CSAMT视电阻率曲线对水平层状大地的识别与分辨

Identification and Discrimination of the Horizontal Layered Earth by Using CSAMT Apparent Resistivity Curves

在三层和五层介质模型上,通过改变各电性层层参数并进行相应的数值计算,比较并分析了可控源音频大地电磁法卡尼亚视电阻率曲线对各层信息的识别与分辨能力。上部覆盖层厚度的增大和电阻率的减小使视电阻率曲线对下部信息的分辨能力下降,而下部地层层参数变化的影响则相对较小;低阻薄夹层对曲线的影响主要由其纵向电导所决定,纵向电导越大异常值越明显;高阻夹层对曲线的影响则取决于其厚度埋深比,比值越大高阻层越易于分辨,而曲线对高阻层电阻率值变化反应不敏感;在10%的分辨标准下,当低阻夹层纵向电导大于覆盖层的0.2倍、高阻夹层电阻率大于围岩5倍以上并且厚度埋深比大于0.2时,各有可分辨异常。相邻高低阻层差异的增大将使曲线的震荡假异常更加明显,导致分辨能力下降。

This work compares and analyzes the capability of CSAMT apparent resistivity curves to identify and discriminate earth layers.Numerical calculations have been made on three-layer and five-layer models with changing electric parameters of each layer.The result shows that when the thickness of the overlying cover increases and its resistivity decreases,the discrimination ability of the curves to the information of the underlying strata declines,while the variation of parameters of the underlying strata has a relatively small influence on this ability.The effect of the thin conductive interlayers to the curves is mainly dependent on the vertical conductance,while the ratio of thickness to depth is more important to the high resistivity layer,i.e.,a larger ration makes discriminating high-resistivity layers easier.While the vertical conductance for the intermediate conductive layer is 0.2 times higher than the cover layer or the ratio of thickness to depth for the high resistivity layer is greater than 0.2 and the resistivity is at least 5 times higher than the wall rock,there are distinguishable anomalies for each case,respectively.Oscillatory false anomalies will be more obvious on curves when the difference of resistivitiy between two adjacent layers increases which will decrease the resolution of the curves.