Yes, that was an earthquake
The tremor occurred at about 1:51 p.m. It was given a preliminary magnitude of 5.8, centered about 35 miles northwest of Richmond. We are evacuating our building, but leave a comment and we will post when we return.
UPDATE, 6:30 p.m.: Well, we're back, and nearly the entire newsroom is working quake-related stories. I've just filed one on the geo-science behind Eastern quakes, with help from Jeff Halka ant the Maryland geological Survey and Michael Scott, a professor of geography and geo-science at Salisbury University.
It turns out today's quake was the largest on record for Virginia, and one of the largest ever felt in Maryland. It was also the strongest of five so far today around the globe of magnitude 5.0 or higher.
The others included a mag. 5.3 in Colorado, and three others in the Fiji Islands of the Pacific; on the Kashmir/India border; and in Papua, New Guinea.