We just had a rather substantial shake here in the metropolitan Tokyo area which woke me up. Time was about 1:48AM local. The Japan Meteorological Agency has details here:
http://www.jma.go.jp/...
Update #1: No tsunami warning issued. The JMA can issue one instantly if merited -- there's one heck of an early warning system here.
Update #2: There was one station on the mainland that clocked in in the lower 5s (on the 7.0 Japanese earthquake scale). That must have been a bit frightening, but I expect people are going to be OK. My section of Tokyo was in the 3s. Books on the shelves were rocking back and forth, slapping against the sides of the bookshelf. The buildings are engineered to sway like that.
JMA uses a 7 point scale, and the instant measurement is that this was 6.7 in a hot spot off the eastern side. There have been a lot of tremors as well leading up to this.
I think everyone is going to be OK, but we'll see. I live in a very modern building, but the fear is always about the older wooden buildings and some of the infrastructure. I'll post more when I have it.
Update #3: The quake was centered at 36.2N 141.7E at a depth of about 40 km. This is off the coast of Ibaraki Prefecture in Japan, a fairly common spot. Magnitude was 6.7 on the Japanese 7.0 scale at that immediate spot. There were no sirens or alarms that went off in my local area in Tokyo.
Update #4: Here's a better link: http://www.jma.go.jp/... -- official time listed at 1:45 AM. I think I'm going to try to get some sleep now. :-) Thank you all for your concern. Good night!