Small Earthquakes Perplex Scientists As SC Buzzes. Will A Big One Occur?
By Sammy Fretwell
Earthquakes are a big topic of conversation these days in South Carolina, where an unusually high number of small temblors has shaken communities from Summerville to Lugoff.
But as people increasingly ask why so many quakes are occurring, the answers remain elusive.
Some questions have surfaced about whether digging and blasting at mines, or water seeping through the ground from lakes, could have caused the ground to shift. Changes in weight or pressure can cause movement below ground.
South Carolina has hundreds of mines, many of them sand and rock mines and scores of man-made reservoirs. Scientists have previously tied construction of Lake Monticello near Jenkinsville in the 1970s to a rash of earthquakes that occurred at the time.
Still, no one has evidence that mining or seepage from lakes has recently triggered the small South Carolina earthquakes, several geologists told The State.
While mining has been known to trigger small earthquakes, those typically are at or next to the mine site. Many of the recent tremors appear to be miles away from mines, they said.
It’s also possible the increased number of earthquakes is simply a natural phenomenon that occurs in some years, more than others, they said.
Geologists said it’s difficult to pinpoint the reason for the shaking — and whether the small-scale temblors are a forerunner of a big one. But the threat is always there.
“Large earthquakes are very rare in the eastern US, but large earthquakes sometimes do have small ones before them,’’ said Tom Pratt, who tracks earthquakes for the US Geological Survey. “So, we can’t eliminate that possibility.’’
South Carolina usually gets up to 10 earthquakes annually — all of them relatively minor — but in the past year, the state has had more than three dozen temblors, according to South Carolina Department of Natural Resources data obtained by The State.
Three small earthquakes, all with a magnitude of 2.0 or less, were recorded in one day in the Elgin area this past week. Fourteen earthquakes have hit the Columbia area since Dec. 27, state officials say. The latest earthquake hit early Saturday morning near Elgin , registering 1.8 in magnitude.
Of the earthquakes recorded since early 2021, 24 occurred in central South Carolina, The State previously reported.
Multiple quakes were reported first in the Jenkinsville area north of Columbia this past fall, and later in the Elgin area northeast of the capital city.
Steven Jaume, an earthquake scientist at the College of Charleston, said the flurry of earthquakes in South Carolina is in some ways typical. The state can get clusters of small earthquakes from time-to-time.
Even so, the recent phenomenon in just one part of the state is unusual, he said. The small quakes that have recently shaken the Elgin area northeast of Columbia occurred for weeks after an earthquake that measured a 3.3 in intensity in late December, he said.
Those later quakes, which he considers aftershocks, should have stopped within three days, instead of weeks, Jaume said.
“’That was not a typical aftershock sequence,’’ he said. “It should die down sooner.’’
Pratt, a geophysicist with the USGS, said South Carolina doesn’t face the same threat as places like California, which has a more extensive history of big earthquakes.
Many of the western quakes occur along plate margins, rocky subterranean layers of the earth, which can lead to more dangerous shaking. In the east, earthquakes don’t occur along plate margins, he said.
Pratt, Jaume and South Carolina Department of Natural Resources geologist Scott Howard said they understand why people are asking questions because some of the recent quakes have been noticeable — and more frequent.
“They are not big enough to really do any damage. They’re not big enough to be a real hazard,’’ Jaume said. “They are a good reminder that we have earthquakes in South Carolina, particularly for people who felt them. They kind of wouldn’t go away.’’
Jaume said the Charleston earthquake of 1886 remains the most infamous temblor in state history.
The 7.0 quake was so powerful it was felt as far away as New York and Illinois, according to the Geological Survey. More than 100 people were killed and many buildings collapsed in South Carolina.
Earthquakes that register 2.5 magnitude or less often go unnoticed and those under a 5.5 magnitude don’t typically cause significant damage. The danger occurs with quakes above that.
More recently, quakes exceeding 5.0 have been recorded in Virginia and North Carolina.
The August 2011 Virginia quake registered 5.8, occurring in Louisa County , a rural area. It caused noticeable damage to some homes and businesses. Video at one store showed merchandise being shaken off shelves during the rumbling.
In Sparta, North Carolina, about two years ago, the earthquake registered 5.1, striking the area near the Tennessee-Virginia border. The rumbling generated about 80,000 reports from people saying they had felt light to strong shaking, according to the US Geological Survey.
Jaume said another quake like the Charleston temblor could occur again, but he said people should be aware that mid-sized earthquakes like those in Virginia and North Carolina are a threat.
“People are always asking me ‘When is the next big one’?’’ Jaume said. “I keep telling them don’t worry so much about the big one, worry about the medium one. You take that Virginia earthquake and put it under downtown Summerville, instead of a rural area, and you will see a lot of damage.’’ – The State
