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首页> 外文期刊>Nature >The Earth's 'hum' is driven by ocean waves over the continental shelves.
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The Earth's 'hum' is driven by ocean waves over the continental shelves.

机译：地球的“嗡嗡声”是由大陆架上的海浪驱动的。

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摘要

Observations show that the seismic normal modes of the Earth at frequencies near 10 mHz are excited at a nearly constant level in the absence of large earthquakes. This background level of excitation has been called the 'hum' of the Earth, and is equivalent to the maximum excitation from a magnitude 5.75 earthquake. Its origin is debated, with most studies attributing the forcing to atmospheric turbulence, analogous to the forcing of solar oscillations by solar turbulence. Some reports also predicted that turbulence might excite the planetary modes of Mars to detectable levels. Recent observations on Earth, however, suggest that the predominant excitation source lies under the oceans. Here I show that turbulence is a very weak source, and instead it is interacting ocean waves over the shallow continental shelves that drive the hum of the Earth. Ocean waves couple into seismic waves through the quadratic nonlinearity of the surface boundary condition, which couples pairs of slowly propagating ocean waves of similar frequency to a high phase velocity component at approximately double the frequency. This is the process by which ocean waves generate the well known 'microseism peak' that dominates the seismic spectrum near 140 mHz (refs 11, 12), but at hum frequencies, the mechanism differs significantly in frequency and depth dependence. A calculation of the coupling between ocean waves and seismic modes reproduces the seismic spectrum observed. Measurements of the temporal correlation between ocean wave data and seismic data have confirmed that ocean waves, rather than atmospheric turbulence, are driving the modes of the Earth.
机译：观测表明，在没有大地震的情况下，接近10 mHz频率的地球地震法线模式几乎以恒定的水平被激发。激发的本底水平被称为地球的“嗡嗡声”，相当于5.75级地震的最大激发。它的起源受到了争论，大多数研究将强迫归因于大气湍流，这类似于太阳湍流对太阳振荡的强迫。一些报告还预测，湍流可能将火星的行星模式激发到可检测的水平。然而，最近对地球的观察表明，主要的激发源位于海洋之下。在这里，我表明湍流是一个非常微弱的来源，相反，它是在驱动地球嗡嗡声的浅大陆架上相互作用的海浪。海浪通过表面边界条件的二次非线性耦合到地震波中，从而使成对的缓慢传播的相似频率的海浪与频率大约为两倍的高相速度分量耦合。这是海浪产生众所周知的“微地震峰”的过程，该峰主导着140 mHz附近的地震频谱（参考文献11、12），但是在嗡嗡声频率下，其机理在频率和深度相关性上有很大不同。对海浪与地震模式之间的耦合进行的计算可再现观察到的地震频谱。对海浪数据和地震数据之间的时间相关性进行的测量已经确认，海浪而不是大气湍流正在驱动地球的模式。

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  • 来源
    《Nature》 |2007年第7129期|P.754-756|共3页
  • 作者

    WebbSC;

  • 作者单位

    Lamont Doherty Earth Observatory, Columbia University, Palisades, New York 10964, USA. scw@ldeo.columbia.edu;

  • 收录信息 美国《科学引文索引》(SCI);美国《工程索引》(EI);美国《生物学医学文摘》(MEDLINE);美国《化学文摘》(CA);
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类 自然科学总论;
  • 关键词

    With frequency; Earthquakes; Ocean brand of sodium chloride nasal; wave;

    机译：有频率;地震;海洋牌氯化钠鼻;波;

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