Oohhh, we’ve just had a big one!!!

“6-” on the Japanese scale of 7!!
Located a fair bit north of Tokyo, in Miyagi-ken. However, by the time the shockwave hit Matsudo (working at home at the moment), it still shook the apartment for a fair while.
Watching TV now, looks like they just issued a localised Tsunami warning, due to arrive at 12:10.

EDIT: BBC now reporting.
All fine down in my part of Japan though.