Not unprecedented, but still... The most recent one is far enough north that I wonder if it isn't part of the Sendai quake aftershocks.

Link is to USGS map search, 2000 through day before M9 quake, M6+, 500km radius near Tokyo.

There haven't been many right close to Tokyo.

Brian

• Tokyo-500km-2000-2011/3/10-M6+