Abstract: The precursory data observed before and after the 44 earthquakes occurred during 1975~1996 are analyzed. The research results show that when the seismicity entered into the short- and medium- term stag of earthquake preparation, the monthly frequency of comprehensive precursors, including the far-field precursors, the near-field anomalies and near-field far-field combined precursors are significantly characterized with the following aspects: 1. The cumulative curves of monthly frequency accelerate nonlinearly; 2. Variation rate of monthly frequency is positive. According to the two features, it is easy to distinguish the short-term and medium-term seismicity. The method can be used widely and easily based on the broadly studied data set and the obvious anomalies.

Key words: Preparation stage, Precursory anomaly, Comprehensive precursory characteristics