摘要
地震破裂能否穿越断层阶区(stepover)引发更大震级的地震是震源动力学研究的重要内容.本文利用不连续变形体接触力学的动态有限单元方法,模拟断层阶区对地震破裂传播的控制作用.通过改变断层周边初始应力场、断层面上的摩擦本构关系以及断层阶区的间距大小来分析各个因素对破裂传播的影响,并定量分析产生这些影响的力学机制.模拟结果表明:断层面上的摩擦系数减小或断层周边区域内的初始剪应力增大,都将增加断层破裂跳跃阶区传播的可能性;此外,若断层阶区间距越小,断层破裂也越容易跳跃阶区传播.计算结果还显示:断层上的摩擦系数大、初始剪应力小、断层阶区间隔大,那么此阶区所在之处将可能是断层破裂的终止位置;相反,当断层面上的摩擦系数较小、初始剪应力较大、断层阶区间隔较小,破裂就容易穿越阶区而出现较大的地震.同时,从模拟结果可以看出,在发震断层破裂停止后,应力将继续向四周传播;当应力积累达到破裂极限时,触发断层阶区中的另一断层产生破裂,因此在破裂跳跃断层阶区的过程中存在一个时间延迟.最后,破裂能否跳跃断层阶区,可以利用库仑应力在空间的分布进行合理的解释.
It is important in earthquake source dynamics to evaluate whether or not the rupture is capable of jumping stepover and triggering a greater magnitude earthquake. This paper used the dynamic finite element method for discontinuous contact mechanics to simulate the effects of stepover on rupture propagation. By changing prestresses, friction coefficients on the fault and stepover width, we analyzed the influences of various factors on rupture propagation and quantitatively studied the mechanisms of producing these impacts. The computed results demonstrate that it will increase the possibility of rupture jumping a stepover when reducing friction coefficient on the fault or increasing shear prestress. In addition, we find that the narrower the stepover, the easier the jumping of rupture. The computed results also show that a stepover will be the endpoint of the earthquake rupture with large friction coefficient, low shear prestress and wider stepover width. In contrast, when the friction coefficient is small, the shear prestress is high and the stepover width is narrow, the rupture will be easy to jump the stepover to produce a great earthquake. At the same time, it could be seen from simulations that after the rupture front reaching the end of the causative fault, the stress will continue to spread to all round; when the stress accumulation reaches fracture limit, the other fault on the stepover will be triggered to produce rupture, therefore it requires a time delay between the rupture front reaching the end of the causative fault and initiating rupture on the triggered fault. Finally, we use the spatial distribution of Coulomb stresses to explain whether or not a rupture could jump the stepover reasonably.
出处
《地球物理学报》
SCIE
EI
CAS
CSCD
北大核心
2014年第5期1510-1521,共12页
Chinese Journal of Geophysics
基金
国家自然科学基金(40974020)
地震动力学国家重点实验室开放基金(LED2012B01)
广西科学研究与技术开发计划项目(桂科攻1377002)
中央级科研院所基本科研业务专项资助(ZDJ2013-21)联合资助
关键词
断层阶区
自发破裂
摩擦关系
应力场
有限单元
Stepover
Fault spontaneous rupture
Friction law
Stress field
Finite element method
