GNGTS 2024 - Atti del 42° Convegno Nazionale

Session 3.2 GNGTS 2024 (2017), Villani et al. (2015, 2017), have proven to be to be efectve in revealing subsurface structures and fault geometries for this kind of applicatons. Methods Electrical tomography (ERT) is efectvely employed in investgatng geological horizons characterized by strong contrasts in electrical resistvity, ofen linked to lithological and structural variatons. Measurements can be made using diferent arrays to maintain a good compromise between the vertcal and horizontal shape of the recovered anomalies (Loke and Barker, 1996). An algorithm based on a least-squares deconvoluton method is employed for the inversion of apparent resistvity, allowing 2D sectons to be obtained through fnite element calculaton modules, also considering topographic correctons. A 10-channel, 72-electrode IRIS Syscal Pro was used for resistvity measurements, and the spatal coordinates of the electrodes were acquired through a Stonex S900 diferental GPS with correcton through the Italpos network. This study focuses on the analysis and interpretaton of two-dimensional electrical resistvity tomography profles; each profle was primarily acquired using both Wenner and dipole-dipole (DD) electrode arrays. The electrical tomography profles were acquired with a sampling interval of 1 m to achieve higher detail and, where possible, at 5 m intervals to reach greater depths of investgaton. Interpretatve models are based on the inversion of a set of mixed apparent resistvity data from the two diferent arrays. To derive accurate true resistvity values from the measured apparent resistvity data, the smoothness-constrained least-squares method was employed. This method considers models with infnite perpendicular extension along the profle strike, as outlined in studies by Constable et al. (1987), deGroot-Headlin and Constable (1990), and Morelli and Labrecque (1996). Preliminary results The inversion models reveal the alternaton of resistve and conductve layers, whose geometry and potental displacement highlight the presence of lateral discontnuites associated with recognized faults exposed at the surface. In a volcanic environment with volcanic and volcano- clastc products, electrical tomography reveals resistvity values ranging from medium-high to very high, consistently exceeding 300 Ohm/m. The dynamic range of resistvity values is characterized by the presence of more conductve layers with resistvity up to 1000 Ohm/m and more resistve layers with signifcantly higher values. These values align with the study area's characteristcs, marked by lava fows and volcano-clastc products (Chiancone Formaton). In general, electrical tomography and capacitve geoelectrics reveal the presence of strong lateral discontnuites, whose geometry can be atributed to the existence of faults. Further studies, together with the integraton of data from all the partcipants to the project, will provide indicaton for selectng the most suitable method/approach compared to diferent geological setngs. The fnal goal is to compile guidelines for professionals, to be adopted as best-practse for future geophysical investgatons.