OK, I am doing the kind of post that I warned about not doing elsewhere on this thread. But, I think it is worth posting as it could be very mildly reassuring to some. Again, I am a research geologist who is not a seismologist and does not work on subduction zones. But, I've seen some presentations on Tokyo area structure (although that was years ago and I've forgotten a lot).

I don't think it possible to have another M8.9 for the next section of subduction zone south of this quake, near Tokyo. See my post on another thread about the rupture area of this one. The map linked there shows a complexity or Triple Junction near Tokyo. I don't think a subduction quake would rupture across a triple junction (it probably is not impossible, because it is, I think, a trench-trench-trench triple junction). Assuming a quake will not rupture across the triple junction, the part of the subduction zone that did not rupture is far smaller than what just ruptured. So, probably capable of only a low range M8 quake.

the link is to the catastropic 1923 quake that pretty much destroyed Tokyo. The link says M7.9 Richter. You can't use Richter for quakes that big: the scale saturates.

Seismologist should pretty quickly have rupture models: it matters where the slip was. Areas that slipped 20 meters are not going to turn around and slip another 20 m. But, areas that slipped 1 m could have a later quake rupture back across part of it (although I don't think that is what happens historically within a couple of years).

Chris

• 1923 Tokyo quake