Relationship between the deep crustal features in velocity structure and the preparation of strong earthquakes in Xingtai area

This paper deals with the effect of the inhomogeneity of the crustal struct ure on the stress field by using 3-D finite element method. The variations in mean stress and in horizontal shear stress for a layered crust model are calculated under conditions with a high velocity body; a low velocity body ; and a combined high-low velocity body in the model respectively. The corr esponding results indicate that (1) the stress concentration due to the exi stence of the high velocity body can reach very high values on the corners and the borders of the body, which would be favorable for the earthquake pr eparation, (2) it is not easy to form a strong earthquake within and nearby the low velocity body, where high enough stress could not be accumulated, and (3) the existence of a combined high-low velocity body might play an im portant role in forming higher stress concentration within the high velocit y body and relative high stress concentration in some places out of the hig h velocity body, which would be advantageous to the earthquake preparation. The calculation results coincide quite well with the spacial distribution of Xingtai earthquake sequence.