At first I thought a very large truck was in front of my house. The roar got louder and I thought maybe there were three trucks in my driveway.  The walls started rattling as the noise intensified and I thought a tree might be crushing the roof.  The vibration escalated, I could hear the house creaking and groaning through the roar, and I wondered if an airplane was on my roof.  At about that point I realized I had just experienced my first earthquake.  I didn't feel frightened. It only lasted about 30 seconds. 

Some things fell off of high shelves, some cabinet doors opened, and just about every piece of artwork on my walls are now askew.  It was quite an experience.  Very cool.