Abstract
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.
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