Ｍ７級余震―揺れても守れる態勢を

2011/04/10
--The Asahi Shimbun, April 9
EDITORIAL: Japan needs to brace for period of big quakes
Ｍ７級余震―揺れても守れる態勢を

Mother Nature is merciless.
　無情というほかない。

It is still less than a month since the Great East Japan Earthquake devastated so many coastal cities and towns in northeastern Japan.
　東日本大震災からまだひと月もたたない。

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.
人々が喪失と向き合い、生活を取り戻すために動きだそうというときである。

But late Thursday night, the ravaged Tohoku region was rocked by another big quake, which registered an upper 6 on the Japanese intensity scale.
深夜の東北地方を、最大震度６強の揺れが襲った。

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.
　震源は宮城県沖でマグニチュード（Ｍ）７．１。それだけでもめったにない大地震だが、Ｍ９だった３月１１日の本震の余震だという。

Experts say we should brace for aftershocks of magnitude 7 or so for at least half a year after that mega-quake.
　Ｍ９の地震後、少なくとも半年はＭ７級の余震を覚悟する必要があるという専門家の指摘もある。

A period of tension and anxiety will continue for a while.
まだまだ気をやすめることができない状態が続く。

Under such circumstances, what is most important is to ensure people in the disaster areas will not suffer additional damage.
　こうしたなかで、なによりも気を配るべきは、被災地の人々が二重、三重の被害に遭わないようにすることだ。

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.
　余震がきたとき、仙台市内の体育館では、照明が音を立てて揺れ「落ちてきそうで怖かった」と感じる住民がいたという。被災者がどれほど揺れにおびえているかがわかる。

The first thing to do is to take sufficient safety measures at the evacuation centers.
避難所の安全策にまず心を用いたい。

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.
　被災地では、復興に向けたさまざまな作業が始まっている。これらの仕事も、大きな余震が今後も起こる可能性を織り込みながら進めてほしい。

What is most worrisome is the damage the aftershock has done to nuclear power plants in the region.
　一方、最も気がかりなのは原子力発電所である。

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.
　この余震で、東北電力の東通原発では外部電源が切れて、非常用発電機を動かすことになった。

The company's Onagawa Nuclear Power Station lost two of its three external power systems.
女川原発でも一部の外部電源しか使えなくなった。

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.
福島第一原発の事故のきっかけが電源喪失だったことを思い返すと、背筋が寒くなる。

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.
　外部電源がこれほどもろいなら、非常用発電機がすぐ働くかどうかを改めて確かめ、それもだめなときは電源車を使うという多重の態勢を万全にする必要がある。

The disastrous failure at the Fukushima No. 1 plant must never be repeated again.
　「福島第一」の失敗を、絶対に再現してはならない。

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.
　東北地方の原発は、本震や余震で何度も揺すられてきた。弱くなっているところがないか心配だ。点検を急ぐべきだ。

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.
　３月１１日の本震のように海底のプレート（岩板）境界で起こる巨大地震は、余震の域を超えた大地震も伴うことがある。

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.
　たとえば、１９４４年の東南海地震の２年後には南海地震が起こっている。

The 1854 Ansei Tokai earthquake was followed by the Ansei Nankai earthquake the next day. The two are called twin earthquakes.
１８５４年には安政東海地震の翌日に安政南海地震が続いた。双子地震と呼ばれる。

A massive movement on the boundaries of plates could also stimulate inland active faults.
　さらに、プレート境界の大きな動きが影響して、内陸の活断層が刺激されることもある。

We should assume that the Japanese archipelago is now facing a high risk of major seismic events.
　日本列島は今、地震リスクが高いとみるべきだろう。

Effective measures should be taken to prepare for an earthquake not just in the Tohoku region but also in the rest of the nation.
東北だけでなく全国で、地震への備えを強めたい。