GNGTS 2023 - Atti del 41° Convegno Nazionale

Session 3.2 ___ GNGTS 2023 Fig. 1: Maps of the bedrock depth (Vs>800 m/s) for San Vito Lo Capo (A), Macari (B), Castelluzzo (C) areas. Map of homogeneous microzones in seismic perspective based on first level studies The processing of the map of homogeneous microzones in seismic perspective (MOPS) is based on the criteria defined by “Gruppo di lavoro MS” (2008). Basing on the available geological, geomorphological and geophysical observations three different categories were identified: A first category is that of stable zones , where no local effects of amplification of the seismic shaking are hypothesized. These zones present an outcropping geological and seismic substrate (Vs > 800 m/s), characterized by flat morphology or inclined less than 15°; stable areas can present a thickness of cover deposits less than 3 m. According to these features two stable zone, 1012 and 1022, were defined. A second category is constituted by stable zones susceptible of local seismic amplification. In these areas the amplification of the seismic input is connected to the presence of a rigid ground (Vs < 800 m/s) outcropping or covered by non-cohesive soils with thickness less than 3 m. Belong furthermore to this category outcrops anthropogenic, eluvial, colluvial and debris deposits characterized by thickness greater than 3 m and Vs less than 800 m/s. In particular, the 2099 zone presents heavily weathered and fractured limestone on the top and silico-clastic deposits up to a maximum of about 12 m. A debris cover characterizes the 2001 zone, while the 2002 and 2003 zones are characterized by alluvial soils and beach deposits respectively. A cover of anthropogenic origin, characterized by the presence of heterogeneous and heterometric material, defines the 2004 zone. Finally, two zones of attention for instability were defined, on the basis of the type of movement and the state of activity (landslides): the 30112001 zone that presents active rockfall and rock topple and the 30152099 zone characterized by widespread erosion processes. All the described MOPS for the three examined areas are shown in Fig. 2. As regards the poorly investigated fault located in the western sector of the San Vito town, reported in the pre-existing cartography, a buffer zone was mapped.