Stress interactions in seismogenic faults through the lens of physics-based earthquake cycle simulations

Recurrence intervals and magnitude distributions of earthquakes are key parameters in probabilistic and time-dependent seismic hazard assessments, yet they are difficult to constrain because the time window of instrumental and paleoseismic records often capture only a smaller fraction of the earthquake cycle of large earthquakes. Physics-based seismic cycle simulators can help to overcome these limitations by generating synthetic catalogues that span thousands of years, offering valuable insights into the statistical behaviour of fault networks. Despite the increasing use of these simulators, the physical mechanisms governing earthquake timing and size distributions remain incompletely understood, in particular the role of fault interactions and spatial variations in long-term slip rates.
Here we use the boundary-element code QDYN to simulate earthquake cycles on normal fault networks of increasing geological complexity, ranging from simplified two-fault configurations to realistic fault networks derived from field data in the Central and Southern Apennines (Italy). Our results show that both fault geometry and slip-rate variability critically influence earthquake recurrence and magnitude distributions. Networks with multiple across-strike interactions produce more complex seismic sequences, irregular recurrence intervals, and broader ranges of rupture sizes and moment magnitudes (Mw) compared to simpler configurations. Similarly, spatially variable slip-rate profiles promote diverse rupture behaviours, including partial ruptures and slow-slip events, that increase variability in stress redistribution, magnitude-frequency relationships and recurrence times. In contrast, models using uniform slip-rate profiles tend to produce regular recurrence patterns and characteristic earthquake magnitudes. These findings highlight the importance of incorporating realistic fault geometries and spatially variable slip rates in physics-based earthquake simulators used to inform seismic hazard assessments.