Saturday 26 November 2016

Fifteen people injured after Magnitude 7.3 Earthquake off the coast of Fukushima Prefecture, Japan.

The Japan Meteorological Agency recorded a Magnitude 7.3 Earthquake at a depth of about 10 km, about 37 km off the coast of Fukashima Prefecture on Honshū Island, slightly before 6.00 am on Tuesday 22 November 2016 Japan Standard Time (slightly before 9.00 pm on Monday 21 November GMT). There are no reports of any serious damage following this event, however fifteen (mostly elderly) people were injured during evacuations triggered by the event and people have reported feeling it across most Honshū as well as on the northern part of Kyushu. The event triggered a small tsunami, with a maximum recorded wave-height of 1.4 m.

The approximate location of the 22 November 2016 Fukashima Earthquake. Google.

Japan has a complex tectonic situation, with parts of the country on four different tectonic plates. Eastern Honshū area lies on the boundary between the Pacific, Eurasian and Philippine Plates, where the Pacific Plate is passing beneath the Eurasian and Philippine Plates as it is subducted into the Earth. This is not a smooth process; the rocks of the two plates constantly stick together, only to break apart again as the pressure builds up, causing Earthquakes in the process. 

The movement of the Pacific and Philippine Plates beneath eastern Honshū. Laurent Jolivet/Institut des Sciences de la Terre d'Orléans/Sciences de la Terre et de l'Environnement.

Earthquakes along subductive margins are particularly prone to causing tsunamis, since these often occur when the overlying plate has stuck to the underlying plate, being pulled out of shape by its movement.. Eventually the pressure builds up to far and the overlying plate snaps back, causing an Earthquake and a tsunami.

Simplified graphic showing tsunami generation along a convergent margin.NASA/JPL/CalTech.

Witness accounts of Earthquakes can help geologists to understand these events, and the structures that cause them. The international non-profit organization Earthquake Report is interested in hearing from people who may have felt this event; if you felt this quake then you can report it to Earthquake Report here.
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