Tuesday, February 17, 2015

A tsunami warning in Tohoku

At 8.06 this morning, northern Japan was shaken by an M6.9 earthquake centred off the Sanriku coast of Tohoku, northeast Japan. Although barely perceptible in Tokyo it was intense closer in and triggered a tsunami warning which appeared on all television and satellite stations within minutes. The city of Ofunato issued an evacuation order for the port area which remained in place for over two hours. Thankfully the wave came in at only a few centimetres, not enough to cause any damage.  

A magnitude 6.9 is a serious earthquake, enough to slam doors 200km away; by comparison the 1995 Kobe event was an M6.8 and that razed a city being closer in. Mild by comparison, here is an M6.6 I filmed on my iPhone sitting in my office in Tokyo about 250km from a quake back in 2011 (we had become a little blasé about aftershocks by then). Remembering that the scale is logarithmic, this morning's rattle will have been significantly stronger than this in Iwate, the closest prefecture to the epicentre. 

You can see the fours and threes being reported across the map below. Rather than representing magnitude (M), essentially a measure of the energy released by an earthquake, the Japanese system measures the local intensity of the temblor, in this case by prefecture. Effectively it tells you the strength of the shaking at any particular location and is recorded on a scale of 1 - 7. Luckily this morning's quake was way offshore, reducing the impact as the shockwaves spread and dissipated, but it still won't have been too pleasant. Hope you guys are OK up there today.

A TV screenshot thirty minutes after this mornings M6.9 

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