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La cittadina di Cefalù, ubicata a circa 70 km da Palermo, è una delle perle del Mediterraneo, per la bellezza dei luoghi, dominati dalla Rocca, imponente rupe carbonatica alta circa 250 m s.l.m., e per i beni architettonici (Figg. 1 e 2). Fondata dai greci con il nome di Κεφαλοίδιον tra il XIV e il XIII a.C., conserva sulla Rocca il palazzo santuario ciclopico-megalitico, noto come Tempio di Diana. Sul ciglio della Rocca e per il suo intero sviluppo si snoda la cinta muraria di tipo megalitico risalente alla fine del V secolo a.C. (periodo pre-ellenico), in parte ricostruita nel periodo bizantino (VII÷IX secolo d.C.). Nel periodo normanno (secolo XII d.C.) furono costruiti i principali monumenti, tra i quali la cattedrale, sito UNESCO dal 2015 (Fig. 2). La Rocca è caratterizzata da un’elevata suscettibilità ai fenomeni di crollo che, spesso, si verificano in concomitanza di eventi sismici o meteorici particolarmente intensi. Tali crolli determinano condizioni di rischio molto elevato per gran parte dell’abitato, compresa la Cattedrale, ubicata ad alcune decine di metri dalla Rocca, e possono coinvolgere le sovrastanti preesistenze storico-archeologiche. In ogni caso inibiscono lo sviluppo socio-economico della cittadina normanna, ad evidente vocazione turistica.

The monumental complex of Maredolce (Palermo) includes an Arab-Norman castle that stands on the banks of an artificial lake carved out of the calcarenitic rock that rests on impermeable clays. The lake was originally filled with water, thanks to the channelling of a spring. Over time, the lowering of the water table and the high hydraulic permeability of the calcarenites have caused the lake to dry up. A project to renovate the monumental complex has recently been launched. It also provides the study of a possible restoration of the original conditions of the lake. To this end, a multidisciplinary geophysical study was carried out to investigate the geotechnical conditions of permeability of the land outcropping and provides valid technical solutions for waterproofing the bottom of the lake. For this purpose, a joint interpretation was performed using data acquired with different geophysical techniques, such as seismic refraction tomography, electrical resistivity and induced polarization tomography, multichannel analysis of surface waves and horizontal-to-vertical spectral ratio of environmental vibration recording. Joint interpretation, supported by cluster analysis techniques, allowed the reconstruction of the geophysical and geotechnical model of the subsoil of the ancient lake, helpful to suggest appropriate techniques for waterproofing the bottom of the lake.

This study concerns the assessment of the rockfall risk for two strategic sectors of the Mount Pellegrino, one of the most relevant place in the city of Palermo. During the last two decades, several rockfalls affected the study area setting up a serious threat to the people, structures and infrastructures preventing the economic and social development. For these landslides a detailed GIS inventory was realized; the most dangerous rockfalls occurred within the two study sectors. In both areas we have carried out detailed field surveys and the geo-mechanical characterization of the rock slopes. These analyses allowed to define the rock mass parameters, the set of discontinuities and the kinematics. The back analyses for the past events were conducted permitting to define the blocks trajectories using a numerical model for rockfall simulation. Through this procedure the hazardous areas have been identified and the map of the landslide risk was produced considering the possible spread of the blocks both on land and at sea. The results were exploited to compare this map with the existent map in the framework of the Sicilian Master Plan for hydrogeological risk (PAI), showing that the new risk areas are larger than those previously mapped.

After very intense rainfalls and pre-failure little ground movements, a large landslide occurred in San Fratello on 14th February 2010. San Fratello is a little town on the Nebrodi Mts., a chain in north-east of Sicily, Italy. The landslide is one of the most devastating phenomena occurred in Sicily. In fact it extends over an area of about 100 hectares and has caused enormous damage in the little town: about 300 buildings have been damaged, tens of which completely destroyed, about 2,000 inhabitants have been evacuated. This landslide is very complex for several reasons: it includes different but complementary ground movements; it develops in structurally complex formations; the water table is close to ground level. Based on the results of experimental investigations and back-analyses, geological and geotechnical landslide models have been implemented. Designed stabilization works also include new technologies, such us trench drains realized by means of permeable concrete secant piles having a length of 12.00m.

In the last 20 years the natural oriented reserve of Monte Pellegrino is affected by several rockfall events. This sector of the Northern Sicily is a strategic urban area and represent the most important element of both the religious and cultural tradition and landscape for the city of Palermo.The rockfalls are here the major natural threats and represent a relevant risk of people, structures and infrastructures and prevents the economic and social development that could be made by high tourist potential of the area. For the above mentioned reasons a detailed geological and geotechnical study in order to define a quantitative risk analysis is now being carried out, concurrently with the implementation of the landslide inventory essential for analysis and monitoring. Monte Pellegrino, located along the Alpine orogenic belt (Catalano et al., 2013) in the emerged Sicilian fold and thrust belt, is an isolated carbonate massif characterized by the presence of poor rock masses and steeply sloping hillsides. The quantitative risk analysis was performed through several steps and taking into account the provisions of directive which is in force in the local institutions. The spread of a rockfall depends on many control factors such as geological setting and geomechanical features for both source area and below area, it is therefore necessary to define different input elements: an inventory of landslides, a database of factors and a dataset that contains the results of the on-site inspections like the geostructural and geomorphological data. The archive of landslides occurred over a period of 20 years was created; the spatial database (constructed in accordance with the standards) contains information on the identification code and date of the event, location, type, involved lithology and related thematic maps. Other thematic maps are those requirements deriving from the factors layers as tectonic features, morphological characteristics, geometric attributes of the slope, type of coverage, structures and infrastructures, trajectory of the block and the stop point. The above mentioned steps allow the implementation and calibration of the model for rockfall analysis; in particular, by means back-analysis stage it is possible to determine the restitution and friction coefficients through a comparison of the points where the rock blocks stop in the simulation with the rockfall history stop points. The next step we took is to produce the map of those areas with different degree of risk defined through the density of the trajectories reconstructed through the model. Finally, are presented here two between the cases studied needed to set up the forecasting model for the rockfall trajectories. Catalano R., Valenti V., Albanese C., Accaino F., Sulli A., Tinivella U., Gasparro Morticelli M., Zanolla C., Giustiniani M., 2013 – Sicily fold-thrust belt and slab roll-back: the SI.RI.PRO. seismic crustal transect. Journal of the Geological Society, 170, 451–464.