角度对于Y型分叉断层自发破裂传播过程的影响

断层的几何形态是地震破裂传播过程的控制因素之一，从而影响着地震的危险性.Y型分叉断层是断层的多种复杂几何形态当中常见的一种，研究断层的分叉特征对震源破裂传播的影响，对于深入认识复杂几何形态断层的动力学特征具有重要意义.本文利用边界积分方程方法，模拟了612个分叉面，通过改变分叉断层面的分叉角度来分析断层分叉对传播的影响，并定量分析了分叉面之间以及主断层对分叉面的应力作用机制.模拟结果表明：分叉断层的一个断层分叉的破裂，既受到主断层作用的影响，也受到该断层另一分叉的作用的影响，是两者共同作用的结果.其中，主断层的作用基本上只与该断层分叉与主断层延长面的夹角有关，而与该断层另一分叉关系不大；该断层另一分叉的作用主要与两个断层分叉的夹角有关，但同时也要考虑其破裂状况.对于破裂以超剪切速度到达断层分叉处的情况，主断层对于大角度和小角度分叉的破裂促进作用较强，而对中等角度分叉的破裂促进作用较弱；该断层另一分叉对破裂的作用随着两个断层分叉之间夹角的增加，由强烈的抑制转为促进.

Effects of angles on dynamic ruptures on Y-type branched faults

Geometries of fault systems are essential to dynamic ruptures, and hence have influences on seismicity. Our discussions about selectivity of rupture propagations on branched faults, which are a common kind of various geometric complexities, are quite meaningful to deep understanding on dynamic feature of fault rupture. By applying the Boundary Integral Equation Method (BIEM), we computed 612 branch surfaces. Effects of branch angles on the dynamic ruptures on branched faults are investigated, and shear stress interaction between the main fault and two branches are analyzed quantitatively. Our results of simulation show that the rupture on one of the branches was affected by both the main fault and the other branch. The effect of the main fault is decided by the angle between the first branch and the extension surface of the main fault, while the effect of the other branch is decided by both the angle between two branches and the rupture process on the other branch. As for the cases in which the rupture velocities are supershear when approaching the triple junction, the contributions to shear stress on the first branch from the main fault are always positive in general, greater for small and large angles, but less for medium ones, while the contributions from the other branch change from negative to positive when the angles between two branches increase.