FEM Simulation Of The Dynamic Processes Of Fault Spontaneous Rupture And Its Application To Earthquake Study

In general,an earthquake process is assumed as fault spontaneous rupture.Therefore,it is significant to study the dynamic processes of fault spontaneous rupture for understanding of earthquake process and seismic disaster reduction.In order to reasonably simulate rupture processes,this paper first improve classical slip-weakening friction law,and then use the finite element method to carry out simulation.The computed results demonstrate that pulse-like rupture is possible by making a modification of the classical slip-weakening friction law.It also shows that the behavior of the fault spontaneous rupture process is affected by the initial stress field of the region and the friction law.When the initial shear stress is low or the dynamic friction coefficient is large,it is easier to generate pulse-like rupture;on the contrary,it is easier to generate crack-like rupture.In addition,we perform 2-D finite element calculations of rupture along a bimaterial interface governed by regularized rate-and state-dependent friction law,with the goal of understanding how the bimaterial interface influences the strong ground motion.The simulated results show that bimaterial mechanism is important for earthquake ruptures and influences the strong ground motion significantly.Strong ground motion caused by seismic waves emanated from the rupture propagation is asymmetrically distributed in space.The asymmetry due to bimaterial effect increases with increasing degree of material contrast across the fault.It is important in earthquake source dynamics to evaluate whether or not the rupture is capable of jumping stepover and promoting supershear earthquake rupture.This paper use dynamic finite element method to simulate the effects of stepover on rupture propagation and the seismic supershear rupture process encouraged by a fault stepover.The results demonstrate that it will increase the possibility of rupture jumping a stepover when reducing friction coefficient on the fault,increasing shear prestress or the stepover is narrower.In addition,we find that the physical parameters of stepover,such as overlap length,step width,and coefficients of friction,etc.,will have effect on the rupture velocity.Under certain conditions,when rupture jumps the stepover,the rupture velocity will change,by the subshear wave velocity on the initial fault into a supershear wave velocity on the secondary fault.Combining with the above results of studying the dynamic processes of fault spontaneous rupture by conceptual models,we construct finite element models based on the actual geometries of the seismogenic faults in the Wenchuan earthquake and Yushu earthquake to study the mechanisms for the fault rupture of Wenchuan earthquake with predominately unilateral propagation and supershear rupture processes of Yushu earthquake.The rupture processes of the 2008 Wenchuan earthquake are very complex.The rupture propagated northeastward a large distance as long as 300 km,but rupture length is short in the southwest direction.Our simulated results show that the different materials between both sides of the Longmen Shan fault may be the reason why the 2008 Wenchuan earthquake is a unilateral fault rupture and a high seismic magnitude.Owing to supershear ruptures,seismic hazards in the 2010 Yushu earthquake is particularly severe.Our simulated results demonstrate that supershear rupture occurred in the Yushu event may be the result of optimum state in which perfect relationship between orientations of initial stress and the strike of seismogenic fault is formed.