36Cl exposure dating of glacial features to constrain the slip rate along the Mt. Vettore Fault (Central Apennines, Italy)

The Central Apennines are among the most seismically active regions in Italy. This region is affected by an extension accommodated by active normal faults. Those faults with high seismogenic potential hosted Mw > 6 shallow damaging earthquakes, such as the Mw 6.5 event of Oct. 30, 2016. Although fault slip rates are crucial to seismic hazard assessments, in the Central Apennines, slip rate assessments encompassing several seismic cycles (> 10 ka) are sparse. This is particularly true for the Mt. Vettore-Mt. Bove Fault system that ruptured during the mainshocks of the 2016–2017 seismic sequence. In this study, we present new geochronological constraints of offset geomorphological markers along the northern portion of the fault system on the Mt. Porche Fault segment using in-situ produced 36Cl cosmogenic nuclides. Offset measurements were made using a 5-cm resolution DEM obtained through a drone survey and constrained a fault scarp height of 15.5 ± 1.4 m and a maximal cumulative offset estimated between 32 and 40.5 m. Samples were collected from the Valle Lunga terminal moraine at 1710 m asl and yielded 36Cl exposure ages of 12.7 + 2.2/−1.9 ka, while the abraded surface, located on top of the tectonic scarp yielded 36Cl exposure ages of 23.4 + 5.3/−4.3 ka. Using the fault scarp height and the exposure age of this abraded surface, we constrained a minimum vertical fault slip rate of 0.7 + 0.2/−0.1 mm/yr. Assuming the offset started to accumulate when climate conditions allowed the scarp preservation, we constrained a maximal vertical slip rate of 1.2 ± 0.2 mm/yr along the main fault of the Mt. Vettore-Mt. Bove Fault system. This rate is higher than those previously obtained from trenches along secondary branches of the Mt. Vettore-Mt. Bove Fault system. Besides, the yielded chronology for the last glacial maximum in that area at ~23 ka is in good agreement with the timing previously proposed for the LGM in the Apennines. © 2022