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受计算机硬件水平限制,大地电磁(MT)三维反演难以在实际中推广应用,MT数据解释仍以二维反演为主.地质构造具有一定的二维性特征,但不同的地质构造走向往往不同、MT测线无法与每个构造的走向垂直,这使得实际MT数据并不满足严格的二维反演条件.因此,有必要开展大地电磁测深二维反演对“准二维”地质构造的适应性研究.本文设计三个理论地电模型,通过三维正演计算获得各测点大地电磁响应,以此模拟实际观测数据.对MT数据进行相位张量分析,结果表明设计的地电模型主要表现为二维性特征.利用非线性共轭梯度(NLCG)反演算法对理论MT数据进行二维反演研究,重点讨论了测线方向、电性主轴旋转策略及反演模式选择,对反演结果的影响.对比分析反演结果,得到如下认识:1.测线方向对反演结果影响较小;2.电性主轴旋转角度对反演结果影响较大;3.TE+TM联合模式及单独TM模式的反演效果较好.研究结果表明:当一条测线下方在横向与纵向上存在走向不同的多个异常体时,对整条剖面分测点、分频段进行电性主轴旋转,反演所得结果最可靠.
Due to the limitation of computer hardware, it is hard to popularize the application of MT (Magnetotelluric (MT)) in the field, MT data interpretation is still dominated by 2-D inversion.Geological structure has some two-dimensional characteristics, but different geological tending tend to The MT line can not be perpendicular to the direction of each structure, which makes the actual MT data does not meet the strict two-dimensional inversion conditions.Therefore, it is necessary to carry out two-dimensional inversion of the electromagnetic electromagnetic survey of the earth This paper presents three theoretical geoelectric models, and calculates the actual electromagnetic field response of each measuring point by three-dimensional forward modeling, which is used to simulate the actual observation data.The phase tensor analysis of the MT data shows that the designed The geoelectric model is mainly characterized by two-dimensional characteristics.The non-linear conjugate gradient (NLCG) inversion algorithm is used to study the theoretical MT data two-dimensional inversion, especially the survey line direction, electrical spindle rotation strategy and inversion mode The results of the inversion are contrastively analyzed and the following conclusions are obtained: 1. The direction of the survey line has a small effect on the inversion results; 2. The influence of the electrical spindle rotation angle on the inversion results is significant; 3.TE + TM joint model and The inversion results of TM mode alone are better.The results show that when multiple anomalous bodies with different directions exist in the horizontal and vertical directions under one line, the principal axis of the measuring points and sub-bands of the whole section are rotated, The result of inversion is the most reliable.