Is Japan's Next Mega Earthquake Coming?

[PeterRS]

Two days before the 2011 9.1 mega earthquake off Japan's east coast near Sendai which devastated much of that part of the country, a 7.3 quake had occurred off the east coast of Iwate province, very close to the area of the Sendai quake.

Two days ago another less powerful quake hit Aomori province in the north of the country. But 7.5 is still a major quake and there are fears that as in 2011 this might be the prelude to another mega quake in the region. 

The one that most earthquake watchers are waiting for is a mega quake virtually under Tokyo similar to the Great Kanto quake of 1923. Although it was only 8.0 on the Richter scale, it was followed within the space of only five minutes by two other major quakes of 7.2 and 7.3 magnitude. The result was devastating. Over half of Tokyo and all of Yokohama were destroyed.  Up to 140,00 died and 2.5 milliion made homeless. 

It must be stressed, however, that Tokyo and Yokohama then were very different cities. Houses were constructed mostly of wood. Today's building standards in Tokyo take into account major quakes and the newer taller buildings around Shinjuku, for example, should withstand very strong quakes with only shaking. However, the 31 meter height limit for buildings in the city was only abandoned in 1963 and the Building Standards Act only came into force in 1971 following a 1968 earthquke. And despite the effects of the 1923 quake and the American fire bombing of Tokyo towards the end of WWII, there are parts of the city which would virtually collapse in a mega quake.

The reason for Japan being so prone to earthquakes is because it sits atop no less than three tectonic plates each pushing in different directions. This diagram from a 2011 edition of The Daiy Telegraph illustrates what is going on under the surface.

 

[a-447]

Katsuhiko Ishibashi was a prominent seismologist at Kobe university.

Back in the 1970s he fled Tokyo and moved up north, convinced that 'the big one' was coming in an area south of Tokyo.

When asked how close we were to the earthquake, he said : imagine you have a pack of cards and you are turning them over, one by one, looking for the joker. You still haven't found it and now only have 3 cards left. That's how close it is.

Ironically, the biggest earthquake ever recorded in Japan occurred.......up north!!! 

It was the 9.1 Tohoku earthquake in 2011.

His escape from Tokyo got enormous media coverage and although there was no general panic, we all went out and bought survival kits. Obsessed with personal hygiene, it comes as no surprise that these kits included a toothbrush.

I used to laugh, thinking about survivors sitting amongst the rubble, brushing their teeth.