Two earthquakes with a magnitude of 3.5 and 3.6, respectively, hit Wednesday close to Elgin, South Carolina, according to the U.S. Geological Survey. Days before that, a 3.4 magnitude earthquake struck in another part of the state, while a 3.9 magnitude earthquake struck near the Georgia-South Carolina state line on June 18.
Both of Wednesday’s earthquakes were the strongest to hit South Carolina since a 4.1 magnitude quake struck McCormick County in 2014.
Geologist Wendy Bohon said in a video released by the state’s Emergency Management Division that they’re part of a string of about 30 quakes that have struck the state so far in 2022, which they suggested is an unusual phenomenon. She described it as an “earthquake swarm,” something common in places like Southern California.
South Carolina’s Emergency Management Division wrote on Twitter the state does in fact have several fault systems and is “one of the most seismically active states on the East Coast.”
“Swarms happen in all seismic regions and the earthquakes continue until they stop,” seismologist Lucy Jones wrote this week in reference to the quakes in South Carolina. “That may not seem helpful, but knowing this is normal can help.”
Jones said that the swarm has been occurring for at least six months, noting seven quakes that were recorded at a magnitude of 3 or above.
But state geologists said they are not sure why the Midlands region is having so many earthquakes at the moment.
“If you can figure that out, you should go get your tux and pick up your Nobel Prize,” Thomas Pratt, regional coordinator of the Geological Survey’s earthquake hazard program, told The State newspaper. “The Eastern United States in general is not on a plate boundary, so it’s a mystery in the scientific community why in this exact location, in the middle of a plate, that something would trigger this.”
Pratt noted that swarms of quakes “can be foreshocks to a larger earthquake,” adding, “There’s no reason to think there will be, but it can’t be eliminated.”
A 7.1 magnitude earthquake was reported in Charleston in 1886, killing at least 60 people, according to historical records.
Earthquakes that are lower than 4.0 on the Richter scale generally don’t cause much damage, according to the USGS’s website.
“Most earthquakes occur where the earth’s plates come together, and they’re the result of the tension and the stress that builds up as those plates are grinding and moving, slamming into each other. That’s not happening to us here on the East Coast,” Bohon told the Weather Channel. “But there are ancient fault lines here from in the past when continents had slammed together … and they are still building up stress and strain but on a much, much slower time scale.”