In view of the objective of suppressing shallow interference and highlighting the useful information from the depth,we selected a field site in the middle section of the Xiaojiang fault as an example,and developed a method for determining the parameters such as the buried depths and intervals of electrodes in the borehole geo-resistivity observation for seismic precursors. The research shows that two major factors,the influence coefficient and the probing depth,should be considered when selecting parameters for borehole geo-resistivity observation,namely the influence coefficients of all the layers above the water table should be far less than that of layers in the deep. The influence coefficient of the bottom-layer(the layer influenced the most by the seismogenic processes)within the detection range should be far greater than that of any other layers; and at the same time,it is also required that the probing depth of the observation system is not less than that indicated by the existing earthquake cases. Finally,according to this method,we selected the parameters of underground resistivity observation,i.e. the buried depth of the electrode is 200 m,the distance between the power supply poles is 1 050 m,and the intervals of electrodes is 350 m. The optimal observation effect can be obtained by arranging the symmetrical quadrupole.
