Saturday 8 December 2012

Magnitude 7.3 Earthquake off the coast of Japan.

On Friday 7 December 2012, slightly before 5.20 pm local time (slightly before 8.20 am, GMT), the Japan Meteorological Agency recorded a Magnitude 7.3 Earthquake at a depth of 10 km, roughly 250 km off the east coast of Japan. This was followed 13 minutes later by a second, Magnitude 6.2 quake at roughly the same location, and a number of subsequent aftershocks have been recorded. No casualties or damage have been reported, but the quake was felt across much of eastern Japan and a tsunami warning was initially issued, though this was later withdrawn. 

The location of the 7 December 2012 quake, and the areas that felt the strongest shaking. Areas coloured the strongest yellow would have been shaken the most severely. Japan Meteorological Agency.

The quake took place on the Japan Trench, along which the Pacific Plate is being subducted beneath the Okhotsk Plate which underlies northern Japan. As the Pacific Plate sinks into the Earth the two plates continuously stuck together then broke apart as the pressure built up, causing Earthquakes in the process. 

The movement of the tectonic plates underlying Japan. Chubu Electric/Earthquake Research Committee.

This is particularly dangerous along a marine trench, as the overlying plate can be bent by the tectonic movement then snap back with the quake that releases the pressure; which causes some of the most severe tsunamis.

The sequence of events that can lead to major Earthquakes on a submarine trench. PennState University.

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