Bug out on foot? Not going to happen. It's too far to any kind of better shelter than what I have right here and both directions necessarily cross the major earthquake faults so the damage would increase.

If a bad earthquake hit while I was at work I'd figure 2-3 mph depending on the amount of damage/obstacles en route on the trip home, assuming I had to walk. I have a light pack that's just perfect for such a trek. The walk will take 8-12 hours, but before I did that I'd hunker down for a few days and camp out with the supplies in my truck. Fix a few roads and I wouldn't need to walk home after all.