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Determination of the structure of the Earth's core using normal mode of the Earth

利用地球法线模态确定地核结构

基本信息

批准号：
13640426
负责人：
TSUBOI Seiji
金额：
$ 2.18万
依托单位：
Japan Marine Science and Technology Center (2002)Yokohama City University (2001)
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
2001
资助国家：
日本
起止时间：
2001 至 2002
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-13640426/
关键词：
Normal modes of the Earth Earth's core 核の構造数値計算

项目摘要

We calculate normal modes for the Earth model, which has a slight rigidity layer at the base of the liquid outer core. We show that such a layer with thickness about 40 km and the shear wave velocity of 0.017 km/sec can produce a normal mode, which has a close eigenfrequency to that of liquid core model, without affecting fundamental modes and most of the higher modes. Our results indicate that the thin finite rigidity layer at the base of the outer core might explain the anomalous splitting of the Earth's normal modes, which has not been fully explained by the anisotropy in the inner core. We also have shown that we may interpret that the soft core mode, which appeared at _3S_2 , may arise as a result of coupling between those trapped modes within thin finite rigidity layer at the bottom of the oute core and the ordinary normal modes. For a preparation of confirmation of the existence of this thin finite rigidity layer at the bottom of the outer core by using body wave, we have set up a computer program to calculate synthetic seismic waveform for fully three dimensional Earth model. We use a spectral element method on the Earth Simulator. We use 243 nodes(1944 CPUs) of the Earth simulator and calculate synthetic seismic wave which is accurate up to 5 seconds. This synthetic waveforms consider all of the heterogeneity inside the Earth and its effect to the seismic wave propagation. Thus we should be able to use these waveforms to study fine structure of Earth's core.

我们计算了地球模型的正常模态，它在液体外核的底部有一个轻微的刚性层。结果表明，在厚度约为40 km、横波速度为0.017 km/sec的地层中，可以产生与液核模型特征频率接近的正态模态，且不影响基模态和大部分高阶模态。我们的研究结果表明，外核底部薄的有限刚性层可能解释了地球正常模式的异常分裂，这并不能完全由内核的各向异性解释。我们还表明，我们可以解释在3s_2处出现的软核模态，可能是外核底部薄有限刚性层内的困模与普通正态模态耦合的结果。为了准备利用体波确认外核底部薄的有限刚性层的存在，我们编制了计算全三维地球模型合成地震波的计算机程序。我们在地球模拟器上使用了谱元方法。利用地球模拟器的243个节点（1944个cpu），计算出精确到5秒的合成地震波。该合成波形考虑了地球内部的所有非均质性及其对地震波传播的影响。因此，我们应该能够利用这些波形来研究地核的精细结构。