GNGTS 2015 - Atti del 34° Convegno Nazionale

114 GNGTS 2015 S essione 3.2 was used, which provided a power line following the boundary line of the buildings. Seven 3D electrical profiles, labeled ERT 1, ERT 2, …ERT 7, were acquired. Their map is shown in Fig. 1. In this way, an comprehensive area about sized 4960 m 2 was prospected. The resistivity and the spontaneous potential maps were achieved making use of the ERTLab software and making use also of a specific homemade MATLAB code. In Fig. 2 (left hand panel) the images relating to the profiles ERT 1 and to the homologous measure of spontaneous potential are shown. The pattern distribution of the electrical resistivity and of the spontaneous potential parameters below the buildings at gradual depth levels (here, for sake of brevity, only one level has been shown) supplied the following considerations: At first, we have recorded the presence of a heterogeneous subsurface with resistivity values up to 50 and 500 Ω m. Afterwards, it is possible to note the presence of: 1) areas indicated with “A”, with resistivity values between 400 and 500 Ω m; these values indicate the probable presence of areas where localized phenomena of instability are present. The relatively low resistivity values indicate that these anomalies are not attributable to the presence of empty volumes, but rather to incoherent materials, probably put there in order fill up previous voids; Fig. 1 – Location of the 3D electrical profiles ERT 1-7. Fig. 2 – Slice of the retrieved resistivity and of spontaneous potential at 70-100 cm.