Mysterious earthquakes in South Carolina may be tied to historic disaster, study says

A new theory has emerged for the ongoing earthquakes in eastern South Carolina, and a century-old culprit has been identified.

Rather than typical earthquakes, the region may be experiencing aftershocks, according to a news release from the American Geophysical Union.

Aftershocks of what, you ask?

The devastating 6.7- to 7.3-magnitude quake that hit Charleston 138 years ago.

It’s suspected more than 70% of the ongoing quakes of 2.5 magnitude or above in the region may be aftershocks from that 1886 temblor, researchers reported. Considered “the most damaging earthquake to occur in the Southeastern United States,” the quake killed 60 people and damaged “many” buildings in the city, according to the U.S. Geological Survey.

South Carolina has had nearly 300 earthquakes east of Columbia since the year 2000, the vast majority unnoticeable at 2.0 magnitude or below, according to the U.S. Geological Survey.

As for quakes of 2.5 or above, the number is just over 30, and they were largely clustered between Sangaree and Ladson, about a 100-mile drive southeast of Columbia.

Aftershocks are the norm after large quakes as the fault readjusts, experts say. They are smaller in magnitude than the main quake, occur within 155 miles of the epicenter, and “can continue to shake the area for days to years after the original earthquake occurred,” experts say.

Scientists began to suspect many of South Carolina’s quakes were aftershocks as the interior of North America has a long history of being stable and void of major earthquakes.

However, there have been three “historic” exceptions to the rule: the Charleston quake of 1886; one near Quebec, Canada, in 1663, and three near the Missouri-Kentucky border in 1811 to 1812, the scientists said.

“Regions near these historic earthquakes’ epicenters are still seismically active today, so it’s possible that some modern earthquakes could be long-lived aftershocks of past quakes,” the AGU reported.

“The stable continental interior of North America is located far from plate boundaries and has less tectonic activity than regions close to plate boundaries. ... As a result, the three study areas don’t encounter earthquakes often, raising even more questions about the origins of their modern (earthquakes).”

The research paper was published in November in the Journal of Geophysical Research: Solid Earth.

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