I propose a method that uses alpha centers for two-dimensional automatic analysis of dc electrical exploration data. Past papers on the alpha centers method have been concerned with relatively simple applications, such as identification of the location of anomalies; but by making a number of improvements on the method, complex two-dimensional structures can be analyzed.The appropriateness of using negative C parameters in the alpha centers method is demonstrated by considering the resistivity and electric potential distribution expressed by the alpha centers. In this way, the structural expression of alpha centers is improved. Using a network of fixed alpha centers both stabilizes the analysis and makes it possible to employ a large number of alpha centers (more than 100). The combination of these improvements, compensation for topography, and application of a nonlinear least-squares method, which has good convergence throughout the iteration process, makes automatic analysis possible.Three numerical experiments demonstrate the effectiveness of this method. The first two simulate standard exploration from the ground surface. One is a simple prism model; the other, an inclined fault model. The final experiment simulates measurements between boreholes or adits. These experiments demonstrate that good results can be obtained by the alpha centers method, which has heretofore not been suitable for highly resistive structures or underground structures having sharp boundaries. Furthermore, the experiments show that this method has high resolution. Finally, the fact that one of the experiments shows the alpha centers method to be effective for cross-borehole data analysis suggests its wide applicability.The applicability of the method is also demonstrated by two field experiments. The first identifies the form and distribution of lava in the ground, and the second investigates the distribution of intrusive rock and alteration zones in a steep, mountainous area.

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