Characteristic analysis and precursory anomaly in weak seismic region

Based on the data of precursory anomaly observed in Shaanxi Precursory Network, we analyzed the characteristics of precursory anomaly in the regions where there are no or few earthquakes. The ratio of precursory anomaly is between 11% to 20% for different precursory means and the comprehensive ratio of anomaly is 15% in Shaanxi Precursory Network. There is no earthquake with M S ≥5.0 and usually only two to three earthquakes with M S ≥3.0 occurred every year and the average magnitude of maximum earthquakes for every year is M L =3.6. The curve variation between the anomaly ratio, seismic frequency and seismic intensity in Shaanxi region is not synchronal. So, it is concluded that the precursory anomaly is not the earthquake precursor, and it may be the interference unknown or the result of aseismic slipping in crust.