Interesting observation.

According to AI search default, On average, there are about 10-15 earthquakes of magnitude 7.0 to 7.9 and one earthquake of magnitude 8.0 or greater each year.

That's pretty common (if it's true). 6+ already is a deadly event. 7s are guaranteed destruction & mass casualties, then somewhere, in the known zones, an 8+ is gonna go off every year!
Japan is very much a known zone for that magnitude. Not lots of places are.

I don't know about 8+s but many (not all) 6-7s are actually preceded by a surge in pre-shocks, almost like before a volcano explodes - building to a crescendo. But i think 921 (7.6) came more-or-less out of the blue.

I'm curious to hear a follow-up of how this quiet - too quiet situation pans out.