存在复杂非均匀层的一维大地电磁正演

1D magnetotelluric forward modeling of complex inhomogeneous layers

二、三维大地电磁(MT)正反演常采用一维反演结果作为初始迭代模型或利用一维模型响应定义边界条件,为进一步研究复杂地层条件下的MT响应,本文推导了非均匀层电导率随深度按线性-指数函数变化和指数-线性函数变化的一维MT正演的解析解形式,在此基础上对不同的地层组合情况进行讨论,分析了非均匀层埋深、厚度对MT响应的影响,并与地下介质均匀以及非均匀层电导率随深度按单一函数变化的MT响应进行对比。结果表明,既存在线性变化又存在指数变化的介质模型MT响应远比单一变化介质模型复杂,随着过渡层厚度增大、埋深变浅,其视电阻率和相位幅值与均匀介质模型响应幅值差异变大。

In 2D and 3D magnetotelluric（MT） inversion,1D inversion data is often used as the initial iterative model or forward modeling to definite the boundary condition.In order to further study MT response under complex stratum condition,the analytical solution for 1D MT modeling is derived where the conductivity of inhomogeneous layers vary with depth are linear-exponential and exponential-linear form.On this basis,the differentstratum combination conditions are discussed,and the effect of depth and thickness of inhomogeneous layer on the MT response is analyzed.The results are compared with analytic solution from homogeneous medium model and single variation model.It is shown that the MT responses of linear-and-exponential variation model with inhomogeneous are more complex than single variation model.With the thickness being larger and the embedded depth being shallower for inhomogeneous layers,the differences of resistivity and phase of MT response with the homogeneous medium model become larger.