Evidence for a Constant Slip Rate Over the Last ∼40 ka Along the Mt. Morrone Fault System in Central Apennines

Located in the easternmost portion of the Central Apennines, the Mt. Morrone normal fault system is one of the highest seismic hazards in Italy. Previous geological and geomorphological observations revealed the presence of a ∼22 km-long NW-SE right-lateral en echelon fault system made of two parallel faults affecting Quaternary deposits. Our analysis focused on the westernmost fault, which bounds the Sulmona Basin. Cumulative offsets were identified and quantified using high-resolution Digital Elevation Models derived from LiDAR, Satellite Pleiades images, and drone acquisition at the three sites. Morphological markers displaced from a few to tens of meters were dated using ³⁶Cl exposure dating. The results would be suggesting a fault slip rate of 0.2–0.4 mm/a. The deformed markers that dated at 36–44 ka consist of alluvial terraces emplaced by the main streams flowing down from Mt. Morrone to the Sulmona Basin, subsequently incised, and preserved when the fluvial base level dropped because of the former Sulmona lake fluctuations. The yielded ages for these markers fit well with the last major aggradational event associated with the 35–40 ka Heinrich event described and dated to other fluvial basins in the Apennines. Furthermore, the estimated rate agrees with the values obtained in previous studies over shorter and longer periods (10⁵⁻⁶ years) and within similar uncertainties. This might then suggest that the period recovered by this study encompasses the entire seismic cycle.