A mysterious, unusual swarm of earthquakes that began last December in South Carolina continues, puzzling geologists and troubling local residents that continue to feel the frequent shakes coming from underground. The last earthquake struck the Elgin, South Carolina area on Friday, marking the 83rd registered earthquake over the last year here.
The mysterious swarm began on Monday, December 27, at 2:18 pm in the afternoon. 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 earthquakes didn’t end then. Since then, dozens of earthquakes have hit the area near Elgin, South Carolina, generating hundreds of reports of shaking to USGS’s “Did you feel it?” tool on their earthquake website. Some earthquakes happen right after another, others have struck after a pause lasting weeks. There doesn’t seem to be any rhyme or reason to this swarm, other than most earthquakes are under a 3 magnitude.
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.
This area has a history of occasional small, scattered earthquakes, but none of particularly large magnitude. The largest earthquake within 50 miles was in 1913 in Union County, when a magnitude 5.5 earthquake struck about 55 miles northwest of the recent earthquakes. That quake caused damage to brick and stone buildings, destroyed chimneys, and displaced furniture in homes.
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 earthquake and the 1913 Union County earthquake. 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 7.0 earthquake which struck Charleston in 1886 is about 87 miles to the southeast of this current swarm.
Scientists tied with the University of South Carolina’s School of Earth, Ocean, and Environment teamed up with Georgia Tech to install 86 nodal seismometers in and around the area experiencing this ongoing swarm. Scientists don’t know what’s driving this earthquake activity and the data from these newly installed devices should give earth scientists and geologists insight in what’s happening under ground here. Data from the new small seismometers are expected to be recorded starting in January.
Experts are concerned that a large scale earthquake will strike at some point of the future and bring about significant damage and loss of life. While more than 100 years have passed since the last large earthquake, a 2001 study titled “Comprehensive Seismic Risk and Vulnerability Study for the State of South Carolina” confirmed the state is extremely vulnerable to earthquake activity. The study, based on scientific research, provided information about the likely effects of earthquakes on the current population and on modern-day structures and systems, including roadways, bridges, homes, commercial and government buildings, schools, hospitals and water and sewer facilities.
No one is sure what’ll become of this steady stream of light earthquakes or whether or not something larger is looming. For now, the SCEMD has been sending out Tweets to the people of South Carolina encouraging them to be prepared for any disaster this year –earthquakes included.
Check out South Carolina’s new, interactive guide to #earthquake safety!
— SC Emergency Management Division (@SCEMD) October 30, 2022