THE CHARACTERISTICS OF INTRAPLATE EARTHQUAKE FAULTS IN NORTH CHINA AND THEIR RELATIONSHIP TO THE DYNAMICAL PROCESSES IN EARTH'S CRUST AND UPPERMOST MANTLE
Ye Hong and Zhang Wenyu (Institute of Geology, State Seismological Bureau)
The mechanical nature of 121 earthquake faults, the strikes of 40 events and the directions of fracture propagation of 15 events are discussed in this paper.On this background,some relationships between the strikes of intraplate earthquake faults in North China and the distributions of uplifted zones of uppermost mantle have been found, e. g. within these zones the earthquake faults run nearly parallel tp their elongation, while on their opposing sides the earthquake faults are mainly perpendicular to them. However, it seems to be that the mechanical nature and the direction of fracture propagation are not controlled by the pattern of rising of uppermost mantle, but coincide with the general characteristic feature in the eastern part of China continent.The authors hold that there exist two types of geodynamical processes in North China, the one is, the North China fault blocks are subjected to a compression trending NEE-SWW due to the eastward movement of the Xizang (Tibet) block, the other is, the diapirism of the upper most mantle and the gravity isostasy make the continental crust of North China thinning and its certain parts having lense-shape. The characteristics mentioned above and the cause of the high seismicity in North China could be explained by the superimposition of these two dynamical processes.