GNGTS 2017 - 36° Convegno Nazionale

654 GNGTS 2017 S essione 3.2 physical parameter useful to define the hydrogeological pattern of the subsoil (Rizzo et al. , 2004; Maillet et al. , 2005; Giampaolo et al. , 2016) . In the investigated area, we carried out seven Electrical Resistivity Tomography (ERT) surveys (T1, T2, T3, T4, T4a, T4b, T5) on the Gnejna Valley (Fig. 2) in five different sites. In one site east of the Gnejna valley (T4 line), we carried out three ERTs along the same line but with different electrode spacing (10 m, 5 m and 2.5 m) in order to acquire the electrical resistivity distribution with high resolution on the shallow geological formation (Upper Coralline Limestone). The acquisition was done by Syscal Instruments (Iris Company, France) with 48 channels and the electrode distance was 10 m with 48 electrodes, in order to obtain profiles that were 470 m long. Furthermore three ERTs were carried out with an electrode space of 5 m (T4a and T5) and 2.5 m (T4b), respectively. The exploited geoelectrical method for all profiles was the Wenner-Schlumberger technique, which allowed us to obtain a good resolution for both vertical and horizontal heterogeneity. For this work, the apparent resistivity data were analysed and converted in real resistivity values by the inversion software for 2.5D interpretation of electrical resistivity tomography ZondRes2D (Zond geophysical software), using the Occam (Constable et al. , 1987) and Marquardt (1963) algorithms. Fig. 3 shows the inverted electrical resistivity data ERT T2, which were obtained from the top of the coast at north of the Gnejna Valley, where the Upper Coralline Limestone outcrops. Fig. 2 - The location of the ERT on Google Earth image (with an overlay of the Geological Map) of the Electrical Resistivity Tomographyes. The red lines are the profiles and the pins the specific electrodes indicated by labels. The symbols of the geological map are described in the text. Fig. 3 - The inverted ERT T2 data with topography correction.