Rupture Propagation and Arrest in Geometrically Complex Fault Systems: Bends, Stepovers, and Damaged Border Zones

地震科学的一个主要问题是通过具有弯曲，分支和台阶的几何复杂断层系统来理解破裂。这种复杂性对破裂的传播和停止起着主要的控制作用。了解破裂何时以及如何停止，这通常与这些特征有关，是了解地震风险的核心。这项研究延续了断层段之间的扭结、弯曲和偏移相遇时断层断裂的理论和建模的最新进展。这是在密切参考解释现场实例中观察到的破裂模式的情况下完成的。这些断层包括主要走滑地震中的分支和台阶（例如2001年西藏昆仑地震、2002年阿拉斯加迪纳里地震和1992年加州兰德斯地震），以及1944年日本南开和1964年阿拉斯加俯冲带记录的类似的逆冲断层，这些断层对海啸的产生有影响。这些研究开辟了断裂动力学和地震物理学的新领域。这些包括如何通过复杂的断层系统选择破裂路径的基本理解，以及制定适当的计算模型（基于动态有限元和边界积分方程方法）来分析通过扭结和分支的滑动传播。在这种情况下，断层支撑的正应力和剪应力分量都存在显著的耦合动态变化，这对表征裂缝扩展提出了新的挑战。将理论与现场（有时是实验室）实例相结合的进展，提供了观察断层几何形状和预应力状态证据的新方法，并将其转化为对破裂路径的预测。研究中的一个重要问题是，是否可以使用带有分支和其他复杂性的残余断层几何形状来推断过去事件中破裂的方向，这对于识别最严重的地面运动区域是重要的。此外，该工作还解决了沿断层的破坏区如何通过连续的破裂而演变，以及这些区域内的非弹性过程如何与应力传递到破裂前缘以及传播动力学相互作用以产生高频地震波发射。上一个筹资周期的项目也有效地帮助妇女参与研究。其中包括联合项目负责人、一名研究生研究助理和三名访问实习生，他们在完成其他学位课程的同时完成了断层破裂的研究，并将其作为顶点项目。

A major problem in earthquake science is to understand rupture through geometrically complex fault systems with bends, branches and stepovers. Such complexities exert major control over the propagation and arrest of rupture. The understanding when and how ruptures stop, which is often associated with such features, is central to understanding seismic risk. This study continues recent developments of the theory and modeling of fault fracture at encounters with kinks, bends and offsets between fault segments. That is done with close reference to explaining rupture patterns as observed in field examples. Those include branches and stepovers in major strike-slip earthquakes (e.g., 2001 Kunlun, Tibet, 2002 Denali, Alaska, and 1992 Landers, California), and splay thrust faulting like that documented for the 1944 Nankai, Japan, and 1964 Alaska subduction zones, with implications for tsunami generation. The studies open new frontiers in rupture dynamics and the physics of earthquakes. Those include a basic understanding of how rupture paths are chosen through complex fault systems, and of the formulation of appropriate computational models (based on dynamic finite element and boundary integral equation methodology) to analyze slip propagation through kinks and branches. In such cases there are significant, coupled, dynamic changes in both the normal and shear stress components supported by the fault, which pose new challenges to representing fracture propagation. Progress in correlating theory with field (and sometimes lab) examples is providing new ways of looking at fault geometry and evidence about prestress states, and translating that into predictions about rupture paths. An important issue under study is whether relic fault geometries with branches and other complexities can be used to infer the direction of rupture in past events, which is important for identifying regions of most severe ground motion. Also, the work addresses how damage zones along faults evolve by successive ruptures, and how inelastic processes within such zones may interact back with stress transmission to the rupture front and with the dynamics of propagation to generate high frequency seismic wave emission. The project during the previous funding cycle was also effective in aiding the participation of women in research. That includes the co-PI, a graduate student research assistant, and three visiting student interns who completed research on fault rupture as capstone projects in completion of their degree programs elsewhere.