GRE课外阅读材料补充 你知道吗?岛屿可能会增强海啸势力

Islands may amplify the biggest waves, not break them.SURFERS shun beaches shielded by islands off the coast.That, as generations of swarthy, golden-haired hulks will tell you, is because such islands create a natural breakwater.This dampens waves and makes for a boringly calm surf best left to sunbathers.The surfers’ reasoning is sound for the short-wave, wind-generated swells that they ride.

岛屿可能会增强海啸，而不会减弱海啸冲浪者不会去海中的岛屿的沙滩上去冲浪。一代又一代的金发肤色黝黑的冲浪者会告诉你，那是因为这类小岛形成天然的防波堤。这类岛屿的沙滩海浪较小，海面很平静，最适合晒日光浴的人了。较短、由风产生浪比较适合冲浪，对于这种浪来说，这种解释很合理。

But Themistoklis Stefanakis, of the Ecole Normale Superieure in Cachan, France, warns it may not be true for the longer wavelengths of tsunamis.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.Anecdotal evidence for this counterintuitive assertion comes from episodes where the same tsunami has battered different types of coastal topography.

但是，来自法国卡尚高等师范学校Themistoklis Stefanakis警告说，对于波浪较长的海啸来说，就不一样了。如Themistoklis Stefanakis跟他的同事在线数据库arXiv发表的文章中所描述的的那样：实际上沿海的岛屿可能会增强长波浪的强度，而不是减弱。这种违反直觉的判断的轶事证据来自很少见的现象—同一海啸会造成不同的海岸地貌。

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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.Dr Synolakis, Mr Stefanakis and their colleagues decided to try to put numbers on their hunch.Rather than valiantly staking out seafront locales, though, they tested the idea with a computer model.

例如，2010年印度尼西亚明达威岛遭遇的海啸，明达威岛后的海岸区域的破坏的最为严重，南加州大学的海啸专家Costas Synolakis这样说道，他是这篇文章的作者之一。博士Synolakis Mr Stefanakis及他们的同事，决定验证这个设想。他们想到用电脑模拟的方法来实验，而不是在海岸实验。

This is harder than it sounds.Simulating the way waves behave as they make landfall means taking account of, literally, oceans of data.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.

实际做起来要比听起来难很多。要模拟当海浪到大陆地时海浪的运动就意味着要严格地考虑到海洋的信息。为了简化问题，在带有海滩的笔直虚拟海岸线可平滑上升的情况下，研究人员观察当模拟的的海浪在平滑的斜海床上与锥形岛屿相遇时，会发生什么。

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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.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.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.

电脑在处理这类问题时，这种近似可以忽略，然而这跟之前认为得减弱海浪的结论已经很相似了.研究组将模拟的岛屿拉高到海平面100米的位置,许多岛屿超出海平面也就是100米。他们将岛屿、海床、沙滩的外围的倾斜度，岛屿和沙滩的距离，海啸的波长做了200种组合来实验观察。

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%.The upshot is that, far from shielding a coastline, offshore islands can make things worse—information that should be incorporated into tsunami evacuation plans.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.

没有一类能有助于减弱海啸。实际上，它好比一个透镜，将海浪的破坏力聚集起来，并且扩大5%-70%。结果是。沿海的岛屿不会保护海岸区域不受破坏，反而会让其更糟。这在海啸救援中应当将其考虑在内。如果海啸来临，跑是不够的。还应该知道跑多远才是安全的。

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