A Vanishing Lake In SoCal May Have Delayed Major San Andreas Quakes — But A 'Big One' Will Still Happen

It’s been about 300 years since the last big earthquake struck on the Southern San Andreas Fault in the area of Bombay Beach. But before this latest stretch of quiet, quakes are believed to have occurred there pretty reliably every 180-ish years or so.

This delay is one of the reasons why scientists and emergency managers are always screaming “the Big One is coming.” Because a big earthquake is statistically likely to occur in the region.

A new paper published today in the journal Nature makes the case that major quakes here may have been in part triggered by the filling of Lake Cahuilla, a long gone body of water that used to intermittently appear where the Salton Sea currently is.

What changed

“Part of the answer as to why the Southern San Andreas is locked and essentially loaded for a major earthquake — and has not had an earthquake for the past 300 years — may be a function of the fact that Lake Cahuilla is no longer possible in this region,” said Matthew Weingarten, assistant professor at the Department of Geological Sciences at San Diego State University, and co-author on the paper.

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That’s because we’ve long controlled the source of Lake Cahuilla, the Colorado River. In the past, the river would occasionally divert into the Salton Sea area through natural processes, filling up over the course of decades.

When full, it’s estimated that Cahuilla was about six times the size of Lake Mead, with a maximum depth of about 300 feet.

The evidence

The idea presented in the latest research is that the influx of water was so heavy that it’d essentially bend the Earth’s crust, both increasing and modifying stress on the fault, ultimately making it more likely to go off. Weingarten said that at least six of the seven major documented quakes that’ve occurred there over the past 1,000 years struck during or after the formation of the lake.

“I think there is likely a connection,” said Belle Philibosian, research geologist with the U.S. Geological Survey, who’s also written about the correlation between the lake and quakes in the area. She wasn't associated with the recent research.

“That earthquake is still gonna happen. The stress is still building up and it has to go somewhere eventually. But it’s possible that because the lake hasn't filled it's taking longer, because there isn't this additional trigger that's causing the earthquakes to happen sooner.”

But, she points out, “because these processes are so complicated, we just have to be prepared for an earthquake to happen at any time.”

So, might as well be responsible and prepare yourself for the Big One.

Get ready for the next Big One