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Encore: Experts aren't sure why South Carolina has been hit with many earthquakes

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An unusually large number of earthquakes have hit South Carolina this year, but scientists don't know why. (Story first aired on All Things Considered on Aug. 26, 2022.)

NATIONAL

Unusually large number of earthquakes hit South Carolina

A MARTINEZ, HOST:

In South Carolina, an unusually high number of earthquakes have rattled the state this year. The thing is experts cannot really explain why. Nick de la Canal of member station WFAE takes us to a town close to where many of the earthquakes have hit.

NICK DE LA CANAL, BYLINE: David Horne sits on his front porch, cooling under a fan. You can often find him on his porch. It's where he was last December 27. That was the date the first earthquake hit the town of Elgin, where he lives, about 25 miles east of Columbia.

DAVID HORNE: I was sitting on the porch when the first one hit.

DE LA CANAL: This porch.

D HORNE: Yes, on this porch right here. My wife was inside with one of the grandchildren.

DE LA CANAL: He remembers sudden shaking and a noise like thunder booming across the sky.

D HORNE: And as soon as it happened, I got out of my chair, and I went and told her. I said, that was an earthquake. I said, that was a three-point plus.

DE LA CANAL: Horne used to live in Alaska, where earthquakes are more common. His wife Whitney, a lifelong South Carolinian, wasn't sure what was going on.

WHITNEY HORNE: Because I'd never experienced...

D HORNE: You never felt an earthquake.

W HORNE: ...An earthquake. We're in South Carolina. You don't have earthquakes that you feel in South Carolina.

DE LA CANAL: Sure enough, it was a 3.3 magnitude earthquake, too small to cause damage but big enough to light up the town's Facebook page with dozens of excited comments. David said at first, he thought it was cool.

D HORNE: Wow, an earthquake. I've heard there was a big fault line near here, and that's all I thought about.

DE LA CANAL: Until the ground continued to shake. Days and months after that first quake, the ground would rumble while the Hornes were out shopping or at night while in bed.

W HORNE: Ah, there's an earthquake.

DE LA CANAL: And the ground continues to move under their feet.

D HORNE: I mean, literally, it seems like we have an earthquake every week. It's not even a surprise anymore.

DE LA CANAL: The U.S. Geological Survey has recorded more than 60 small earthquakes near the town since December. The largest, a 3.6, rumbled through in June. All the shaking has fascinated geologists, who say this is the longest-running series of earthquakes in recent South Carolina history. Scott Howard is South Carolina's state geologist. He says this is what's known as a swarm - that is, a series of small earthquakes with no apparent main shock.

SCOTT HOWARD: Well, it could be a magnitude 2, 3, 1. You know, it just kind of bounces up and down.

DE LA CANAL: South Carolina is on a minor fault line, he says. And the state has had swarms before. They traced a series of small earthquakes in the 1970s to the creation of a new reservoir.

HOWARD: Water and fluids tend to be always involved in faulting.

DE LA CANAL: This time, there's no clear explanation. Howard says it's possible heavy rain may have played a role early in the year, but it's hard to know for sure. Residents fear the swarms are building up to a big earthquake. Seismologists say that's unlikely. Still, emergency officials have told people to look into earthquake insurance, and some have, like Phil Crowley. He moved to Elgin a year ago.

PHIL CROWLEY: You know, what can we control? We can control getting insurance. Really, that's about it.

DE LA CANAL: There have been no reports of major damage so far. But the earthquakes keep coming. Crowley and his wife don't think a big one will hit, but they worry.

CROWLEY: She'll look at me when we're going to sleep and say, I hope it's not going to happen tonight.

DE LA CANAL: If it does, they're ready. They keep two bags packed with clothes and other essentials sitting by their front door just in case.

For NPR News, I'm Nick de la Canal in Elgin, S.C.

(SOUNDBITE OF THURSTON MOORE SONG, "THE SHAPE IS IN A TRANCE")