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　　背景知识

　　海啸，是由海底地震、火山爆发、海底滑坡或气象变化所产生的破坏性海浪，海啸的波速高达每小时700~800千米，在几小时内就能横过大洋；波长可达数百公里，可以传播几千公里而能量损失很小。

　　在茫茫的大洋里波高不足一米，但当到达海岸浅水地带时，波长减短而波高急剧增大，可达数十米，形成含有巨大能量的“水墙”。海啸主要受海底地形、海岸线几何形状及波浪特性的控制，呼啸的海浪冰墙每隔数分钟或数十分钟就重复一次，摧毁堤岸，淹没陆地，夺走生命财产，破坏力极大。

　　全球的海啸发生区大致与地震带一致。全球有记载的破坏性海啸大约有260次左右，平均大约六、七年发生一次，发生在环太平洋地区的地震海啸就占了约80%。而日本列岛及附近海域的地震又占太平洋地震海啸的60%左右，日本是全球发生地震海啸并且受害最深的国家。

　　正文阅读

　　A mega-tsunami in the Pacific north-west?

　　太平洋西北部发生特大海啸？

　　Scientists have long predicted a giant 9.0-magnitude earthquake that reverberates out from the Pacific north-west’s Cascadia fault and quickly triggers colossal waves barreling to shore. But what if these predictions were missing an important piece of information – one that, in certain scenarios, could tell an even more extreme story?

　　科学家们早就预测，太平洋西北部卡斯卡迪亚断层会引发一场9.0级地震，并导致巨浪迅速冲向海岸。但是，万一这些预测漏掉了一条重要信息呢？在某些情况下，这样一条重要信息可能会说明一个更严重的问题。

　　A new study, published last month in the peer-reviewed journal Earth-Science Reviews, points toward such a missing piece. Researchers revealed a previously unknown relationship between the severity of a tsunami triggered by an earthquake and something known as “the outer wedge”, the area between the main earthquake fault and the seafloor. Sylvain Barbot, a co-author of the study, described the outer wedge as the “garbage bag of subduction zones”, the place where two tectonic plates crash into each other and can produce an earthquake, because it’s where sediment piles up.

　　上个月发表在同行评议期刊《地球科学评论》上的一项新研究指出了这一遗漏信息。研究人员透露了此前由地震引发的海啸其严重程度与所谓的“外楔”（地震断层和海底之间的区域）之间的未知关系。这项研究的合著作者西尔万·巴伯特（Sylvain Barbot）将外楔描述为“俯冲带的垃圾袋”，因为这里是沉积物堆积的地方。两个构造板块在这里相互碰撞，从而发生地震。

　　The researchers’ findings suggest that the wider it is, the larger the maximum size of the tsunami will be. The connection adds a new element to consider when making tsunami predictions, one that the authors suggest could mean heightened worst-case scenario predictions for some faults, including Cascadia. “There are places where [the outer wedge is] tiny, so great news,” said Barbot, an associate professor in earth science at the University of Southern California. “And there are places where it’s huge. And that’s the case in the Pacific north-west.”

　　研究人员的发现表明，外楔越宽，海啸的最大规模就越大。在预测海啸时，这种关联增加了需要考虑的一个新因素，作者认为这可能意味着为一些断层（包括卡斯卡迪亚断层）的最糟情况提供更精准的预测。南加州大学地球科学副教授Barbot表示:“有些地方的（外楔）很小，这是好事。而有些地方（的外楔）是巨大的。太平洋西北部就是个例子。”

　　今日单词