STEREOSCOPIC FIGURES OF THE TIME-VARIATION IN THE SPACE DISTRIBUTION OF FOCI OF THE XINGTAI EARTHQUAKES AND THEIR OCCURRENCE PROCEDURE

In this paper,the procedure of the time-variation in focal space distribution during the high seismicity period of the Xingtai earthquakes of March 1966 is studied by using seismic data obtained by the Xingtai Local Seismic Network.A series of stereoscopic figures showing the process of seismogeny and rupture of the strong shocks,adjustment of the stress field and seismo-structure are given. A further study is made of the relation between earthquakes and barriers existing in the crustal medium of the seismic region. It is this kind of non-uniform structure in the seismic area that caused the rupture of the Xingtai earthquake to be a discontinuous growing procedure expanding along the NNE direction,through which the occurrence of several earthquakes stronger than Ms 6.0 and the phenomenon of flip-flops from one and to the other of the fault of big aftershocks after the high seismicity period can be well explained.Besides,the ruptures of strong shocks bigger,than Ms 6.0 are discussed and compared with some results obtained before. And a survey is made of the relation between the variation in focal depth with time and the occurrence of big earthquake in the Xingtai region.