Anisotropic change in apparent resistivity before earthquakes of M S ⩾ 7.0 in China mainland

Abstract

Since 1967 when DC apparent resistivity observation was carried out in China, there have been 16 times or groups of earthquake of M S ≥ 7.0 occurred within about 400 km from the monitoring stations. The apparent resistivity showed medium-short term continuous changes before 13 times or groups of these earthquakes. The medium-term changes usually lasted for several months to about two years. Apparent resistivity of monitoring arrays placed in different directions at the same station showed anisotropic change related to the maximum principal compressive stress orientation (i.e. P axis). The larger the angle between a monitoring array and the P axis is, the greater the magnitude of change in apparent resistivity is. According to the results from rock physics experiments, resistivity model of cracked rock-soil medium, and fault virtual dislocation model, the changes in apparent resistivity before earthquakes may be related to the seismogenic process through a way of resistivity change caused by medium deformation.