Seismic imaging of the Solfatara crater (Campi Flegrei caldera, southern Italy): New evidence of the fluids migration pathways in the shallow structures

Seismic imaging is used in this work, to reconstruct the shallow structure of the Solfatara crater, a surface marker of deep magmatic activity inside Campi Flegrei caldera (Southern Italy). We analyze the 1D orthogonal seismic arrays deployed in NNE-SSW directions for 400 m through the Solfatara crater during the recent active experiment RICEN (Repeated Induced Earthquake and Noise) performed in the framework of the EU project MEDSUV. Seismic data have been edited in the pre-stack stage by removing the noisy traces, low-frequency noise, and reduce the ground roll phases. Then, a velocity analysis has been carried out starting from the velocity spectrum to obtain a RMS velocity model, which has been followed by NMO, residual statics, and DMO corrections. We used the post-stack Kirchhoff migration technique before the extraction of the energy, root mean square, envelope and sweetness attributes defining the highest amplitude zones, the time-gain attribute in order to interpret the deep reflectors and the variance attribute to define the faults, discontinuities, and chaotic zones. Amplitude Versus Offset (AVO) analysis has been performed to identify the gas-saturated zone using partial angle-stacks, which is a benchmark to verify the presence of gas. The main contribution of this work is to provide a more detailed and improved seismic reflection image of the shallow depth of the Solfatara crater. The reliability of our velocity model has been assessed through the use of the Vp velocity model previously obtained by the non-linear Bayesian technique. This provides a final stack showing that the shallower minor faults and the extension of the major faults represent the main pathways for the uprising fluids. We present the visual evidence for the fluids trapped in the shallower part of the crater at depths between 20 and 50 m below the surface of the crater.