DETAILED MAPPING AND PALEOSTRESS ANALYSIS OF ACTIVE FAULTS IN THE NORTHERN VETTORE - BOVE FAULT ZONE, SIBILLINI MOUNTAINS, ITALY

The Sibillini Mountains, which make up the southern part of the Umbria-Marche Apennines, Italy, were struck by a series of earthquakes in 2016, including five with magnitudes greater than 5. The largest event, M_w6.5, occurred on October 30^th, 2016. A M_w5.9 earthquake on October 26^th, ruptured several faults in the northern third of the Vettore-Bove fault system, and the M_w6.5 event produced surface ruptures along the entire 30-km length. Ground surveys conducted shortly after these earthquakes showed that many, but not all, of the surface ruptures corresponded to previously mapped faults. Also, some faults that had been mapped as Quaternary did not produce surface ruptures during the earthquakes. In this study, we present the results of detailed field mapping that was conducted prior to the 2016 earthquakes and provide evidence that all of the surface ruptures in the northern part of the Vettore-Bove fault system occurred along preexisting faults. Paleostress analysis shows that the reactivated faults had been active prior to 2016 in stress fields with similar orientations to the modern-day stress field. A slip-tendency analysis yielded similar results to the paleostress analysis. In addition, we show that a likely Quaternary fault, which is the southern continuation of a major fault that slipped during the 2016 earthquakes, was not reactivated in 2016 because it was unfavorably oriented. Paleostress analysis can be a useful tool in determining which faults are likely to be active in a known stress field.