Sumatra M8.6 earthquake - minor adjustment at a bend
It's hard to think of this size of earthquake being 'minor', but it really is in this part of the world. This earthquake is 4 times shorter than an M9, and is apparently strike-slip. It's those weird bends in the subduction zones. They stop the major rips, and then things have to work through them.
Eventually, it opens up for the next big rip to the south, which will also be an M9+.