唐山地震震源应力场的数值模拟研究-三维有限单元法在计算震源应力场中的应用

震源机制结果与极震区地裂缝的力学性质,都说明唐山地震是以右旋剪切走向滑动为主且兼倾向滑动的主震型大地震。这说明唐山地震是在水平力和垂直力同时作用下产生的。本文利用三维有限单元法,采用弹性模式对唐山地震震源应力场进行了数值计算,並考虑了体力与表面力两种受力情况。表面力又分为水平作用应力与垂直作用应力,水平作用应力随深度变化,且最大水平压应力等于同一深度上静水压力的3倍,而最小水平压应力等于同一深度上静水压力。最大水平压应力取北85°东,即与唐山地震震源机制解的最大主压应力轴基本上是一致的。垂直力取其静水压力的1.5倍所得结果与地震实际发生的过程比较一致,所以,唐山地震很可能是在水平力与垂直力同时作用下产生的。

NUMERICAL ANALYSIS OF STRESS FIELD OF TANGSHAN AREA APPLYING THREE DIMENSIONAL FINITE ELEMENT METHOD TO COMPUTE FOCAL STRESS EIELD

From the Point of view of the focal mechanizm and behaviour of grou-nd crack,the component of right-lateral shear strike slip was dominant and at the same time with dip slip during Tangshan earthquake.This sho-wed that the event had occurred by reason of horizontal and vertical force.Inthis paper the authors use three dimensional finite element method to compute the stress field of Tangshan area.It is believed that there are two kinds of distributive force:body force and surface force.And the latter force may be classified into horizontal direction and vertical direction.Horizontal stress field changes with the depth,and maximum horizontal compressive stress is equal to 3 times of hydrostatic pressure,the depth being equal.Its orientation is N85°E.The vertical stress is equal to 1.2 times of hydrostatic pressure results of computation are in the main con-sistent with the occurrence of the event.Tangshan earthquake occurred per-haps by reason of both horizontal stress field and vertical stress field,the former being dominant.