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Yes, The Big One Will Happen

Published: May 15, 2014

Nate Onderdonk says the big one is inevitable.

“When people talk about the big one, it’s not exactly clear what they mean by that, but big earthquakes in Southern California are inevitable,” said the geological sciences’ associate professor. “We know they’ve been occurring for hundreds of thousands of years in Southern California and we seem to have a really big one every 150 to 200 years. So, the logic is, as long as something completely weird doesn’t change with the tectonic system that we’re familiar with, we’re going to continue having big earthquakes in Southern California.”

When it will happen is, of course, anyone’s guess, but Onderdonk is quite certain there is no such thing as an earthquake season, mainly because most of the bigger earthquakes that we feel start pretty deep down in the earth.

“In Southern California, most of our big earthquakes are starting at seven miles deep,” he said. “Whereas, if you have very hot, dry weather there at the surface, that’s only affecting maybe three feet deep, so weather at the surface really doesn’t have any impact on the rocks down at the depth at which these earthquakes are starting. If there was an earthquake season, we’d have a better idea when an earthquake was coming and people have looked into this for years.”

Onderdonk, who earned his Ph.D. at UC Santa Barbara in 2003 and did post-doc work at the University of Oslo in Norway for two years, said geologists are constantly trying to find any signs that may indicate a warning of earthquakes—such as animals sensing it before humans or release of gases—but so far no one has really found anything consistent or solid that can be used.

“Maybe animals can feel the vibrations, sensitive vibrations better than we do,” he said, “but if they are sensing it before us, it’s probably a few seconds, not days in advance as some people have claimed.”

As for where the next big earthquake will take place, Onderdonk doesn’t hesitate sharing his opinion and the reasoning behind it.

“When we try to figure out where the next big one would occur, the best we can do is look at the pattern of earthquakes throughout history and prehistoric times in the last couple thousand years and make kind of probability maps,” he said. “The short answer is the highest probability for a big earthquake is probably in the Santa Barbara Channel, Santa Barbara Coast area, as well as the Inland Empire areas along the San Andreas and San Jacinto faults. So San Bernardino down through Palm Springs, Riverside, those two areas are where we would expect a big earthquake most likely to occur in the near future.

“The thing about Santa Barbara is that the rate of stress accumulation is very high there,” he added. “The coast of Santa Barbara is coming out of the ocean at something like greater than six millimeters per year, which is pretty fast. So we know stress is building up there really quickly and wherever you have areas of stress that’s building up fast that’s where you assume a more likelihood of a big earthquake coming.”

When asked if earthquakes, such as 5.1 magnitude one in Brea on March 28, actually alleviate some of the pressure of future quakes, Onderdonk said it does, with a caveat.

“It’s relatively insignificant compared to the big earthquakes we know we can have on these faults,” he said. “Just to give you an example, that magnitude 5, in order to step up one step in the Richter Scale and go from a 5 to a 6, that’s 30 times more energy release. So you would need 30 magnitude 5s to equal a magnitude 6. So if we were talking about will this relieve stress for the big magnitude seven earthquake, you would need something like 900 of those magnitude 5s to even get close to the amount of stress that’s released in a seven.”

And as for the notion that California will fall off into the ocean when the big one finally does hit, well, Onderdonk just chuckles.

“The idea that California would fall off into the ocean during a big earthquake is absolutely false,” he said. “There’s nothing for it to fall into. There’s crust underneath the ocean as well so I have no idea where that idea came from, Hollywood I would guess, but it’s absolutely untrue.”