One year later, the unusual earthquake swarm continues in South Carolina

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An area near Elgin, South Carolina, has had more than 80 earthquakes over the past 12 months. The points on this map reflect the epicenters of the earthquakes over the past seven days; Dots captured within the concentric colored circles reflect the South Carolina swarm area. Photo: USGS

A mysterious and unusual swarm of earthquakes that began last December continues in South Carolina, baffling geologists and locals who can still feel the frequent tremors coming from underground. The latest earthquake hit the Elgin, South Carolina area on Friday, marking the 83rd earthquake recorded over the past year here.

The mysterious swarm began on Monday, December 27 at 2:18 PM. The first quake, with a magnitude of 3.3 on the Richter scale, struck 30 miles north of Columbia, South Carolina, at a depth of only 3.1 kilometers. More than 3,100 residents reported to the USGS that they felt it at the time, with one report of shaking coming from as far away as Rock Hill, which is located on the North/South Carolina border. While the earthquake was felt by many, no damage was reported in the Palmetto State. This earthquake was followed by 10 other events ranging in magnitude from 1.5 to 2.6. The second earthquake occurred three hours and twenty minutes after the first. The last earthquake in that series occurred on the morning of January 5, bringing a temporary end to the earthquakes there.

But the earthquakes did not end then. Since then, dozens of earthquakes have struck the area near Elgin, South Carolina, resulting in hundreds of reports of shaking to the USGS “Did You Feel It?” tool on their website. Some earthquakes occur right after another, while others occur after a weeks-long hiatus. There doesn’t seem to be any rhyme or reason for this swarm, unlike most earthquakes of less than 3 magnitude.

Sign welcomes people to Elgin, “Home of the Catfish Stomp.” Photo: Elgin/Facebook

According to the USGS, the swarm is a series of mostly small earthquakes with no identifiable main shock. “Swarms are usually short-lived, but they can last for days, weeks, or sometimes even months,” the USGS adds. However, the South Carolina event does not fit the typical definition of a squadron because the first event was much larger than the rest.

This area has a history of occasional small, but not particularly large, earthquakes. The largest earthquake within 50 miles was in 1913 in Union County, when a 5.5-magnitude quake struck about 55 miles northwest of the latter quakes. The earthquake caused damage to brick and stone buildings, destroyed chimneys, and displaced furniture in homes.

According to the South Carolina Emergency Management Department (SCEMD), there are approximately 10-15 earthquakes each year in South Carolina, most of which are not felt by residents; On average, only 3-5 are felt per year. Most of the earthquakes in South Carolina are located in the Middleton Place-Summerville seismic region. The two most important historical earthquakes in South Carolina were the Charleston-Summerville earthquake of 1886 and the Union County earthquake of 1913. The 1886 earthquake in Charleston was the most damaging earthquake in the eastern United States. It was also the most destructive earthquake in the United States during the nineteenth century. The 7.0 earthquake that struck Charleston in 1886 is located about 87 miles southeast of this current swarm.

Scientists associated with the University of South Carolina’s College of Earth, Ocean, and Environment teamed up with Georgia Tech to install 86 nodal seismometers in and around the area experiencing this persistent swarm. Scientists don’t know what’s driving this seismic activity, and data from these newly installed instruments should give earth scientists and geologists an insight into what’s going on underground here. Data from the new micro-seismographs are expected to be recorded starting in January.

Experts worry that a large-scale earthquake will strike at some point in the future and cause significant damage and loss of life. Although it has been more than 100 years since the last major earthquake, a 2001 study titled “A Comprehensive Study of Seismic Hazards and Vulnerabilities for South Carolina” confirmed that the state is highly susceptible to seismic activity. The study, based on scientific research, provided information about potential effects of earthquakes on existing populations and on modern structures and systems, including roads, bridges, homes, commercial and government buildings, schools, hospitals, and water and sanitation facilities.

No one is sure what will happen to this steady stream of photo-quakes or whether or not something larger is on the horizon. Right now, SCEMD is sending out tweets to South Carolina residents encouraging them to prepare for any disaster this year — including earthquakes.

Check out South Carolina’s new interactive guide to #earthquakesafety!

Visit https://t.co/G1LqlYe2qx to find out why earthquakes happen here. Plus what you can do before, during and after a major experience. like fr. #SCTweets pic.twitter.com/yE2rTKQgII

– Supreme Committee Emergency Management Department (SCEMD) October 30, 2022

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