Macroscopic Asymmetry of Dynamic Rupture on a Bimaterial Interface With Velocity- Weakening Friction
Macroscopic Asymmetry of Dynamic Rupture on a Bimaterial Interface With Velocity- Weakening Friction
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DOI：
10.1111/j.1365-246x.2008.03736.x
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发表时间：
2006-12
期刊：
影响因子：
--
通讯作者：
J. Ampuero;Y. Ben‐Zion
中科院分区：
文献类型：
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作者：
J. Ampuero;Y. Ben‐Zion
我们研究了双材料断层上的面内破裂，该断层受具有正应力响应的减速摩擦的支配。数值模拟和分析估计提供了速度衰减尺度、成核长度和背景应力的范围的特征，在这些范围内，破裂表现为裂缝或脉冲、衰减或持续、双侧或单侧。在强烈减速摩擦的情况下，破裂发生在很宽的条件下，作为具有优先传播方向的大规模脉冲，即更柔顺的材料的滑移。这种破裂具有宏观的不对称性，表现为在优选方向上的地震强度和传播距离明显较大，并由滑移率时空分布的二阶矩得到的方向性比清楚地量化。大尺度脉冲宏观破裂的不对称性是由于双材料界面上的非对称法向应力变化导致各破裂方向自持传播的临界条件不同所致。相反，裂纹状断裂在约束条件下表现出宏观不对称性。所讨论的机制在正则化参数、应力不均匀范围和断层外屈服方面是稳健的，即使在没有速度减弱的情况下，也应该对地壳尺度的破裂脉冲起到类似的作用。在加工区尺度上，由双材料法向应力降低驱动的小尺度脉冲可以从沿优先方向传播的大尺度脉冲的破裂前沿分离。然而，它们的发生取决于正应力响应正则化过程中的松弛程度，而断层外屈服会阻碍它们的发展。
We study in-plane ruptures on a bimaterial fault governed by a velocity-weakening friction with a regularized normal stress response. Numerical simulations and analytical estimates provide characterization of the ranges of velocity-weakening scales, nucleation lengths and background stresses for which ruptures behave as cracks or pulses, decaying or sustained, bilateral or unilateral. With strongly velocity-weakening friction, ruptures occur under a wide range of conditions as large-scale pulses with a preferred propagation direction, that of slip of the more compliant material. Such ruptures have macroscopic asymmetry manifested by significantly larger seismic potency and propagation distance in the preferred direction, and clearly quantified by the directivity ratio derived from the second order moments of the spatio-temporal distribution of slip rate. The macroscopic rupture asymmetry of the large-scale pulses stems from the difference in the criticality conditions for self-sustained propagation in each rupture direction, induced by the asymmetric normal stress changes operating in bimaterial interfaces. In contrast, crack-like ruptures show macroscopic asymmetry under restrictive conditions. The discussed mechanism is robust with respect to regularization parameters, ranges of stress heterogeneities and a proxy for off-fault yielding and should operate similarly for crustal-scale rupture pulses even in the absence of velocity-weakening. Small-scale pulses, driven by the bimaterial normal stress reduction at the scale of the process zone, can detach from the rupture front of the large-scale pulses that propagate in the preferred direction. However, their occurrence depends on the relaxation scale in the regularization of the normal stress response and their development can be hindered by off-fault yielding.