Scientists Caution California Quakes Should Be A Wake-Up Call

Originally published on July 8, 2019 10:12 am
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RACHEL MARTIN, HOST:

California can't quite breathe a sigh of relief. Two of the biggest earthquakes to rattle the state in decades did not result in any major injuries. But scientists say it's a sign of what's to come. Here's how Governor Gavin Newsom put it.

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GAVIN NEWSOM: We all have an opportunity now to get more prepared, to be more vigilant, to look at our building codes, look at our home hardening.

MARTIN: Ross Stein is a scientist emeritus at the U.S. Geological Survey and creator of the seismic risk tool called temblor.net. He joins us now. Thanks so much for being with us.

ROSS STEIN: Happy to do so.

MARTIN: First off, just how unusual is it to have back-to-back earthquakes like this, the second even stronger than the first?

STEIN: Well, it happens. It's not the typical deal. Normally, we have a big earthquake, and it's followed by smaller ones that get spaced farther and farther apart. But three years ago in Japan, we had a magnitude 6 in Kumamoto on the south island of Japan. And a day later, we had a magnitude 7 at the same spot, expanding, much like this earthquake that occurred in the last few days.

MARTIN: Why didn't a 7.1 earthquake cause more damage?

STEIN: Well, first of all, let's just take the good news where we can get it. That's wonderful. But second, it's all about location. This is one of the most sparsely populated, though beautiful, parts of California - the high desert area. So there were no tall buildings. And there are very, very few homes compared to if we put this same earthquake, for example, in the San Francisco Bay area on the Hayward Fault. We would have a hundred times, a thousand times more buildings exposed to the shaking, and we would have much softer sediments that amplify the shaking.

MARTIN: How much better prepared is the state of California for a devastating earthquake than it was 20 years ago?

STEIN: Well, that's kind of a trick question. On the good news side, PG&E has done an enormous job in bolstering and hardening their system of pipelines and conduits. Caltran (ph), the state transportation department, has done the same. And there are more ordinances that require or encourage people to retrofit multiunit buildings.

But on the flip side, only a small percentage of the population carries insurance. And a very small percentage of older homes have been seismically retrofit to make them stronger. So it's definitely a good news-bad news situation. And maybe this is another reminder that we can turn this into all good news if we get prepared.

MARTIN: Do earthquakes like this - does this increase the risk in other parts of the state? I mean, should people along other fault lines be concerned right now?

STEIN: Probably not. Nevertheless, this earthquake has stressed its neighboring faults, and we are beginning to see earthquakes on those faults. So just to the south of this rupture is the Garlock Fault that's almost 200 miles long, and it connects to the San Andreas. And in the last day, we've seen about a dozen earthquakes on it, not far from where this one occurred. So it's always possible that this earthquake will trigger another event on a neighboring fault. And that could propagate into more populated areas.

MARTIN: What did you learn from this?

STEIN: Well, earthquakes are in a kind of conversation. They're not isolated events. We talk about the big one; we should instead talk about the big ones. The most surprising thing about this earthquake is it occurred on a fault - a very straight, simple fault that we didn't know about. And we would have thought that for California, any fault capable of a magnitude 7 would have been mapped and known. And so it's a humbling moment when we realize that there's a lot of surprises out there for us, even in California.

MARTIN: Ross Stein of the U.S. Geological Survey and founder of temblor.net. Thanks so much for your time.

STEIN: You bet. Transcript provided by NPR, Copyright NPR.