Is an Earthquake Large Enough to Cripple the Entire West Coast of North America Possible?
Never say never, but it's unlikely.
Every geological fault is not uniform. There are bumps and snags of varying size and strength along its three intentional surfaces. As once fault surface moves over the other some of the snags can break off resulting in localized quakes at the site of the breakages.
Similarly, for very strong, robust snags (protuberances) which ride over the other surface as they suddenly hit a dimple in the other surface or simply just ride along another surface protuberance on the surface of the other side of the fault it slams into the other surface. This causes another form of localized earthquake.
For an earthquake to hit the entire north west region of the US, these type of events would have to occurs along the entire length of the fault simultaneously.