Abstract: This paper summarized the dynamic background of seismic activity of northeast China. The results show that there is relationship between deep focus earthquakes and western Pacific subduction plate. These deep shocks are resulted from the western Pacific plate thrusting under the continent of northeast China with small angle (about 26°) and high velocity by means of the relationship between Japan sea trench western Pacific subduction plate and deep focus earthquakes of northeast China, as well as the average results of focal mechanism of deep focus earthquakes of northeast China and the relationship between strong earthquakes of Japan sea trench and deep focus earthquakes of northeast China. The result of space-time distribution of deep focus earthquakes and shallow focus earthquakes as well as activity period of shallow focus earthquakes show that there are five activity periods of shallow focus earthquakes for northeast China, and there is individual difference for shallow focus earthquakes in every activity periods. Based on these, the space-time distribution characteristics of the closing earthquakes of every activity periods for shallow focus shocks are analysed, and find that there is a long calmness of 4.19 years before closing earthquakes characterized by double earthquakes.

Key words: Dynamic background, Japan sea trench, Northeast China, Deep focus shock, Shallow focus shock