GNGTS 2022 - Atti del 40° Convegno Nazionale

454 GNGTS 2022 Sessione 3.2 Fig. 2 - Overlapping of all considered HVSR curves. Palermo Plain (Giammarinaro et al. , 2000; Canzoneri et al. , 2002; Martorana et al., 2018; Cappadonia et al., 2020; Agnesi, 2021). This approach proved useful to correlate the available data with the bedrock depth maps defined basing on the stratigraphic data of the Oreto River. In particular Figure 1 shows the iso-depth contour lines of the top of the Numidian Flysch, as reported by Contino et al. (2000). Basing on the analysis of the HVSR curves trend (Fig. 2), a geological-stratigraphic model has been developed for the studied area. According to this model, the low frequency main peaks (0,8 -2.5 Hz) are probably generated by the contact between the Pleistocene clays and the higher portions of the Numidian Flysch. The blunt shape of the peaks also suggests that these are probably caused by the contact between the Oligo-Miocene Flysch deposits and the underlying Meso-Cenozoic carbonate basement. The reversal of velocity, that is evident at higher frequencies in almost all the H/V curves, could be attributed to the contact between calcarenite deposits and the underlying Pleistocene clays. For even higher frequencies, the further increase of the spectral ratio and the presence of other secondary peaks could be attributed to the boundary between alluvial, colluvial and coastal Holocene surface soils and the underlying more cemented portions of the “Sintema di Barcarello” and “Sintema Buonfornello-Campofelice”, as well as to the presence of the Calabrian calcarenites in this area, well recognizable along the outcrops that border the Oreto River. The future aim of this work is to deepen and develop these preliminary results through a planning of detailed geophysical investigations, that will be realized in different profiles of the study area. In particular, we will focus on the mouth of the Oreto River and on sectors in which the river course seems to be controlled by tectonic structures. This approach, in addition to increasing the geological knowledge on the subsoil in the Oreto river area, has a double value: on the one hand, to define with more accuracy the features of the area in terms of local seismic response and, on the other, to describe the sedimentary deposits overlying an impermeable bedrock, that could be sites of surface aquifers.