Active Tectonics and Ground Failure Hazards In The Crati Graben (northern Calabria, Southern Italy): The Bisignano-Rogliano Fault System

In the study area, located on eastern boundary of the Crati valley (Northern Calabria), a regional normal fault system, oriented N-S, developed from the area of Bisignano to Rogliano (Cosenza province). Thanks to the activity of this tectonic structure, the horst of the Sila Massif, on the east, mainly constituted by igneous-metamorphic rocks belonging to the Palaeozoic "chain", was upthrown with respect to the graben of the R. Crati, on the west, filled by clastic Plio-Quaternary sediments. The above mentioned tectonic structure is made of a complex of synthetic normal step faults, downthrow- ing toward W, generally oriented between N and NNE. Moreover, an antithetic fault, oriented NNW and developed between the village of Paterno Calabro and Cosenza, can be referred to the same tectonic structure. On the whole, the Bisignano-Rogliano tectonic structure extends for about 50 km, with a mean width of ca. 10 km. In the same area, several villages are to be found (besides the above mentioned: Mangone, Aprigliano, Spezzano della Sila, S. Pietro in Guarano and Rose) and notable roads, such as the Highway "A3", the State Roads SS.270 and SS.107. Historic investigations pointed out that, in the same area, numerous catastrophic earthquakes originated, char- acterised by MCS intensities greater than X, which had a significant role in hamper- ing the socio-economic development of the area. Furthermore, several seismic shocks (Magnitude 4-5) have recently been recorded, with epicentres located in the same area of study: these latter events allowed a detailed characterisation of the instrumental seismic activity. The recentmost of them, felt by the population within a large ter- ritory, have been recorded between October and December 2001: in particular, these epicentres have been localised along a segment (oriented NNE) of the considered fault system, in the area between Rogliano and Spezzano della Sila. Morpho-neotectonics and structural investigations have been performed in the study area, by means of field surveying and interpretation of air-photographs. The obtained morpho-structural map, together with the above mentioned seismologic data, constitute an indispensable tool for seismic hazard evaluations in the Bisignano-Rogliano fault