Objective The conventional inversion of surface direct-current (DC) resistivity data faces challenges such as limited exploration accuracy and depth. This study aims to enhance the accuracy and reliability of exploration in complex engineering and geological settings through the joint inversion of borehole-surface DC resistivity data.

Methods First, different geoelectric models were constructed through three-dimensional (3D) forward modeling of full-space DC resistivity. Then, the potential response characteristics under surface and borehole observation methods were systematically analyzed to determine the differences in detection sensitivity between surface and borehole observations. Accordingly, a joint 3D inversion technique for borehole-surface DC resistivity data was developed using the Gauss-Newton method. Finally, the effectiveness and superiority of the joint inversion technique were verified using theoretical models and actual data.

Results and Conclusions  The inversion of surface observations yielded high lateral resolution but a limited vertical resolution, while the inversion of borehole observations exhibited a high vertical resolution. In contrast, the joint inversion of borehole-surface data provided more accurate resistivity structures and physical property values. The effectiveness of the joint inversion technique was verified using both theoretical models and actual data. The verification results demonstrate that the joint inversion technique combines the advantages of the surface and borehole observation methods, thereby enhancing both the spatial resolution of inversion results and the capability for identifying deep anomalies. Therefore, the developed joint inversion technique provides technical support for improving the exploration accuracy in complex engineering and geological settings.