大地电磁测深曲线的畸变及校正

The distortion of magnetotelluric sounding curves and its correction

石油物探局物探地质研究院,涿州 0722751

Geophysical & Geological Research Institute Bureau of Oil geophysical Prospecting, zhuozhou 072751

在Cagniard(1953)提出的大地电磁测深方法中,定义视电阻率时,作了两个重要假定：天然电磁场是垂直向下传入地球的平面波;地球是横向均匀的。通常这两个假定是不成立的。造成大地电磁测深曲线畸变的两个最主要的原因：一是近场源的干扰,二是非一维构造。现在,大地电磁测深解释仍是以一维解释为主,也就是所谓的“一维形式化解释”。其中非一维构造引起的大地电磁测深曲线畸变(又称为“构造畸变”),是相对于一维构造的大地电磁测深曲线而言的、目前大地电磁测深解释中的一项工作就是对畸变的曲线进行识别和校正。本文从理论和实际曲线分析两方面阐述了曲线畸变的机理和特征,并提出了合理的校正方法。

In the magnetotelluric sounding method proposed by Cagniard (1953),two important assumptions arc made when defining the apparent resistivity:the natural EM field is a plane wave vertically downward propogating to the carth,and the earth is transversely homogeneous. Usually,these two assumptions are untenable. Two main reasons causing the magnetotelluric sounding curves distorted are the intcrfercnce near ficld source and the non-1D structure. Up to now, 1D interpretation is still the main body of the magnetotelluric sounding interpretation, which is so-callcd "1D formalization interpretation ". The distortion of magnctotelluric sounding curves causcd by mon-1D structure (also called"structurc distortion") is in respect to thc magnetotelluric sounding curves of 1D structure. At present,onc job in the magnctotelluric sounding interpretation is to recognize and correct the distorted curves. In this paper,the mechanism and character of curve distortion are expounded in terms of both the theory and the real curves analysis,and the reasonable correction method is presented.