14 Mar 2011

Sendai earthquake

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Friday’s earthquake, with epicenter just 373 km from Tokyo and only 200 km from the nearest point of Japan’s coastline, reached 8.9 on the Richter magnitude scale and the country continues to experience aftershocks of up to 6.2. It’s Japan’s biggest earthquake in record history (records started being kept 140 years ago) and it’s said to be the seventh largest on record int he world just slightly stronger than the quake that hit Chile in 2010.

The official death toll has reached 1800, with fears it could climb to more than 10 000. The earthquake also triggered a tsunami with up to 7 meter waves slamming Japan’s eastern coast on Friday just 10-30 minutes after the quake, killing hundreds of people as it swept away boats, cars and homes. Seismologists have warned that another massive earthquake with a potential magnitude of 7.9 may strike Japan in the next two days, sparking fresh fears it will trigger another tsunami in the country’s devastated north-east.

The Japanese more commonly use the shindo scale for measuring earthquakes. Shindo refers to the intensity of an earthquake at a given location, i.e. what people actually feel at a given location, while the Richter scale measures the magnitude of an earthquake, i.e. the energy an earthquake releases at the epicenter.

  • Shindo 1: a slight earthquake felt only by people who are not moving.
  • Shindo 2-4: minor earthquakes that do not cause damage.
  • Shindo 5: objects start to fall.
  • Shindo 6: heavier damage occur.
  • Shindo 7: a severe earthquake.

As a result, the measure of the earthquake varies from place to place, and a given quake may be described as “shindo 4 in Tokyo, shindo 3 in Yokohama, shindo 2 in Shizuoka”. Japan experiences approximately 400 earthquakes every day, although the vast majority are shindo scale 0. Friday’s quake was registered as a maximum 7 in Kurihara. Fukushima, Ibaraki and Tochigi registered an upper 6 and Tokyo upper 5.

The earthquake and tsunami combined to knock out the cooling system of the nuclear power plants in Fukushima located 250km northeast of Tokyo. Technicians have been battling to cool the three reactors at the Fukushima Daiichi plant since Friday. Reactor No. 1 exploded on Saturday due to a hydrogen build up and today the same thing happened to reactor No. 3. The primary containment vessels are in both cases said to still be intact but more radioactive steam was released in today’s explosion. A third reactor at the Fukushima Daiichi plant is now said to have lost it’s cooling system and also the Fukushima Daini plant is struggling with the cooling of their four reactors.

All reactors are boiling water reactors which is the second most common type of electricity-generating nuclear reactor. They are cooled down in two ways. The core is cooled down with water in a reactor pressure vessel. This is done by using steam turbines. Heat is produced by nuclear fission in the reactor core, and this causes the cooling water to boil, producing steam that run the cooling system. This cooling system is malfunctioning and it’s still unknown why the cooling water levels drops in some of the reactors. One theory is that the quake bursted some of the pipes.

Secondly the containment chamber, that surrounds the reactor vessel is cooled down by using electric powered cooling systems. But since the regular grid has blackouts in the area and the auxiliary system, a number of diesel generators, is reported to be out of order too the technicians are struggling to reach a cold shut down of the reactors.

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