Here are some of those speculations, with some going into great detail:
"Was there a struggling jet this morning taking-off/landing at IAD, or did we just experience an earthquake? ... I heard what at first sounded like a typical passenger jet about to pass overhead. However, a rumbling surge replaced the normal overflight noise which I am used to out here, and my entire house began shaking and rattling in a rather violent manner. ... I have NEVER experienced such a thing as this before, and therefore I am curious as to what is truly was (An extremely low-flying jet from IAD, or an earthquake?). I have even had the experience of being buzzed by a C-130 Hercules on final approach at NSN once before, but even that did not compare to this."
"Was there an earthquake in Northern Virginia this morning about 5:03AM? I felt a 5 or 10 second rumble that was either an explosion somewhere or an earthquake."
"Was this an earthquake? What caused this? ... I live in Silver Spring near Aspen Hill. I called the near-by Glenmont Police Dept. and the policewoman on duty was freaked out because she felt it too about 3-4 miles from my house. Her phone was ringing off the hook about this as were 911 calls being transferred to her!"
"Just was awakened at 5:05 am by loud, very deep rumbling that increased and shook the house somewhat (for 30 seconds?) then dissipated. This was quite frightening and we wondered if it was a small earthquake, an explosion somewhere (or possibly a really large military plane?) We would really like to know what this was because it's nerve-wracking to try to go back to sleep not knowing the explanation...."
"Did DC just have an earthquake? 11 second tremor in the Woodley Park neighborhood (very close to the Vice Presidents House)? Or did Air Force One land someplace nearby? Can anybody answer what just happened?"
"Sounding like a freight train coming in to the station..... Bed began to shake and the crystal in all of our china cabinets began to clink together and "sing." Sounded somewhat like the screech of tires..... Lasted about 5 seconds. We vote for......EARTHQUAKE!!!"
"I was just woken up by a large house/ window rattling sound that would remind me of a sonic boom from a jet? We live in Middletown, Frederick County MD and this was something that woke me from a dead sleep to the point that I am now wide awake. Not my normal status at this hour. This rattled the windows and was about 3-5 secs in length. No lightning visible. Sound faded as it proceeded. Even woke our dog? Anyone else hear this. More than likely anyone that was on their way to work. This was an unusual storm. Heat occurrence if that was it."
"My whole house shook from something resembling a huge explosion. What was it??"