Abstract: In areas with sharp variations in coal seam thickness, the electrical properties often exhibit low resistivity, which is similar to the transient electromagnetic  response characteristics of low-resistance faults. In full-space roadway transient electromagnetic  detection, distinguishing the geological sources of these two types of low-resistance responses is of great significance for selecting appropriate mine treatment measures. To address this issue, this study systematically investigates the conical transient electromagnetic response characteristics of coal seams in full-space underground mining environments based on the three-dimensional finite-difference time-domain  method. By constructing various geological models, the electromagnetic response patterns of high-resistivity coal seams in roadway roofs, floors, and sidewalls are analyzed in detail, and the dynamic effects of water-bearing faults and coal seam thickness variations on   transient electromagnetic signals are further explored. The results show that the electromagnetic responses of roof and floor coal seams are analogous; The lateral extension trend of apparent resistivity contours for high-resistivity coal seams is generally consistent with the coal seam thickness, forming distinct resistivity gradient zones at abrupt thickness change positions; Water-bearing faults exhibit significant anomalies in induced electromotive force  decay curves, multi-channel curves, and apparent resistivity sections, where lateral discontinuities can effectively indicate fault locations; And by combining multi-channel  curves with apparent resistivity inversion results, quantitative identification of thickness variations in high-resistivity coal seams can be achieved.

Key words:  transient electromagnetic method, finite-difference time-domain (FDTD) method, whole-space effect, high-resistivity coal seams, water-bearing faults