You can still see many remnants of the earthquake, while walking through the peninsula. Many old building and homes have large screw-like structures sticking out of the outer walls. These are what they used to press the fractured walls back together following the quake. Crazy stuff to think about. You have to remember, the Earth beneath us is always in motion. I was in Richmond during that larger quake that hit a couple years ago. Pretty strange feeling, when you are on the 4th floor of a semi-tall building. That swaying feel just isn't comforting.
earthquakes are the trippiest natural phenomena....
i did 10 years in San Fran - '82-92' - and went thru a variety of seismic events, including the big '89 Loma Prieta quake that went off in the middle of an A's-Giants World Series game (Mother Nature bats last!). it's the weirdest sensation - we always knew it was a quake when hanging houseplants started swaying and the cat would dive under the clawfoot bathtub.
i actually enjoyed the experiences, for the most part - they go off without warning, right out of a clear blue sky. one minute, you're trucking through your day, with all your normal cares and worries - the next minute, everything is cleared from your mental radar and the only thing that matters is the well-being of you and your family. you instantly shed all the superficial mental bs and get jolted back to what's really important, right now.
I still don't believe it was any type of sonic sound wave. Remember that one in August 2011? I was in the same location and this one was the same strength. Definitely came from the ground the way my house shook, not from the sky. We've heard all the normal sonic booms and whatnot. If it was from the sky it was not done in clear sight. I think it has to do with fracking or underground explosive device testing.