Variation Characteristics of Geoelectrical Resistivity Anisotropy Values before Moderate-strong Earthquakes in Heze and Tancheng Stations

Based on the processed observation data of geoelectrical resistivity from Heze and Tancheng stations in Shandong province,the characteristics of precursor anomaly of geoelectrical resistivity anisotropy values are researched.The result indicates that there are obvious precursor anomalies of the anisotropy in both stations before M≥5 earthquakes occurring in range of 300 km,and the anisotropy values change in a stable variation range near the high value.Meanwhile the physical mechanism of this phenomena is discussed.