A small point:Japan has quite a few volcanoes. And the occasional shaking. Korea does not even compare in this aspect. Might wreck your colony.
http://www.volcano.si.edu/volcano.cfm?vn=282090
http://www.volcano.si.edu/volcano.cfm?vn=282110
http://www.volcano.si.edu/volcano.cfm?vn=282100...