Testing time-predictable earthquake recurrence by direct measurement of strain accumulation and release

Probabilistic estimates of earthquake hazard use various models for the temporal distribution of earthquakes, including the ‘time-predictable’ recurrence model formulated by Shimazaki and Nakata 1 (which incorporates the concept of elastic rebound described as early as 1910 by H. F. Reid 2 ). This model states that an earthquake occurs when the fault recovers the stress relieved in the most recent earthquake. Unlike time-independent models (for example, Poisson probability), the time-predictable model is thought to encompass some of the physics behind the earthquake cycle, in that earthquake probability increases with time. The time-predictable model is therefore often preferred when adequate data are available, and it is incorporated in hazard predictions for many earthquake-prone regions, including northern California 3 , southern California 4 , 5 , New Zealand 6 and Japan 7 . Here we show that the model fails in what should be an ideal locale for its application — Parkfield, California. We estimate rigorous bounds on the predicted recurrence time of the magnitude ∼6 1966 Parkfield earthquake through inversion of geodetic measurements and we show that, according to the time-predictable model, another earthquake should have occurred by 1987. The model's poor performance in a relatively simple tectonic setting does not bode well for its successful application to the many areas of the world characterized by complex fault interactions.