The Influence On The Earthquake-related Anomalies Of Apparent Resistivity From The Active Faults

It is known from the research of earthquake cases that the spatial distributions of anomalies of apparent resistivity related to an approaching earthquake are influenced by active main faults near the focal area and the focal mechanism. The influences include:(1) the anomalies appear mostly along or near the faults;(2) most anomalies are distributed in the two areas that are symmetrical about the epicenter and that azimuthally tie to the P-or T-axis areas that correspond to the focal fault movement; and (3) if there is an active fault between a recording station and an epicentral area, and the fault strike is along or near to the foregoing P-or T-axis, then, no anomaly is usually recorded at the station in the period approaching the EQ, or an anomaly is generally weak in amplitude.In recently years, it is noted that major active faults also appear to influence the spatial distribution of medium-term AR anomalies as follows. The anomalies are usually distributed near such faults in the vicinity of a focal area and appear synchronously along a same fault.In view of this problem, this paper has studied the faulting influence on the spatial distribution of apparent resistivity anomalies through analyzing typical cases of earthquake, in association with the spatially non-uniform distribution of underground media deformation. The geological body model applied to the2-D elasto-plastic finite element method, in which a fault is contained, is formed in order to simulate the faulting influence. Then, the strain changes in the geologic body model is calculated on the condition that the strike of the fault is different. Using the constitutive relations of the relative changes in apparent resistivity to media’s micro cracks, framework resistivity and crack-water resistivity. Finally, the calculated strain changes in a geologic body model are converted into the relative changes of apparent resistivity. This paper well explained a possible reason for the spatially non-uniform distribution of changes of apparent resistivity before an earthquake due to the influence of faults. According to the research results of the paper, the spatially non-uniform distribution of the anomalies of apparent resistivity around a focal area is mainly caused by the spatially non-uniform distribution of underground media deformation due to the active faults and different focal mechanisms; And different strikes of fault, different loading directions and the distributive configuration of the weak belt in the geological body resulted obviously in the spatially distribution of changes in apparent resistivity. The numeral simulation results are in accord with the existing research of earthquake cases.