大柏舍深井地电阻率观测布极方式分析

为了评估观测质量,本文结合大柏舍地震台电测深资料,采用水平层状介质模型分析了该台站对称四极装置深井地电阻率观测时影响系数随电极深度和观测极距的变化。分析结果表明:大柏舍台现有的深井地电阻率观测水平测道虽然能有效地抑制来自地表的干扰,但是由于观测极距较小,不能很好地反映深部介质电阻率的变化信息;垂直测道因电极埋深位于地下水位变动层位,观测数据受地下水位波动影响较大,较难识别来自深部介质的信息。为有效地记录可能的孕震信息,水平测道极距AB/2取250~350m、埋深H150m能满足需求,并建议增加NS向水平测道观测。

Analysis on Deep-Well Apparent Resistivity Measurement at Dabaishe Seismic Station

In order to evaluate the quality of observation,we interpreted the horizontally layered homogeneous medium model of Dabaishe station according to the electric sounding data.The measurement arrays at the station are the fixed Schlumberger arrays.The deep-well measurement has two set of arrays.One was horizontally placed shorter than 100 meters,and the other was vertically arranged.Under the layered model,we analyzed the sensitivity coefficient variations of deep-well apparent resistivity measurement versus the different electrode depth and the spacing of current electrodes.The results show that the horizontal deep-well measurement has strong ability on inhibiting from surface disturbances.However,its current electrodes spacing is relatively short,only 60 meters, thus the measurement data didn't effectively reflect the resistivity variations from deep mediums.The electrodes of the vertical deep-well measurement array is located within the layer where underground water level changes;therefore,its measurement data suffer a strong affection from water level variations,and it is very difficult to distinguish the resistivity variations of deep mediums from the data. In order to better detect the information associated with earthquakes,the spacing of horizontal arrays of AB/2 should be set as 250-350 m,and the bury depth should exceed 150 m.A horizontal array along NS direction is also recommended for a better result.