AMT地形影响与带地形反演研究

通过设计1组二维不同宽度、不同坡度的峰谷综合地形模型,分别从极化模式、不同频率、测点位置、山顶宽度、地形落差、地形坡度、相位曲线7个方面来研究总结山区不同起伏地形对AMT资料的影响程度和畸变特征,发现TM模式较TE模式更容易受到地形影响;起伏地形对AMT响应的高频部分影响较小,而在低频部分地形影响较大,某一测点不同频点的视电阻率和相位是对应趋肤深度水平范围内所有地形的综合影响,并非仅仅是该测点附近单一山峰或山谷的影响;山顶测点较山谷测点更容易受到影响,且山顶越窄、地形落差越大、地形越陡,影响越大。此外,文章还通过对比理论模型的不带地形和带地形2D_TE模式反演结果,发现带地形的二维反演可以有效地消除地形影响,并对实测AMT资料开展带地形的二维反演,结果显示带地形的二维反演可以有效消除虚假高低阻异常,改善了“挂面条”现象,与3口钻孔的见锰层位对应较好。

Audiomagnetotelluric data: Influence of terrain and the inversion considering terrain

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.