After the great Sumatra subduction earthquake in 2004, crustal stress increased in the adjacent segment of the subduction zone, where a magnitude-8 event occurred four months later. So naturally I'm concerned about what the March 11 Sendai earthquake will do to the plate boundary on either side of the slip zone.
US Geological Survey scientist Ross Stein and coworkers in the US and Japan have been running the models and have initial results showing a rise in stress to the north, off northernmost Honshu. This is no surprise. That side of the subduction zone is a straightforward extension of the segment off Honshu, which is the boundary between the Pacific plate on the east and the North American platespecifically, the Okhotsk microplate that has recently been delineated thereon the west.
The image below shows the southern end of the rupture zone.
I want to make it plain that this image is only an unpublished, first-take approximation. But what it appears to show is that the Sendai quake has slightly loaded the "Sagami trough megathrust" that marks the south end of the plate boundary. That boundary, unlike the one where the Sendai quake occurred, lies between the Pacific and Philippine Sea plates. (It's the same fault that accounted for the 1923 Kanto earthquake.) The plate dynamics are quite different there, and I can say that the stresses from last week's quake have probably not loaded the Tokai segment, which runs from west of the Boso Peninsula, left of the "S" in "Sagami", down to the lower left corner. It lies between the Philippine Sea plate and the Eurasian plate (Amur microplate).
So does the Sendai quake put Tokyo in greater danger? Not in an obvious way. Do not expect a definitive answer from the scientific community, and do not trust every TV commentator who may assert such an answer (unless it's Ross Stein).