There was a M7.3 quake far offshore of northern Honshu. The focal mechanism shows nodal planes (potential faults) that are either nearly flat or nearly vertical. The epicenter is east of the trench as shown by the USGS map.
USGS has a summary (the link below is to CNN):
http://earthquake.usgs.gov/earthquakes/eventpage/usc000e5n4#summary

Oddly, it is either reverse on a plane dipping 85 deg, or left-lateral on a plane dipping 10 deg.
There was a 1 m tsunami and USGS says reverse, so OK.
well, not OK, the aftershocks are spread out in a cloud like the fault was flat. A M6.2 aftershock is oblique normal, and is west of the trench.

I am not more qualified to say this than others here: the M9 was preceded by a M7.4 a few days earlier. But, I doubt this one will directly trigger a much larger quake on the adjoining subduction zone because that part already broke. Instead, I think this one is a response to the M7.3; it is an aftershock.
That is not the same as saying it is impossible that there could be a larger quake at least indirectly related to this one. It just seems unlikely.

Chris

• M7.3