Paleoseismic evidence of five magnitude 7 earthquakes on the Norcia fault system in the past 8,000 years (Central Italy)

Many large-magnitude faults (6.5<= Mw <=7.2) of the Italian Apennines are characterized by multi-century return times, so historical sources may have missed their last earthquake or other predecessors. Hence, even in Italy, where seismic catalogs are among the most comprehensive and time-extensive worldwide, there is a need for complementary studies that might fill the lack of historical information and enhance the knowledge concerning the recurrence times of destructive earthquakes. As paleoseismology is the discipline that can do this, in this study, we present results collected in five new trenches opened along the 33-km-long Norcia fault system (central Apennines) where, in addition to the historically known 1703 earthquake (Mw 6.9), we uncovered indications of four Holocene predecessor, with a recurrence time of 1,825 ± 420 years. Considering also the paleoseismic results already published on the nearby Mt Vettore fault system (2016 earthquake of Mw 6.6), we guess that now the seismic hazard of this region could be assessed more robustly.