Abstract: There are six common features for precursory anomalies before strong earthquakes. The following features are in seismological aspect:first, the quiescent anomaly appears in the gap segment between occurred strong earthquakes; second, moderate and small earthquakes or swarms are quite active outside the source areas of strong earthquakes and quiescent within the source area during medium- and short-term stage, forming a ring or R-tgap. The features in the fixed station precursors are as follows: first is the nonlinear feature for the starting time of anomaly; second is noncontinuous feature for the spatial dist ribution of anomalo us stations; third is the sudden increase feature of anomaly quantity in the short-term and impending stages; fourth is the huge variation feature of anomaly amplitude in the short-term and impending stages. The evidences mentioned above can not be explained by the existed DD and IPE models, but can be taken as basis of hardening model of source. In the prediction practice of strong earthquakes, the gap segment and area can be taken as index of location, and increase of anomaly quantity and accompanying huge anomaly as the index of entering short-term and impending stages. The anomaly is not obvious within the source areas in other time segments except some cases 1~2 days before strong earthquakes. It certainly makes a mistake according to the traditional model to guide the practice, and it can be avoided if using the revealed common features to direct prediction.

Key words: Medium-and short-term precursor for strong earthquakes, Common features, Quiescence in the source area