Earthquake recurrence and seismic cycle variability in the Central Apennines from simulated earthquake catalogues

SUMMARY

The Central Apennines (Italy) host a distributed network of active normal faults capable of generating infrequent but destructive earthquakes with recurrence intervals that often exceed the duration of available historical and paleoseismological records. This observational limitation hampers our understanding of long-term fault behaviour, seismic cycle variability and multifault rupture potential. In this study, we apply the MCQsim earthquake-cycle simulator to a 3-D fault model comprising 42 major active normal faults in the Central Apennines, generating seven 100 000-yr synthetic earthquake catalogues by systematically varying rupture-controlling parameters: fault strength magnitude and heterogeneity, and numerical mesh resolution. We evaluate how these parameters influence seismic productivity, the shape of magnitude–frequency distributions and the scaling of rupture area and average slip with magnitude. Simulated catalogues are compared with the Italian Parametric Earthquake Catalogue (CPTI15) and with empirical magnitude–scaling relationships to assess consistency with observed seismicity. The simulations reproduce the regional magnitude–frequency distribution and yield rupture scaling consistent with empirical relationships, with the strongest sensitivity observed for changes in the difference between static and dynamic friction coefficients and the parameters controlling fault strength heterogeneity. Analysis of interevent times for earthquakes with Mw ≥ 6 shows that recurrence variability is broadly consistent with a quasi-periodic process, while intermittent clustering at multicentennial timescales is also captured. Although the use of a uniform fault dip and a simplified seismogenic depth boundary, rather than depth-varying fault geometry, may affect the detailed representation of individual ruptures, the overall consistency between synthetic and observed seismicity demonstrates that MCQsim provides a physically grounded framework for investigating long-term fault system behaviour and earthquake recurrence variability in the Central Apennines.