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Science and technology
科學技術
Seismology and tsunamis
地震學與海嘯
Making waves
掀起新浪潮
A better tsunami-prediction system is now under development
更精準的海嘯預測系統現已在開發中
Next time, they might see it coming
下次海嘯來襲時，人們可提前準備
GEOLOGISTS have long known that some marine earthquakes generate fierce tsunamis and some do not.
地質學家們早已知道有的海洋地震會引起強烈海嘯，而有的則不會。
But, as the situation in Japan makes painfully clear, there is no good way for people being tossed around by a tremor to know the difference until a wave arrives.
但是，日本的慘痛教訓告訴我們，被地震震得驚慌失控的人們根本意識不到一場海嘯即將到來。
A new earthquake-monitoring system developed by Andrew Newman and Jaime Convers at the Georgia Institute of Technology may, however, help to change that.
而現在，由喬治亞理工學院的安德魯?紐曼與亞伊梅?康弗斯共同研發的最新地震監測系統有望改變現狀。
During an earthquake, the Earth's crust is uplifted.
地震時，地殼板塊隆升。
If the epicentre is on the seabed, that also lifts the water above the bed, creating a wave.
如果震中位于海底，板塊運動帶動上方海水起伏，形成波浪。
However, the size of this wave varies with the nature of the uplift.
波浪大小因板塊隆升性質而定。
For tsunami-generating purposes, earthquakes can generally be divided into two sorts.
按照是否引發海嘯，地震可分兩類。
Deep ones generate small or non-existent tsunamis because their uplifting effects are absorbed by the overburden.
一是深震，隆升通常被表層所吸收，因此不引發海嘯或只引發小型海嘯。
Shallow ones, whose full crust-displacing force is felt at the surface, are the danger.
二是淺震，由于地表震感強烈，因此也更危險。
The problem is deciding which is which.
當前的問題是如何區分這兩者。
Once all the data are in, an earthquake's depth can be worked out with reasonable accuracy.
只要有全面的數據，則可較精準地測算地震的深度。
But that takes time.
然而，這一過程需花費一定時間。
The recent Japanese quake, for example, was thought initially to have happened 83km down.
例如，近期日本地震最初深度測算為地下83km，
The latest measurements suggests its depth was actually 30km.
而最近的一次測算結果卻顯示，深度實為30km。
Normally, that would still put it in the class of safe earthquakes, but it was so powerful that the usual rules did not apply.
通常來說，30km仍可劃入安全等級。但此次地震能量巨大，以往的經驗概不管用。
The secret of the new method is that depth changes an earthquake's character in ways other than just its tsunami-generating propensity.
新系統的秘密在于地震深度對地震性質的改變不僅僅停留在是否引發海嘯的問題上。
The rupture in the rock that causes a deep earthquake propagates rapidly—at about 3km a second.
巖層斷裂引發深震傳播速度很快—大約3km/秒。
A shallow rupture moves more slowly: 1?km a second is common.
而淺震傳播速度較慢：一般約1.5km/秒。
The speed seems related to the rigidity of the rock that is rupturing, and deep rock, which is under more pressure, is more rigid.
速度可能與斷裂巖層的堅硬程度有關，深層巖體受壓力更大，也更堅硬。
Shallow rocks bend, and that slows the rupture down.
淺層巖體有韌度，可減緩斷裂。
The effect is to give seismologists a tool they can use to make an instant estimate of an earthquake's depth and thus, if it is submarine, the risk of its creating a big tsunami.
地震學家可據此迅速估算地震深度，如果是海洋地震，還能估算地震是否引發強烈海嘯。
The system Dr Newman and Mr Convers have developed taps into hundreds of seismic monitoring stations around the world.
紐曼博士與康弗斯先生研發的新系統接入了世界各地幾百所地震監測站。
When an earthquake is detected, the software immediately looks at the size of the tremor and the location of its epicentre.
當檢測到地震時，該系統軟件立即測算地震規模與震中位置。
If the quake's magnitude is greater than 6.5 and the epicentre is underwater, it then requests information from the relevant stations on how long the earthquake took from beginning to end.
如果級數超過6.5級且震中位于水下，系統則要求相關監測站報送地震全程持續時間。
That allows it to work out how quickly energy was released by the earthquake, and thus how fast the rupture propagated.
這一信息可幫助計算地震能量釋放速度，并以此計算巖層斷裂速度。
An energy-release rate indicating a rupture rate of 1?km a second or less sets the alarm bells ringing, for the earthquake has probably spawned a tsunami.
巖層斷裂速度達1.5km/秒以下的能量釋放速度將會拉響警報，而這時極有可能引發海嘯。
though the system is also sensitive to the actual earthquake magnitude, and adjusts accordingly, so it did not miss the tsunami-creating potential of the Japanese earthquake either.
盡管如此，該系統也能檢測出地震級數并作出相應調整，因此也檢測出了日本地震會引發海嘯的風險。
The two researchers tried their invention out last year and analysed a great many quakes, including one of magnitude 7.8 that happened on October 25th in western Indonesia.
兩位研究者去年對該發明進行了測試，用以分析了許多地震，包括去年10月25日印尼西部發生的里氏7.8級地震。
The epicentre was 70km from the Mentawai islands, and the quake was felt there only weakly.
震中位于距民大威群島70km處，島上只有輕微震感。
But it still raised a devastating tsunami that killed more than 400 islanders.
但是，地震隨后引發了一次破壞力極強的海嘯，導致400多位島民死亡。
The system quickly detected this quake and the two researchers reported recently in Geophysical Research Letters that it automatically identified the tsunami threat 8? minutes after the earthquake began.
該系統迅速檢測到印尼地震，兩位研究者近期在向《地理物理研究快報》的報告中指出，系統在地震開始后8.5分鐘自動檢測到震后海嘯威脅。
It then ran a series of checks, and after 16? minutes was completely certain that conditions were right for a tsunami to form.
隨后，系統啟動了一系列檢查程序，震后16.5分鐘便完全確定海嘯即將發生。
Since it took 35 minutes for the tsunami to come ashore, the system could, had it been used to sound the alarm, have given people 18? minutes to flee.
因為海嘯將在震后35分鐘后到達，如果使用該系統發出警報，則為人們贏得了18.5分鐘寶貴的逃生時間。
Unfortunately, it was not then attached to any sort of alarm that could let the Mentawai islanders know that they were in danger.
不幸的是，該系統當時還未與警報系統結合，因此無法及時通知民大威群島島民海嘯險情。
With luck, such a lack of warning will not happen again.
而幸運的是，缺乏警報機制的這種情況以后不會再有了。
By the summer the system should be hooked up to alarms around the world, and will be able to determine tsunami risk within seven minutes of a shock being detected.
今年夏天之前，該系統將會與全世界警報系統相連接，并將會在檢測到地震后7分鐘內確定海嘯發生的概率。
It will then be up to local authorities to have evacuation plans in place.
隨后則由地方政府開展撤離計劃。
But they will no longer be able to say they did not see it coming.
到那時，政府便不可能再推脫說不知道海嘯會來了。
