| Electrical prospecting is one of traditional geophysical exploration methods. It has been widely applied in the fields of geological examination, ground water development, mining exploration, et al. From 1980s, having higher horizontal resolution of electrical profiling and higher vertical resolution of electrical sounding, resistivity tomography has become an important approach of geoscience CT that have had seismic wave tomography and electromagnetic wave tomography. It has been carried out in 2-D and 2.5-D numerical calculation and disposal of practical materials, and applied in hydrology, archaeology, architectonics, et al. Now, 3-D resistivity tomography is still an advanced problem in the world, and it is also under development, whether in theoretical research or in practical application.In this paper, author developed detailed and comprehensive system work in 3-D resistivity tomography theoretical research and practical application. These works included:1. Author detailedly deduced the calculation process of 3-D resistivity forward with finite element method when adopting tetrahedron element griddings, gave two calculation methods, anomalous potential method and total potential method, then discussed in the programming of 3-D resistivity finite element forward. When the location of point current is altered and the resistivity distribution is changed, the location and distribution could not be considered during constructing the griddings, calculated and storedtwo ratios of each tetrahedron element, DekAsub(Asub)T/I, AIe,kAT/2, in disk files. As soon asresistivity distribution and location of point power was concentrated, those ratios were read from disk files directly, then total coefficient matrix was assembled rapidly with element coefficient matrixes. A new compressible store method is brought out in which elements locating fifty diagonals in total coefficient matrix are only stroed, which could be store total coefficient matrix effectively, and save a lot of memories. Linear equation, AX=B, was resolved by SSORCG algorithm and some examples demonstrated that in this algorithm, griddings scheme and electrical property distribution need be considered. Besides numeric simulation of homogeneous medium modal, two horizontal layers modal, and vertical fault modal, author firstly added in 3-D sphere model, the result indicated that 3-D resistivity forward with tetrahedron elements is right, that abnormal potential method is prior to total potential method and that Adopting above methods to build forward programming is right and effective to calculate complex 3-D forward problem.2. Author discussed resistivity tomography equation, 3-D resistivity measurement, establishment of initial model, calculation of partial derivative and inversion method, detected depth, and resolution of abnormal bodies in order. A effctive to constructure initial modal was developed, in which step-layered inversion was employed. The results indicated that the initial model established with this method was very close to the true model, and this method would lead to inversing successfully. When modifying an initial model with step-layered inverion method, author used integer inversion in whch all data were used to inverse whole imageing region, and some modelling indicated that this way was proper to deal with one or two times iteratation and it would avoid over-inversion. Author also put forward the arithmetics to calculate and accelerate dump factor in dumping least squares method. To multi-solution character in 3-D resistivity inversion problem, author definitely inducted constraint condition ,such as non-negative condition. A lot of theoretical inversion simulation showed that better inversion result can be obtained by combining step-layered inversion method to establish initial model and integral inversion method to modify model, that the depth-coefficient, 0.8, is appropriate during calculating the projection depth of apparent resistivity measured with 3-D measurement under pole-pole configuration and that...
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