井下地电阻率观测影响系数分析——以江宁地震台为例

Sensitivity Coefficients Analysis of Deep-well Resistivity Observation in the Jiangning Seismic Station

摘要:

采用水平层状均匀介质中点电源位于任意深度时的电位解析表达式，以江宁台3层电性结构为例，分析了井下对称四极地电阻率观测时各层影响系数随深度、极距的变化，并结合探测深度探讨了实施井下观测时影响系数在选择供电极距和电极埋深时的作用。结果表明，对于"K"型电性结构，江宁台井下观测对地表、浅层干扰有较强的抑制作用，其短极距观测对地表、浅层干扰的抑制能力显著优于长极距观测；长极距观测在电极埋深H小于100m时对地表介质季节性的干扰具有放大作用；浅层影响系数一定时，电极埋深和供电极距需同时增加；江宁台井下观测供电极距AB/2取100~150m、电极埋深H为250m较为合理。

Abstract:

With the analytical expression of the potential of a point-level power supply with a horizontal layered uniform medium at an arbitrary depth,we take the three-layer electrical structure of the Jiangning seismic station as an example,analyze the variation of the influence coefficient of each layer with depth and pole distance when the symmetrical quadrupole resistivity is observed,and combined with the depth of detection,explore the distributions of influence coefficients with the spacing and depth of electrodes when the Schlumberger arrays are used in the resistivity observation. The results show that the deep-well observation of the Jiangning seismic station has good inhibition to surface and shallow interference. The short-range observation has a significantly better ability to suppress shallow surface disturbance than the long-range observation. Disturbances from surface might be amplified when the deep-well observation is within 100m for the K-type electrical structure. For the fixed sensitivity coefficient,the electrode burial depth increases with the current electrode length. The annual variation features are analyzed by calculating the influence coefficient of each layer. It is reasonable to take 100~150m from the electrode length and 250m from the electrode buried depth. The calculated results could be used as reference for the selection of electrode buried depth and current electrode length when deep-well observation would be used in similar stations.