GNGTS 2014 - Atti del 33° Convegno Nazionale

GNGTS 2014 S essione 3.1 101 Geostructural and geophysical surveys for the stability analysis along a rock slope in the cultural heritage site of Ispica (south-eastern Sicily) G. Pappalardo 1 , S. Imposa 1 , S. Mineo 2 , S. Grassi 1 1 Dipartimento di Scienze Biologiche, Geologiche e Ambientali, Università degli Studi di Catania, Italy 2 Dip. di Scienze della Terra, dell’Ambiente e delle Risorse, Università degli Studi Federico II di Napoli, Italy Introduction. 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 Pozzallo- Ispica-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 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. Table 1 - historical earthquakes at Ispica village (http://emidius.mi.ingv.it/DBMI04/ ). Number of events: 12 Effects Earthquakes Is Year Mo Da Hr Epicentral area Np Ix Mw 10 1693 01 11 13 30 Eastern Sicily 181 11 7.41 3-4 1727 01 07 Noto 14 7-8 5.37 7-8 1818 03 01 02 45 Iblean Mountains 24 7-8 5.63 5-6 1848 01 11 Augusta 33 8-9 5.48 5-6 1903 02 10 08 04 Noto 10 6 4.83 2 1905 09 08 01 43 Calabria 827 10-11 7.06 NF 1908 12 10 06 20 Novara di Sicilia 64 7 5.00 6 1949 10 08 03 08 Noto 32 7 5.18 3 1959 12 23 09 29 Catania Plain 108 6-7 5.23 2-3 1978 04 15 23 33 Gulf of Patti 332 8 6.06 5-6 1980 01 23 21 Modica 122 5-6 4.63 6 1990 12 13 00 24 South-eastern Sicily 304 7-8 5.68 The cultural heritage site comprises several worship constructions such as the Friars Minor Monastery, which had been a Franciscan Friary since 1515 A.D. and now is the headquarter of Friars Minor. The cloister is one of the oldest constructions of the village, so an important tourist attraction.