After A Not-So-Big Quake This Week, We Got This Question: Can One Big Quake Trigger Another?

After last night’s 4.2 magnitude quake near San Bernardino, listener Marcos Garcia-Nuñez reached out with an excellent question: How likely is it that a big earthquake on a fault like the San Andreas, will trigger another quake nearby?

Possible, but not very likely

“It’s certainly possible, but the likelihood of that happening is pretty low,” said U.S. Geological Survey seismologist Clara Yoon.

Anytime there are major stress changes in the Earth, a nearby fault that’s been loaded and ready to go could also slip.

“Ideally we’d like to know how much stress has built up pretty much at every point underground in the Los Angeles area, but we just don’t have that information. So we can’t tell, 'hey this earthquake is triggering a fault in this area, but this other earthquake will not,'” said Yoon.

It’s been speculated that the 2023, 7.8 magnitude quake that first struck Turkey last year helped trigger the nearby 7.5 magnitude quake that followed.

There were fears after the 2019 Ridgecrest quake that the nearby Garlock fault — the second largest fault structure in California — could potentially trigger the San Andreas. Fortunately, that didn’t happen.

“The chance of one earthquake triggering a larger earthquake than itself is about 5%,” said USGS seismologist Elizabeth Cochran.

So, how do scientists determine if two quakes are related?

It essentially comes down to the amount of time between the two events. If it's shorter than the usual estimated rate between quakes on a fault, then there's a chance they could be.

“It’s not an exact science in terms of directly linking one event to another,” said Cochran.

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You’re at Union Station when the big one hits. The next two minutes are terrifying. By the time you make your way outside, the Los Angeles you know is gone. In Episode One, you experience what the first hours after a massive earthquake could be like.

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