Quaternary normal faulting in southeastern Sicily (Italy): A seismic source for the 1693 large earthquake

We present geological and morphological data, combined with an analysis of seismic reflection lines across the Ionian offshore zone and information on historical earthquakes, in order to yield new constraints on active faulting in southeastern Sicily. This region, one of the most seismically active of the Mediterranean, is affected by WNW-ESE regional extension producing normal faulting of the southern edge of the Siculo-Calabrian rift zone. Our data describe two systems of Quaternary normal faults, characterized by different ages and related to distinct tectonic processes. The older NW-SE-trending normal fault segments developed up to approximate to 400 kyr ago and, striking perpendicular to the main front of the Maghrebian thrust belt, bound the small basins occurring along the eastern coast of the Hyblean Plateau. The younger fault system is represented by prominent NNW-SSE-trending normal fault segments and extends along the Ionian offshore zone following the NE-SW-trending Avola and Rosolini-Ispica normal faults. These faults are characterized by vertical slip rates of 0.7-3.3 mm yr(-1) and might be associated with the large seismic events of January 1693. We suggest that the main shock of the January 1693 earthquakes (M similar to 7) could be related to a 45 km long normal fault with a right-lateral component of motion. A long-term net slip rate of about 3.7 mm yr(-1) is calculated, and a recurrence interval of about 550 +/- 50 yr is proposed for large events similar to that of January 1693.