Abstract: Based on some given criteria, the earthquake activity patterns are obtained by special and temporal scanning in North China for M2.0 earthquakes since 1970. There are 115 items that are determined to be abnormal according to the criteria, and the relationship between the abnormal patterns and later moderate-strong earthquakes are analyzed in this paper. Results show that the following 3 conditions are the necessary ones for a future moderate-strong earthquakes in North China: ① no earthquake takes place within a period of 40 days within an ellipse area in North China with major and minor axes over 300 km and 100km respectively; ② M2.0 earthquakes are concentrated in a subarea with a quieter periphery; ③ M2.0 earthquakes take place along a belt or around a gap lasting more than 30 days. The abnormal patterns could be used as a signal to determine moderate-strong earthquakes in North China in the near future.

Key words: North China, Moderate-strong earthquake, Seismicity, Abnormal pattern