Scientists have been trying to figure out what’s causing a mysterious swarm of earthquakes north and east of Columbia, South Carolina since December 2021.
In the meantime, USGS reports that there have been six more recent earthquakes in South Carolina, Tennessee, and North Carolina in the last week, all of which were far from the initial area of concern.
Geologists like Scott Howard are working hard to explain why it’s happening.
“Swarms are not unusual, but they usually are shorter lived than what we are experiencing here in Elgin,” Howard said.
The first one happened on August 13 near Spruce Pine, North Carolina. A magnitude 2.0 event, that earthquake happened at a depth of 6.7 km. Even though the center of the earthquake was in western North Carolina, people in eastern Tennessee told the USGS that they felt it.
On August 14, there was an event in Alcoa, Tennessee, with a magnitude of 2.4. This quake was 11.6 km deep and happened south of Knoxville.
On August 15, a magnitude 1.5 earthquake rattled Elgin, South Carolina at 3.6 km deep. In this area, there is still an ongoing swarm that no one can explain. South Carolina has had dozens of earthquakes since December. After a group of tremors came and went in December, these weak to moderate quakes happened.
It was Monday, December 27 at 2:18 pm when the strange swarm began. The first earthquake, which was only 3.1 km deep and had a magnitude of 3.3, happened 30 miles north of Columbia, South Carolina. More than 3,100 people told the USGS that they felt it. One person felt it in Rock Hill, which is on the border between North and South Carolina. Even though many people felt the quake, no damage was reported in the Palmetto State.
After that quake, there were 10 more that ranged in size from 1.5 to 2.6 on the Richter scale. The second earthquake occurred three hours and twenty minutes after the first one.
Since then, there have been dozens of earthquakes in the Elgin area, making it a swarm that is still ongoing. USGS defines a swarm as a group of mostly small quakes with no clear main earthquake. “Swarms are usually short-lived, but they can continue for days, weeks, or sometimes even months,” according to USGS.
The South Carolina event, on the other hand, doesn’t fit the usual definition of a swarm because the first event was much bigger than the rest.
USGS defines “aftershocks” as a series of smaller quakes that happen on a fault after a bigger main earthquake.
“Aftershocks occur near the fault zone where the mainshock rupture occurred and are part of the ‘readjustment process’ after the main slip on the fault,” according to USGS.
However, aftershocks of a 3.3 magnitude earthquake should only last a few days, not the many months they have.
There was also a 2.0 quake in Tellico Plains, Tennessee on August 15. The quake in South Carolina earlier in the day has nothing to do with this one. It was 11.1 kilometers deep.
On August 16, an earthquake with a magnitude of 1.8 hit Troutman, North Carolina, which is north of Charlotte and far to the east of where the August 13 quake hit North Carolina. At only.1 km deep, it was not very deep.
On August 18, an earthquake with a magnitude of 1.9 and a depth of 12.8 km hit Benton, Tennessee. 10 hours later, a 2.1 earthquake hit Homeland Park, South Carolina, which is halfway between Atlanta, Georgia and Charlotte, North Carolina.
According to WeatherBoy.com, it is rare for this many earthquakes to strike such a large area of the southeast US at the same time.
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