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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。
The results of focal mechanism and the mechanical properties of ground fissures in the extremely seismic zone all indicate that the Tangshan earthquake is a major earthquake with a major dextral shear strike-slip pattern and a dip-dip slip. This shows that the Tangshan earthquake is produced by the simultaneous action of horizontal force and vertical force. In this paper, the three-dimensional finite element method is used to calculate the source stress field of Tangshan earthquake by using the elastic mode, and the force and surface force are considered. Surface force is divided into horizontal and vertical stress, horizontal stress changes with depth, and the maximum horizontal compressive stress is equal to three times the hydrostatic pressure at the same depth, while the minimum horizontal compressive stress is equal to hydrostatic pressure at the same depth. The maximum horizontal compressive stress takes the north of 85 ° east, which is basically consistent with the maximum principal compressive stress axis of the focal mechanism solution of the Tangshan earthquake. The vertical force takes 1.5 times of hydrostatic pressure. The result is consistent with the actual happening of the earthquake. Therefore, the Tangshan earthquake is likely to occur under the simultaneous action of horizontal force and vertical force.