Geostructural and geophysical surveys for the stability analysis along a rock slope in the cultural heritage site of Ispica (south-eastern Sicily)

The aim of this study is to evaluate the degree of fracturing and the stability conditions of the calcareous rock cliff on which the cultural heritage site of Ispica lies. Ispica is a 16.000 inhabitants village belonging to the Ragusa district. It is located in the southeastern coastline of Sicily, where tectonics affects the geology and morphology, as well as the seismicity. Indeed, from a geological point of view, the studied sector is a calcareous horst, with direction NE-SW, bordered by the Gela-Catania foredeep to the west and to the Malta Escarpment to the east (Fig.1a). The main structural element is represented by a NE-SW fault system, known as PozzalloIspica-Rosolini system (Ghisetti and Vezzani, 1980; Lentini et al., 1987; Grasso et al., 2000). In the study area, this system is named “Ispica fault system” and shows strike slip motion. Faults are sub-vertical, with maximum throws of 80-100 m. This system mainly adjoins the marls and calcarenites of the Ragusa Formation (lower Miocene) to the west with the blue clays of the Tellaro Formation (middle Miocene) to the east (Grasso (Grasso et al., 1992). The seismic activity related to this faults is historically known, with the 1727 and 1903 earthquakes (M>5) (Azzaro and Barbano, 2000). Moreover, on 11 January 1693, Ispica village was destroyed by a M <= 7.4 earthquake (Table 1), which is the strongest shaking ever occurred in the area.