I woke up in the middle of last night, and wasn't quite sure why. I thought I'd heard a big bang, so I did a quick check around my house and immediately outside my house but didn't see anything untoward and so went back to bed and eventually back to sleep. I didn't think anything more about it until this evening, when I read an article stating that there had been a 3.4 magnitude earthquake last night in the Seattle area. Not a big one, but enough for the shaking to be felt throughout Western Washington. So I wonder if this was the reason my sleep was interrupted last night. That certainly sounds better than all the more obvious reasons - diet, exercise, stress, poor sleep habits, etc.
