Yes, it was an earthquake
The US Geological Survey is reporting a 3.6 magnitude shaker at 5:04 a.m. EDT today, centered in the Gaithersburg area. That's pretty minor, but unusual for Maryland and quite enough to be felt across much of Central Maryland, as the map suggests.
UPDATE: Here is the current Sun story on the quake.
I had this report this morning from Brian Heinz, in Columbia:
"I was sleeping and felt the bed shaking and felt as if the house was shaking as well. When I came to, I looked at my Verizon cable box and the clock said 5:05. I immediately thought it was an earthquake or a plane going overhead, because of the noise. I feel like the earthquake actually made noise or it was the house shaking.
"I went back to bed and just woke up and checked the USGS earthquake map. An earthquake happened at 5:04 am in the Potomac/Shenandoah Region. AWESOME.
"Finally met one of my three random goals in life. Feel an earthquake, see a tornado, and be in a hurricane."
Steve Zubrick, the science officer at the National Weather Service forecast office in Sterling, Va., sent this:
"Big news down here. I felt the house shook as it woke me out of a dead sleep just after 5 am."
Any one else? Leave a comment.
There are some details from the USGS about this here. And here's more on the history of earthquakes in Maryland. And here's a little on the most recent quake reported in Maryland, just outside of Baltimore, in 2007.