基于电场矢量有限元三维高频大地电磁倾子响应与感应矢量研究

一个或多个异常体的识别与区分及边界的确定是电磁法探测中提高分析精度的难点。本文利用基于电场的矢量有限元开展了复杂模型三维倾子响应及感应矢量研究。实感应矢量对电流聚集方向的指向性与分析频率的趋肤深度及介质的相对电性大小有关,通过这种指向性能有效地判定异常体的上界面和多个不同性质异常体的存在,但难以对下界面进行判定;虚感应矢量反映了感应电流(涡流)的流动方向,不同电阻率的地质体其感应电流的大小和方向不同,利用虚感应矢量的旋转方向、中心轴及分析频率的探测深度可有效地确定异常体的中心和上下界面。虚感应矢量相对于趋肤深度具有反映更大探测深度的能力,能有效地显示深部异常体对感应电流大小和方向的影响。数值模拟结果表明:虚感应矢量对异常体的识别与区分优于传统的电阻率和倾子参数。

Three-dimensional high-frequency earth electromagnetic tipper response and induction vectors based on the electric field vector finite element

The identification and differentiation of one or more anomalous bodies and determination of boundaries are crucial to improve the accuracy of analysis in electromagnetic surveys. In this paper, the three-dimensional tipper response and induction vectors of complex models are studied by using the vector finite element method in the electric field. The directivity of real-induced vectors to the direction of current aggregation is related to the skin depth of the frequency and the electrical amplitude of the medium, which permits to effectively identify the upper interface of anomalous bodies and the existence of multiple anomalous bodies. While it is difficult to identify the lower interface. The imaginary induction vectors show the flow direction of the induced current (eddy current), and the amplitude and direction of geological body induced currents with different resistivity are different. It is possible to effectively identify the center and upper-lower interfaces of the anomalous body by using the directivity of rotation of the image induction vectors, the central axis, and the depth of detection of the frequency. The imaginary induction vectors have the advantage to identify a larger depth in detection relative to the skin depth, which can effectively show the effect of deep anomalous bodies on the amplitude and direction of induced current. The numerical simulation results show that the image induction vector is better in identification and differentiation of anomalous bodies than the traditional resistivity and tipper parameter.