GNGTS 2023 - Atti del 41° Convegno Nazionale

Session 1.2 - POSTER GNGTS 2023 Detection of near-surface fault systems in the Casamicciola area (Ischia, Italy) through Electrical Resistivity Tomography C. De Paola 1 , M.G. Di Giuseppe 1 , R. Isaia 1 , R. Toccaceli 2 , A. Troiano 1 1 Istituto Nazionale di Geofisica e Vulcanologia, Osservatorio Vesuviano, Naples, Italy 2 Freelance Geologist, Sapri, Italy Introduction  The Ischia island hosts a resurgent caldera, which volcanism has been correlated with the dynamics of a shallow magma body and its volcano-tectonic configuration (e.g. Di Giuseppe et al. 2017). Since the caldera-forming eruption, which laid down the Mt. Epomeo deposits about ~50-60 ka, the central part of the island has undergone approximately 800-900 m of intermittent uplift. During such uplift, large-scale deformation and faulting affect the northern rim of the Mt. Epomeo resurgent structure. The island’s northern region was recently also affected by destructive earthquakes (e.g., 1769, 1828, 1881, 1883, and 2017), producing damage and fatalities at Casamicciola Terme. The edges of the resurgent block are marked by a system of sub-vertical faults with NW-SE, NE-SW, and N-S strike (Vezzoli 1988; Acocella and Funiciello, 1999; Tibaldi and Vezzoli 1998; Sbrana and Toccaceli, 2011), which facilitate the development of an intense hydrothermal circulation that, in combination with the high temperature of the geothermal field present along the structural boundary of Mt. Epomeo, produces an intense alteration of the rocks. The hydrothermal circulation, which develops in that part of the island, and the related geological structures can be reliably characterized through geophysical prospecting. Remarkably, the success of Electrical Resistivity Tomography (ERT) in the structural modelling of relatively complex geological areas has been demonstrated by numerous Literature studies showing how such a technique results capable of reconstructing the contact between different geological formations and the flexure structure produced by faulting in terms of electrical resistivity contrasts (Isaia et al., 2021; De Paola et al., 2019; Troiano et al., 2021; Vitale et al., 2019). Fault systems are usually detected through ERT as sharp lateral resistivity contrasts caused by the juxtaposition of different sediment layers and/or by different hydrological conditions on both sides of the fault. Considering the specific relevance of characterizing the hydrothermal circulation and geological structures in the northern sector for the Ischia volcano-tectonic and local evolutionary context (also from a seismic perspective), geoelectrical surveys were carried out in such part of the island,