Using dense 36Cl profiles to assess the seismic history of the Roccapreturo Fault (Italy)

The Roccapreturo fault, part of the Middle Aterno Valley Fault system in the central Apennines (Italy), is a key structure for understanding the region’s seismic hazard. Despite evidence of Quaternary activity, its Holocene seismic history remains poorly constrained, with no historical earthquakes directly attributed to this fault. In this study, high- and low-resolution ³⁶Cl cosmogenic nuclide profiles from five sites along the Roccapreturo limestone fault scarp were used to reconstruct the seismic history of this fault. The seismic history was constrained using PyMDS inversion algorithm (Llinares et al., 2025), which relies on Markov Chain Monte Carlo (MCMC) approach to infer the timing and slip of past surface-rupturing earthquakes.

Our results indicate at least five major seismic events over the last ~18,000 years, with coherent clusters at ~5 ka, ~3.5 ka, ~2–3 ka, ~1 ka, and <0.5 ka BP on at least two sites. The most recent event, dated at ~300 years BP, could correspond to a previously unattributed historical earthquake. Slip Rates (SRs) over the Pleistocene, estimated from high resolution profiles, range from 0.1 to 0.4 mm/yr, which is consistent with previous studies (Falcucci et al., 2015; Tesson et al., 2020) and InSAR data (Daout et al., 2023).  SRs over the Holocene are higher (~1–2 mm/yr), suggesting temporal variability. The study also discusses methodological advances, including the value of dense sampling, the use of statistical changepoint detection, and the integration of fuzzy statistics to address uncertainties in seismic history derived from ³⁶Cl dataset from limestone fault scarp.

These findings provide new constraints on the seismic behavior of the Roccapreturo fault, highlight the importance of multi-site and high-resolution approaches, and underscore the need for further paleoseismological and historical investigations to refine the seismic hazard assessment in the central Apennines.