A minor earthquake rattled Howard County on Sunday night, the latest in a series of small tremors that part of the state has seen over the past 25 years.
The quake registered at a magnitude of 1.5, a level most people don’t usually notice. In this case, though, many thought they heard something strange.
“We didn’t really feel it — it was more of a thump, like something akin to a big tree falling down,” said Stephen Schatz, a spokesman for the state Department of Natural Resources who lives in Columbia.
He inspected his house looking for what might have caused it and, not finding anything, went to explore his yard by flashlight — only to find several neighbors doing the same thing. Threads on NextDoor and Facebook speculated over whether it might have been a sonic boom or some other strange phenomenon.
Schatz immediately suspected an earthquake, remembering that when a 5.8-magnitude quake rattled the East Coast in August 2011, it sounded to him like a construction crane had fallen down.
He alerted the Maryland Geological Survey, whose scientists were able to confirm the tremor.
“We normally wouldn’t be tracking anything this small,” said Richard Ortt, the geological survey’s director.
But the geologists were interested because there was a swarm of quakes around Columbia in 1993. Since then, there have been one or two small quakes detected in that part of the state each year, Ortt said.
The Sunday earthquake occurred about 8:34 p.m. about 2 miles beneath an area about 3.5 miles northwest of Glenelg and 1.2 miles southwest of Glenwood, Ortt said. That placed the epicenter near the Cattail Creek Country Club in western Howard County.
There is no fault line there, he said — the quake and others in the area likely occur because of weaknesses in the Earth’s crust.
“There’s no reason to believe we would have larger types of events in that area,” he said. “There’s also no reason to believe it would stop or increase or anything like that.”
To confirm and locate an earthquake, geologists need data from at least three different seismographs. In this case, they were lucky to get that, because Maryland has only one seismograph, in the Reisterstown area, and earthquakes typically have to be of at least 2.0 magnitude to be felt by many people.
Quarry blasts or large trucks have been known to produce 1.5-magnitude readings, Ortt said. But in this case, the “signature of an earthquake” was detected on several seismographs in Pennsylvania — where dozens of monitors have been installed to detect any quakes linked to the natural gas-harvesting process known as fracking — and even one in Delaware, he said.
“It must have been a really quiet day for them to feel that,” Ortt said.