SC geologists outline key takeaways from report on Elgin-area earthquakes, detail path forward

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Published: Jul. 18, 2022 at 9:56 PM EDT
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COLUMBIA, S.C. (WIS) - A new report from some of the state’s leading geologists looks at the potential factors that could be leading to the state’s recent earthquake swarm, which has been centered near Elgin.

When asked what one of the main takeaways from the report was, Dr. Steven Jaume, one of its authors, said, “To really know what’s going on, we need information.”

Scott Howard, the state’s chief geologist with the South Carolina Department of Natural Resources, the first author on the report, said it was important to address the concerns of the community, limit confusion and provide a source of reliable information on the latest thinking behind the earthquakes from the state’s earthquake scientists.

There have been more than 60 earthquakes centered near Elgin since Christmas, and three of the most powerful earthquakes in the swarm happened in the last month.

A 3.4 magnitude quake hit overnight on June 26. A few days later, earthquakes of 3.5 and 3.6 magnitude rattled through the area just hours apart.

Howard said the idea for the report came about following the pair of earthquakes above 3.5 magnitude that hit on June 29.

The report states that while the current swarm is uncommon, it is it not “unexpected,” nor is it unprecedented in the state of South Carolina.

However, the geologists reiterated that earthquakes are impossible to predict.

“It’ll stop when it stops,” Howard said. “When that is, I don’t know. Will there be another big one? I don’t know. Nobody makes any money predicting earthquakes.”

For the first time, the scientists are putting forth one possible factor that could be keeping this swarm going: water from the Wateree River seeping into the ground, speeding up additional tremors.

This is based on the idea of Hydro-seismicity, which is that water moving above ground could change the pressure on water below ground. In turn, this could cause the earth to move.

“The fluids aren’t the cause,” Howard said. “It is more of a facilitator, it just makes it happen a little easier, but that’s our guess. And it’s a guess.”

Both Jaume, who is also an Associate Professor of Geology at the College of Charleston, and Howard emphasized that this is not yet a theory, or even a hypothesis, because there are not multiple lines of scientific evidence to back it up.

“But the state of knowledge of other earthquake swarms caused by or affected by water and pore-pressure changes indicates that this issue should be considered,” the report states.

According to the report, this part of Kershaw County is along an ancient fault system known as the Eastern Piedmont Fault System. It runs from Georgia into Virginia and is not connected to the faults near Charleston.

The thought from geologists is that water from the river could be getting into the cracks in the earth’s crust along the fault system, which is putting pressure on the faults.

Dr. Pradeep Talwani, Professor Emeritus at University of South Carolina’s School of the Earth Ocean & Environment and co-author of the report, specializes in Hydro-seismicity.

After reviewing federal data indicating that Wateree River water levels were higher in parts of March, April and May than in previous months, Talwani is conducting additional research on the topic.

Jaume said there is evidence that additional water in the earth’s crust has acted as a “lubricant” in other cases, but it’s difficult to determine whether it is happening in this case because there is not a well nearby.

“The initial earthquake back in December sets things off, right?” Jaume said. “One thing [Talwani] mentioned, it may have opened up some additional cracking in the crust that allowed the fluid that couldn’t get down to that depth to now make it there, and that additional fluid kind of keeps things going.”

Howard said that if water were a contributing factor, there would be a lag time to its impact, which could explain why there have been more earthquakes centered near Elgin in the last two months than during any other period amid the swarm.

Jaume said that using the area’s lone seismic monitoring station, he hopes to compile data to get a better idea of exactly where along the fault system some of the smaller earthquakes are occurring -- and how big the faults are.

“To get a bigger earthquake, have to have a big fault,” he said. “It has to be a long, connected crack in the earth to host a large earthquake. So, getting a full detailed idea of exactly where all these earthquakes are occurring, we can start to size those faults. Like, ‘Ok, this one, there’s a fault running through here, it’s about this long; therefore, the biggest earthquake that can fit on this is magnitude X.’”

Geologists believe there appears to be more than one fault contributing to the shaking, and sorting those out may allow scientists to determine what the maximum possible magnitude earthquake in this area could be.

Jaume said this would be particularly beneficial for the South Carolina Emergency Management Division in their planning, and also for residents of Kershaw County and the surrounding communities.

Jaume said he expects to have preliminary data from the seismometer by October.

Both Howard and Jaume said that more sensors in the area could help give geologists a clearer idea of what has been happening in Kershaw County for the past several months.

They said that at least three would be preferrable, and Howard suggested a portable monitoring system.

To this point, Howard said his requests for additional equipment have been turned down.

“We tried to get some sensors out of the USGS in Washington – they had other fish to fry,” Howard said. “We’ve requested [a seismic monitoring station] in our budget so we’ll see how that goes.”

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