Currently there really isn't enough data to accurately predict earthquakes on a regular basis. Most of what the California seismic group does is collects data about various structures after a quake and then turns the data over to architects, engineers, scientists for study. Depending on the severity of the quake, the Office of Emergency Services gets notified within a short period after the quake to determine if, when and where to send help.
I do remember reading several years ago about trying to make predictions based on changes in ground temperature. I believe a change of less than 1 degree C over a particular short period of time measured by infrared satellite indicated an earthquake was likely very soon. Kind of makes sense. Temperatures rise, pressure rises. Pressure has to be released somehow. Not sure what happened to that theory and have never seen the follow up on it.
Lots of earthquake info can be found at this site...
California Geological Survey - quake.ca.gov
JJ