Losts of studying about foreshocks has been done, but not in their relation to aftershocks that I'm aware of.

Our quakes along the San Andreas are completely different than what happened up in Seattle and as such, there are different precursors to these different types of events. As dib said, there really aren't foreshocks/aftershocks to these subduction quakes like there are to quakes here in California.

I have been musing a bit - the Juan de Fuca plate, Gorda and the Cocos plates are all remnants of the Farallon plate as its being subducted underneath the North American plate. I wonder what the status of the farallon plate is underneath the NA plate where it is completely subducted - is it still somehow attached to the Juan de Fuca, Gorda and Cocos plates? does this subduction quake transfer any stress along it north south along the plate remnants? More than a few miles but as far south as Salvador? They had a 6.1 shortly after the 6.8... Was there any connection since they were all one plate?

Hard to tell - Canie