GNGTS 2018 - 37° Convegno Nazionale

GNGTS 2018 S essione 3.2 635 Fig. 1 - 3D representation of the Bellolampo landfill project area. White lines are the traces of the geophysical surveys. domain extensively crops-out (Catalano et al. , 1996). The outcropping succession represent a portion of a tectonic unit belonging to the Sicilian Fold and Thrust Belt, which in this sector shows SW-ward tectonic transport. These tectonic units are affected by more recent transpressive high-angle faults with N-ward tectonic transport. Geological investigations, aimed at defining the morphological, geomorphological, stratigraphic and structural characteristics of the outcropping units, were carried out in correspondence of over 60 measurement stations, which provided hundreds of stratigraphic and sedimentological data and the kinematics of the tectonic elements. We carried out two trenches across the study area (perpendicular to the direction of the fault being studied and parallel to it) to analyse the fracturing pattern and the stratigraphic and lithological features along the excavation walls. Based on the collected and processed data, the geological model of the site was defined. The integrated geological and geophysical analysis and the k-means cluster analysis allowed to reconstruct the lateral variations of the deformed carbonate breccias and better define the stress- field-orientations. The fracturing and kinematic analysis on fault planes observed along the trenches, highlighted systems of left and right-lateral transtensional faults NW-SE, NNW-SSE and NE-SW trending, respectively, which antedate the extensional tectonic event. Geophysical survey. In order to obtain detailed information on the geological structure of the investigated area, integrated geophysical surveys (Fig. 1) have been performed using electrical resistivity tomography (ERT), induced polarization tomography (IPT) and seismic refraction tomography (SRT) techniques. In particular, five seismic tomographies were performed for a total of about 928 m in length. Coincident topographic traces were used for the electrical tomographies, in order to facilitate the joint interpretation of the different geophysical methods. The sequences of about 5000 resistivity and 1000 chargeability measurements have provided for the use of the multiple gradient (Dahlin and Zhou, 2006) in the modified multi- coverage version (Martorana et al. 2016; 2017). The surveys were supported by a detailed photogrammetric survey. The tomographies generally show high values of P-wave velocities (1000-3000 m/s) and electrical resistivity values from medium to very high (10 3 -10 4 ohm.m) according to the carbonate lithologies outcropping in the area. In the shallow part, a layer of fractured limestone shows thicknesses varying from 2 to 5 meters, characterized by lower P-wave velocity and resistivity values. The lateral variations of the seismic velocity and resistivity values are well correlated with the geological and tectonic discontinuities from the detailed geological-structural survey. Relatively lower seismic velocity and resistivity values have been correlated with tectonized Upper Jurassic carbonate breccias, whereas the presence of clayey intercalations is evidenced by chargeability values greater than 0 ms, which never exceed 20 ms, however compatible with the absence of leachate (Mondelli et al. , 2007). The interpretation model related to the resistivity tomography (ERT3), chargeability tomography (IPT3) and refraction seismic tomography (SRT3) are shown in Fig 2.