摘要
可控源音频大地电磁测深法(CSAMT)基本上是基于电性各向同性理论的假设,而实际地层普遍表现为电性各向异性现象,因此研究各向异性地层条件下CSAMT方法的电磁响应具有重要的理论意义和应用价值.本文从有源Maxwell方程出发,推导出了二维各向异性地层条件下无限长线源频率域的电磁场响应,得到了一组平行于线源方向的电场分量E_x和磁场分量H_x的偏微分方程,并采用有限元法进行求解.模型的计算结果表明:不论是对均匀半空间还是一维层状介质中的各向异性二维体模型的计算,均能从结果中明显地看出各向同性背景场和各向异性异常体的存在;在计算中通过改变各向异性系数或各向异性旋转角,其结果在视电阻率和相位曲线上均存在显著区别.计算结果表明了在各向异性地层中,仍然采用各向同性的假设进行CSAMT资料的处理与解释,可能会带来比较严重的误差,这种情况下必须采用基于各向异性的地质模型对CSAMT资料进行处理和解释.研究结果对于提高CSAMT方法的勘探效果和应用水平具有重要的指导意义.
The controlled source audio-frequency magnetotellurics （CSAMT） is traditionally based on the electrical isotropic theory. However, it has been well recognized that the electrical anisotropic is widely present in the earth interior. So it is significant theoretically and practically to calculate EM responses with anisotropic earth model. Based on Maxwell equations with source terms, EM responses to an infinite linear source in 2D anisotropic formation in the frequency domain are derived. A set of partial differential equations of the electric field component Ex and the magnetic field component Hx parallel to the linear source direction are obtained and solved by the finite element method. The results indicate that the isotropic background and anisotropic anomalous body can be clearly figured out by calculating the 2D anisotropic anomalous body in either homogeneous half-space or one-dimensional layered media. When changing the anisotropic coefficients and rotation angle from main electrical axis of the anisotropic model, the results are obviously different from the anisotropic case in both apparent resistivity and impedance phase curves. The results indicate that errors will be very large if we still use electrical isotropic theory when dealing with CSAMT data in anisotropic media. In such situation, the calculation should be based on anisotropic theory instead of electrical anisotropic one. The result is significant for improvement of the application of the CSAMT method to exploration.
出处
《地球物理学报》
SCIE
EI
CAS
CSCD
北大核心
2017年第5期1937-1945,共9页
Chinese Journal of Geophysics
基金
国家自然科学基金项目(41274115
41674107
41574064
41404087)
国家重点基础研究发展计划(973)项目(2013CB228605)联合资助
关键词
各向异性
CSAMT
有限元
正演
线源
Anisotropy
CSAMT
Finite element
Forward modeling
Linear source
