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

这些研究的重点是对以下假设的详细检验：在不同弹性性质的岩石之间的断层上，地震破裂优先向断层更柔顺的一侧的滑动方向传播。最近对沿不同材料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。最近的实验室观测和一些地震数据支持了这一观点。如果单向破裂是具有物质对比的天然断层结构的持续行为，那么反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。对南加州圣哈辛托断层、圣安德烈亚斯断层和庞奇碗断层的初步观察显示，断层泥和损伤带都存在不对称的特征，这些特征支持了这一模型，并为进一步的研究提供了依据。继续进行的调查系统地绘制了断裂带断层泥的结构和结构，以及沿着一些大型走滑断层的几个地点的破坏情况，其具体目的是制定准则来解决破裂传播方向。在观测工作的同时，还对破裂进行了理论参数空间研究，该破裂可以在多个界面之间迁移并同时沿着多个界面传播，并对可能产生非断层破坏的破裂进行了理论模拟。这些研究对大断裂断裂传播的有效本构规律、分支抑制、断层相互作用、触发、热流悖论、地震滑动短上升时间、大断裂断裂地震震动危险性估计等地震地质和物理研究具有重要意义。

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.