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

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

Published September 8, 2024, SCEC Contribution #13998, 2024 SCEC Annual Meeting Poster #208

Seismic source hazard-models endeavor to predict earthquake likelihood from elapsed time since a prior event. Here we show that recurrence intervals from long paleoseismic records (n>10 events) from plate-boundary strike-slip faults in California and New Zealand are well fit by the Weibull distribution, with hazard functions that increase as a power-law of time. Two modes of earthquake-cycle behavior emerge. For the Alpine fault, strongly convex hazard functions (exponent k≥2) indicate 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 irregular recurrence behavior, 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, supercycles can be produced when infrequent, system-spanning ruptures are followed by long periods of quiescence before returning to a partial rupture mode. By aggregating ratios of inter-event times from shorter paleoseismic records from across California, we show that k<1 in most cases. This finding suggests that irregular patterns of earthquake rupture extent and timing is the norm, and that cyclic renewal-type behavior is rare.

Key Words
paleoseismology, Weibull distribution

Citation
Oskin, M. E., Lau, W., Scharer, K. M., & Usher, E. H. (2024, 09). Earthquake-Cycle Modality Revealed by Paleoseismic Inter-Event Time Distributions. Poster Presentation at 2024 SCEC Annual Meeting.

Related Projects & Working Groups
Earthquake Forecasting and Predictability (EFP)