基于速率-状态摩擦定律研究剪切应力扰动对地震断层演化的影响

本文从Nagata提出的与应力变化率有关的速率-状态摩擦定律出发, 结合1D弹簧-滑块模型, 采用Runge-Kutta算法, 对静态应力扰动和周期性应力扰动下的断层演化过程进行了数值模拟, 探讨了应力扰动对断层演化进程和断层失稳机制的影响.研究结果显示, 与无扰动情形相比, 正向静态扰动使断层失稳时刻提早, 且时间提前量与扰动量的指数成正比; 负向静态扰动使断层失稳时刻推后, 且时间推迟量正比于扰动量.在周期性扰动下, 断层失稳的发生总早于无扰动情形, 且扰动幅值越大, 失稳提前量越大; 但是, 扰动频率对失稳时刻没有明显的影响.这也进一步表明, 地震应力波总是会导致断层失稳提前发生.同时, 对于相同的扰动量, 正向静态扰动下的失稳时间提前量比周期性扰动情形更大.周期演化过程的数值模拟结果表明, 当远场加载速率给定且为常量时, 若无应力扰动, 则断层演化过程具有确定的周期性; 但在周期性应力扰动下, 断层失稳时间间隔出现明显的非周期性, 断层在时间域上的演化变得更为复杂.

Shear stress loading perturbation on the earthquake faulting based on the rate-and state-dependent friction law

With a combination of 1D-spring slider model and a revised rate- and state-dependent friction (RSF) law related to the stressing rate proposed by Nagata (Nagata Law), in this study we have simulated the fault evolution process under static and periodic stress perturbations using the Runge-Kutta numerical algorithm. The direct effects of the stress perturbation to the fault's evolution associated with its frictional instability have been investigated. The numerical results indicate that, for a static stress perturbation, the fault instability time will be advanced or delayed. For a positive static change, the time advance behaves an exponential function of magnitude of stress change; and for a negative static stress change, the time delay is linearly proportional to the magnitude of stress change. For a sinusoid periodic stress perturbation, the instability time is always advanced, the larger the amplitude of periodic stress change has, the larger the instability time advance will have; but the frequency of sinusoid time variation of periodic stress change has little effect on the instability time, indicating that the radiated seismic stress wave with a certain magnitude could always lead to the occurrence of fault instability ahead of a time. Meanwhile, for the same magnitude of perturbation, the instability time advance under a positive static perturbation is larger than that under periodic case, which means that the static stress perturbation has a higher earthquake triggering potential than periodic stress perturbation. In addition, for multiple seismic cycle simulation, our results show that, under a constant far-field shear stress loading rate, the fault evolution process has a perfect periodic cycling without any stress; however, such kind of periodicity related to the fault evolution will loses under periodic stress perturbation, the seismic cycling pattern becomes much more complicated in temporal domain.