An ancient fault line caused an earthquake in Maryland, but you probably didn’t feel it

Published 10/12/2022 3:46 p.m. EDT, Updated 10/12/2022 5:40 p.m. EDT

A map from the U.S. Geological Survey that shows the epicenter of the Oct. 11 earthquake in the southeast part of Carroll County. The epicenter is represented with a star.

A small earthquake — just a 2.0 on the Richter scale — shook Baltimore late Tuesday night, according to the U.S. Geological Survey.

The earthquake, centered in the southeastern corner of Carroll County, happened just before 11:50 p.m. Tuesday. A magnitude 2.0 earthquake is not generally considered dangerous. People reported feeling the quake as far east as Bel Air and as far west as Frederick, though most reports to the USGS came from people in and around Carroll, Howard and Baltimore counties. There were not any notable reports of damage.

“It’s low on the scale. A 2.0 is pretty much the [weakest earthquake] you could feel,” said Richard Ortt Jr., director and state geologist at the Maryland Geological Survey. “If you were laying in bed asleep, it probably would not have woken you up.”

What caused the earthquake?

It’s not practical to apply a direct causation to any particular earthquake. Generally, quakes are caused by movement along the boundaries of tectonic plates — the supermassive structures beneath the surface that are responsible for the shape of the continents. Pressure and stress slowly build up over time, and an earthquake is the result of the release of that energy.

Earthquakes are more common in areas along plate boundaries, as found in California and in a ring around the Pacific Ocean. Maryland, though, is squarely in the middle of a tectonic plate, miles away from any boundaries. So what gives?

Ortt said it’s important to think of the tectonic plates as not being uniform. Just like a pie crust might have thin spots or tears, so might a tectonic plate. Those stress points can allow for earthquakes on the interior of plates.

Maryland typically has two or three earthquakes per year around the same strength as Tuesday night’s, Ortt said, adding that they usually occur along a line between Columbia and Lancaster, Pennsylvania.

“That gives us indication there is likely an ancient fault there,” Ortt said. “We’re talking hundreds of millions of years old.”

Does this happen in Maryland often?

Not really, no. Like Ortt said, there may be two or three noticeable quakes in Maryland each year. When you consider that the global average is about 55 quakes per day — or 20,000 annually — a small handful in Maryland is not very much activity.

That doesn’t mean Maryland or the region never get more significant quakes, though.

There was a 4.6 magnitude earthquake in the Atlantic Ocean about 130 miles off the coast of Ocean City in early 2019, and a 4.1 magnitude quake near Dover, Delaware, in 2017.

Sign Up for Alerts
Get notified of need-to-know
info from The Banner

And the strongest to hit the region in recent memory is the 5.8 magnitude quake in August 2011 that rattled much of the East Coast. Nobody was killed, but reports estimate it caused hundreds of millions of dollars in property damage. That earthquake, which had its epicenter in Virginia, southwest of Washington, D.C., was felt by millions and caused damage to landmarks like the National Cathedral and the Washington Monument.