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地球内核相对于地幔差动旋转的第一个证据,来自地核震相差异走时异常30年变化的观测(Song and Richards,1996.地球内核差异旋转的地震学证据。Nature,382:221～224)。成双的远震的对照比较,对于测量这种差异走时以及检验它们的时间变化,提供了一种强有力的手段。与直接测量差异走时的方法不同,这一技术不需要有准确的地震定位。这一方法首先在认为无差异走时的成双的远震的例子中受到检验。这些检验使我们得以指出双远震方法在应用中可能遇到的困难,如极性反转。之后又在法国记录的汤加深震和阿拉斯加科利奇站(COL)记录的南桑德威奇群岛地震应用了这一方法。以上地震使Song和Richards提出了内核旋转的观点。对第一条路径我们没有发现时间的变化,这与以前的研究一致。对于南桑德威奇岛至科利奇的路径,成双的地震分析表明:在这一方法的分辨率内(大约0.05s)不能检测到PKP走时的显著时间变化。Song和Richards观测的残差变化是30年约0.3s,这在很大程度上可能归于震源的定位误差。因此,当前的地震学观测没有检测到内核的差异旋转,这是因为如果有差异,也小于目前地震学的检测能力,即小于0.2°/a。
The first evidence of differential rotation of the earth’s core relative to the mantle is derived from the observation of a 30-year change in the travel time of the Earth’s core phase difference (Song and Richards, 1996. Seismological evidence of differential rotation of the Earth’s core. Nature, 382: 221-224 ). A comparison of pairs of teleseismic comparisons provides a powerful tool for measuring this difference in travel time and examining their time variations. Unlike the method of directly measuring the difference travel time, this technique does not require accurate seismic location. This method is first examined in the case of the twin telekinesses that see no difference in travel time. These tests allow us to point out the difficulties that may be encountered in the application of the teleseismic method, such as polarity reversal. This method was then applied to the South Sandwich Islands earthquake recorded by France in the Tonga and Earthquakes stations of Alaska (COL). The above earthquake caused Song and Richards to propose a kernel rotation perspective. We did not find any time change for the first path, which is consistent with previous studies. For the South Sandwich Island-Kolichi route, a double seismic analysis shows that within the resolution of this method (about 0.05 s) no significant temporal changes in PKP travel can be detected. The residual variation observed by Song and Richards is about 0.3 s over a 30-year period, which is probably due in large part to the positioning error of the source. Therefore, the current seismological observations do not detect a differential rotation of the kernel because, if there is a difference, it is less than the current seismological detection capability, ie less than 0.2 ° / a.