly at east of Pozzuoli city.

Subsequently, we perform a 3D Finite Element Model of the active source at CFc taking into account, as a physical model constrains, the seismic tomography and the temperature distribution in the upper crust . We evaluate the best solution by varying eight parameters starting from a general ellipsoid model (i.e., center coordinates (3), ellipsoid axes (3), dip and strike); the results suggest the existence of an oblate ellipsoidal source located at about 3 km beneath the CFc and just above the deep thermal source (about 5 km). In addition, we also compare the stress field retrieved by the thermo-mechanical model with the seismicity distribution in the analysed periods.

Finally, we demonstrate that the joint exploitation of InSAR, GPS and natural seismicity data allows to better constrain the active deformation source at CFc.