THE FEATURE OF SEISMICITY IN NORTHEAST CHINA AND ITS RELATION TO THE SUBDUCTION OF THE JAPAN SEA PLATE

Based on the analyses of grouped activities of deep-focus (m b≥6.0) and shallow-focus (M S≥5.0) earthquakes in Northeast China, the spatial and temporal correlation between the deep-focus earthquake group and shallow-focus earthquake group was studied. The study was focused mainly on the characteristics of earthquake distribution along the collision zone between the west Pacific plate and Eurasian plate, as well as its relation to the form of the west Pacific subduction zone. Moreover, emphasis was also laid on the analyses of the effect of the west Pacific plate on the seismicity in Eurasian plate. The results show that in the region where the west Pacific plate subducts at low angle, the seismicity along the plate collision zone is very strong, and the effect of plate subduction on the seismicity in Eurasian continent is most significant. In this condition, the subduction zone is subjected to relatively strong compressive stress. However, in the region where the west Pacific plate subducts at high angle, the seismicity along the plate collision zone becomes weaker, and the effect of plate subduction to the seismic activity in Eurasian continent becomes less significant. In this condition, the tensile stress produced by the subduction zone at depth is enhanced. We propose, therefore, that the seismic activity of Northeast China will enter the active period of shallow earthquake group in forthcoming 10 years. In this period, 6 earthquakes of M S≥5.0 may occur in this region. It is emphasized that the monitoring and prediction of seismic activity in Northeast China should be enhanced.