基于大地电磁三维响应的二维反演解释研究

发布时间：2018-05-27 14:46

本文选题：大地电磁 + 三维响应　；参考：《成都理工大学》2017年硕士论文

【摘要】：实际的地电构造是三维的,故应在大地电磁中采取三维的反演方法来得到地下的电性结构,但现在大地电磁三维的反演因为存在一些问题而仍未得到广泛使用。故研究大地电磁三维响应的二维反演解释是较有意义的。本文首先介绍分析大地电磁三维正演基本的一些理论和公式、三维响应特征,然后简要介绍了二维反演的一些基本理论和公式并对比介绍了不同二维反演方法的特点及其在不同极化模式下的特征;其后对大地电磁的阻抗张量进行了理解和学习,重点学习了相位张量分解的特点和用法;然后建立了一个三维空间中存在不同电阻率块体的典型三维模型,以分析其在不同极化模式下的三维响应特征,深刻研究其特征差异,即不同极化模式对电性分界面分辨的灵敏度,并探究了其原因;建立了另外一个空间中存在一个低阻块体的三维模型,以分析其在不同极化模式下的二维反演结果,探究了极化模式的选择对二维反演的影响;最后综合利用上述的研究成果对两个较复杂的模型进行了试算,采取阻抗相位张量分解,进行构造维性分析、寻求最佳旋转角,并将旋转后的数据作二维反演,探求了一种大地电磁资料处理解释的合理流程。发现对于同一异常体,不同极化模式的正演响应是不一样的,其不同极化模式的反演结果也会出现一些差异,有时差异较大,也就是说不同的极化模式对电性分界面的分辨能力是不一样的;在野外工作,布设测线时,应当尽量垂直于构造的走向,并且采取合适的极化模式来进行反演。并且对于三维响应尤其是实测资料很容易出现受浅表低阻体等影响而引起畸变的情况,或者遇到采样方向不与构造走向垂直的情况,假设不对观测资料进行任何的校正,而直接做反演解释,那么所得到的结果将会出现偏离实际构造的情况;另外,假如采用的校正方法不恰当的话,也会使得后续的反演结果得到错误的结论;故应首先选取合适的地球物理模型、张量分解方式,进行阻抗张量分解、构造维性分析、求取最佳旋转角,并将数据旋转到最佳角度,再进行合适极化模式的二维反演,最终将可能消除冗余构造、达到合理的反演效果。
[Abstract]:The actual geoelectric structure is three-dimensional, so the three-dimensional inversion method should be adopted in magnetotelluric to obtain the underground electrical structure, but the magnetotelluric three-dimensional inversion is still not widely used because of some problems. So it is meaningful to study the two-dimensional inversion interpretation of magnetotelluric response. This paper first introduces some basic theories and formulas for the analysis of magnetotelluric three-dimensional forward modeling, and the three-dimensional response characteristics. Then, some basic theories and formulas of two-dimensional inversion are briefly introduced, the characteristics of different two-dimensional inversion methods and their characteristics under different polarization modes are compared, and then the impedance Zhang Liang of magnetotelluric is understood and studied. The characteristics and usage of phase Zhang Liang decomposition are studied emphatically, and then a typical three-dimensional model with different resistivity blocks in three dimensional space is established to analyze the three-dimensional response characteristics of different polarization modes and to study the difference of their characteristics. That is, the sensitivity of different polarization modes to the resolution of electrically separated interfaces, and the reasons for the resolution, and the establishment of a three-dimensional model with a low resistivity block in another space to analyze the two-dimensional inversion results under different polarization modes. The influence of the choice of polarization mode on two-dimensional inversion is explored. Finally, two more complex models are calculated by synthetically using the above research results. The structural dimension is analyzed by using impedance phase Zhang Liang decomposition, and the optimum rotation angle is obtained. A reasonable flow of magnetotelluric data processing and interpretation is obtained by using two dimensional inversion of the rotated data. It is found that for the same anomalous body, the forward response of different polarization models is different, and the inversion results of different polarization models will be different, sometimes quite different. In other words, different polarization modes have different ability to distinguish the electric boundary surface, and in the field work, the line should be perpendicular to the strike of the structure, and the appropriate polarization mode should be adopted to carry on the inversion. It is also assumed that the 3-D response, especially the observed data, is easily distorted by shallow low resistivity, or that the sampling direction is not perpendicular to the direction of the structure, assuming that no correction is made to the observed data. In addition, if the correction method is not appropriate, it will make the subsequent inversion result get the wrong conclusion, and the inversion result will deviate from the actual structure directly, and if the correction method is not appropriate, it will make the subsequent inversion result get the wrong conclusion. Therefore, it is necessary to select the appropriate geophysical model, Zhang Liang decomposition method, impedance Zhang Liang decomposition, construct dimension analysis, obtain the best rotation angle, rotate the data to the best angle, and then carry out the two-dimensional inversion of the appropriate polarization model. In the end, redundant structures will be eliminated and reasonable inversion results will be achieved.
【学位授予单位】：成都理工大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：P631.325

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