Geological Reconstruction by 2D-ERT of the Maddaloni-Durazzano Ridge (Italy) for a Railway Line Design

Summary We present a geophysical study for the executive project of a railway tunnel across the Maddaloni-Durazzano carbonate ridge (southern Italy). To reconstruct the geological setting of the area, a N-S oriented electrical resistivity tomography (ERT) profile, about 4 km long, was performed, which allowed an exploration depth of about 200 m from the surface level. The results of the 2D inversion model of the ERT profile clearly highlight anomalous resistive blocks that can be associated with fractured/karst sectors of the Cretaceous carbonate succession affected by significant water circulation, while there are no evident resistivity anomaly features linked to the presence of large cavities. Significantly, the geophysical model identifies at the northern end of the ERT profile, where the entrance to the tunnel was planned, the presence of the regional thrust fault bounding the northern side of the ridge, which was hypothesized by the geological cartography but not supported by field observations. The validation of the geological-structural model provided by the ERT interpretation was derived from geognostic boreholes and direct observations carried out during the excavation of a tunnel crosscutting the ERT section.