THE COMMON FEATURES OF DEEP STRUCTURES IN SOME LARGE-EARTHQUAKE AREAS OF THE NORTH CHINA PLAIN AND THEIR IMPLICATION FOR EARTHQUAKE SITE PREDICTION

This work deals with the deep structure of the earth's crust and the uppermost mantle as revealed by a method using P-SV converted waves from earthquakes in Beijing-Tianjin-Tangshan and some large-earthquake areas of the North China Plain. During the last ten years a series of seismic profiles have been completed in the studied region with a total length of about 2, 000 km. The comparison of deep structure with the distribution of earthquakes indicates that most strong earthquakes are located at the boundary of fault-blocks and especially at the intersection of deep-seated fault zones where the depth of deep boundaries changes discontinuously. Some common features of the deep structure have been revealed in Tangshan and other large-earthquake areas of the North China Plain. These include shallow crystalline basement, deep Moho discontinuity, thick crystalline crust, and intersection of deep-seated faults with different trends. By way of structural comparison, some areas with deep structures similar to those of large-earthquake areas have been established in the northern part of the North China Plain, which could be considered the areas with potential risk for strong earthquakes.