滇西地区几个测点的大地电磁视电阻率影响系数分析

Analysis on Influence Coefficient of MT Apparent Resistivityat Several Sites in Western Yunnan

采用水平分层均匀的地电阻率结构模型,研究了滇西地区3个测点的MT视电阻率影响系数随频率变化的特征。结果表明:①各地层视电阻率影响系数都随周期变化,为了更好地获得地震多发层内地电阻率变化信息,可以通过影响系数值选择合适的电磁场频段;②在某一特定周期内的短周期段,视电阻率主要反映易受干扰的第一层的变化,对于地震观测而言,应避开该周期段,该周期值可以通过影响系数分析确定;③各地层影响系数之和并非常数,而是随周期变化,在不同频段观测的视电阻率反映地层电阻率变化的能力不同。影响系数分析对MT地震观测频段和测点的选择具有一定的指导意义。

We studied the characteristics of MT apparent resistivity influence coefficients varying with frequency at three sites in Western Yunnan using the stratified homogeneous geo-resistivity structure.The result shows:①The apparent resistivity influence coefficients of each layer vary with the period,we could select the appropriate electromagnetic field frequency band through the influence coefficient value so as to obtain better information on the change of resistivity of the stratum in the earthquake-prone layers;②In the short period within a certain period,the apparent resistivity mainly reflects the change of the first layer that is susceptible to interference.This period should be avoided for seismic observation,and the periodic value can be determined by influence coefficient analysis;③The sum of the influence coefficients of each layer is not a constant but varies with the period.The apparent resistivity observed in different frequency bands has different ability to reflect the variation of the formation resistivity.The influence coefficient analysis has certain guiding significance for the selection of electromagnetic field frequency band and observation site of MT seismic observation.