In fact, the movement along these faults is neither smooth nor constant. The motion of the plates builds up strain along these faults until the stress becomes too much and the built up pressure is released through an earthquake. By studying these, and other faults scientists recognize the patterns of earthquakes that relieve the stress in this constantly moving system. The history of earthquakes in the San Francisco area suggests that this area is rocked fairly regularly, on a geologic time scale, with large earthquakes. The seismicity gap, or lack of seismic activity as evidenced on this poster, is part of the temporal pattern of strain release for this part of the fault.
Scientists continue to study earth- quake patterns.
As our understanding of earthquake systems increases, so does our ability to predict the impact on the human environment. In the early to mid 80s, scientists began forcasting the Loma Prieta earthquake. Scientists had judged the Santa Cruz Mountain section of the fault as having the highest probability of an earthquake of any segment of the San Andreas Fault that had ruptured in 1906. In July of 1990, after the Loma Prieta Earthquake, the National Earthquake Prediction Evaluation Council convened a panel of experts to re-evaluate predictions for the San Francisco Bay area. The Council estimated that the probability is about 25 percent for a large earthquake on each one of these fault segments within 30 years.