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What made Columbia, Lexington homes rattle Friday night? It was 2 different events.

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Flooding and aftermath around the state (copy)

Water pours from a gate in the Lake Murray dam near Columbia. The release of a natural gas valve near the dam was one of two incidents that rattled area homes Friday night. The other was a small earthquake. File/AP

COLUMBIA — Depending on where you live in the Columbia and Lexington areas, a boom heard and felt Friday night could have had separate sources in what officials say is a near-simultaneous coincidence.

Two potentially jarring events happened within about an hour of each other: an earthquake in Columbia and a natural gas line release near Saluda Dam near Irmo.

The U.S. Geological Survey confirmed a 2.4 magnitude earthquake in Columbia at 8:37 p.m. The quake was centered just north of Benedict College in the old Allen-Benedict Court public housing community.

A safety valve released at a natural gas regulatory station near Saluda Dam close to the same time.

The mechanism is triggered when pressure builds in a gas line due to trash or similar blockage and the sound of the valve venting can be a boom or a champagne cork popping, said Tom Allen, safety director for the S.C. Office of Regulatory Staff, which oversees utilities in the state.

Depending on the size of the gas line and amount of pressure, the sound can seem as loud as a jet engine. Allen said the first calls he received related to the gas valve were about an hour after the earthquake.

"It served its purpose; that escape valve vented the natural gas as it was designed to do," Allen said. "I would say it was probably more of a mundane issue than it was the earthquake."

The valve is designed to open based on pressure and shouldn't be affected by physical jostling as from earthquake tremors — cars have crashed into the regulatory stations without triggering the valve, Allen said. 

Lexington, Irmo and St. Andrews residents might have heard the gas incident and other areas of Columbia were probably experiencing the earthquake, Allen said.

The federal agency that monitors earthquakes received about 160 reports from Columbia-area residents, said Paul Caruso, a geophysicist with the U.S. Geological Survey in Golden, Colo. Most of those reports were from Columbia ZIP codes, but some came from residents in areas that likely were reacting to the valve release.

No injuries or damage were reported, a S.C. Emergency Management Division spokesman said.

The state experiences 10-20 low-magnitude earthquakes each year, emergency officials say, with a handful felt by people. There have been 10 in 2020.

A shallow earthquake like the one Friday can produce an audible sound, said Tom Owens, a University of South Carolina professor and director of the S.C. Seismic Network. He said the gas incident and earthquake were most likely coincidental but that more information is needed to know when people heard the boom and where.

South Carolina isn't at much risk for major earthquakes outside of the Charleston and Summerville area. An earthquake in Union County in 1913 and one in Edgefield more recently registered above 4 in magnitude. 

"Most of them are these little things that some people don't even feel," Owens said. "Something right in the middle of a metro area like this, people are going to notice a little bit."

The gas line where the valve released is owned by Berkshire Hathaway Energy and runs through multiple states, meaning it is federally regulated, while the state regulates lines running within its boundaries.

Allen said first responders fielding calls about the gas boom didn't know what to tell concerned residents and that regulators will talk with utilities about how to better communicate in the event of future incidents.

A phone message for the energy company was not returned Monday.

Follow Stephen Fastenau on Twitter @StephenFastenau.

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