邢台地震区地壳速度结构特征与强震孕育发生的关系

运用三维有限单元法，探索地壳结构的非均匀性对地壳应力场的影响．假定分层地壳结构中镶嵌高速块体，低速块体，高、低速块体３种情况，分别计算壳内平均应力与水平剪应力的变化图像．结果表明：高速块体单独存在可导致高应力在高速体内的局部集中，并在其边缘和四个角区形成应力的高度集中，有利于强震的孕育和发生；低速体单独存在时，由于低速体本身不能积累应力，而其上部的应力集中程度不大，难以形成强震；高、低速体的同时存在则有利于高应力在高速体内的高度集中和在高速体外的地壳上、下部的相对集中，形成对大地震孕育、发生更加有利的条件．本文结果与邢台地震序列的空间分布图像吻合甚好．

RELATIONSHIP BETWEEN THE DEEP CRUSTAL FEATURES IN VELOCITY STRUCTURE AND THE PREPARATION OF STRONG EARTHQUAKES INXINGTAI AREA

This paper deals with the effect of the inhomogeneity of the crustal structure onthe stress field by using 3-D finite element method. The variations in mean stress andin horizontal shear stress for a layered crust model are calculated under conditionswith a high velocity body; a low velocity body; and a combined high-low velocitybody in the model respectively. The cormsponding results indicate that （l） the stressconcentration due tO the existence of the high velocity body can reach very highvalues on the corners and the borders of the body, which would be favorable for theearthquake preparation, （2） it is not easy to form a strong earthquake within andnearby the low velocity body, where high enough stress could not be accumulated,and （3） the existonce of a combined high-low velocity body might play an importantrole in forming higher stress concentraton within the high velocity body and relativehigh stress concentration in some places out of the high velocity body, which wouldbe advantageous to the earthquake preparation. The calculation results coincide quitewell with the spacial distribution of Xingtai earthquake sequence.