Wow. Just had a fair sized earth tremor – hit Niigata on the north side of the main island at 18:34JST with a strength of 6.4 about 10 mins ago, and we got a 3.x here in Tokyo, and I have to say that it went on for a couple of minutes causing the apartment building to roll quite a lot. TV channels urged people to open doors to escape hatches (commonly on balconies). More news as it appears on the net.