It's not that the ground motions in 1906 were significantly larger than those in 1989it's that the area experiencing intense shaking was much, much greater. We don't know if the next rupture will look like 1906 earthquake, but we know that many of the same areas hit hard in 1906, like San Francisco, Santa Rosa, and the Santa Cruz mountains will be hit hard again in the next large earthquake on the San Andreas Fault .

Brad Aagaard