I've always wondered why japan and the islands northwards have the
same formation as the greatest deeps in the pacific ocean (like the
worlds greatest deep would be somewhere about Kobe city in comparison.
I find it weird since I believe I've read that Japan once was a part
of the main land around China or Khamshakta (the big peninsula)
Pardon my bad english. I'm from Norway

http://en.wikipedia.org/wiki/Image:Tectonic_plates.png

Japan is partly on the North American plate and partly on the
Phillipine plate, and is being crushed between the Pacific plate and
Eurasian plate.

Where plates come up against each other, one plunges beneath the
other, creating mountain ranges and/or oceanic deeps. You get lots of
earthquakes and volcanism in the meantime.

By contrast, Norway's earthquakes come from the post-glacial rebound
the earth's crust.