Research On Multi-dimensional Magnetotelluric Forward Modeling With General Anisotropy And Its Sensitivity Analysis

Anisotropy widely prevails in the earth materials among different scales.Electrical anisotropy of deep earth has not been routinely and deeply investigated,especially from an aspect of taking a multi-,or higher dimensional anisotropic effect into consideration while interpreting the inverted models.It's considerably appropriate and helpful to systematically study electrical anisotropy by magnetotelluric(MT)soundings,as it can detect earth from surface to upper mantle,which will benefit detailing deep structures in the earth.However,a complete system for numerical modeling is a prerequisite.Based on the principle of staggered-grid finite difference method,a suite of tools for simulating MT responses of anisotropic models is developed,which can handle 1D,2D and 3D anisotropic forward modeling for general anisotropy,and forms the basis of data analysis for anisotropic responses.For 1D,the method is tested by comparing with analytic and quasi-analytic solutions,which proves the accuracy of the methods,and the solution can be used as boundary conditions of higher dimension problems.For 2D,we implement three variants based on different governing equations,and after some comparison test,the result shows the flexibility and feasibility of our numerical philosophy.And then,for 3D,limited by the availability of published algorithms,the 3D method is verified in a self-consistent way,where 3D model is constructed by intercepting a 2D model,and then responses are compared by running 2D and 3D forward modeling and rotating the response of 3D method.According to the published modular approach of deriving sensitivity of electromagnetic data,we formulate all the necessary components with pre-defined numerical operators to group the resulting sensitivity matrix.With this completed,routine anisotropic inversion will be possible after sensitivity analysis is integrated into the development of inversion algorithms.