Geological experts say the risk of earthquakes for Maryland and Virginia remains low to moderate following a small earthquake in Clarksville and ahead of the upcoming 10th anniversary of a larger earthquake in Virginia, although they note the science still cannot predict when earthquakes will happen or how strong they will be.
A 2.1 magnitude earthquake shook parts of Howard County near Clarksville, Maryland, early Wednesday, prompting nearly 750 people to report feeling the vibrations to the U.S. Geological Survey (USGS). The USGS has also recorded two other earthquakes near Clarksville this year: a 1.6 magnitude earthquake near Irvington on June 27 and a 2.6 earthquake near Woodlawn on June 25.
The Columbia, Maryland, region usually sees one to three earthquakes a year with magnitudes ranging from 1.5 to 2.5, according to Richard Ortt, director of the Maryland Geological Survey. He said there are likely many more smaller tremors with magnitudes lower than 1.5, but those can be difficult to detect.
“There should be no cause for alarm from these earthquakes. These events are relatively small. More importantly, we are not sitting on a tectonic fault line where there is active plate movement below our feet,” Mr. Ortt said. “The earthquakes that we experience are from ancient — hundreds of millions of years old — weak points inside of the North American Plate that are relieving some internal pressure built up from multiple reasons.”
He added there is no reason to think that these earthquakes should increase in numbers or strength and that the region should continue to experience one to three earthquakes a year.
“However, one can not predict when these will occur,” he noted.
Virginia has recorded two earthquakes so far this year: a 2.2 magnitude earthquake near Ashland on June 22 and a 2.3 magnitude earthquake near Deerfield on Jan. 16. Last year, Virginia recorded a couple of earthquakes with a magnitude of 2.0 or greater, while Maryland didn’t record any detectable earthquakes, USGS data showed.
Mr. Ortt noted that Virginia is at a slightly increased risk for earthquakes than Maryland, but even in Virginia described the risk as low to moderate.
Don Blakeman, a geophysicist at the USGS’ National Earthquake Information Center, said small earthquakes can happen just about anywhere in the U.S., although North Dakota and Florida don’t see much activity.
“Almost any state can have these little quakes. We see them all the time,” he said. “Even though they are not on the margins, the edges of tectonic crustal plates, which is where most earthquakes are, on the edge of the plate. … There are still stresses throughout the crust in almost all places in the world and so that’s how you get these little quakes.”
Could there be a big one?
“It’s certainly possible,” he said, referring to the 5.8 magnitude earthquake that struck Mineral, Virginia, 10 years ago this month on Aug. 23, 2011.
The earthquake, which tens of millions of people along the East Coast felt, damaged the National Cathedral, the Armed Forces Retirement Home and the Washington Monument in the District of Columbia. It was the largest earthquake in the eastern U.S. since the 5.8 earthquake in 1944 near Cornwall and Massena, New York, according to the USGS.
“Those are pretty rare,” Mr. Blakeman said of the 5.8 magnitude earthquakes. “It’s possible that a much larger quake like that could happen, but the occurrence of these little ones doesn’t indicate that one way or another. They are not like foreshocks or harbingers of bigger quakes or anything like that.”
“There just isn’t enough science. There isn’t anybody who can predict when a specific earthquake is going to happen or where,” he said. “History’s just shown us that we just see these little quakes all the time without any major other quakes occurring.”
The Mineral, Virginia, earthquake occurred in what scientists call the “Central Virginia Seismic Zone.” The USGS said it identified more than 4,000 aftershocks from the 2011 earthquake in analyses so far.
Compared to the West, the USGS said the Mineral earthquake showed how much farther ground shaking can stretch in the eastern U.S., which has faults on older rocks that allow seismic waves to cross them more efficiently when an earthquake hits. The agency added the eastern U.S. has many older structures that were built before the 1970s and not designed to withstand strong shaking from earthquakes.
While earthquakes are not a significant risk of danger for the area, Mr. Ortt said they are something everyone should be ready for.
“The most likely areas to see damage are higher masonry structures that are aged. All families should have a plan for any disaster including an earthquake,” he said.
• Shen Wu Tan can be reached at stan@washingtontimes.com.
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