Except, that segment just broke only in 2004 - 8 years ago. Isn't that a little short to have built up enough strain for it's usual M6ish quakes?

Or, maybe there is enough, and in 2004 there was MORE than enough, and maybe there's some unknown mechanism at work that actually limits Parkfield segments to breaking in no more than M6, and therefore 2004 did not release all the strain and now it's getting back in sync? (yeah, a rambling sentence)

Brian