The Earth Moves. Annandale Yawns.
Wednesday, May 7, 2008
At the epicenter, there was calm. No panic, no yelling. That's because no one really knew that an earthquake struck Annandale yesterday.
As quakes go, the rumble that measured a magnitude 1.8 was more of a "microquake." No one was hurt, and nothing was damaged in an area just south of Wakefield Chapel Park near the Little River Turnpike and the Capital Beltway in Fairfax County. The Red Cross was not alerted.
But anyone who was home at 1:30 p.m. on Holborn Avenue, which the U.S. Geological Survey in Reston calculated to be the epicenter, heard a loud boom and maybe felt a little tremor. Not enough to make anyone dive into a doorway, but something.
"I heard a large boom," Lilienne Conklin said. "I went outside to see if my gas tank had exploded." She said she also noticed that her dog, Tug, "was acting funny. Dogs know."
"I heard a really low boom and very slight shaking," Mel Warrenfells said. "I thought it was an explosion." Warrenfells said he sometimes feels slight rumbles at night, which might be amplified "because I have a waterbed."
Earthquakes happen in the Washington region every year or two, USGS geologist Bill Leith said. But why Annandale? Why now?
"There's no good explanation for that," Leith said. He said the quakes that hit the area are usually felt by a "small number of people." He said Northern Virginia is not mapped by the agency as being a "high seismic hazard."
Quakes are caused when the Earth shifts along fault lines, and there are no known fault lines in Annandale, Leith said. But that's because much of the area "is buried under sedimentary layers, so we don't see the bedrock faults," he said. He said the earthquake yesterday might have originated as far as six miles below the Wakefield Chapel neighborhood, where the Annandale High School lacrosse team practiced just yards from the epicenter, as if nothing had happened .
The USGS tracks tens of thousands of earthquakes every year around the globe. In fact, within three hours of the seismic shock in Annandale, 20 quakes occurred elsewhere, mostly in Alaska. An earthquake with a magnitude of 6.0 or higher, which would mean serious shaking and no wisecracking from reporters, happens somewhere every two or three days, Leith said.
And the "boom" that will become part of Annandale legend? "It's from the actual shifting of the Earth," Leith said. "It was probably the seismic waves exiting the surface and coupling with the air."
The most recent earthquake recorded in Northern Virginia occurred in September 1997 near Manassas. It was a 2.5 magnitude event. Baltimore had a widely felt 2.1 shake in February 2005. And Columbia felt a series of seismic events in March and April 1993 that ranged from 0.5 to 2.5, USGS spokeswoman Clarice N. Ransom said.
The strongest earthquake recorded in Virginia occurred May 31, 1897, near Giles County in the southwestern part of the state. That quake measured 5.9 on the Richter scale and extended from Lynchburg west to Bluefield, W.Va., and south to Bristol, Tenn., Ransom said.