New constraints on the seismic history of the Castrovillari fault in the Pollino gap (Calabria, southern Italy)

The Pollino Range area represents the most prominent gap in seismicity within the southern Apennines. Geomorphic and trenching investigations along the Castrovillari fault indicate that this normal fault is a major seismogenic fault within the southern part of this gap. At least four surface-faulting earthquakes have occurred on this fault since late Pleistocene age. Radiocarbon dating coupled with historical consideration set the time of the most recent earthquake as most likely to be between 530 A.D. and 900 A.D., with the possible widest interval of 530-1100 A.D. No evidence for this event has been found in the historical records, although its age interval falls within the time spanned by the seismic catalogues. Slip per event ranges between 0.5 and 1.6 m, with a minimum rupture length of 13 km. These values suggest a M 6.5-7.0 for the paleoearthquakes. The minimum long-term vertical slip rate obtained from displaced geomorphic features is of 0.2-0.5 mm/yr. A vertical slip-rate of about 1 mm/yr is also inferred from trenching data. The inter-event interval obtained from trench data ranges between 940 and 7760 years (with the young part of the interval possibly more representative; roughly 940-3000 years). The time elapsed since the most recent earthquake ranges between a minimum of 900-1100 and a maximum of 1470 years. The seismic behavior of this fault appears to be consistent with that of other major seismogenic faults of the central-southern Apennines. The Pollino case highlights the fact that geological investigations represent a potentially useful technique to characterize the seismic hazard of `silent' areas for which adequate historical and seismological data record are not available.