Coseismic Excitation of the Earth's Polar Motion
Coseismic Excitation of the Earth's Polar Motion
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DOI：
10.1017/s0252921100061492
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发表时间：
2000
期刊：
影响因子：
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通讯作者：
B. Chao;R. Gross
中科院分区：
文献类型：
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作者：
B. Chao;R. Gross
除了震中附近的地震外，地震事件还会在整个地球上造成永久的位移场。质量的这种重新分配改变了地球的惯性张量(略微)；地球的自转将根据角动量守恒而改变。与地球自转变化的地震激发类似，相同的质量重新分布导致地球引力场(可用其调和展开的斯托克斯系数的变化来表示)发生(轻微)变化。本文介绍了这一课题的历史背景，讨论了相关的物理问题，并基于简正波求和格式计算了地震引起的地球动力学效应。根据哈佛大学质心矩张量目录提供的1977年1月至1999年2月期间15,814次大地震的质心矩张量(CMT)解来计算其影响。计算结果进一步加强了这些发现和结论：(I)地震使地球变得更圆和更紧凑(尽管略有)的强烈趋势仍在继续；(Ii)地震使自转极朝着大致约的方向“轻推”的趋势也是如此。140 E，与观测到的极地漂移大致相反，但漂移速度小两个数量级。
Apart from the "shaking" near the epicenter that is the earthquake, a seismic event creates a permanent field of dislocation in the entire Earth. This redistribution of mass changes (slightly) the Earth's inertia tensor; and the Earth's rotation will change in accordance with the conservation of angular momentum. Similar to this seismic excitation of Earth rotation variations, the same mass redistribution causes (slight) changes in the Earth's gravitational field expressible in terms of changes in the Stokes coefficients of its harmonic expansion. In this paper, we give a historical background of the subject and discuss the related physics; we then compute the geodynamic effects caused by earthquakes based on normal-mode summation scheme. The effects are computed using the centroid moment tensor (CMT) solutions for 15,814 major earthquakes from Jan., 1977, through Feb., 1999, as provided in the Harvard CMT catalog. The computational results further strengthens these findings and conclusions: (i) the strong tendency for earthquakes to make the Earth rounder and more compact (however slightly) continues; (ii) so does the trend in the seismic "nudging" of the rotation pole toward the general direction of approx. 140 E, roughly opposite to that of the observed polar drift, but two orders of magnitude smaller in drift speed.