This study designed a group of 2D peak-valley comprehensive terrain models with different widths and slopes and investigated the influence of differently undulating terrains in mountainous areas on the audiomagnetotelluric (AMT) data and corresponding distortion characteristics from seven aspects, namely polarization modes, frequency, positions of measurement points, the width of a mountain top, the elevation difference and slope of terrain, and phase curves. The results are as follows. The transverse magnetic mode (TM mode) is more susceptible to terrain than the transverse electric mode (TE mode). The undulating terrain has little influence on the high-frequency parts of AMT data but has a great influence on their low-frequency parts. The apparent resistivity and phase of different frequency points at a measurement point reflect the comprehensive influence of all terrains within the skin depth level rather than just the influence of a single mountain peak or valley near the measurement point. Measurement points located at the mountain peaks are more easily affected by terrains than those in the valleys. Moreover, narrower mountain tops correspond to greater elevation differences of terrain, and steeper terrain exerts greater influence. In addition, the comparison of the 2D_TE results of the inversion considering and not considering terrains show that the 2D inversion considering terrains can effectively eliminate the influence of terrain. The 2D inversion considering terrains was carried out for measured AMT data. As indicated by the inversion results, the 2D inversion considering terrains can effectively eliminate the false high and low resistance anomalies and relieve the "hanging surface" phenomenon of signals, and the results corresponded well with the horizons with encountered manganese of three boreholes.
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