Two Dimensional Inversion Interpretation Based On 3d Forward Response Of The Magnetotelluric

The actual underground electrical structure is three-dimensional,so the 3D inversion magnetotelluric method was adopted to obtain the 3D inversion of underground electrical structure,but three-dimensional inversion because there exist some problems which have not been widely used.Therefore,it is meaningful to study the two-dimensional inversion of magnetotelluric response.This paper first introduced the 3D magnetotelluric forward theory and formula,the analysis of the basic three-dimensional response characteristics.Then,some basic theories and formulas of 2D inversion are briefly introduced,and the characteristics of different two-dimensional inversion methods and their characteristics in different polarization modes are compared.In this paper,the impedance tensor of magnetotelluric is understood and studied.Then,a different block composed of typical 3D resistivity model,to analyze the characteristics of different polarization modes of the three-dimensional response,understanding of the differences,the different polarization modes of the sensitivity of the electric interface resolution,and explore the reasons.In this paper,a three-dimensional model of a low resistivity block in a space is established to analyze the two-dimensional inversion results under different polarization modes.Finally on two more complex model is tested by using the above research results,take the impedance tensor decomposition,structural dimension analysis,optimal rotation angle and rotation of the data inversion.In order to explore a reasonable process of magnetotelluric data processing and interpretation.It is found that for the same anomalous body,the forward response of different polarization modes is different,and the inversion results of different polarization modes will be different,sometimes the difference is large.That is to say,different polarization modes have different resolving power to the electrical interface.In the field work,the line should be perpendicular to the direction of the structure,and take the appropriate polarization model for inversion.And it is very easy for the three-dimensional response,especially the measured data to be influenced by the shallow low resistivity body,or the sampling direction is not perpendicular to the structure.If we do not make any correction to the observation data,and do the inversion interpretation directly,the result will deviate from the actual structure.In addition,if the correction method is not appropriate,it will make the subsequent inversion results get wrong conclusions.It should first select the appropriate geophysical model,tensor decomposition method of impedance tensor decomposition and dimensionality analysis,to determine the optimal rotation angle,and rotating the data into the best angle,then the appropriate 2D inversion of polarization mode,could eventually eliminate redundant structure,achieve reasonable inversion effect.