The top cross section below shows earthquakes along the San Andreas fault before October 17, 1989 and the one on the bottom shows earthquakes along the same fault after that date. These two cross sections illustrate that

he Working Group on California Earthquake Probabilities estimated after the 1989 Loma Prieta earthquake that the probability of a magnitude 7 earthquake in the next 30 years in the San Francisco Bay region was 67 percent

Explanation:

But this estimate is not precise because earthquakes do not occur "like clockwork", and because other factors not included in our simple model may be involved. So, while the most likely time for a 1906-like earthquake to strike again is perhaps late in the next century, there is a small chance (about 2 percent) that it could happen in the next 30 years

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