A MAJOR SEISMOGENIC FAULT IN A SILENT AREA - THE CASTROVILLARI FAULT (SOUTHERN APENNINES, ITALY)

Large historical earthquakes in Italy define a prominent gap in the Po llino region of the southern Apennines, Geomorphic and palaeoseismolog ical investigations in this region show that the Castrovillari fault ( CF) is a major seismogenic source that could potentially fill the sout hern part of this gap. The surface expression of the CF is a complex, 10-13 km long set of prominent scarps. Trenches across one scarp indic ate that at least four surface-faulting earthquakes have occurred alon g the CF since Late Pleistocene time, each producing at least Im of ve rtical displacement. The length of the fault and the slip per event su ggest M=6.5-7.0 for the palaeoearthquakes, Preliminary radiocarbon dat ing coupled with historical considerations imply that the most recent of these earthquakes occurred between 380 BC and 1200 AD, and probably soon after 760 AD; no evidence for this event has been found in the h istorical record. We estimate a minimum recurrence interval of 1170 ye ars and a vertical slip rate of 0.2-0.5 mm yr(-1) for the CF, which in dicates that the seismic behaviour of this fault is comparable to othe r major seismogenic faults of the central-southern Apennines, The lack of mention or the mislocation of the most recent event in the histori cal seismic memory of the Pollino region clearly shows that even in It aly, which has one of the longest historical records of seismicity, a seismic hazard assessment based solely on the historical record may no t be completely reliable, and shows that geological investigations are critical for filling possible information gaps.