【摘要】 地震是断层的摩擦失稳过程.摩擦本构关系对断层的破裂成核、破裂传播、破裂速度、能量释放、破裂终止等起着至关重要的控制作用.为了比较不同摩擦关系在断层自发破裂动力学过程中的影响,文中引入目前应用最为广泛的4种典型摩擦本构关系,它们分别是:滑移弱化摩擦关系,速率弱化摩擦关系,以及速率-状态相依摩擦关系中的老化定律和滑动定律.研究中利用有限单元方法对上述4种摩擦关系控制的断层自发破裂过程分别进行模拟计算,模拟结果显示:当模型参数相同时,不同摩擦关系模拟的破裂行为总体上具有一致性,都可以产生亚剪切破裂或超剪切破裂,并且破裂传播速度的大小与摩擦本构关系的类型无关.此外,它们之间还存在着较大的差异:(1)速率弱化摩擦关系可以模拟脉冲型破裂;而其他3个摩擦关系只能模拟裂纹性破裂.(2)不同摩擦关系模拟的超剪切破裂转换长度不同,速率-状态相关摩擦关系的老化定律相比其他摩擦关系需要更大的转换长度才能实现亚剪切破裂转变为超剪切破裂;而速率弱化的摩擦关系的超剪切转换长度可以为0,即不需要转换距离就直接产生超剪切破裂.(3)速率弱化摩擦关系模拟的破裂速度自成核后很快就达到稳定值;而其他类型摩擦关系模拟的破裂传播则要经历由缓慢破裂到逐渐加速直至达到稳定破裂的过程.值得特别指出的是,本文所使用的4种摩擦关系都不能完整地反映实际大地震破裂过程的摩擦属性,需要进一步深入研究.更多还原

【Abstract】 Earthquakes are processes of frictional instability of faults. The friction constitutive law plays an important role in controlling the rupture nucleation, rupture propagation, rupture velocity, energy release and rupture arrest. To reveal the effect of different friction laws in the dynamic faulting, in this paper, four kinds of friction constitutive laws are introduced, which are widely used in simulations at present. They are slip weakening, rate weakening, and aging and slip laws in rate-and state-dependent friction laws, respectively. Then, the finite element method is used to simulate the spontaneous rupture behaviors governed by the above four different frictional laws. The modeling results show that the fracture behaviors simulated by different friction laws are consistent, on the whole, which can produce subshear and supershear ruptures, and the rupture velocities are independent of the types of friction laws. Meanwhile, the slip rates simulated by different frictional laws are larger than those by the corresponded friction laws. However, the simulated results suggest that there exist prominent differences among the results simulated through different frictional laws. The differences are as follows.(1) The rate weakening friction law can be used to simulate the pulse-like rupture, while the other three friction laws cannot simulate the pulse-like rupture which can only model crack-like rupture.(2) The transition lengths of subshear-to-supershear ruptures simulated by different friction laws are different. Aging law of rate-and state-dependent friction law needs larger transition distance than those of the other friction laws. In particular, there is almost no transition length for rate-weakening law to simulate supershear rupture. And(3) the stable rupture velocity is quickly achieved with short distance of rupture propagation in simulation using rate weakening friction law, but it experiences a long and slow process at the rupture beginning for other three frictional laws. What is more important, the modeling results show that the four typical frictional laws used in this study cannot represent the realistic constitutive law in rupture process of natural earthquakes correctly and completely, which may need to be further studied.更多还原