The initially existing damage has apparently affected on wave stress propagation and stress distribution as long as its quantity exceeds a threshold value.

Meanwhile during the process of dynamical stress propagation, its amplitude decays. So the aftershock occurrence of the Tangshan earthquake is a negative feedback process.

In calculation, adopted load-unload criterion of stress wave propagation was to decide load-unload state of element and to adjusts and transfers internal stress for tensile failure element as well.