Slightly before 2.30 pm local time (5.30 am GMT) on 1 January 2012 a large Earthquake occurred beneath the Pacific Ocean, roughly 365 km to the south of Japan. The quake was measured as having a magnitude of 6.8 on the Richter Scale and occurring at a depth of 348.5 km by the United States Geological Survey and as having a magnitude of 7.0 on the Richter Scale and occurring at a depth of 370 by the Japan Meteorological Agency. There re no reports of any injuries or serious damage occurring, and no tsunami warning has been issued, but the quake was felt across much of eastern Honshu, remarkable for a quake of this depth.
Map of Japan showing the location of the quake (red cross) and the areas where it was felt (yellow and cyan). The cyan areas suffered shaking at Level 3 on the Japan Meteorological Agency (JMA) Intensity Scale, enough to be felt indoors by most people, to make dishes rattle and to cause power cables to visibly swing. The yellow areas suffered shaking at Level 4 on the JMA Intensity Scale, enough to waken sleepers, frighten many people, knock small objects from shelves, make cables swing wildly and be felt in moving cars. Map from the Japan Meteorological Agency.
Japan lies on the boundary of four tectonic plates (Eurasia, North America, The Philippine Sea and The Pacific) and is particularly prone to earthquakes and volcanic activity as a consequence. The country occasionally suffers widespread damage from major quakes which make the headlines around the world, but is probably the best prepared nation in the world to deal with quakes, and rides out quakes that would destroy cities in other parts of the world several times a year.
This quake appears to have occurred on the boundary between the Philippine Sea and Eurasian Plates, where the Philippine plate is passing beneath the Eurasian plate as it is subducted into the Earths interior. As this occurs the plates stick to one another, pressure builds up, then they release sharply causing quakes (this is a vast oversimplification). Curiously the area where the quake was felt lies on the North American Plate, to the North of the Philippine Sea Plate and to the east of the Eurasian Plate.
The movement of the tectonic plates beneath Japan.