| Bimaterial contrast across the fault plays an important part on seismic rupture propagation.As we know,the anisotropy of the earth's medium is omnipresent,so what is the impact of the anisotropy of the materials across the fault on the dynamic processes of fault spontaneous rupture?This question remains unclear.However,we havenft seen any research reports concerned all over the world.To this end,in the study we simulated rupture processes along fault with dissimilar anisotropic media across the fault by means of finite element method.The simulated results show that the anisotropic properties of the materials across the fault have a major impact on the dynamic process of fault rapture,and the relationship between the material property and rupture behavior is very much complex.For orthotropic materials,when the Young's modulus in the main direction of anisotropic media on both sides of the fault is different,especially when the principal axis of orthotropic material is parallel to the fault's strike and its Young's modulus on one side is significantly larger than the other one,the fault rupture propagation appears asymmetrically distributed in space.Meanwhile,the dislocation on one side of the nucleation center is significantly larger than on the other side,and the corresponded length of the rapture is also greatly larger,which is also known as a unilateral rapture.The Young's modulus in the principal direction of the orthotropic material along the fault strike has a greater influence on rupture behaviors than that of the Young's modulus perpendicular to the fault strike,but the influence changes with the orientation of the material's principal axis,even if in some cases the effect of the changes of material orientation on the rupture process is not particularly significant.In addition,it has been found through simulation that when the anisotropic media across the fault are the same anisotropic material(i.e.,the same anisotropic material is assigned on both sides of the fault),the rupture is symmetrically distributed in space,similar to the case where the media on both sides of the fault are homogeneous.Meanwhile,with the changes of principal axis orientation of the anisotropic material on one side of the fault,the spatial symmetry of the fault rupture will be affected to some extent,but the orientation change has small effects on the rupture dynamic process.However,with the increase of shear modulus of orthotropic material,the rupture may propagate shortly along the fault from the nucleation zone,and it will stop quickly,in which no large earthquake could occur.Thus,it can be expected that the results of this study have important scientific significance and some implications for the better understanding of the focal processes and seismic hazard assessments.In addition,there are abundant active faults and earthquakes in north China.Due to its special geographical location,frequent seismic activities are closely watched.To this end,according to the elastic dislocation theory and hierarchical lithosphere model,we calculate the Coulomb stress changes produced both by coseismic slips and by postseismic viscoelastic relaxation from the events with Ms?6.0 that occurred in the north China region since 1820.The simulated results show that 19 of the 24 earthquakes since the Bohai Bay event in 1888 have fallen in the positive region of coulomb stress change,with a triggering rate as high as 79%.Particularly.based on the earthquake geological data and the coulomb stress calculation results.it is possible that future earthquakes may occur mainly on the Luanxian-Yueting fault.Panzhuangxi fault.Dongming-Chengwu fault,Yuncheng fault.and Longyao fault of Ninghe-Xinxiang seismic belt;Yingkou-Weifang fault of Tanlu seismic belt:Xiadian fault.Huangzhuang-Gaoliying fault in the Capital area.Thus,further research is necessary. |
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