大地电磁相位张量和倾子的三维主轴各向异性反演  

Three-dimensional axially anisotropic inversion of magnetotelluric phase tensor and tipper data

作　　者：孔文新 余年 李鑫[4] 张学健 陈煌 李天阳 王恩慈 KONG WenXin;YU Nian;LI Xin;ZHANG XueJian;CHEN Huang;LI TianYang;WANG EnCi(School of Resources and Safety Engineering,Chongqing University,Chongqing 400044,China;State Key Laboratory of Coal Mine Disaster Dynamics and Control,Chongqing University,Chongqing 400044,China;School of Electrical Engineering,Chongqing University,Chongqing 400044,China;State Key Laboratory of Isotope Geochemistry,Guangzhou Institute of Geochemistry,Chinese Academy of Sciences,Guangzhou 510640,China)

机构地区：[1]重庆大学资源与安全学院,重庆400044 [2]煤矿灾害动力学与控制国家重点实验室,重庆400044 [3]重庆大学电气工程学院,重庆400044 [4]同位素地球化学国家重点实验室,中国科学院广州地球化学研究所,广州510640

出　　处：《地球物理学报》2023年第9期3928-3946,共19页Chinese Journal of Geophysics

基　　金：国家自然科学基金项目(42204078,42222404,42104071)资助。

摘　　要：地壳和上地幔普遍存在的电性各向异性是大地电磁测深方法在实践应用中的关键和难点问题,而由近地表局部地电异常引起的电流型畸变可进一步加剧各向异性反演的多解性和不确定性.为压制电流型畸变影响,本文实现了一种利用大地电磁相位张量和倾子数据获取地下介质主轴电性各向异性结构的三维反演算法.该算法正演问题的求解采用交错采样有限差分法,反演问题的求解采用非线性共轭梯度法.理论模型测试表明,相位张量和倾子的三维各向异性反演不仅恢复了真实的各向异性异常分布特征,且压制了为拟合电流型畸变出现的假异常.由于相位张量和倾子数据不含幅值信息,先验模型选取对反演模型电阻率值的恢复效果影响较大,但初始模型的改变基本不影响反演结果.为进一步验证该算法的有效性,将其应用于USArray项目在美国西北部采集的109个长周期大地电磁实测数据.反演结果表明,相对于阻抗数据,相位张量和倾子数据的各向异性反演结果对浅层结构的刻画更为准确,与地表地质特征更为吻合.Electrical anisotropy is ubiquitously observed in the crust and upper mantle,which is a key and difficult problem in the practical application of magnetotelluric method.In the meanwhile,galvanic distortion caused by local scatters near surface can further exacerbate the ambiguity and uncertainty of anisotropic inversion.In order to suppress the influence of galvanic distortion,this paper implements a three-dimensional inversion algorithm for magnetotelluric phase tensor and tipper data to obtain the axially anisotropic structure of the underground medium.In this algorithm,the staggered grid finite difference method is used to solve the forward modeling problem,while the non-linear conjugate gradient method is applied to implement inversion.Synthetic tests show that the three-dimensional anisotropic inversion of phase tensor and tipper data not only resolves the actual electrical features of the subsurface structure,but also suppresses the artifacts caused by fitting the galvanic distortion effect.Since the phase tensor and tipper data do not contain amplitude information,the choice of the prior model has a great influence on the recovered resistivity value,but the change of the initial model basically does not affect the inversion results.In order to further verify the effectiveness of the algorithm,it is applied to 109 long-period magnetotelluric data collected by the USArray project in the Northwest of the United States.The inversion result shows that using phase tensor and tipper is better for recovering the shallow-depth structure than impedance and can obtain results more consistent with surface geology.

关 键 词：大地电磁法 各向异性 电流型畸变 相位张量 反演 

分 类 号：P631[天文地球—地质矿产勘探]