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Inversion of Paleomagnetic Data

古地磁数据反演

基本信息

批准号：
10440124
负责人：
KONO Masaru
金额：
$ 4.93万
依托单位：
Okayama University (1999)The University of Tokyo (1998)
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (B)
财政年份：
1998
资助国家：
日本
起止时间：
1998 至 1999
项目状态：
已结题

项目摘要

First of all, we examined the problem which arise because of the fact that paleomagnetic data are mostly given by inclination and declination, which depend nonlinearly on the parameters (Gauss coefficients) of the magnetic field model. Gubbins and Kelly (1993) and Johnson and Constable (1995, 1997) already published models of the time-averaged field for the last 5 million years. However, they implicitly assumed that there is a direct correspondence between the parameters and the data (I, D), which is not correct. By using the Taylor expansion method we showed that the mean of the nonlinear data depend not only on the means of parameters but on the variances of parameters. The variance of the data, on the other hand, depend only on the variance of the parameters, at the approximation to the second order terms.Next, in order to avoid the complexity discussed above, we applied the inversion only to paleointensity data for the last 5 million years. Paleointensity data are usually accompani … More ed by the directional information, so that they can readily be converted to the three components (X, Y, Z) which are linear functions of the parameters. In this case, it is possible to solve the inverse problem separately for the means and for the variances. The results show that the mean magnetic field is more axial dipole like than the present field, and that largest nodipole power is contained in the (2, 1) harmonics. The inversion of variances resulted in a large g【0!1】 component, which is about 30% of the mean value. For other terms, unambiguous results were not obtained possibly because of the number of paleointensity data were not enough.Thirdly, we developed a three-dimensional dynamo code in this research period and studied the origin of the geomagnetic field. Using the simulation results obtained by this code, we analyzed the behavior of dynamo magnetic field from the point of view of paleosecular variation. The comparison with the observed field show that dynamo field has many similar properties such as the dominance of the axial dipole component, about the same power on the surface of the core in harmonics of different degrees, and Gauss coefficients behave as random variates following zero-mean normal distributions. Other interesting properties such as the westward and eastward drift of surface features was seen only in the models. Less

首先，我们研究了由于古地磁数据主要由倾角和倾角给出的事实而产生的问题，倾角和倾角非线性地依赖于磁场模型的参数（高斯系数）。Gubbins和Kelly（1993）以及约翰逊和Constable（1995，1997）已经发表了过去500万年时间平均场的模型。然而，他们隐含地假设参数和数据（I，D）之间存在直接对应关系，这是不正确的。利用泰勒展开法证明了非线性数据的均值不仅依赖于参数的均值，而且依赖于参数的方差。另一方面，数据的方差仅取决于参数的方差，近似为二阶项。接下来，为了避免上面讨论的复杂性，我们仅将反演应用于过去500万年的古强度数据。古地震烈度数据通常是 ...更多信息由方向信息进行艾德化，使得它们可以容易地被转换成三个分量（X，Y，Z），这三个分量是参数的线性函数。在这种情况下，可以分别求解均值和方差的逆问题。结果表明，平均磁场比现状磁场更具有轴向偶极子性质，最大非偶极子功率包含在（2，1）谐波中。方差的反演导致大的g[0！1]分量，约为平均值的30%。对于其他项，可能是由于古地磁强度数据的数量不够，没有得到明确的结果。第三，在本研究期间，我们开发了一个三维发电机程序，研究了地磁场的起源。利用该程序的模拟结果，从古地磁场变化的角度分析了动磁场的行为。结果表明，发电机场与观测场具有许多相似的性质，如轴向偶极分量占主导地位，不同阶次的谐波在核表面上的功率大致相同，高斯系数服从零均值正态分布。其他有趣的特性，如向西和向东漂移的表面特征只在模型中看到。少