Research on the effect of topographic distortion on AMT and its inversion with terrain

The paper designs a group of two-dimensional peak-valley comprehensive terrain models with different widths and slopes, and under the condition of different terrain, we studied distortion characteristic of AMT information from polarization mode, different frequency, the measuring point position, terrain elevation difference, the top width, the terrain slope, phase curve, the uniformity of underground medium. The results showed that: TM mode is more easily affected by topography than the TE mode; The undulating terrain has little influence on the high-frequency part of the AMT response, but has a greater influence on the low-frequency part. The apparent resistivity and phase of different frequency points at the same measuring point are the comprehensive influence of all terrain within the skin depth level, not just the influence of a single peak or valley near the measuring point; Measuring points located in the peaks than in the valleys more easily affected by topography; The narrower the top, the greater the terrain gap, the steeper the terrain, the greater the topographic effects. In addition, the paper also compares the 2D_TE inversion results with and without terrain of the theoretical model show that the two-dimensional inversion with terrain can effectively eliminate the influence of terrain; The twodimensional inversion with terrain is carried out on the measured AMT data, and the results show that the two-dimensional inversion with terrain can effectively eliminate the false high and low resistance anomalies, improve the “hanging surface” phenomenon, and correspond well with the manganese horizon of three boreholes.