地电阻率季节干扰变化分析

ANALYSES OF THE SEASONAL VARIATION OF DISTURBANCE IN GEORESISTIVITY

  • 摘要: 结合我国实际,本文提出四类地电阻率季节变化的干扰模型.经模型理论计算及同有季节变化的四十多台站的实测资料对比得出:(1)地电阻率季节变化是探测深度偏浅时,地表层电性变化,特别是表层地下水水位年动态变化所引起的一种与地震无关的干扰变化.其变化形态与量级取决于干扰模型、地电断面类型以及探测深度.(2)通常地电阻率季节变化与浅层电阻率变化的符号一致,呈现出正常季节变化;但对 K,Q 型地电断面,当干扰层位于地表第一层时,将从某一供电极距开始,出现反常的季节干扰变化.(3)当探测深度大于300m 时,不论正常的还是反常的季节变化,其幅度都将小于2%.因此,只要适当选择台址或加大供电极距使探测深度足够大,便可排除或压低这种干扰.

     

    Abstract: Four models for the seasonal variation of disturbance in georesistivity are presented in the light of specific conditions in China. As the result of theoretic calculation of the models and in comparison of the calculated results with the seaonal variations observed at 40 georesistivity stations, the following points are found: (1) the seasonal variation of georesistivity is caused by the change in resistivity of the surface layer, especially by the annual variation of groundwater level when the sounding depth is too shallow. This is one of the interference changes and is irrelevant to the occurence of earthquakes. The feature and amplitude of the seasonal variation depend on the types of disturbance models, geoelectric sections and the sounding depth. (2) The seasonal variation of georesistivity usually has the same sign as that of the change in resistivity of shallow layer and thus the normal seasonal change appears. However, as far as the K or Q type of geoelectric section are concerned, the abnormal seasonal variation in georesistivity starts from a certain electrode separation when the interference layer is located in the surface layer. (3) Both abnormal and normal seasonal variations in georesistivity will be smaller than 2% when the sounding depth is deeper than 300 m. Therefore, the seasonal variations can be removed or limited when the location of observation is properly chosen and larger electrode .spacing is used, so that the sounding depth is large enough.

     

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