9 Décembre 2012
December 8, 2012
The magnitude 7.3 earthquake that occurred off of the east of Japan on Dec. 7 was an "outer-rise" tremor, with its hypocenter located past the Japan Trench in a risen part of the Pacific plate, it has been learned.
Outer-rise earthquakes readily occur as aftershocks following large earthquakes at plate borders, like the Great East Japan Earthquake. Often the hypocenters are shallow, and when they involve a vertical sliding of faults, as in the Dec. 7 quake, they are thought to be capable of easily producing tsunami that are comparatively large for the scale of the quake.
Because of this, the Japan Meteorological Agency and tsunami experts were on heightened guard after the Great East Japan Earthquake. The Dec. 7 quake was the second large outer-rise quake since the Great East Japan Earthquake, the first being on the same day as the disaster.
In April this year, a magnitude 8.6 outer-rise earthquake occurred off of Sumatra, Indonesia, and may have been an aftershock of the magnitude 9.1 earthquake eight years before that caused a tsunami that took around 220,000 lives and injured around 130,000 more.
Professor Fumihiko Imamura of Tohoku University says, "I don't know when, but an even larger outer-rise earthquake could occur in the future (off the Tohoku coast). I want people to have places ready to evacuate to in case of disaster."