科學家擔憂日本會發生更多大地震

Significant aftershocks continue to shake Japan, more than two months after the magnitude 9.0 earthquake that triggered massive tsunami, leaving 25,000 people dead or missing and creating a catastrophe at a coastal nuclear power plant.

在日本發生九級大地震兩個多月後，較強的餘震仍時有發生。那場大地震引發了海嘯，造成2萬5000人死亡或失蹤，並導致一座沿海核電站發生核災難。

Five tremors in excess of magnitude 5.0 on the Richter scale have shaken Japan just this week. But scientists are warning that the largest expected aftershock has yet to hit. And, new, devastating inland quakes can also be expected.

僅在這個星期就有五個震級在里氏五級以上的餘震發生。然而，科學家警告說，最大的餘震還尚未發生，而且日本內陸也有可能會發生新的地震。

Japan hopes to never again hear these chilling words. An NHK announcer describing the scene on March 11 as a huge tsunami washes away homes, fishing trawlers and vehicles in coastal communities.

But scientists are cautioning that a repeat for Japan - on a smaller scale - is not a matter of if, but when.

科學家警告說，日本還會再次發生地震，這不過是早晚的問題，只不過規模會相對小一些。

After analyzing the magnitude 9.0 quake, scientists in Japan and the United States are making that sobering conclusion.

日本和美國的科學家在對這場九級大地震進行分析後得出了這樣令人感到警醒的結論。

Several studies indicate the descending Pacific Ocean plate and the overlying plate on which Japan sits, slipped past each other by up to 60 meters. The research indicates five portions of the fault - covering more than 600 kilometers - were ruptured in the quake. That forebodes more seismic activity.

一些研究指出，下沉的太平洋板塊和日本所處的位於上方的板塊相互交錯達60米。研究顯示，斷層中有五個區域在地震中發生斷裂，這些發生斷裂的斷層涵蓋600多公里的地區。這也就預示會有更多地質活動發生。

And, because the March 11 quake seems to have transferred stress along the same fault, some scientists are cautioning about a magnitude 8.0 closer to the Tokyo metropolitan area, home to more than 30 million people.

同時，由於3-11大地震把同一斷層的壓力轉移，一些科學家發出警告，一場8.0級的地震會在更靠近東京大都會的地區發生。東京大都會地區居住着3000多萬人口。

However, others offer a wider geographical target, as far to the north as Hokkaido.

但也有一些專家劃定了一個範圍更大的區域，北側甚至到達北海道。

A frequently cited time frame, by some of Japan’s most senior seismologists, is between now and the next ten months.

日本一些資歷最深的地質學家估計，這場地震發生的時間範圍將是現在到未來10個月之間。

However, professor Takeshi Sagiya at Nagoya University’s Research Center for Seismology, Volcanology and Disaster Mitigation is cautious about that narrow chronology.

不過，名古屋大學地震、火山和減災研究中心的鷺谷威教授對這樣的短期預測持謹慎態度。

"I'm not quite sure about the basis of those specific kind of prediction about aftershocks," said Sagiya. "Those aftershocks happening are quite variable from place to place, from time to time. It can happen with a month, or within days, from the main shock. But also it can happen within some decades."

他說：“我不是很肯定這些有關對餘震發生的具體預測的理論依據。餘震發生的時間和地點都有很大差異。餘震可以在主震發生後的一個月或者幾天之內發生。但也可能會在幾十年之內發生。”

Geophysicist Seth Stein of Northwestern University in the U.S. state of Illinois says the forecast intensity is in line with historical data but, like professor Sagiya, he is more comfortable expressing an extended timeline.

美國西北大學的地球物理學家賽斯.斯坦說，對餘震強度的預測和歷史資料像吻合。與鷺谷威教授一樣，斯坦也認爲餘震會在更長的時間範圍內發生。"They are thinking of the possibility you could have a magnitude eight, which makes sense. The largest aftershocks of an earthquake over the years around the world we've observed tend to be about one magnitude unit less than the main shock, more likely within months, but it could be years."

“他們在考慮發生八級地震的可能性，這也是有道理的。我們所觀測到的世界上地震發生後強度最大的餘震通常要比主震小一級，一般是在幾個月內發生，但也可能是在幾年後。”

Professor Sagiya of Nagoya University says the March 11 quake also “activated” inland faults.

名古屋大學的鷺谷威教授說，3-11大地震還“激活”了內陸的斷層。

"They may be not as large as magnitude eight, but because they occur just beneath our cities, our house, they can be quite disastrous," said Sagiya.

“它們可能不會有八級那麼大，但是因爲地震就在我們城市、房屋下面發生，這些地震將會是災難性的。”

Professor Stein - a former editor of the Journal of Geophysical Research - agrees that as a result of the March 11 temblor - the fourth most powerful ever recorded - the quake risk has increased for Japan, one of the world’s most seismically active places.

西北大學的斯坦認爲，鑑於3-11大地震是有記載以來的第四大地震，日本發生更多地震的危險增加。日本是世界上發生地震最頻繁的國家。

"We sometimes use this analogy of a kid's game called 'booby trap' where you have a bunch of little blocks and there's a spring piston and it pushes on them. And, once you disturb one piece then you increase the possibility that the other pieces are going to be pushed and slip also," said Stein. "So if you think of Japan in that way you can realize that once you've had a huge earthquake of this sort there's a chance that a lot of faults could have smaller earthquakes."

他說，“我們有時候把地震和小孩子們玩的一種叫做‘陷阱’的遊戲做比較。你有一些小磚塊和一個活塞彈簧，彈簧擠着磚塊。如果你推動一塊磚，那麼其它磚塊被擠壓和交錯的機會也就增加了。因此如果你把日本想象成那樣的話，你就會發現在這麼大一場地震發生後，其它斷層上發生很多較小地震的可能性就會存在。”

Seismologists caution the public that their work is still an inexact science. They note improvements for indicating where a big quake approximately will occur, but not when.

地震學家提醒公衆，他們的研究仍然無法十分精確。他們表示，在預測大地震有可能發生的位置方面有了一些進步，但他們仍然不能預測地震發生的時間。

They also acknowledge that this year’s huge magnitude 9.0 was not anticipated, looking at the historical data.

地震學家還承認，通過研究歷史數據他們並沒有預期日本今年會發生這次大地震。

That was also the case with the December 2004 earthquake off western Indonesia, which measured magnitude 9.3.

同樣，2004年12月印度尼西亞以西海域發生的9.3級大地震也沒有被預測到。

That prompted seismologists and geologists to re-examine the world’s subduction zones, areas where oceanic plates slide beneath either a continental plate or another oceanic plate.

這就使地震學家和地質學家重新對世界隱沒帶進行研究。隱沒帶是指一個大洋板塊沉入到一個大陸板塊或另一個大洋板塊而形成的聚合板塊邊緣區域。

Some of the researchers, analyzing fresh data, are now challenging the conventional thinking and willing to state that most, if not all, of the world’s subduction zones (more than a dozen are recognized) are able to generate quakes equal to or exceeding magnitude 9.0.

一些學者通過對新數據的分析後對傳統理論提出挑戰。他們指出，世界上絕大多數隱沒帶都可以產生九級或九級以上的地震。