基于高阶叠层矢量有限元法的回线源瞬变电磁法带地形三维正演

项目名称： 基于高阶叠层矢量有限元法的回线源瞬变电磁法带地形三维正演

项目编号： No.41504088

项目类型： 青年科学基金项目

立项/批准年度： 2016

项目学科： 天文学、地球科学

项目作者： 李建慧

作者单位： 中国地质大学（武汉）

项目金额： 20万元

中文摘要： 地面可控源电磁法由于勘探深度大、抗干扰能力强是第二深度空间（500-2000m）找矿的主要技术，但是由于其发射源敷设于地表，资料解释受地形起伏影响较大。鉴于现有数值方法用于可控源电磁法带地形三维正演的近区数值解精度不理想，本课题拟采用基于非结构化四面体网格的高阶矢量有限元法实现可控源电磁法带地形的精确三维正演。本课题以受场源奇异性影响较大的回线源瞬变电磁法为例，首先将回线源分解为有限多个电偶源并以Delta函数逐个处理，然后采用非结构化网格对电偶源周边区域进行局部加密，最后采用高阶叠层矢量有限元法获取精确的瞬变电磁响应。在此基础上，本课题拟进一步研究起伏地形引起的瞬变电磁场畸变效应，并以典型斑岩型矿床为例开展实例研究。本课题研究成果不仅可提高回线源瞬变电磁法带地形三维正演的精度，而且还为进一步改善瞬变电磁法资料解释水平奠定基础。

中文关键词： 可控源电磁法；起伏地形；三维正演；高阶叠层基函数；斑岩型矿床

英文摘要： Due to the larger exploration depth and better resistance to cultural disturbances, surficial controlled-source electromagnetic (CSEM) methods have already been the indispensable techniques for prospecting the deposits located in the second deep space of lithosphere (500-1000m). However, the CSEM methods are susceptible to the interference caused by rugged topography, and the precision of existing numerical methods is relatively low at the observation points near the transmitting source due to its singularity. In this study, the higher-order vector finite element method based on unstructured tetrahedral grids will be employed in order to obtain high-accuracy electromagnetic response, and the loop source is taken as example because it is affected seriously by the source singularity. In our scheme, the loop source will be viewed as the combination of finitely many horizontal electric dipoles, which could be denoted in the form of Delta function. Then, the mesh near the dipoles will be refined locally by the unstructured meshing technique. Finally, the accurate electromagnetic response will be obtained by the higher-order vector finite element method based on hierarchical basis functions. Additionally, we will study the distortion effect to electromagnetic response caused by rugged topography, and take porphyry deposit as a example. In conclusion, the research from this project will not only enhance the accuracy of three dimensional forward with topography for loop-source transient electromagnetic method, but also lay a solid foundation for improving data interpretation level.

英文关键词： controlled-source electromagnetic method;rugged topography;three dimensional forward;hierarchical higher-order basis function;porphyry deposit