Ubiquitous interactions and subcritical patches explain the irregularity of repeating earthquakes
Nadia Lapusta, & Linxuan LiSubmitted August 30, 2026, SCEC Contribution #15353, 2026 SCEC Annual Meeting Poster #TBD
Repeating earthquakes, or repeaters, are commonly interpreted as ruptures of the same fault patch and widely used to study fault slip behavior, including creep rates, healing, and stress drops. Despite their apparent simplicity, repeaters exhibit strong variability in their recurrence intervals, even when events within a given sequence have nearly identical magnitudes. Previous studies have shown that repeating earthquakes are neither time- nor slip-predictable. We investigate the physical origin of this irregular recurrence by combining statistical analysis of earthquake catalogs with physics-based numerical modeling of coupled seismic and aseismic fault slip.
Using repeating earthquake catalogs in Northern California, we find that most repeaters have at least one neighboring sequence within a few hundred meters and show clear evidence of interaction, as indicated by short intervals between earthquakes occurring in nearby sequences beyond what would be expected by chance. We further identify a substantial population of small repeating sequences that rupture extremely infrequently and are preferentially activated following nearby larger repeaters. These sequences exhibit behavior inconsistent with self-nucleation, suggesting that they occur on subcritical patches and are triggered by stress perturbations from nearby events. Numerical simulations of rate-and-state faults with two velocity-weakening patches quantitatively reproduce both the observed interaction patterns and recurrence variability, and confirm the importance of interactions and subcritical patches. The simulations also show that the source patches of the infrequent repeaters experience slow-slip transients between triggered seismic events, allowing them to keep up with nearby creep.
Our results indicate that repeating earthquakes are rarely isolated systems, provide observational support for a minimum patch size required for earthquake self-nucleation under slow tectonic loading, and highlight the need to account for both seismic and aseismic slip when considering properties of seismic events.
Key Words
Earthquake cycles, repeating sequences, interaction, nucleation, seismic and aseismic slip
Citation
Lapusta, N., & Li, L. (2026, 08). Ubiquitous interactions and subcritical patches explain the irregularity of repeating earthquakes. Poster Presentation at 2026 SCEC Annual Meeting.
Related Projects & Working Groups
Fault and Rupture Mechanics (FARM)
