A method to express pattern of seismicity anomaly before strong earthquakes and its predictive value

Two parameters describing the pattern of seismicity anomaly before strong earthquake were proposed in this paper, and it was used in North China, Xinjiang and South-North seismic zones. The predictability of those two parameters was tested; the relation between the anomalous distribution pattern and the position of strong earth- quakes was studied. The results show that those two parameters could better express the anomalous seismic quiescence and anomalous seismic clustering within the seismic zone be- fore strong earthquakes. From the time-space anomalous pattern of,we can see that the anomaly distributed around the epicentral area from three months to one year before moderately strong earthquakes obviously,and with the time approaching to the origin time of an earthquake, the size of anomalous area is relevant to the earthquake magnitude. Re- gardless of the variation of pattern with time, we Just regard the earthquake occurred in one year after anomaly appearing as correct forecasting, the forecast evaluation marks R for three seismic zones are greater than 0.5.