評論
打印
Science and technology
科學技術
Modelling tsunamis
模擬海嘯
The dangers of insularity
島國的危險
Islands may amplify the biggest waves, not break them
島嶼可能會增強海嘯，而不會減弱海嘯
SURFERS shun beaches shielded by islands off the coast.
沖浪者不會去海中的島嶼的沙灘上去沖浪。
That, as generations of swarthy, golden-haired hulks will tell you, is because such islands create a natural breakwater.
一代又一代的金發膚色黝黑的沖浪者會告訴你，那是因為這類小島形成天然的防波堤。
This dampens waves and makes for a boringly calm surf best left to sunbathers.
這類島嶼的沙灘海浪較小，海面很平靜，最適合曬日光浴的人了。
The surfers’ reasoning is sound for the short-wave, wind-generated swells that they ride.
較短、由風產生浪比較適合沖浪，對于這種浪來說，這種解釋很合理。
But Themistoklis Stefanakis, of the Ecole Normale Superieure in Cachan, France, warns it may not be true for the longer wavelengths of tsunamis.
但是，來自法國卡尚高等師范學校Themistoklis Stefanakis警告說，對于波浪較長的海嘯來說，就不一樣了。
As he and his colleagues show in a paper posted on arXiv, an online repository, littoral islands may actually exacerbate, rather than diminish, the effects of these waves.
如Themistoklis Stefanakis跟他的同事在線數據庫arXiv發表的文章中所描述的的那樣：實際上沿海的島嶼可能會增強長波浪的強度，而不是減弱。
Anecdotal evidence for this counterintuitive assertion comes from episodes where the same tsunami has battered different types of coastal topography.
這種違反直覺的判斷的軼事證據來自很少見的現象—同一海嘯會造成不同的海岸地貌。
In 2010, for instance, when one hit the Mentawai islands in Indonesia, areas of coastline directly behind islets bore the brunt of the damage, according to Costas Synolakis, a tsunami expert at the University of Southern California who is one of the study’s co-authors.
例如，2010年印度尼西亞明達威島遭遇的海嘯，明達威島后的海岸區域的破壞的最為嚴重，南加州大學的海嘯專家Costas Synolakis這樣說道，他是這篇文章的作者之一。
Dr Synolakis, Mr Stefanakis and their colleagues decided to try to put numbers on their hunch.
博士Synolakis Mr Stefanakis及他們的同事，決定驗證這個設想。
Rather than valiantly staking out seafront locales, though, they tested the idea with a computer model.
他們想到用電腦模擬的方法來實驗，而不是在海岸實驗。
This is harder than it sounds.
實際做起來要比聽起來難很多。
Simulating the way waves behave as they make landfall means taking account of, literally, oceans of data.
要模擬當海浪到大陸地時海浪的運動就意味著要嚴格地考慮到海洋的信息。
To simplify the problem, the researchers looked at what happens when a computerised wave encounters a cone-shaped island on a smoothly sloping seabed in front of a straight cyber-coastline with a beach that continues to rise smoothly as it progresses inland.
為了簡化問題，在帶有海灘的筆直虛擬海岸線可平滑上升的情況下，研究人員觀察當模擬的的海浪在平滑的斜海床上與錐形島嶼相遇時，會發生什么。
These approximations allow a computer to cope with the problem, yet are sufficiently similar to many real places for the conclusions drawn from them to, as it were, hold water.
電腦在處理這類問題時，這種近似可以忽略，然而這跟之前認為得減弱海浪的結論已經很相似了.
The team made their virtual islet jut out of the ocean to an altitude of 100 metres, a typical height above sea level for such outcrops.
研究組將模擬的島嶼拉高到海平面100米的位置,許多島嶼超出海平面也就是100米。
They then looked at 200 combinations of gradients for the sides of the island, the seabed and the beach; the distance between the island and the beach; and the wavelength of the encroaching tsunami.
他們將島嶼、海床、沙灘的外圍的傾斜度，島嶼和沙灘的距離，海嘯的波長做了200種組合來實驗觀察。
In none of these did an island offer any succour to the coastline behind it. Instead, it acted as a lens, focusing the wave’s destructive power and amplifying its size by between 5% and 70%.
沒有一類能有助于減弱海嘯。實際上，它好比一個透鏡，將海浪的破壞力聚集起來，并且擴大5%-70%。
The upshot is that, far from shielding a coastline, offshore islands can make things worse—information that should be incorporated into tsunami evacuation plans.
結果是。沿海的島嶼不會保護海岸區域不受破壞，反而會讓其更糟。這在海嘯救援中應當將其考慮在內。
For if a big wave is coming, running from it is not enough. You also have to know how far to run before it is safe to stop.
如果海嘯來臨，跑是不夠的。還應該知道跑多遠才是安全的。
