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SC Geologist explains what’s known, unknown about recent seismic activity

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US Geological Survey
Map of earthquakes' magnitudes, from US Geological Survey.

Since December of 2021, earthquakes recorded in Kershaw County have measured between the unnoticeable 1.1 magnitude, to the very noticeable 3.6 magnitude felt on June 29. For the most part, a reason this swarm, or series of low-measuring quakes, continues is unknown. Scientists say getting to an answer will require more time and more earthquakes.

Earthquakes continue to rumble through parts of South Carolina. According to the state’s Emergency Management Division, the latest was a 2.1 magnitude in Anderson County on Thursday, August 18- far from the more than 70 felt in Kershaw County, since December of 2021.

Those earthquakes have measured between the unnoticeable 1.1 magnitude, to the very noticeable 3.6 magnitude felt on June 29. For the most part, a reason this swarm, or series of low-measuring quakes, continues is unknown. Scientists, like geologist Scott Howard, say getting to an answer will require more time and more earthquakes.

“The more of these earthquake swarms go on, the more and more definition comes to the structure.”

Howard is one of four geologists studying what is now considered record-breaking seismic activity for South Carolina; the swarms felt in the Elgin area have lasted longer than others recently recorded.

“Swarms are not unusual, but they usually are shorter lived than what we are experiencing here in Elgin.”

To get a better understanding of why the earth is moving in this area, Howard says more information is needed. What is known, comes from the recordings from seismograms.

“There are monitoring stations throughout the Southeast and East coast, and they receive these signals, even though they are hundreds and thousands of miles away.”

Howard said a major limitation to learning more about the Kershaw County quakes is that there is only one monitor in the area, leaving scientists to gather basic information like the number of earthquakes, the magnitude, and depths.

But there is a lot, scientists do know. For example, the quakes felt in South Carolina are different from the ones felt on the West Coast.

“These are what are known as intraplate earthquakes; they occur in the interior of plates. They are known as stable continental regions. They may be more stable than the West coast, but they still have earthquakes.”

Plate interactions, he said, are what causes earthquakes on the West coast. He said what goes on in the intraplate earthquakes is harder to decipher.

But some findings suggest pre-existing structures, like old faults, may be a key component to getting answers.

“It looks like there might be a couple of intersecting directions of faults; as I see those directions develop, I’m kind of going, those are familiar directions.”

And as for or a nearby river structure causing the quakes or hydroseismicity, Howard said it’s a common study that’s recognized in many countries, including the United States, but again, more research is needed.

The complete report on the Elgin-area earthquakes is available online.

Thelisha Eaddy is a reporter/producer for South Carolina Public Radio.