Research And Applicationof 2D Constrained Inversion Of Controllable Source Audio Magnetotelluric

The controllable source audio magnetotelluric method(CSAMT)has the characteristics of strong anti-interference ability,large exploratio n depth and high resolution.It is widely used in the search of geothermal resources and the investigation of groundwater resources.However,there are still some problems in CSAMT that need to be solved urgently.For example,in some strong interference areas,the electromagnetic field is not stable,resulting in low coincidence and poor quality of the measured data,and thus an inversion interpretation with a large deviation from the actual geoelectric structure.As a result,the data processing and interpretatio n methods under complex terrain conditions are still not mature,and there is no accurate inversion interpretation software.The existence of these problems requires us to effectively and accurately measure the measured data of CSAMT,and further carry out various inversion methods.The deepening of the improvement.Therefore,this paper proposes a method of geoelectric constrained inversion,which aims to solve the multi-solutio n and non-uniformity problems of conventional inversion methods.This paper first briefly describes the basic equations of the earth's electromagnetic field and then studies the earth's electromagnetic field in a uniform half-space to further explore the magneto-electromagnetic response under complex conditions.In order to make the theoretical study of electromagnetic field to match the electromagnetic corresponding characteristics under the actual geological structure to the maximum extent,the two-dimensional model earth electromagnetic field is studied on the basis of uniform half space,and the basic principle of CSAMT is deduced,and the apparent resistance is derived.The relationship between the rate ? and the horizontal component of the electric field and the vertical component of the magnetic field.Based on this,the basic algorithm of CSAMT two-dimensional finite element forward modeling is studied.The response characteristics of TM and TE polarization modes are analyzed by establishing an anomalous body model in uniform half space.The accuracy of the algorithm is verified.Secondly,the CSAMT two-dimensional regularized OCCAM inversion is introduced.On this basis,the model roughness matrix is modified and the model constraint is added to derive the iterative format of the modified objective function.As a constrained inversion algorithm for a priori information,the parameter introduces the BOSTICK inversio n theory,which aims to construct a constrained inversion theory with the one-dimensional BOSTICK inversion results as the initial model.Five geoelectric models of single low-resistance,double low-resistance,fault,mantle and ground are established to perform OCCAM inversion and BOSTICK inversion as constrained inversion of initial model,local constrained inversion and total constrained inverse The performance of the geoelectric constrained inversion is better than the local constrained inversion.The local constrained inversion accuracy is better than the BOSTICK inversion as the initial model constrained inversion,and the BOSTICK inversion as the initial model.Constrained inversion can better define the boundary between the anomalous body and the surrounding rock or the boundary of the geological structure,which can be used to optimize the conventional OCCAM inversion.Finally,through the CSAMT field measurement work in the mining area,the OCCAM inversion of the collected data is preprocessed,the one-dimensional BOSTICK inversion results are used as the initial model constrained inversion,the geoelectric constrained inversion,and the three inversions are compared and analyzed.The results show that conventional OCCAM inversion and BOSTICK constrained inversion can reflect large scale anomalous bodies,but the resolving power of smaller anomalous bodies is insufficient,while geoelectric constrained inversion is based on the condition of adding prior information.Can significantly improve the resolution of the anomalous body;compared with the conventional OCCAM inversion,BOSTICK constrained inversion and geoelectric constrained inversion have higher resolution of the formation with electrical differences;apparent resistance obtained by geoelectric constrained inversion The rate value is closer to the true value,and the BOSTICK constraint inversion is second.The apparent resistivity of the conventional OCCAM inversion has a large deviation from the true value.The validity and feasibility of the constrained inversion method are verified by an example.