复杂地区大地电磁测深曲线的性质及资料解释问题综述

OVERVIEW OF THE CHARACTERISTICS OF MT CURVES AND THE INTERPRETATION OF MT DATA IN COMPLEX AREAS

本文详细地综述了各种常见二维地电断面(如浅层电性不均匀体、地形、断层、地堑、地垒、逆掩断层、推覆体等复杂地区)上MT曲线的特征及其解释方法。在二维情况下,浅层电性不均匀主要使TM曲线发生平行移动;在其它二维断面情况下,两条视电阻率曲线表现为强烈的各向异性。一味选择一种极化的视电阻率曲线解释会发生严重的错误。在这种情况下,正确的解释方法应该是:首先,根据张量阻抗、倾子以及已知地质、地球物理资料确定岩层的走向和倾向;其次,根据不同情况,选择不同的曲线,或TE,或TM,或综合曲线进行解释,或作二维反演。只有这样,才能求得比较接近真实的地电断面。

So-called complex areas are referred to those in which geoelectrical sections are quite different from 1-D models. It shows that MT curves from these areas are seriously distorted. In this paper, we have summarized the characteristics and steps of interpretation of MT data from some of 2-D models which are always met in practice, such as shallow conductive inhomogeneities, terrain, fault, graben, horst, thrust, and so on. It is clear that shallow conductive inhomo-geneities make MT curves shift and others make M.T curves show anisotropy, The steps of interpretation of MT data are as follows: firstly,to determine strikes and dips of strata with tensor impedance rotation, tipper or geological and other geophysical information; secondly, according to different cases, to choose proper curves (such as TE, TM or ρm =(ρTE.ρTM)1/2 to interprete them with 1-D inver-sion or to do 2-D inversion directly. By this way, one can get a result close to the true one.