Manda - Here are some good basic links on Earthquake Hazard in Southern California:
Southern Cal Earthquake Center:
http://www.scecdc.scec.org/ - if you click on the seismicity button on the left you will then see a link for a Fault Map.

When you click on an individual fault there is usually information about how often its expected to break (averages at least) and what size quake is possible on that fault.

The biggest danger here is that not all faults have been mapped - the Northridge quake and I think the whittier quake both occurred on previously unknown faults. Those are the 'blind thrust faults' - A good rule of thumb is anywhere you see a hill there's probably a fault under it.

Then there's another link at the SCEDC site - its a booklet called Putting Down Roots in Earthquake Country - its a great booklet to read - there is a link to it from this page:
http://www.scecdc.scec.org/education.html

Good luck and keep asking those question!
Canie