A Little Bit of Shakin' Going On....

May 7, 2008 — -- As earthquakes go, it wasn't much of one.

It was only a magnitude 1.8 on the scale geologists use. But its center was just a mile from Annandale, Va., in the suburbs of Washington, D.C. — enough to get the attention of scientists and local emergency officials.

It happened on Tuesday afternoon, and though it did no damage, hundreds of people called local news outlets saying they had heard a bang and felt a mild jolt.

"Of course, this was a very small earthquake, but we've had larger ones in this part of the country in the past," said Leonardo Seeber, senior research scientist at the Lamont-Doherty Earth Observatory of Columbia University in Palisades, N.Y.

Several others have made news lately: The normally quiet area around Reno, Nev., has had dozens of tremors since late April, the largest measuring 4.7.

Southern Illinois had one on April 18, measuring 5.2.

And there was one on April 30 in northern California, about 190 miles north of Sacramento, with a magnitude of 5.4.

What's going on? Nothing unusual, say scientists — unless the shaking is going on under your feet.

An Earthquake? In Virginia?

Virginia, like most of the world, is geologically stable. There hasn't been much seismic activity in the Washington suburbs since 1997, and the quake that happened then only had a magnitude of 2.5.

Below the level of 3.0, scientists refer to tremors as "microquakes," and say it's unusual for people to feel them. About a thousand of them happen somewhere on the planet every day.

"Quakes of this size are strong enough to be felt in dense population areas, especially in high-rise buildings," said Bruce Presgrave, a geophysicist with the U.S. Geological Survey in Golden, Colo., in an interview with the Associated Press.

Scientists say something of magnitude 5 is a "moderate" earthquake. A magnitude 4 is "light." A 3 is "minor" and below that is "micro."

"We can laugh at a 1.8," said Lamont-Doherty's Dr. Seeber, "but the issue is how small a quake in this part of the world can be damaging."