MT约束反演研究

发布时间：2018-10-09 10:55

【摘要】：大地电磁测深法(MT)是利用天然场源勘探地下电性结构的一种频率域地球物理勘探方法。与人工源电磁勘探方法相比,大地电磁测深法具有独特的优点,如施工方便、探测深度大、对低阻体反映灵敏等。目前大地电磁测深法主要应用于深部矿产资源勘探、大地构造研究、天然地震预报等领域。大地电磁测深反演直接影响其在各个领域的应用效果。大地电磁反演存在多解性,加上电磁场在地下快速衰减,使深部分辨率降低。大地电磁约束反演的研究对于提高大地电磁反演精度、减小多解性,及广泛应用具有重要意义。本文回顾了大地电磁约束反演的研究现状,推导、总结了大地电磁测深基本理论和约束反演基本理论。针对大地电磁反演中模型参数修改量的修正选取困难问题提出了基于约束条件修正模型参数修改量的约束反演方法。通过最小二乘约束反演方法,计算、分析对比了不同参数反演、不同约束方式及不同约束误差限的反演效果。HKHKH型地电断面不同计算结果表明:被约束层的反演效果得到提高,被约束层的反演效果提高的幅度与约束误差限成反变关系;累层约束的层数越多,约束误差限越小,对整体反演效果提高越显著;总参数平均相对误差与约束误差限成正变关系。对下邻层反演精度的提高幅度与约束误差限成反变关系,但可能会降低无约束反演时已经反演得较好的层位的反演结果。无约束反演时的层参数平均相对误差越大,累层约束把该层约束后,对模型整体反演效果提高越显著,反之亦然。累层约束反演情况下,参数总平均相对误差与约束反演的累层层数成反变关系。研究结果表明:大地电磁约束反演可在一定程度上提高整体反演精度,有利于减少多解性。
[Abstract]:Magnetotelluric sounding (MT) is a frequency-domain geophysical method for the exploration of underground electrical structures using natural field sources. Compared with artificial source electromagnetic exploration method, magnetotelluric sounding method has unique advantages, such as easy construction, large detection depth, sensitive to low resistivity body, and so on. At present, magnetotelluric sounding is mainly used in deep mineral resources exploration, geotectonic research, natural earthquake prediction and other fields. Magnetotelluric sounding inversion directly affects its application in various fields. There are many solutions in magnetotelluric inversion and the fast attenuation of electromagnetic field in underground makes the deep resolution lower. The study of magnetotelluric inversion is of great significance for improving the precision of magnetotelluric inversion, reducing the multiplicity of solutions and its wide application. This paper reviews the research status of magnetotelluric constrained inversion, deduces the basic theory of magnetotelluric sounding and the basic theory of constrained inversion. In this paper, a constrained inversion method based on the modified model parameters is proposed to solve the difficult problem of modifying the parameters of the model in magnetotelluric inversion. Through the least square constrained inversion method, the inversion effects of different parameters inversion, different constraint ways and different constraint error limits are analyzed and compared. The results of different computation results of HKHKH type geoelectric section show that the inversion effect of the constrained layer is improved. The amplitude of the inversion effect of constrained layer is inversely related to the constraint error limit, the more layer constraints are, the smaller the constraint error limit is, and the more significant the inversion effect is to the whole inversion. The mean relative error of total parameter is positively correlated with the constraint error. The improvement of the inversion accuracy of the lower adjacent layer is inversely related to the constraint error, but it may reduce the inversion results of the unconstrained inversion. The larger the average relative error of the layer parameters in the unconstrained inversion is, the more significant the inversion effect of the model is when the layer is constrained by the layer constraint, and vice versa. In the case of constrained inversion, the total average relative error of parameters is inversely related to the cumulative layer number of constrained inversion. The results show that magnetotelluric constrained inversion can improve the whole inversion accuracy to some extent and reduce the multiplicity of solutions.
【学位授予单位】：长安大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：P631.325

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