Predictive modeling of the seismic cycle of the Greater San Francisco Bay Region

TLDR

The San Francisco Bay seismic cycle is modeled by integrating pre‑ and post‑1906 seismic histories. The study aims to test whether the Bay region is entering a 20–50‑year quiescent period above magnitude 6 following the Loma Prieta subcycle. The authors use time‑to‑failure analysis, modeling seismic release rate as inversely proportional to a power of remaining time to failure, to capture long‑term and short‑term accelerations. The model shows a scale‑invariant time‑to‑failure exponent, estimates a 269 ± 50‑year cycle, predicts the 1989 Loma Prieta event within 2 years and 0.5 magnitude, and suggests a great earthquake like 1906 is more than a century away.

Abstract

The seismic cycle for the San Francisco Bay region is synthesized by a model combining the pre‐and post‐1906 seismic histories. The long‐term acceleration of seismic release (seismic moment, Benioff strain release, or event count) in the seismic cycle and the shorter‐term accelerations preceding the larger earthquakes within that cycle are modeled using an empirical predictive technique, called time‐to‐failure analysis, in which rate of seismic release is proportional to an inverse power of the remaining time to failure. The exponent of time to failure in the accelerating sequences appears to be scale invariant, and the length of the full cycle is estimated at 269 ± 50 years. The 1989 Loma Prieta earthquake, which is the culmination of the first subcycle in the present long‐term seismic cycle, should have been predictable with an uncertainty of 2 years in time and 0.5 in magnitude, although the specific location (at Loma Prieta) was not predictable by this technique. If our model is correct and if the Loma Prieta earthquake is the culmination of a subcycle, the San Francisco Bay region should be entering a relatively long (20–50 years) period of seismic quiescence above magnitude 6. A great earthquake, such as the 1906 San Francisco event, would appear to be more than a century in the future.