As for a root cause, could it be related to North Korea's recent nuclear test? http://www.express.co.uk/news/world/849381/tremor-North-Korea-nuclear-test http:

As for a root cause, could it be related to North Korea's recent nuclear test? http://www.express.co.uk/news/world/849381/tremor-North-Korea-nuclear-test http://www.express.co.uk/news/world/849381/tremor-North-Kore...