Don, You have to know what the reference is for the little GPS arrows. If they do not have the same reference, you cannot compare them directly. If the reference is the stable interior of North America, the GPS vectors in California will point to the northwest, and will be longer in western California. If the reference is the stable interior of the Pacific plate, the arrows in California will point to the southeast...getting longer as you move east. Sometimes the reference is somewhere in between, like San Nicolas Island, or Palos Verdes, or JPL.
As for your question about migrating stress, no, that is not what is happening.
Chris