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.
Regularity of seismic slip along a 9 km segment of the Calaveras fault zone is believed to result from steady‐state loading of a creeping fault to generate stresses on an isolated stuck patch which moves in a stick‐slip event in the magnitude range 3 to 4 whenever a critical threshold is reached. The patch behavior can be described by a simple model similar to the spring‐driven frictional models used in laboratory simulations of stick‐slip. The (M ≥ 3) recurrence time for this model is directly proportional to the seismic slip (computed from magnitudes) since the last time the threshold was reached. If the model is correct, an (3 ≤ M ≤ 4) earthquake should occur at 37° 17′ ± 2′ N, 121° 39′ ± 2′ W within 48 days of January 1, 1977.
Temporal clustering of the larger earthquakes (foreshock-mainshockaftershock) followed by relative quiescence (stress shadow) are characteristic of seismic cycles along plate boundaries. A global seismic-moment release history, based on a little more than 100 years of instrumental earthquake data in an extended version of the catalog of Pacheco and Sykes (1992), illustrates similar behavior for Earth as a whole. Although the largest earthquakes have occurred in the circum-Pacific region, an analysis of moment release in the hemisphere antipodal to the Pacific plate shows a very similar pattern. Monte Carlo simulations confirm that the global temporal clustering of great shallow earthquakes during 1952-1964 at M Ն 9.0 is highly significant (4% random probability) as is the clustering of the events of M Ն 8.6 (0.2% random probability) during 1950-1965. We have extended the Pacheco and Sykes (1992) catalog from 1989 through 2001 using Harvard moment centroid data. Immediately after the 1950-1965 cluster, significant quiescence at and above M 8.4 begins and continues until 2001 (0.5% random probability). In alternative catalogs derived by correcting for possible random errors in magnitude estimates in the extended Pacheco-Sykes catalog, the clustering of M Ն 9 persists at a significant level. These observations indicate that, for great earthquakes, Earth behaves as a coherent seismotectonic system. A very-large-scale mechanism for global earthquake triggering and/or stress transfer is implied. There are several candidates, but so far only viscoelastic relaxation has been modeled on a global scale.
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