yes, that is certain, on many California faults, the stress is building, and something larger (than what?) will come. We just don't know when. What is more complicated are faults that are relatively closely-spaced like the Newport-Inglewood, Palos Verdes, and faults farther offshore, that we know are active, but it is harder to tell how GPS velocities are related to each fault. For example, work published by McNeillan et al 1996 give 3+ mm/yr right-lateral on the Palos Verdes fault at Long Beach Harbor since ~8000 years (I think)(is offset, dated channel). But, work in the Mojave desert after 1992 Landers quake shows that block motions and earthquake activity move around on a time frame of thousands of years
Chris