Three-Dimensional Forward Modeling And Inversion Of Tensor Controlled-Source Audio-Frequency Magnetotellurics

CSAMT is widely used in geological prospecting, mineral resources exploration, hydrogeological investigation, engineering investigation and many other areas, and most of the researches using this method are carried out with scalar data acquisition system. However, tensor data collected from CSAMT tensor acquisition system contains much more geoelectric information than scalar data and has a higher signal-to-noise ratio, compared to AMT. Along with the development of the CSAMT data acquisition device and the increasing demands in precise and accurate electrical prospecting, it requires a faster and more accurate forward and inversion algorithm for tensorCSAMT.The CSAMT 3-D forward problem has been solved through staggered-grid finite difference method based on the control equation concerning the electric field. A 2-D model and several 3-D models have been designed to test the validity and accuracy of the 3-D forward algorithm as well as analysis the characteristics of CSAMT tensor impedance data. The advantage that the tensor impedance data shows compared to scalar data demonstrates a new option for precise electric prospecting.An iterative approximate solution for three-dimensional data-space inversion and an approche for sensitive matrix are formulated. Based on the former work, we accomplish the CSAMT three-dimensional data-space OCCAM inversion with tensor data with Fortran program language. We have test the inversion programme with two sets of synthetic data and it turns out to be valid. We have also studied three factors which may affact the inversion procedure and they are the resistivity of the initial and background model, transmitter-receiver distance and the resistivity structure of the transmitters zones. From the tests the following conclusions are drawn, the resistivity of the initial and background model has a great impact on the inversion result; the inversion programme is hardly influenced by the transmitter-receivers distance; it has little influence on the inversion result when there is a large scale of low resistivity struct in the transmitters zones.