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

这些研究的重点是详细测试的假设，地震破裂之间的岩石不同的弹性性能的故障传播的方向更符合一侧的断层滑动优先。最近的分析和数值研究动态断裂沿着界面之间的不同材料预测，一个方向的断裂将有利于其他。最近的实验室观测和一些地震数据证实了这一点。如果单向断裂是具有物质对比的天然断层结构的持久行为，则重复的单向断裂应在断层带的微观结构上留下明显的不对称印记。在加州南部的圣哈辛托、圣安德烈亚斯和潘奇鲍尔断层沿着的几个暴露点进行的初步观测揭示了断层泥和破坏区的几个不对称特征，这些特征支持了该模型，并保证了进一步的工作。继续进行的调查系统地绘制了沿若干大型走滑断层沿着若干地点的断层带断层泥和损害的结构和构造图，其具体目的是制定标准，以确定破裂的传播方向。观测工作是伴随着一个理论参数空间研究破裂，可以迁移和传播同时沿沿着几个接口和理论模拟破裂，可以产生故障的损害。这些研究对地震地质学和大断层破裂传播物理学的许多方面都有深远的影响，包括有效的本构律、分支抑制、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.