David J. Varnes

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

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.

Predicting earthquakes by analyzing accelerating precursory seismic activity

AbstractDuring 11 sequences of earthquakes that in retrospect can be classed as foreshocks, the accelerating rate at which seismic moment is released follows, at least in part, a simple equation. This equation (1) is

Gravitational spreading of steep-sided ridges (“sackung”) in Western United States

d(\Sigma \sqrt {M_0 } )/dt = C/(t_f - t)^n

Landslide Hazards and Their Reduction

,where

LANDSLIDE TYPES AND PROCESSES

\Sigma \sqrt {M_0 }

Mechanics of gravitational spreading of steep-sided ridges («sackung»)

is the cumulative sum until time,t, of the square roots of seismic moments of individual foreshocks computed from reported magnitudes;C andn are constants; andtfis a limiting time at which the rate of seismic moment accumulation becomes infinite. The possible time of a major foreshock or main shock,tf,is found by the best fit of equation (1), or its integral, to step-like plots of