The area home to a swarm of earthquakes that started nearly 3 years ago saw another quake during the overnight hours, keeping seismicity in South Carolina active. According to USGS, at 3:16 am, a magnitude 2.2 earthquake struck from a depth of only 2.4 km between Elgin and Lugoff north and east of Columbia. More than 50 people used the “Did you feel it?” web reporting tool on the USGS website to report they felt and/or heard the earthquake. No damage or injuries were reported.
On Monday, December 27, 2021 at 2:18 pm in the afternoon, an unusual earthquake struck in this same general area and the quakes have continued on and off since, with dozens reported in 2022 and 2023. That first 3.3 magnitude earthquake hit 30 miles north of Columbia, South Carolina at a depth of only 3.1 km. More than 3,100 residents reported to USGS they felt it at the time, with one report of shaking coming from as far away as Rock Hill, which is at the North/South Carolina state border. While many felt the earthquake, there was no reported damage in the Palmetto State. That earthquake was followed by 10 more ranging in intensity between a magnitude 1.5 to a magnitude 2.6 event. The second earthquake struck three hours twenty minutes after the first one. The last earthquake in that series struck on the morning of January 5, bringing a temporary end to the earthquakes there. But the swarm returned many times throughout 2022, rattling locals and unnerving local officials that weren’t sure of their source or cause.
Things have been quiet in the Elgin/Lugoff area for more than 30 days, with no earthquake activity reported here. However, a new and unusual swarm of weak earthquakes have been rattling an area north and west of Columbia. According to USGS, there have been 10 earthquakes in the last 30 days in this area, ranging from a magnitude 1.6 event to a magnitude 2.4; event. The largest event struck on November 30 and was strong enough to get residents to use the “Did you feel it?” earthquake reporting tool on the USGS website. The earthquakes have been too weak to create any damage or injuries.
The location of this other South Carolina earthquake swarm has been concerning residents because it is located around the Virgil C. Summer Nuclear Generating Station. Construction of that site began in 1973. Unit 1 on the site was due to be shut down due to its age in 2022, but authorities approved extending its use license by another 20 years, allowing operation of the facility through 2042. The nuclear power plant hasn’t been directly impacted by these earthquakes.
According to USGS, a swarm is a sequence of mostly small earthquakes with no identifiable mainshock. “Swarms are usually short-lived, but they can continue for days, weeks, or sometimes even months,” USGS adds. However, the South Carolina event doesn’t fit the typical definition of a swarm since the first event was substantially larger than the rest.
USGS has been unable to say with certainty why either of these swarms northeast and northwest of Columbia are occurring.
According to the South Carolina Emergency Management Division (SCEMD), there are approximately 10-15 earthquakes every year in South Carolina, with most not felt by residents; on average, only 3-5 are felt each year. Most of South Carolina’s earthquakes are located in the Middleton Place-Summerville Seismic Zone. The two most significant historical earthquakes to occur in South Carolina were the 1886 Charleston-Summerville quake and the 1913 Union County quake. The 1886 earthquake in Charleston was the most damaging earthquake to ever occur in the eastern United States; it was also the most destructive earthquake in the U.S. during the 19th century.
The 1886 earthquake struck at about 9:50 pm on August 31; it was estimated to have been rated a magnitude 6.9 – 7.3 seismic event. The earthquake was felt as far away as Boston, Massachusetts to the north, Chicago, Illinois and Milwaukee, Wisconsin, to the northwest, and New Orleans, Louisiana to the south. The earthquake energy even traveled as far away as Cuba and Bermuda, where some shaking was felt too. The initial earthquake lasted about 45 seconds.
The 1886 Charleston earthquake was responsible for 60 deaths and over $190 million (in 2023 dollars) in damage. The area of major damage extended out 60-100 miles from the epicenter, with some structural damage even reported in central Alabama, Ohio, eastern Kentucky, southern Virginia, and western West Virginia from the initial quake.
A study published in 2008 in the Journal of Geotechnical and Geoenvironmental Engineering hypothesized that if such an earthquake were to strike the region today, it would lead to approximately 900 deaths, 44,000 injuries, and damages in excess of $20 billion in South Carolina alone.
The initial earthquake was followed by an aftershock 10 minutes later; over the first 24 hours, seven additional strong aftershocks hit. Over the following 30 years, a total of 435 aftershocks were measured.
