Yea I think the theory is sound, though you have to remember his theory only deals with those that occur after the initial quake. I think the initial quakes are indeed due to friction between the plates. The geological record is clear that parts of the crust move against each other.
So likely the initial quake is due to tectonics, but the remainder are wave related per his theory. That would indicate that tectonic quakes occur less often then currently thought.
I've been lurking on DUTCHSINSE'S site for a couple of years, primarily because my daughter lived in earthquake-prone Oregon.
It appears deep quakes in New Zealand is the origin of earthquake progression. It is a mystery when and how large they will be.