Abstract: It is of great significance to understand the preparation process and precursor of large earthquake based on analyzing the characteristics of seismic activity and studying on the basic laws of seismic activity. In this paper, RTL (Region-Time-Length) algorithm and seismic density calculation algorithm are used to analyze the seismic activity characteristics of the medium and strong earthquake in Hebei. The RTL algorithm is used to temporally and spatially retrospectively examine the earthquakes above M_W5.0 in the study area since 1970, and the seismic catalogues of 6 years ago are used. Time scanning result shows that the seismic activity is calm before the four earthquakes and the seismic activity is stronger before one earthquake. The spatial scanning results show the scanning image in one-year-scale for three years before the earthquake, and the result is consistent with temporal result. The selected data of seismic density algorithm is same as the RTL algorithm, the spatial scanning of three years scale slip before the earthquake is carried out for the three major earthquakes (M_L≥6.0) in the earthquake cases. The results show that, with time sliding, the seismic density of the area near the epicenter gradually decreases and tends towards calm before the earthquake. The results of the two methods show that the low point of seismic activity and the high value point of seismic activity may have some reference value for the prediction of earthquake in this region.

Key words: Region-Time-Length algorithm, Seismic density, Seismicity, Temporal scanning, Spatial scanning