I think a good question would be how far east would one feel shaking? LIke Utah? New Mexico? Or just AZ and NV? I wouldn't say never as the whole length rupturing, not in our lifetimes. If you think of it, the 1906 ruptured from just north of Parkfield all the way up to close to Eurkea, and in 1857 the south ruptured from Parkfield all the way down San Bernardino. So....seeing Parkfield is the boundary between the 2 ruptures, whos to say like very 1000 or even 10,000 years or so the 2 rupture zones aren't prime and ripe and one starts and it just keeps going all the way down, or up? If I had to bet, I'd say in the last 50,000 years, its HAD to have happened like 2 or 3 times. Rare but I'm sure it could.