Cathryn, I also think you are mis-interpreting Petra's comment...she would not call a post from you pitiful.

Now I'm scared to post because it could be taken wrong..

But, I agree that Don did not really answer your question.....let me take a shot...
Below some depth the various active faults are smoothly slipping at their 10 mm/yr or so each (for the large ones). That is what is seen by the GPS...the fault bounded blocks are moving by each other...except close to the faults. Except for the Calavaras fault (hello Don), the southern Hayward, and part of the San Andreas fault north of Parkfield, the faults are locked shallower than some depth...usually about 15 km for California strike-slip faults. That means they are just flexing, not slipping...until they snap. As long as the GPS shows that they are flexing, and that the flexing is increasing, you know that they must snap....
Chris