It's been awhile since we've had a bad one Dan. You might be better off not paying for it as Lin mentioned. Of course we did get hit a few months ago by a 5.6 earthquake, I think it was centered in San Jose. Shook our whole office in the city though. It really isn't that expensive, many places include it in the HOA fees.
Regular home owner insurance runs $100/mo excluding earthquake. Honestly, in all of the hundreds of deals I've done, not one of my clients purchased earthquake insurance. They would rather save the money and put that into retrofitting the home. Earthquake insurance varies depending on the zones it's in from liquifaction (worst case) to fault zone to no within a fault zone.....you need to add on hundreds of dollars more for the earthquake insurance.