The Awakening of the Dormant Mount Vettore Fault (2016 Central Italy Earthquake, Mw 6.6): Paleoseismic Clues on Its Millennial Silences

The Mount Vettore normal fault ruptured between August and October 2016, sourcing three earthquakes of Mw 6.2, 6.1, and 6.6. The first one caused the death of 299 people, while the entire sequence reached the highest macroseismic intensity levels in Italy since the catastrophic 1915 Fucino event (Mw 7.1). This fault was known to be one of the historically dormant faults of the Italian Apennines, and its sudden activation, not preceded by any foreshocks, has caught people and scientists off guards. We describe here the results from three new paleoseismic trenches opened across splays of the main antithetic fault that ruptured at surface on 30 October together with the 30-km-long Mount Vettore master fault. Data account for six surface faulting events since 9 ka, with a return time of 1.8 ± 0.3 kyr. The penultimate, probably stronger earthquake occurred in Late Roman times, perhaps in 443 AD, when also Rome suffered damage to its monumental buildings. Once again, paleoseismology turns out to be a powerful tool in seismic hazard assessment, especially for earthquakes that recur hundreds or thousands of years apart.