Sometimes is it a shaking motion that lasts for a while. Sometimes it is more like a truck hitting the building, one whack. If it happens at night and lasts more than 10 seconds it is probably a 4+ and that is enough time to roll out of bed and think about leaving the building, and also think about peeling the cat off the wall. But then it's over.
I am about 20 miles west of Pittsburgh, PA, and I was on FR. If the earthquake made it this far it sounded like a low flying propeller plane in trouble. About 20 minutes later I heard the same sound.