Research published this week confirmed that California has been in a century-long earthquake drought. Analysis of geologic records on the state’s main faults — the San Andreas, San Jacinto and Hayward — going back 1,000 years shows that the gaps between large quakes are, currently, longer than to be expected from random variation. Southern California has been particularly quiet for the last 25 years, with the rate of small and moderate earthquakes almost half of what it had been in the previous half a century.
This hiatus in major shaking means that we aren’t getting as much movement as plate tectonics require. So at some point we’ll start having more frequent earthquakes, and things will — over geologic time — average out again. (We won’t necessarily have a bigger earthquake, just a period in which they are more frequent.)
As the U.S. Geological Survey scientists point out, because we don’t know why we are in a drought, we don’t know when it will end.
But we do know that it will end. The Pacific plate is still on its very slow move carrying Los Angeles toward San Francisco. Just as the rains came this winter, some year the big earthquake will come.