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New Movement Along Garlock Fault Line In California Could Mean Bigger Earthquakes


The bulging of a fault line in California can be seen from outer space. The Garlock Fault is moving in ways never seen before. And, as always, the question for California is, does this raise the risk for the big one? I am moving back out to California soon, so this is a question I am very personally invested in. And here to help me and you understand more is Jacob Margolis. He's a science reporter with KPCC in Pasadena.

Hey, Jacob, future neighbor.


CHANG: (Laughter) Well, I'm worried about these earthquakes. I mean, there's this huge San Andreas Fault that I know a lot about. It basically runs parallel to the coastline. But there's then this Garlock Fault that runs east-west, right?

MARGOLIS: Yeah. So the Garlock bisects California, and it connects to the San Andreas. And it was right next to the Ridgecrest quakes that happened back in July. And so the big concern was - and what people are kind of zoning in on now - is that after those Ridgecrest quakes, which were sizable - a 6.4, a 7.1 - we actually saw the first movement on that fault that has been recorded. And it was creep - so it was about 2 centimeters...

CHANG: Ever?

MARGOLIS: Well, not ever in the history of the fault. We know about 500 years ago was likely the last time we saw a big quake there. But that 2 centimeters of creep was significant enough for scientists going, oh, that's interesting. That doesn't necessarily mean a humungous 8.0 magnitude earthquake is imminent on the Garlock, but, you know, it caught people's attention.

CHANG: Well, how could movement on the Garlock impact movement on the San Andreas Fault?

MARGOLIS: Yeah. Theoretically, if the Garlock went, it could change stresses on the San Andreas over near the coast. That said, the San Andreas is such a high-risk fault anyway. The probability of a big earthquake happening where the Garlock connects to it all the way down to, like, Palm Springs is pretty high. So I'd be worried about the San Andreas anyway, regardless of the Garlock.

CHANG: So if there's movement along the Garlock, that could actually be bad news for the San Andreas, whereas I feel like I hear sometimes small movements actually are good. That means, like, stress is being released. But that's not necessarily the case is what you're saying.

MARGOLIS: Yeah. When we see movement of the earth, it's not like all that stress just disappears. It gets put off on to other faults. And so the likelihood of bigger quakes happening actually go up after big earthquakes, at least for a short period of time. And that - over time, that probability kind of goes down and settles into long-term probabilities and likelihoods. But I, like I said, would be more worried about the San Andreas on its own, just in terms of the Garlock.

CHANG: OK. So also this week, California announced the release of this app called MyShake to help prepare residents. I'm going to download this app soon. Can you just tell me how this is supposed to work, this app?

MARGOLIS: Yeah. So over four years now, the U.S. Geological Survey, Caltech, a bunch of organizations have been building out this network of sensors and computers that basically track movement from faults in California. And so let's say a fault does slip. It picks up - those sensors pick up those initial waves and then send it over to computers. The computers kind of analyze the movement, and then it flags it for people before...


MARGOLIS: ...Hopefully before the shaking arrives. That said, if you are right on top of the fault, you're not really going to get a warning.

CHANG: Yeah.

MARGOLIS: In Los Angeles, when it comes to the San Andreas, we could have seconds, possibly tens of seconds because we're far enough away. For people in Palm Springs, if that portion breaks, you know, they're going to experience it right on time. And it's really important, this earthquake early warning system, because we could do things like stop surgeries, open firehouse doors, slow down trains or even just give people a minute to - or a couple seconds to drop cover and hold on.

CHANG: I love how you say tens of seconds as if that's all the time the world. But in certain situations, that is enough time.

MARGOLIS: Yeah, absolutely.

CHANG: Jacob Margolis hosts the podcast The Big One: Your Survival Guide.

Thanks so much, Jacob.

MARGOLIS: Thank you. Transcript provided by NPR, Copyright NPR.

Jacob Margolis