Study Of 3D Numerical Simulation Of Controlled-source Audio Electromagnetic

CSAMT (Controlled Source Audio-frequency Magnetotelluric ) is the mostlyimportant method to geophysics prospecting of shallow stratum . It finish the soundingwork that take over electromagnetic wave of different frequency. Now most of CSAMTdata processing methods are developed in one dimension , that is that supposing theearth media is horizontal layers , this will cause some wrong results for an earth whoseconductivity varies in two or three dimensions. For some case, the survey lines areparallel to the geologic structure dip direction. In such situation , to consider threedimensions numercial modeling is necessary. Base on the study of CSAMT, Weinvestigated some theories about magnetotelluric modeling. After carefully studyingthe algorithm of 3-D magnetotelluric modeling using staggered-grid finite differencemethod , and we recomposed a 3-D inversion procedure that Bi-conjugate gradientiterative methods, and base on the programme ,we add a extraneous electric dipole .In order to construct the finite difference scheme for the solution of the maxwellequations ,we used the staggered grid discretization , which was Yee introduced .wecan express electric and magnetic fields as a sum of the background fields andanomalous fields ,which the background field can be resolved by analytic method, Theadvantage of the FD approach to 3D forward modeling is that one can apply a veryflexible grid for discretization of the model parameters using differential methods ,andaccord with right helical code, further, it resolve the problem about no-sequence ofelectric field tangential component when the general grid on node, the disadvantage isthat we have to discretize the entire model. Resultant field can be decomposed tobackground field and anomalous fields and the latter can be resolved by thestaggered-grid finite difference method..We can take out the background field byanalytic solution, and combined with the Bi-conjugate gradient iterative solverprocessed with divergence correction, we can efficiently accomplish the numericalforward modeling of three dimension. At the same time ,we make some simulationanalysis with the programme and hole satisfactory result.