2D/3D Tipper Forward Modeling And Joint Inversion Of Magnetotelluric

The magnetotelluric has been widely used in the field of geophysical exploration,and how to improve the accuracy of the exploration of the magnetotelluric is a veryurgent problem. At present, the tipper data as an important parameter, but only appliedto the qualitative interpretation of the tectonics and petroleum exploration. As the thequality improvement of the vertical magnetic field component, the systematic researchof the tipper simulation and quantitative interpretation is very necessary.In this thesis, we use the finite element method, the quadrilateral mesh andtetrahedral mesh to implement2D/3D three-dimensional forward modeling ofmagnetotelluric;2D tipper, apparent tipper and3D tipper are numerically simulated, wedescribed the property characteristics of the tipper data; achieved the2D tipper datainversion which based on the theory of the OCCAM inversion; Last, tipper andapparent tipper were applicanted in the study of deep structure and shallow engineeringexploration.1. The finite element method as the numerical simulation tool, we derived theboundary-value and variational problem of2D magnetotelluric, the quadrilateral meshgeneration forward calculation was achieved; The apparent resistivity and impedancephase curves results of K-type layered media model are coincide to analytical solution;quadrilaterals and rectangular mesh finite element forward simulation were analyzedrespectively on the anomalous body model and the Slope terrain model,the resultsshowed that the quadrilateral mesh reflected the characteristics of the anomalous bodyvery well, meanwhile reflected on the characteristics of the terrain better, which verifythe reliability of the two-dimensional forward modeling.2. on the basis of2D forward, we completed the forward formula of2D tippervector. By tipper data forward modeling analysis of lithologic boundaries, the level ofblocking layer, conductive overburden, the anomalous body and the static displacementmodel, we summed up the response characteristics of the tipper data: the real part andamplitude of the tipper reflects the basically the same characteristics, and have a goodcorrelation between them, which can be used as identification tipper anomalycharacteristics; The tipper is more suitable for the study of the characteristics of the lowresistivity fault then the high resistivity; tipper reflect the width of the fault very well; conductive overburden press the abnormal position of the tipper data down, thedepression scale proportional to the thickness; the static displacement has littleinfluence on the tipper; magnetotelluric terrain affect the causes are analyzed, whilebuilding multiple models to simulate the positive terrain, the negative terrain andcomplex models of the anomalous body tipper data characteristics, which obtained aconsistent conclusion is that the impact of terrain only in high frequency.3. on the basis of the definition of the apparent tipper, we perfected the tipper dataderivation and the formula, and which calculated by the TE mode apparent resistivityand impedance phase data. Depending on the tipper comparison of vertical low-resistivity fault model, low-resistivity anomaly body tilted fault model, we found thatthe good correspondence between tipper and apparent tipper in the mid and highfrequency band (frequency≥1Hz), and the real and imaginary part reflect better then theamplitude and phase part. So we use observations of four components to calculate themid and high frequency apparent tipper as the good data, which assists theinterpretation of MT data in areas such as engineering and mineral exploration4. We discussed the boundary value and The weighted margin equation of the3Dmagnetotelluric, using the conjugate gradient method to calculate the coefficient matrixof equations of the finite element solution process, and ultimately achieved the3Dtetrahedral element meshing magnetotelluric modeling; compared simulation results ofK-type layered media model which forwarded by3D/2D numerical simulation andanalytical solution, prove the correctness and validity of the3D modeling program.5. Discussed the relationship between components of the electromagnetic field,the tensor impedance and the tipper vector on the basis of3D forward, derived theforward calculation of the3D tipper formula. By the3D tipper simulation results ofvertical faults,2D anomalous body,2D static displacements and fault model arebasically the same compared with2D, which proved the correctness of the simulationof3D tipper; through the simulation of the3D anomalous body and3D staticdisplacement model, we found that:Tz ycomponent is basically the same with2Dmodel, but the abnormal range variable offset to the high frequency band; theTzxcomponent better reflects the effect of the anomalous body thenTz ycomponent, andthe real, imaginary and amplitude part ofTz xcomponent can be a better reflection ofthe boundary of the anomalous body; static displacement greater impact on theTz xcomponent.6. Started from the the basic theory of OCCAM inversion, we added the real andimaginary part of tipper in the objective function, achieved2D tipper joint inversionalgorithm. Through imulation of the fault model, abnormal body model with the staticdisplacement and complex model, we found that: tipper data reflect sensitive on thetransverse electrical uneven, tipper joint inversion reduces multiple solutions andimproved inversion interpretation effect; in the process of inverse calculation, select a good initial model can effectively reduces the inversion iterations and improves theinversion effect; the inversion effect depending on the resistance separate rate is poor;inversion joint of real and imaginary part of tipper can effectively eliminate the staticeffect; the inversion of joint tipper can greatly improved the vertical resolutioncapability of the TM mode.7. In the research of structure of the Longmen Shan thrust deep electricalconductivity, we analysised features of the tipper data section, and2D tipper data jointinversion applied to data processing interpretation, has been relatively satisfied with theinversion effect, laid a solid foundation for the electrical structure and geologicalintegrated interpretation; in the study of Zhong-Yi tunnel of Li-Xiang railway line, wecomputed and analysed the features the apparent tipper, through the comparison of thedirect inversion result and tipper data joint inversion result of the original data foundthat the latter one is more consistent with the geological conditions of the actualsituation, which verified the effect of the tipper data in shallow explorationimprovedthe accuracy of magnetotelluric in engineering exploration.