Japan lies at the meeting point of several of the world's major tectonic plates. This means that there is an everpresent threat from a range of natural hazards earthquakes,volcanoes and tsunami. The map shows the Philippine and Pacific Plates which are slowly moving north west towards Japan. As they move north west they slip under the Eurasan and North American Plates When one Plate slips underneath another the movement is called subduction. This whole area is very unstable and earthquakes and volcanic activity are common along both sides of plate boundaries.

http://www.emu.org.uk/curriculum/projects/japan/ASPECTS/EARTHQUAKE/PLATE...