Collaborative Research: Asymmetry in Gouge and Fault Zone Damage as an Indicator of Preferred Rupture Direction: In-Situ Test of Theoretical Models

这些研究集中于对这样一种假设的详细检验，即地震在不同弹性性质的岩石之间的断层上沿断层顺应性较好的一侧的滑动方向优先传播。最近对不同材料之间界面的动态破裂的分析和数值研究预测，一个方向的破裂将比另一个方向更有利。最近的实验室观察和一些地震数据支持了这一点。如果单向破裂是具有物质对比的天然断层结构的持久行为，那么重复的单向破裂应该在断裂带的微观结构上留下明显的不对称印记。对加利福尼亚州南部圣哈辛托、圣安德烈亚斯和彭奇堡断层沿线的几次暴露的初步观察显示，在断层和损伤区都有几个不对称的特征，这支持这一模型并值得进一步研究。继续进行的调查系统地绘制了沿一些大型走滑断层的几个地点的断裂带断层泥和损伤的组构和结构图，其具体目的是制定确定破裂传播方向的标准。伴随着观测工作的是对可以在几个界面之间同时迁移和传播的破裂的理论参数空间研究，以及对可能产生断层外损害的破裂的理论模拟。这些研究对地震地质学和大断层破裂传播物理的许多方面都有深远的影响，包括有效的本构关系、分支的抑制、断层相互作用、触发、热流悖论、地震滑动的短上升时间以及与大断层破裂相关的地震震动危险性的估计。

The studies focus on detailed tests of the hypothesis that earthquake ruptures on a fault between rocks of different elastic properties propagate preferentially in the direction of slip of the more compliant side of the fault. Recent analytical and numerical studies of dynamic rupture along an interface between dissimilar materials predict that one direction of rupture will be favored over the other. This is supported by recent laboratory observations and some seismic data. If unidirectional rupture is a persistent behavior for natural fault structures with material contrasts, repeated unidirectional ruptures should leave a distinct asymmetric imprint on the microstructure of the fault zone. Preliminary observations at several exposures along the San Jacinto, San Andreas and Punchbowl faults in southern California reveal several signatures of asymmetry in both the gouge and damage zones that support this model and warrant further work. The continuing investigations map systematically the fabric and structure of fault zone gouge and damage at several sites along a number of large strike-slip faults, with the specific purpose of developing criteria to resolve rupture propagation direction. The observational work is accompanied by a theoretical parameter-space study of rupture that can migrate between and propagate simultaneously along several interfaces and theoretical simulations of rupture that can produce off-fault damage. The studies can have profound implications for many aspects of earthquake geology and physics of rupture propagation on large faults, including effective constitutive laws, suppression of branching, fault-interaction, triggering, the heat flow paradox, short rise-time of earthquake slip, and estimates of seismic shaking hazard associated with rupture of large faults.