Recurrence times of central-southern Apennine faults (Italy): Hints from palaeoseismology

Despite Italy has one of the most complete and back-in-time extended seismic catalogue worldwide, our knowledge concerning the periodicity of the strongest earthquakes is still poor and debated. Whereas we are aware that almost all the highest magnitude classes (6 <= M <= 7) in the Italian peninsula are sourced by the normal fault systems paralleling the Apennines divide, the relatively low slip rates of these faults imply that the average recurrence time is often longer than the historical completeness period. This biases probabilistic seismic hazard assessment based only on historical catalogues. Since in the past 30 years the Italian earthquake geologists produced many valuable palaeoseismological data in hundreds of trenches opened across active faults, here I have tried to collect and match their results in order to evaluate the recurrence times of the faults having the most robust chronological constraints. Resulting average recurrence spans from few centuries to 3,000 years during the Holocene, whereas it is shorter in the historical period.