--The Asahi Shimbun, April 9
EDITORIAL: Japan needs to brace for period of big quakes

Mother Nature is merciless.

It is still less than a month since the Great East Japan Earthquake devastated so many coastal cities and towns in northeastern Japan.

The victims of the massive quake and tsunami are struggling to come to terms with their painful losses and trying to take steps toward rebuilding their shattered lives.

But late Thursday night, the ravaged Tohoku region was rocked by another big quake, which registered an upper 6 on the Japanese intensity scale.

The Thursday quake, centered off Miyagi Prefecture, measured magnitude 7.1. This is a powerful earthquake in its own right, the kind that rarely occurs. But it is an aftershock of the March 11 temblor, which measured magnitude 9.0.

Experts say we should brace for aftershocks of magnitude 7 or so for at least half a year after that mega-quake.

A period of tension and anxiety will continue for a while.

Under such circumstances, what is most important is to ensure people in the disaster areas will not suffer additional damage.

When the Thursday aftershock hit, lighting equipment at a gymnasium in the city of Sendai that is used as an evacuation center shook wildly and made ominous sounds. Some of the evacuees reportedly feared that the equipment could fall on them.

The first thing to do is to take sufficient safety measures at the evacuation centers.

In the quake-stricken areas, various efforts for rebuilding have started. These efforts should be made under the assumption that more big aftershocks could occur.

What is most worrisome is the damage the aftershock has done to nuclear power plants in the region.

An emergency generator was activated at the Higashidori Nuclear Power Station, operated by Tohoku Electric Power Co., after its external power was knocked out by the aftershock.

The company's Onagawa Nuclear Power Station lost two of its three external power systems.

These facts are frightening, given that the ongoing crisis at the Fukushima No. 1 nuclear power plant was triggered by the loss of all power sources.

If external power sources are so vulnerable to earthquakes, all the emergency diesel generators at nuclear power plants must be checked now to see if they will kick in immediately. In addition, power generation vehicles should be readied as a second backup to have multiple fail-safes in place.

The disastrous failure at the Fukushima No. 1 plant must never be repeated again.

Nuclear power plants in the Tohoku region have been shaken repeatedly by the March 11 quake and its aftershocks. We fear that some parts of them may have been weakened. They all should be checked for safety.

A mega-quake that occurs at the boundaries of sea-floor plates, like the one that hit northeastern Japan on March 11, could be followed by another giant quake that is too big to be categorized as an aftershock.

For instance, two years after the 1944 Tonankai earthquake, with an estimated magnitude of 7.9, struck off the city of Owase, Mie Prefecture, the magnitude-8.0 Nankai earthquake took place off nearby Wakayama Prefecture.

The 1854 Ansei Tokai earthquake was followed by the Ansei Nankai earthquake the next day. The two are called twin earthquakes.

A massive movement on the boundaries of plates could also stimulate inland active faults.

We should assume that the Japanese archipelago is now facing a high risk of major seismic events.

Effective measures should be taken to prepare for an earthquake not just in the Tohoku region but also in the rest of the nation.

by kiyoshimat | 2011-04-12 08:26 | 英字新聞

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