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这种被追踪的信号与我们日常所遇到的地震学并不相同;冰川的滑动与地壳的滑动起因不同,动态相异,并且如果有人执意聆听,发出的声音也有所差别。虽然大型地震能使远处构造活动区颤抖,但是地震与冰震被认为是不相干的活动。但是这周一篇发表于自然地球科学(Nature GeoScience)上的文章首次将两者联系起来。

THE title of glacial seismologist is, relatively speaking, a new one in science. It took until the early 1950s for scientists at Baffin Island in Canada to report “icequakes”, the sudden movement of ice and frozen, saturated earth. The field has grown considerably as both interest and instrumentation have progressed, and scientists are now accustomed to listening intently to the groaning and creaking of ice sheets in frozen regions around the globe.

But the pursuit has been considered inherently separate from seismology as we normally think of it; the slippage of ice sheets and that of slabs of the Earth’s crust arise from different causes, follow different dynamics and, for those who go to the trouble to listen, make different sounds. While a large earthquake can trigger tremors in distant, tectonically active regions, earthquakes and icequakes have been considered unconnected events. But this week saw the publication, in a paper in Nature Geoscience, of the first evidence linking the two.

Zhigang Peng, a seismologist at the Georgia Institute of Technology in America, and colleagues noticed that glacial calving—the falling of large chunks of ice from the end of a glacier into the sea—can be triggered by earthquakes that originate thousands of kilometres away. The tsunamis created by such quakes tug on icesheets, inciting ruptures and fractures.

But Dr Peng wondered whether remote earthquakes could trigger icequakes farther inland in Antarctica. To be sure, seismic activity is not uncommon in Antarctica; ice formation, too, triggers icequakes of smaller intensity. But the team was looking for something more substantial. They chose to examine data around the time of the 2010 earthquake in Chile—among the strongest on record, and not too distant from Antarctica. They suspected that only so-called surface waves, which travel along the Earth’s surface rather than through its bulk, could trigger icequakes. Such waves travel at a known speed and have characteristic frequencies, so the team knew what to look for and when.

On analysing the data from 42 Antarctic seismographs, they found 12 clear signals that marked the occurrence of icequakes within six hours of the Chilean quake, leaving little doubt as to the cause. Relatively speaking, the icequakes were minuscule. But as Kate Allstadt, an icequake specialist at the University of Washington, puts it, “things we think of as strong, like glaciers, can still react to them if the conditions are right'. Dr Allstadt has found that the annual load of snow on Washington’s Mt Ranier is enough to trigger thousands of icequakes each year.

Understanding these delicate mechanisms as they play out in Antarctica is critical because the vast majority of the planet's ice is trapped there. The movement and eventual loss of glaciers at the Earth’s poles will have a tremendous global impact; the collapse of the Western Antarctic Ice Sheet, which has arguably论文英语论文网提供整理,提供论文代写英语论文代写代写论文代写英语论文代写留学生论文代写英文论文留学生论文代写相关核心关键词搜索。

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