What Was That?!?

OK, so this isn't really a howto, but I wanted to write something about it while it's still fresh in my mind...

Back in the summer of 1993, there was a rash of small earthquakes (less than magnitude 3) that hit the Columbia, MD area.  I was a senior at the University of Maryland at the time, and working as a co-op for a business with an office near the interchange of US 29 and MD route 32.  Sitting at my desk one afternoon, our office building lurched with a thump -- we thought the building had been hit by a car.  We found out a few minutes later that we had experienced a small earthquake.

That had been my only experience with earthquakes until this morning.  I woke shortly before 5am this morning and was just resting still in bed, trying not to wake my wife.  As I lay there thinking about the day to come, I heard a long, low rumble outside.  It didn't sound like a truck, but reminded me of an experience I had in England a few years back.  There I was resting in my room at an inn about 40 miles outside of London one evening as a thunderstorm approached from the south.  Because of the inn's perch on a south-facing hillside, the sound of thunder from the coming storm rolled long and low, much like the sound I heard this morning.

The rolling "thunder" continued for more than five seconds.  As I lay in bed recalling my experience in England, and wondering why no weather report from the night before had mentioned the possibility of thunderstorms, the house shook violently for a second or two.  And this was an unusual shake -- the house was rattled to the foundation.  This was no thunderstorm!  Did a car hit the house?  No, it couldn't be that.  There was no breaking of glass or splintering of wood.  Was it a terrorist attack?  Did someone just detonate a large bomb over DC?  Probably not.  There was no flash, and the event was not concussive, as would be expected with a large blast.  Before the "thunder" had rolled away -- another ten seconds or so after the house settled down -- I was left to assume we'd just experienced an earthquake.  I looked at the alarm clock.  It showed 5:04am.  "Did you feel that?  I think we just had an earthquake," I said to my wife.  The rumble and shaking had jolted her awake as well.  I got out of bed and peered out the window just to make sure there wasn't a large car or truck sticking out of the side of our house.

Back in bed, and still leaning towards the event being an earthquake, I tuned my radio to WTOP.  I was relieved to hear that WTOP was still broadcasting.  It wasn't a large bomb.  Within a couple of minutes, WTOP was reporting calls to their studio from Gaithersburg to Falls Church asking about an explosion or other event that caused the earth to shake.  "Wow, that's 20, 25 miles," I said to my wife, "There were several earthquakes in Columbia back in 1993, but none were felt that far apart."  Reports from the USGS began flowing in before 5:30.  The initial report was a magnitude 3.7 quake centered near Gaithersburg, MD.  Before 6am, the initial report had been revised to a 3.6 quake centered slightly farther north in Germantown.  Reports were rolling in from Harpers Ferry to Delaware about the earth shaking.  Remarkable!

I've travelled a bunch of times to the Silicon Valley area.  I've been to Mexico City a few times, and I've even spent some time along the Pacific "Ring of Fire".  For all those trips, I've never experienced an earthquake outside of the metro DC area.  And after today, that's just fine with me.  Today's event was a small quake by any measure, but it was disconcerting enough that I don't think I need to experience anything larger.  Still, it was a unique event -- the largest recorded quake in DC history.  So we'll talk about it, write about it, and someday tell our children and grandchildren how we survived the Great Washington DC Quake of 2010!

-- Terp