GNGTS 2023 - Atti del 41° Convegno Nazionale

Session 3.2 ___ GNGTS 2023 detachment niches, while the flat sectors present extensive terraced surfaces and debris deposits. The perimeter of the area subjected to first-level SM corresponds to the main urban center of San Vito Lo Capo and the areas of Macari and Castelluzzo fractions. Definition of the basic hazard for seismic classification Through the reconstruction of the seismic history of an area it is possible to evaluate the danger of the site and consider the possible impacts of an earthquake on the territory in time. The seismic events that characterized the area were chosen by consulting the Italian Macroseismic Database (DBMI15, Locati et al., 2022), the Italian Earthquake Parametric Catalogue (CPTI15 v3.0) (Rovida et al., 2021), the Italian Macroseismic Historical Archive (ASMI; Rovida et al., 2017) and the Catalogue of Strong Earthquakes in Italy (461 BC-1997) and in the Mediterranean area (760 BC-1500) (CFTI5Med; Guidoboni et al., 2018). The main historical earthquakes that from the 4th century BC had significant macroseismic effects in Western Sicily and those that, starting from the 1900 have recorded significant effects in the municipality of San Vito Lo Capo include the Mw 6.41earthquake in the Belice Valley, dated 1968, and the Mw 4.79 earthquake of 29.05.1988 with epicenter near the Egadi islands. To reduce the effects of the seismic shaking expected on the national territory, with a view to safeguarding human life, Italian legislation has made a reclassification of the seismic hazard of the entire country. This classification is based both on the intensity and frequency of past earthquakes and on the application of technical standards for constructions in seismic classified areas. According to the latest seismic classification of the Region, dated 24.02.2022, the municipality of San Vito Lo Capo falls in an area characterized by a medium basic seismic hazard since it has maximum acceleration values to the ground (ag) between 0.15 g and 0.25 g. For the evaluation of the basic seismic hazard of an area an important element is the seismogenic zonation of the Italian territory. The recent seismogenic zonation ZS9 (Meletti and Valensise, 2004) divides the entire Italian territory into 36 zones. According to this the study areas do not fall into any seismogenic zone. As regards the definition of the seismic hazard of the area, reference was made to the data published on the web database of the National Institute of Geophysics and Volcanology (INGV) (http://esse1.mi.ingv.it) described by Meletti et al. (2006). In this dataset was researched the values of maximum horizontal acceleration to the ground, named ag, with probability of excess of 10% in 50 years. The examined area presents ag values between 0.050 < ag < 0.075 g. Finally, a fundamental element for the classification of the seismicity of an area is the recognition of active and capable faults. For this purpose we consulted the ISPRA online database which is