Coulomb Stress Changes Induced by Cangshan M_S5.2 Earthquake Based on Visco-elastic Model
LIU Fang-bin;QU Jun-hao;TIAN Zhao-yang;LIU Cheng-yu;Earthquake Administration of Shandong Province;
The Cangshan MS5.2earthquake,which occurred on September 20,1995,was one of the largest earthquakes of the past century in southern Shandong Province and inflicted huge financial losses.As it was also a significant example of the new active phase in North China,it is necessary to determine the seismicity and potential seismic hazard in the areas affected by this earthquake.Earthquakes are natural phenomena caused by fault movement when stress accumulates to a certain extent.Coulomb stress change occurs due to coseismic dislocations and visco-elastic relaxation after an earthquake.Research shows that a small change in the Coulomb stress can trigger an earthquake.In order to calculate the Coulomb stress changes of the Cangshan earthquake and their influence on surrounding faults,in this paper,we use field investigation results in a multi-layered visco-elastic model to determine the Coulomb stress changes from the coseismic dislocations and visco-elastic relaxation following the Tancheng and Cangshan earthquakes.We also discuss the triggering relationship between the two earthquakes,the influence of the aftershock distribution features of the Cangshan earthquake,and the influence of stress on the surrounding area.The results show that:(1)The Tancheng earthquake changed the conditions of failure in Cangshan,and the Cangshan earthquake wasdelayed by the Coulomb stress change(-3.23bar)caused by the Tancheng earthquake in this area.(2)By analyzing the relationship between the Coulomb stress changes caused by the Cangshan earthquake and the aftershocks distribution,we found most of the aftershocks to have been located in regions where the Coulomb stress increased 0.08~0.12 bar.(3)With respect to visco-elastic relaxation,the calculation results show the Tancheng and Cangshan earthquakes to have had a significant influence on nearby faults.The northeast Anqiu-Junxian fault,the middle of the Cangni fault,the east Fushan fault,the Hanzhuang fault,and the Yicheng fault are all located in regions where the Coulomb stress has increased(≈5bar),and there the potential for strong seismic hazard in these areas.