Well, I just experienced my first earthquake. I thought that what it was, but wasn't sure until michelle1963 confirmed it. I gotta tell you, the not knowing was almost as scary as going through it. I live in a fairly substantial house - with a second-level concrete basement, so when the entire house started shaking I couldn't imagine it being much else.
I was sitting at my desk when it starting vibrating and there was a low rumble outside. It shook for several seconds, paused, then shook again.
4.8 magnitude earthquake! Yikes!