Abstract：Considering complex geoelectric model,the study of 3-D inversion approaches of borehole-to-surface electric data is always a challenge. As a direct 3-D electromagnetic forward approximate modeling method,the traditional integral equation approach is characterized by a great deal of computational effort and lower precision.In order to avoid the shortcomings of integration approach,the quasi-analytic approximation (QA) emerges with characteristics of rapid computational speed and high precision.On the basis of quasi-analytic approximation and re-weighted regularized conjugate gradient method (RRCG),the paper deduced a set of algorithms practically used and used Visual Fortran 6.5 to develop the program of 3-D quasi-analytic approximation inversion of borehole-to-surface electric data. The inversion tests of synthetic data of theoretical models showed the 3-D inversion program of borehole-to-surface electric data based on QA and RRCG is characteristics of rapid computational speed and high precision of inversion.
