Low slip rates and multimillennial return times for Mw 7 earthquake faults in southern Calabria (Italy)

The Calabrian Arc is the epicentral region of one third of the strongest earthquakes of Italy (Mw ≥ 7.0). These are confined within a narrow peninsula which is the emerging portion of a slab-related accretionary wedge, and all occurred in the past four centuries. Therefore, here more than anywhere in Italy, historical seismicity alone is not sufficient for seismic hazard assessment. We carried out geological and paleoseismological studies in southern Calabria that allowed characterizing the seismogenic behavior of the Cittanova fault which was responsible for one of the most catastrophic earthquakes to ever occur in Europe, the Mw 7.0 5 February 1783 event. We have found out conclusive evidence for four Holocene earthquakes prior to 1783, with a recurrence time longer (~3.2 kyr) than the other Apennine faults (0.3–2.4 kyr). We have also estimated a robust slip rate for the late Upper Pleistocene (0.6 mm/yr) and an extension rate (0.4 mm/yr) that could reflect the residual back-arc opening of the Tyrrhenian Basin.