Abstract: On the basis of the seismic activity feature and tectonic background of the Southeast China coastal seismic belt, several locations where seismic activity is highly con-centrated are determined, and the seismic swarming windows and magnitude structure concepts are introduced to analyze the partial features of these locations. The results show that the seismic activity level changes of these seismic swarming window sreflect the stressstate of the large area where the earthquakes occurred. When some seismic swarming windows show the anomaly of their magnitude structure and seismic swarming events with the features of precursory seismic swarms, it probably indicates that the medium properties of those seismic swarming windows or their related parts have been changed. Therefore, this method has some efficiency in mid-term prediction of the moderately strong earthquakes or strong events.

Key words: Southeast China coastal seismic belt, Seismic swarming window, Magnitude structure, Concentration magnitude, Precursory seismic swarm