Earthquake-Cycle Modality Revealed by Paleoseismic Inter-Event Time Distributions

Michael E. Oskin, Katherine M. Scharer, & Wing Yee Winnie Lau

Submitted September 3, 2025, SCEC Contribution #14978

Time-dependent seismic hazard models endeavor to predict earthquake likelihood from elapsed time since a prior event. Here we show that long paleoseismic records (n≥10 events) from plate-boundary strike-slip faults in California and New Zealand are well fit by the Weibull distribution, defined by hazard increasing as a power-law of time. Two modes of earthquake-cycle behavior emerge. The Alpine fault exhibits a system-spanning rupture mode, with strongly convex hazard functions (exponent k≥2) indicating cyclic renewal: As the fault recovers from the previous system-spanning event, greater fault area contributes to the likelihood of rupture through a paleoseismic site. The San Andreas and San Jacinto faults exhibit a partial-rupture mode and irregular recurrence behavior, often with concave hazard functions (k<1) that indicate a survivor effect: Partial-rupture events elsewhere temper the likelihood of an earthquake initiating and propagating through a site. On these systems, super-cycles can be produced when infrequent, system-spanning events are followed by long periods of quiescence before returning to a partial rupture mode.

Citation
Oskin, M. E., Scharer, K. M., & Lau, W. (2025). Earthquake-Cycle Modality Revealed by Paleoseismic Inter-Event Time Distributions. Science, (submitted).