Geologist and anti-nuclear power campaigner Kazuro Kawamoto talks to Simon Piggott

Q. Why do earthquakes occur?

A. Apart from its core, most of the Earth is made up of soft rocks. And these rocks are hot. They still retain heat from the birth of the Earth around 4600 million years ago. However, from the Earth’s surface to a depth of about 100 kilometers the rocks have cooled down. This upper layer includes a number of “plates”. The islands of Japan are located at a point where two of the plates, the Pacific plate and the Philippine Sea plate, come into contact with two continental plates, the Eurasian plate and the North American plate. In fact, the Japanese islands came into being as a result of this collision, which pushed up sedimentary rocks from the seabed to form 3000 meter-high mountains.

These plates are still moving. For example, the Ogasawara islands are located on the Philippine Sea plate, and we know that every year they get 3.8 centimeters closer to Honshu. Where the Philippine Sea plate has pushed under the Southwest Japan plate (which is part of the Asian continent) the two plates are meshed tightly together. Meanwhile, tension continues to build. When the strain becomes too great sudden movement at the interface of the two plates occurs. This is an earthquake, and the amount of energy released is expressed numerically in the earthquake’s magnitude.

Do earthquakes happen at regular intervals?

In Japan they do. For example, a Tokai earthquake resulting from plate movements under Suruga Bay and Shizuoka Prefecture

will occur every 100 to 150 years. Nankai earthquakes, which are centered off the coast of Shikoku, have a cycle of the same sort. Actually the two are related. In 1707 and 1854 Tokai and Nankai earthquakes occurred almost simultaneously.

Can we expect a large earthquake in the Tokai region in the near future?

Yes. The last major Tokai quake was in 1854. The one before that was in 1707. That’s an interval of 147 years. So the next one is due.
How easy is it to predict exactly when an earthquake will strike?

This is much more difficult. For example, in the Tokai region a major quake is expected to be directly preceded by sudden fluctuations in the level of Omaezaki cape. The Japan Meteorological Agency has bored holes in this area to detect any sudden rock deformations that occur at the very beginning of the quake. In all probability there will be a few hours warning. But there is no guarantee.

What power of quake and what sort of damage can be expected?

The latest predictions, in 2001, were for a magnitude-8. This is ten times greater than the earthquake in Kobe in 1995.
According to the Japan Meteorological Agency, in many places the seismic intensity will be at the top of its scale of 7 (equivalent to XII on the international Mercalli Scale).

A quake’s “intensity” indicates the actual movement of the ground. According to JMA, an intensity-7 quake will destroy at least 30 per cent of all buildings. In Kobe only a very small area experienced such an intensity, with catastrophic results. In the Tokai earthquake it will be much larger. Wide areas of newer sedimental strata between Mishima and Hamanako lake could receive intensity-7 shocks. Projections are for 5,900 deaths and 19,000 injuries in Shizuoka Prefecture. However, these calculations were made before the latest predictions, which suggest more deaths and injuries in the western part of the prefecture.

What is the scale of damage outside Shizuoka likely to be?

The official figures envisage 1010 deaths in Kanagawa, 344 in Yamanashi, 211 in Gifu, 95 in Aichi and 71 in Nagano. I feel that the figure for Aichi is rather conservative. The new predictions show the city of Nagoya experiencing an intensity-6 shock, which will cause weak wooden buildings to collapse.
However, the greatest worry is the safety of the nuclear power plant at Hamaoka, which is located in a part of Shizuoka with considerable seismic crustal deformation. Here the land could rise 1-2 meters in little more than a minute. Hamaoka is a large plant with four reactors (and an additional one under construction). If any one of these reactors suffers a meltdown as a result of damage incurred during the quake it may lead to thousands of radiation-related deaths.

But surely the danger of a major earthquake was taken into account in the planning and construction of the plant?

The construction of the first two reactors, which went into operation in 1976 and 1978, did not take into consideration the high risk of their location. They were designed to resist only a 450-gal acceleration level in the intensity of the impact. It was not until 1976 that a detailed model for the coming Tokai earthquake was made — with resultant and widespread public concern. This was followed in 1978 by a law requiring the implementation of an earthquake observation system. Consequently, a new resistance level of 600 gal was established for reactors 3 and 4, as well as for reactor 5, now being constructed. However, in Kobe in 1995 a level of 800 gal was recorded in some places. For Tokai, the authorities’ estimation of the intensity derives from a simplified model based on a premise that all of an earthquake’s energy will emanate from the central point of the earthquake fault plane. This point is set at a distance away from Hamaoka. But, here there are two problems: first, there could be a considerable underestimation of the impact on Hamaoka, which is located on a big earthquake fault. And second, they haven’t taken into account the possibility of the earthquake being much more complex in nature.
No nuclear reactor anywhere in the world has ever experienced such as powerful earthquake as we expect to strike Hamaoka in the near future. So the situation is extremely worrying.

Won’t the reactors shutdown automatically in an earthquake?

In the case of Hamaoka there is an automatic shutdown mechanism when the shock exceeds a certain level. However, after shutdown it requires a number of days for the reactor core to cool. If the earthquake destroys the normal and emergency cooling systems, meltdown is unavoidable. Reactors 1 and 2 are nearing their life expectancy of 30 years and have lately suffered several malfunctions. This makes us even more anxious. In fact, operations at both reactors have been suspended since November 2001 due to the hydrogen explosion of a pipe connected to the emergency core cooling system of reactor 1. At the moment a campaign is being conducted by a citizens’ groups to prevent the two problematic reactors from being put back into service and to halt the operation of reactors 3 and 4 until after the expected earthquake has occurred. Legal proceedings are being taken.

In the worst case, if an earthquake did cause one of the Hamaoka reactors to explode what would happen?

In a large-scale steam explosion resulting from a meltdown, around 20 per cent of the radioactive material in the reactor would be released into the environment. It would be approximately the same amount as that of the Chernobyl disaster in 1986. With average winds, the radiation would take two hours to reach Shizuoka and Hamamatsu, five hours to Nagoya and seven hours to Tokyo.

In such a situation how should one react?

You must remember that serious damage from the earthquake will have put out public transport and caused enormous traffic jams. So it will probably be impossible to escape from the radiation area. Anyway, first, check the direction and speed of the wind (the prevalent wind direction at Hamaoka is eastward towards Tokyo, but on one out of four days there will be a west wind blowing towards Nagoya). On a fine day the radiation will be spread over a wider area. On a cloudy day it will stay lower. If it’s raining stay out of the rain!

Radioactive particles can be inhaled from the air. If you think that you have been exposed, remove your clothing and wash your body. Short-life, high-level radioactive isotopes cause acute radiation disease. Also, remember that children are at high risk from radioactive iodine, which causes thyroid cancer. Since the body absorbs iodine from the atmosphere, as well as from drinks and food, it would be useful to have an emergency supply to cover the crucial first several weeks (the first tablet must be taken before exposure). Radioactive iodine has a relatively short half-life of 8 days. This means that its power decreases by half every 8 days--down to 50 per cent after the first 8 days, to 25 per cent after 16 days, and so on. Local government offices within 8 kilometers of nuclear plants have free supplies of iodine tablets to distribute to citizens, but distribution will be almost impossible. No other towns have any such contingency plans.

Over a wide area locally produced vegetables, meat, milk and other fresh foods will be polluted, so avoid them. Water supplies may also be affected.

It’s an apocalypse scenario. But, although the earthquake itself is unavoidable, the authorities can certainly avoid the concomitant Chernobyl-style disaster by taking the decision to suspend operations at Hamaoka. As citizens and residents of this country, each of us possesses the freedom and right to encourage them to do so.

Kazuro Kawamoto is curator of the award-winning Median Tectonic Line Museum in Oshika, Nagano. The museum, which is open Tues-Sun 9:30-16:30, is about 3 hours by car from Nagoya. Tel. 0265-39-2205 (Japanese or English).

Photo captions:
Kazuro Kawamoto