Abstract: An evaluation method of prediction effectiveness of precursory anomalies is proposed,and the prediction effectiveness of water level anomaly at Banqiao station, Beijing,is evaluated by comparing with that of the random and regular anomalies. The results show that the five-day mean of the water level, taking the residual of Weinna filtering over the standard deviation as anomaly,can predict earthquakes with moderate magnitude along Zhangbei-Tangshan seismic belt.When the anomaly occurs,prediction with 80days time window can be made.In this case,R-value could reach 0.43and the confidence can be over 70％. This method can be applied to evaluate the prediction effectiveness of the precursory anomalies.

Key words: Earthquake precursor, Prediction effectiveness, Evaluation method