Active faults and inferred seismic sources in the San Vito lo Capo peninsula, Northwestern Sicily, Italy

Two independent active faults, capable of generating medium-sized earthquakes in the San Vito lo Capo peninsula, northwestern Sicily (Italy) have been identified as a result of detailed field studies. In western Sicily, instrumental seismicity is low; in fact, except for the 1968 Belice earthquake (Ms = 5.4), historical records indicate that this area is relatively quiescent. Most of the seismicity is in the offshore sector of the Sicilian Maghrebian Chain, which is characterized by several medium- to low-magnitude events. The main shock of the 2002 Palermo seismic sequence (Mw = 5.9) represents the largest earthquake felt in the area in recent years. The deformation pattern characterizing the most recent faults mapped in northwestern Sicily includes a grid of high-angle faults consisting of major east-west-striking right-lateral and north-south-striking left-lateral features. This fault grid is related to a regional transcurrent right-lateral shear zone, here named the UEKA shear zone, bounded to the north by the Ustica-Eolie fault and to the south by the Kumeta-Alcantara fault. The UEKA shear zone accommodates the regional strain induced by the current stress field acting in the area, which, as emerges from both structural and seismological data, is characterized by a NW-SE-striking main compression.