GNGTS 2021 - Atti del 39° Convegno Nazionale

GNGTS 2021 S essione 3.2 454 (see Fig. 2b), could be ascribed to the occurrence of CO 2 in the gaseous state responsible for increasing the resistivity of poorly consolidated materials (Revil et al., 1999; Byrdina et al., 2009). In particular, the anomalies highlighted with black dashed ellipses in Fig. 2b seem to identify possible preferential pathways of CO 2 rising from the underlying fractured carbonate basement, the latter found as a resistive layer (ρ >100 Ωm) in the deepest part of the north- western and central sector of the ERT3 section. In correspondence of the progressives 220 m and 370 m along the ERT2 and ERT3 profiles, respectively, a clear vertical resistivity contrast is observed, which could be indicative of a high-angle fault dipping towards the east (fault A, Fig. 2b). This blind fault would be responsible for dislocation of the sedimentary succession, whose stepped geometry could have influenced the shape of the aquifer, reasonably coinciding with the very low resistivity band observed in the north-eastern and south-eastern sectors of the ERT2 and ERT3, respectively. Indeed, the conductive anomaly is located at the intersection between the two resistivity tomographies indicating that the fault has a N-S orientation, a dip of ~65° towards the east (fault A, Fig. 3), and a minimum throw of about 100 m (Fig. 2b). Furthermore, based on the results obtained from the three electrical resistivity tomographies, we suppose the presence of a further N-S trending fault in the central part (fault B in Figs. 2b and 3). This fault would coincide with the step placed at the top of the fractured carbonate bedrock found at 150 m a.s.l. in ERT3, and with the small step highlighted in ERT2, respectively (see Fig. 2b). In addition, the projection of the fault coincides with the pathways for fluids and CO 2 highlighted in ERT1 and ERT2 (blue ellipses in Fig. 3). The projection of the fault on ERT1 indicates that the fault could have a splay (fault B1, Fig. 3). The proposed existence of fault B is consistent with the local geomorphology, where a N-S trending, E-facing, ~8 m high scarp is found ~20 m west of the fault and likely represents its morphological expression (Fig. 3). Fig. 2 - a) Arrangement of the 2D ERT profiles (green lines) in the survey area. b) Inverted resistivity 2D models from the ERT profiles.