Modelling the Source of 2017 Casamicciola Earthquake (Ischia Island, Italy): A Critical Review and New Insights into the Interaction Between Volcanic and Tectonic Processes

We investigate the source of the 21st August 2017, Md 4.0 Casamicciola volcano-tectonic earthquake (Ischia Island, Italy), which caused heavy damage on the northern flank of the Mt. Epomeo resurgent block of the Ischia caldera. We adopt a multidisciplinary approach that combines geophysical, geological and coseismic ground deformation data mapped since after the earthquake occurred. Building on a critical review of previous studies, we incorporate new geological field mapping, stratigraphic boreholes, and geophysical surveys to better constrain the seismogenic source of the 2017 Casamicciola earthquake. The results support a model involving the activation of a graben-like fault system, in which the Grande Sentinella Fault acts as an antithetic structure, while the main seismogenic faults correspond to a system of N-dipping normal faults controlling the evolution of the northern flank of Mt. Epomeo. This model implies the involvement of multiple sub-parallel fault segments and provides a physically consistent interpretation of the observed deformation pattern. The proposed solution differs significantly from previously published models and is fully compatible with the geological framework of the area. Our results have profound implications on the seismotectonic modelling and volcano-tectonic earthquakes and for seismic hazard assessment in this crucial region of the Ischia Island.