Research On Modeling And Inversion Of Two-Dimensional MT With IP Effect

The Magnetotelluric Sounding Method?MT?uses electromagnetic waves that are physically present and constantly changing as an excitation source,and its low-frequency information can reflect deep information.However,under normal circumstances,the signal is weak,and it is easy to cause electromagnetic interference.Because it does not require a transmitter and a power source,it is widely used in the survey area far from the town.The complex resistivity method based on the difference in electrochemical properties has been popularized in many fields such as solid minerals by virtue of its ability to perform multi-parameter inversion.The combination of the advantages of the two methods has attracted the attention of scholars or research and production units.The collected MT data itself contains geoelectric information from the deep geological body of the stratum.After the IP effect is taken into account,multi-parameters can increase the ability to interpret the nature of the anomaly.Based on the previous studies,this paper carries out the complex resistivity one-dimensional forward modeling and two-dimensional finite element method forward and inversion of MT.Firstly,the calculation method of MT complex resistivity electromagnetic response under horizontal layered medium and two-dimensional geoelectric model is realized.The specific method is:starting from the Maxwell equation,introducing the expressions that can describe the complex resistivity spectrum characteristics,and the Cole-Cole model to the partial differential equation of the frequency domain electromagnetic method,to realize the electromagnetic effect and the induced electric effect as a whole;Using the finite element method,the triangulation is performed to discretize the continuous function in the partial differential equation;the Cholesky decomposition is used to solve the electromagnetic secondary field.Finally,the calculation of the MT complex electromagnetic response under the two-dimensional geoelectric model is realized.In order to solve the problem that the two effects are difficult to separate,and the true propagation law of the electromagnetic wave can be completely and accurately reduced.Then,starting from the MT resistivity definition formula Cagniard apparent resistivity,the sensitivity matrix of apparent resistivity and impedance phase versus complex resistivity parameters??₀?m?c???is derived in detail using the exchange theorem and chain-based derivation law.The inversion method uses an Occam inversion that is less dependent on the initial model and has a stable convergence.In addition to the smooth model constrained inversion,the complex resistivity parameter range constraint is added to avoid the inversion results without actual physical meaning.Finally,the difference between the derivation of the Jacobian matrix expression is verified by comparing the two forwards to the Jacobian matrix solved by the quasi-positive algorithm in the inversion program.Finally,the spectral characteristics of complex resistivity at high and low frequencies are studied.The forward-polarized half-space model and the high-and low-resistance double-prism models are forward-formed.The common high-and low-resistance polarized prism models are tested.Count.The study found that the observation data of TE and TM polarization modes are sensitive to the polarization rate,and the low frequency data can better reflect the polarization rate information.The correctness of the inversion procedure is confirmed by setting the theoretical model.A good result.