Impedance Tensor of Network‐MT and the Influencing Factors
Impedance Tensor of Network‐MT and the Influencing Factors
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DOI：
10.1002/cjg2.1208
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发表时间：
2008
期刊：
影响因子：
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通讯作者：
Xiaobin Chen;Guoze Zhao;Ji Tang;M. Uyeshima;H. Utada
中科院分区：
文献类型：
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作者：
Xiaobin Chen;Guoze Zhao;Ji Tang;M. Uyeshima;H. Utada
Network-MT(N-MT)方法是利用几公里至几十公里的电话线作为电极线来测量电场。很难得到两条笔直且相互垂直的电极线，因此不能像MT方法那样直接计算N-MT的阻抗张量。本文根据阻抗张量的旋转规则，提出了一种计算N-MT阻抗张量的简单方法。利用该方法计算了中国东北地区5个N-MT台站的阻抗张量，并随后推导出视电阻率、阻抗相位和最佳走向。进一步研究了阻抗张量旋转计算结果与朝阳站6条电极线观测结果的差异。仔细分析了造成差异的因素，提出“电场等效各向异性效应”作为主要影响因素。这种效应意味着地壳中存在一些尺度与电极线长度类似的异质结构，不同的电极线沿不同方向穿过异质结构，因此在不同电极线中观测到的电场不是同一电场矢量的分量，则地表观测三角形的阻抗分量不满足阻抗张量的旋转规则。
In Network-MT(N-MT) method, several to tens kilometers telephone lines are used as the electrode line to measure the electric field. Two straight and mutually perpendicular electrode lines are hardly obtained, thus the impedance tensor of N-MT can not be calculated directly as in MT method. In this article, a simple method to calculate N-MT impedance tensor is presented based on the rotation rule of impedance tensor. Impedance tensors of five N-MT stations in NE China are calculated with this method, and the apparent resistivity, impedance phases, and optimal strike directions are derived subsequently. Furthermore, the differences between calculated results by impedance tensor rotation and observed results with six electrode lines at Chaoyang station are studied. The factors inducing the differences are analysed carefully and “Equivalent Anisotropy Effect of Electric Field” is presented as the main factors. This effect means that there are some heterogeneous structures in the crust whose scale is analogous with the length of electrode lines, and different electrode lines traverse the heterogeneous structures along different direction, thus the electric field observed in different electrode lines is not the component of the same electric field vector, then the impedance components of the observation triangle on surface do not satisfy the rotation rule of impedance tensor.