Abstract: For the aim of deleting the aftershocks as scientific as possible and preserving the valuable information for earthquake prediction, a method of deleting the aftershocks, called SMRZ method in short, which not only considers the earthquake sequence features, but is based on the contrast between the aftershock activity frequencies in the seismogenic zones after main shocks and the regional seismic activity frequency during normal period also. And the corresponding computation program has been compiled. Taking several relatively large earthquakes occurred in Northwest region as the examples; the contrast study has been done on the effects of deleting aftershocks through comparison between the SMRZ method proposed in this paper, the K-K method widely in use at present and the G-C method. The results show that, comparing with other methods, the method proposed by authors is relatively rational in recognizing the temporal and spatial distribution ranges of aftershocks. At the same time, the foreshocks have been preserved which have important prediction meaning to future earthquakes. Its practical use effects are better.

Key words: Seismic activity, Earthquake frequency, Aftershock deleting method, Northwest region