GNGTS 2017 - 36° Convegno Nazionale

GNGTS 2017 S essione 3.2 629 2009). In the study area Holocene age lavas, that can be referred to the Mongibello eruptive phase, widely outcrop (Fig. 1c). From the structural point of view, no significant structures intersect the study area. The closer tectonic structures are represented by theAcireale-Sant’Alfio and theAcicatena faults located at a distance of about 1.0 km to the est and at about 1.5 km to the west of the study area, respectively. Both the structures, trending NNW-SSE, show a direct mechanism (Gresta et al. , 1997). Methodology. The not invasive geophysical techniques used (GPR and seismic tomography) allow, through the analysis of the variations of physical-mechanic characteristics of the medium (electromagnetic properties, geo-mechanical coefficients, seismic waves velocities, etc.) the identification of buried bodies and the modeling of underground structures. The observed anomalies can be linked to several issues such as the presence of buried objects, changes in the lithology or in the mechanical features inside the lithotype itself (fractures and/or cavities). Ground Penetrating Radar. The GPR survey was performed using a georadar device (RIS MF Hi-Mod) with a multi-frequency (200-600 MHz) aerial. This technique is founded on the input of electromagnetic waves in the subsoil in order to record the reflections due to the existence of hidden bodies having a sharp difference with respect to the electromagnetic properties of the medium (Davis and Annan, 1989). It is therefore possible to evaluate through the relationship: the depth ( h ) of the reflector, using the travel time values ( t ) of the electromagnetic waves and a preliminary estimate of the average velocity ( v m ) of the waves in the medium. The investigation was planned by deploying a series of scans distributed in a rectangular mesh having X andYaxis respectively oriented parallel to the longitudinal and transversal extent of the church. Altogether, 21 longitudinal profiles and 24 transversal ones were performed, each interspaced by 1 m, for a total length of 397.47 m (Fig. 2). The acquired data were processed through the GRED 3D software (IDS, 2009). The radargrams (Fig. 3a) were drawn after a suitable filtering process of the recorded signal, in order to enhance their quality. In particular, the use of the C-scans function allowed us to infer planar depth-slices for 6 intervals each having 0.5 m depth (Fig. 3b) showing the amplitude distribution of the electromagnetic signal in the subsoil (Goodman and Piro, 2013). Fig. 2 - Planimetry of the church with the GPR scans and seismic arrays location.