Abstract: Resistivity in the North-south direction at Tanggu station increased obviously after the measuring space was shortened.In order to further understand the variation causes, the resistivity was contrasted to the original spacing for several times and was analyzed by using forward calculation and inverse explanation.The result shows that the resistivity variation was related to the shortening of spacing.The affection of near-surface layer to geoelectric resistivity measurement was increased and the affection of deeper layer was decreased with the shortening of spacing.However, the resistivity variation due to the shortening of spacing is not associated with earthquake precursor.

Key words: Resistivity sounding, Abnormity determinant, Forward calculating and inversion explaining