Influences Of Lateral Non-uniform Viscosity On Seismic Cycle In A Three-dimensional Strike-slip Fault Model

Geodetic evidence shows that the interseismic deformation rate on each side of fault tends to be asymmetric,which could usually be explained by lateral viscosity contrast.In addition,many postseismic deformation inversions prove that there may exist large difference in the viscosity of lithosophere across faults.The difference of viscosity can influence the efficiency of media stress transfer and stress accumulation on fault surface.Hence,the viscosity contrast across fault may have a great effect on seismic cycle.At present,how the lateral viscosity contrast on each side of fault affects seismic cycle is still not well understood.Firstly,we construct three-dimensional horizontally uniform strike-slip fault models controlled by slip-weakening friction law and power-law rheology.After exerting reasonable far-field plate loading rate,we can simulate spontaneous seismic cycle successfully.Our simulation results are basically consistent with the simulation results of previous two-dimensional model,and there are obvious ductile shear zones on both sides of fault in the depths of viscoelastic models,which effectively hinders the deep penetration of coseismic slip.Moreover,the rheology defined by geothermal gradient on each side of fault are set as different values separately to construct horizontally non-uniform seismic cycle models.Then we analyse the main characteristics of earthquake recurrence interval,Coulomb stress accumulation on fault plane,internal stress and strain distribution,ground surface deformation and gravity anomaly.The viscosity contrast can cause the asymmetric interseismic surface deformation rate on each side of fault.As the viscosity contrast increases,the difference of interseismic surface deformation rate also gradually increases.Low viscosity in either side of fault can cause an increase of earthquake recurrence interval.On the one hand,low viscosity will result in a smaller Coulomb stress accumulation rate at the end of interseismic phase.On the other hand,critical Coulomb stress for coseismic rupture will increase as well.The combined effects of them can make earthquake recurrence interval and magnitude increase a little.Lateral viscosity contrast across fault can also cause asymetric gravity anomaly,so we may infer lithosopheric viscosity structure through gravity observation in the future.