大地电磁测深二维反演方法求解复杂电性结构问题的适应性研究

摘要

为探讨二维反演方法在三维电性结构中的适应性问题,本研究中设计了一系列的二维/三维正演模型进行实验计算,分析了三维高阻/低阻异常体对模型响应的畸变作用,并从反演模式选择和数据旋转方向两个方面进行模型二维反演的对比分析,与三维反演的结果进行了比较,最后采用了实测数据进一步进行了二维和三维反演的比较实验.实验和研究结果表明,在剖面选择方面,在剖面方向与垂直主构造方向相差不大的情况下,截取剖面方向,将电性主轴旋转到垂直剖面方向的二维反演结果与垂直主构造方向的反演结果都可以较好地还原正演模型,在大的构造的反映上并无太大差异.在地下为二维或近三维条件时,正演模型的主要结构都可以较好地被二维和三维反演解析出来.二维的反演结果可能甚至会比三维的反演结果的边界更清晰,更精确.然而,对于具有较强的三维结构的模型而言,其二维反演结果与原始模型可能仍然存在较大差异,其中TM+TP或TM模式的二维反演结果相对更接近原始模型,而TE模式的结果往往会有较大误差,需要在解释时特别注意以免得出错误结论.%To study the validation of two-dimensional (2D) inversion methods in three-dimensional (3D) cases, a series of 3D synthetic models are designed. Synthetic data are hence generated and analyzed to estimate the distortion effect of 3D bodies. 2D inversions are carried out on the profile direction and the main strike directions of synthetic models. Inversion results are analyzed to compare the models of different polarization modes, profile directions, and the difference between the results and synthetic models. The tests performed show that, in most of the cases, the main features of the synthetic models could be well recovered by both 2D and 3D inversions. 2D results even tend to get sharper and more precise boundaries in 2D or quasi-3D cases. However, for rather complex 3D structures, the 2D result could be quite different from the original model. TM + TP or TM modes are recommended while the TE mode should be carefully avoided. Talking about the selection of the profile, when the actual profile direction is not substantially different from the regional electrical strike direction, 2D MT inversion results of the profile direction and that perpendicular to the strike direction can both retrieve the synthetic model well. The major structures from these results are not much different.