What is the Big One?
The Big One is an earthquake-to-happen in Tokyo. Not an everyday earthquake, a huge one. The Big One is special. The Big One gives nightmares to Tokyo Building Officials. They don’t scare their kids with the boogieman. They scare them with The Big One. According to the Seismology experts from the University of Tokyo, there is a 75% probability that a magnitude 7 (Ritcher Scale) earthquake strikes Tokyo Bay before 2016 (cue for end-of-the-world music here. I bet there’s a Mayan mummy out there counting the days). If we consider the next 30 years, this probability goes up to 98% (cue for Jaws music here). The worst prediction to date is 7.3 on Richter Scale the with a shallow hypocenter.
Why is the Big One going to happen?
The isles of Japan are a geological formation generated because the Pacific and Philippine tectonic plates slide under the Eurasian plate. This process moves tons and tons and some more tons of rock and earth crust and it is very slow. This causes a lot of energy to pent up and every number of years that energy releases with a bang that makes the whole area shake. The point where the energy is released is the hypocenter, and the projection on the surface (the point just above it, on the earth soil) is the infamous epicenter. The higher the energy released, the tremors are stronger, and the wider the area that shakes.
In the case of the Big One, pressure has been building up under Tokyo Bay since the last release (the Great Kanto Earthquake in 1923), so it’s bound to happen again. Soon.
Another theory says that Japanese earthquakes are caused by the Namazu (鯰), a giant catfish that lives in the mud under the islands, restrained by a stone put on him by the god Kashima. When Kashima slacks off, Nazamu trashes and earthquakes happen. Apparently the Big One is expected for the next guys-out party among the Japanese gods. Tsk.
Why is the Big One Scary?
While 7.6 does not seem like such a high number considering last year’s Tohoku one (9.0), it is a chilly thought to know that it is coming and that there is nothing that can be done to stop it.
Even chillier: the predicted death toll is almost 10,000 people. Still not chilly enough? Tokyo University’s study reports that a 7.3 earthquake at occurring at 6 p.m. in winter in Tokyo Bay would cause about 9,700 deaths (5,600 due to the tremors and 4,100 in the following fires), would injure 147,600 people, 21,900 critically, damage 304,300 buildings and force to evacuate 3.39 million people (check the whole summary here). And remember that we are talking about the best prepared city in the world for this, with the most modern earthquake-proof buildings).
Will the Big One create a Tsunami?
That depends. A tsunami is only caused if the movement of the plates that releases the energy is vertical (one plate snaps up or down), not if they slide side by side. Also the hypocenter needs to be out under the sea. The University of Tokyo has calculated that the Big One might cause a wave of up to 2.61 meters high in Shinagawa Ward, and assured that the waves would not go over the defences.
What can be done about the Big One?
Be prepared. Unfortunately nothing can be done to stop the quake itself.
The Tokyo Metropolitan Government is compiling a renewed set of local disaster management plans that are scheduled to be done by September. The figures shown are the worst case scenario – 6pm combines rush hour and high use of fire, so if that can be tackled, anything can be done. The Tokyo University study itself states that deaths and other casualties will be avoided if evacuation procedures are properly followed.