Study on the medium-and short-term anomaly pattern of seismic activity in North China

After studying different kinds of earthquake activities systematically, we have found that about 83% of the anomalous seismic bands, seismogenic gaps and signal earthquakes with magnitudes 3 or 4 appeared at the same time before moderately strong earthquakes (ML36) since 1970 in North China. 92% of earthquakes were followed signal earthquakes, and 83% of these signal earthquakes are within distance of 150 km from the main earthquakes and 67% of which were followed by main earthquakes occurred in less than a year. 90% of seismic bands formed in two years, and 83% of main earthquake occurred in 5 months after the formation of seismic bands. 83% of seismic gaps formed in a year and half and 91% of main earthquakes occurred in 50 days after the formation of seismic gaps. These characteristic are very significant short-term anomaly features of seismic activity pattern. We also discussed the relationship between quantitative discriminant index of anomalous band pattern and the future strong earthquakes, which is practicable in earthquake prediction.