The updated multi-2D image of the gas accumulation zone inferred by seismic attributes and AVO analysis at the Solfatara Volcano, Italy

The imaging of volcanic structures by means of seismic techniques is aimed at the structural characterization and monitoring purposes. The quiescent volcano of the Solfatara belong to the caldera of the Campi Flegrei Italy, a resurgent nested caldera that has been extensively investigated through active seismic investigation.

The fumaroles of Bocca Grande and Bocca Nuova at the Solfatara volcano, represent some of the main markers of deep magmatic shallow hydrothermal activity. In this article we identify the gas accumulation zone using the attributes and scaled Poisson ratio extracted from multi-2D seismic profiles. The 400 m long profiles,  have been acquired during the active experiment RICEN (Repeated Induced Earthquake and Noise) performed in the context of the EU project MEDSUV between May and November 2014. The seismic arrays were deployed along the NE-SW and NW-SE directions within the crater across the zones of the fumaroles and the “fangaia”.

The time- and depth-sections are reconstructed after applying residual statics, DMO corrections, CMP gathering, and the post-stack Kirchhoff migration technique. The energy, root mean square, envelope, and sweetness attributes have been computed and extracted for determining the maximum and minimum values of amplitude zones on the migrated, post-stack seismic sections. Furthermore, we have investigated the time-gain attribute, which is used to interpret deep reflectors, and the variance attribute, that is a geometrical attribute providing information on location of faults, discontinuities, and chaotic zones. To better detail the reflectivity of shallow events, enhanced by the post stack attributes, the Amplitude Versus Offset (AVO) technique has also been used to discriminate and identify shallow gas pockets. The seismic profile, seismic attributes, and near-surface structural interpretation of the Solfatara volcano have been combined into a final structural image of the Solfatara subsoil. This show a clear evidence of the fluids trapping zones at 10-50 m depth beneath the crater's surface, as well as their migration paths down to 150 meters depth.