Cathryn,
I agree with what you say here...except for one things...which depends on how you define FFA: Roger's analysis shows no FFA trigger for M5+ quakes. I'm not 100% giving up on the possibility of FFAs, because no one tried to reproduce what Lowell W. had done, but it really does not seem like there is any strong FFA ewffect (if there is any at all.). On the other hand, it is well established now that the actual ground motions and stress redistributions can set off quakes within a couple 1000 km....I still don't know what is going on with the large aftershocks that are 100s of km north of the modeled rupture area.
Chris