山区电磁测深的地形影响分析

Topography effect on MT surveys in mountainous areas

1. 成都理工大学,四川成都 610059;2. 中国石油东方地球物理公司国际部,河北涿州 072751;3. 中国石油东方地球物理公司研发中心,河北涿州 072751

Chengdu University of Technology, Chengdu 610059, China

探讨了山区地形对大地电磁测深曲线的影响。设计了山地地形的二维和三维模型,并进行了模型正演。正演结果的对比表明,地形相对高差越大,畸变越大。在二维情况下,地形起伏变化主要引起TM极化模式曲线畸变,而对TE极化模式曲线影响较小;在三维情况下,地形起伏变化主要引起2种极化模式曲线低频段畸变, 且畸变的情况较复杂。针对实际地形条件进行了地形对测深影响的高差实验,实验结果表明,当地形起伏不大于极距的30%时,基本上可以忽略地形起伏对测深资料的影响,某山区的实测资料也证明了这一结论。综合分析正演模拟、野外高差试验及山区实测资料表明,在山区进行大地电磁测深时,地形起伏产生的地表不均匀性引起的静态影响十分严重,远远大于地形影响。

The mountainous areas were impacted to Magnetotel-luric (MT) surveys curve. To forward modeling by simulation calculation with 1-D, 2-D and 3-D methods: The rugged topography undulation distortion of TM polarization model and less affection for TE polarization model in 2-D. In 3-D, the rugged topography undulation distortion of TM and TE polarization models, the distortion principally affects low frequency of apparent resistivity curves. Also, the experiment of MT electrodes with various elevations is made; it is shown that the effect of topographic relief on MT data can be ignored when the volume of topographic relief difference is less than 30% of polar distance volume. Due to the undulate topography, the static effect for surface heterogeneity is serious and must be eliminate (or suppress). Static effect correction is a key technology for MT data processing and interpretation.