Interaction of earthquake rupture with idealized fault inhomogeneities: Effects on rupture speed, slip, and seismic radiation

这项研究将促进我们对地震发生断层的动力学和物理的基本理解，重点关注断层特征与地震辐射之间的关系，并将其应用于地震减灾。该项目旨在回答的一个关键问题是，断层不均匀性的存在是否会导致地震破裂以超剪切速度加速和传播。了解超剪切地震发生的条件是很重要的，因为超剪切破裂比亚剪切破裂在离断层更远的地方引起更强烈的震动。这种破坏性的地震会发生在美国的断层上吗？例如，在圣安德烈亚斯断层上，它的一些部分被锁定并加载了新的大地震？根据公认的理论，均质断层需要高水平的剪切应力才能以超剪切速度传播。然而，大量的现场观测表明，超剪切地震发生在成熟的走滑断层上，这些断层在低整体剪切预应力水平下运行。最近，数值模拟表明，与具有均匀强度的模型相比，具有较高应力或较低强度斑块的非均质断层在更大范围的预应力条件下可以过渡到超剪切速度。在这些发现的激励下，我们计划开展一项结合实验室和数值研究，研究地震破裂的速度，以及它们的累积滑动和由此产生的地震辐射，是如何受到自然断层上可能存在的几种断层不均匀性特征的影响的。我们还将研究辐射波场能告诉我们断层性质变化的补充问题。除了阐明地震的动力学和物理性质外，所开展的具有良好特征的非均匀性断层实验可以作为验证运动学反演模型和动态破裂代码的基准。通过数字图像相关和高速摄影相结合的新实验技术可以增强动态破裂过程的表征，这将成为地震科学和固体力学中瞬态现象研究的宝贵工具。

This study will advance our fundamental understanding of the dynamics and physics of earthquake-producing faults, focusing on the relation between fault features and seismic radiation, with applications to seismic hazard mitigation. One key question this project aims to answer is if the presence of fault inhomogeneities may cause earthquake ruptures to accelerate and propagate at supershear speeds. It is important to understand the conditions under which supershear earthquakes occur, since supershear ruptures can cause much stronger shaking farther from the fault than subshear ones. Can such destructive earthquakes occur on faults in the US, for example, on the San Andreas fault, some parts of which are locked and loaded for the new big one?According to well-established theories, homogeneous faults require a high level of shear stress to propagate at supershear speeds. Yet numerous field observations reveal that supershear earthquakes occur on mature strike-slip faults that operate at low overall levels of shear prestress. Recently, numerical simulations have shown that heterogeneous faults with patches of higher stress or lower strength can transition to supershear speeds under a much wider range of prestress conditions than what is obtained in models with homogeneous strength. Motivated by these findings, we plan to carry out a combined laboratory and numerical study of how the speed of earthquake ruptures, as well as their accumulated slip and resulting seismic radiation, are affected by several fault inhomogeneity features likely to be present on natural faults. We will also investigate the complimentary question of what the radiated wave fields can tell us about the variations in fault properties. In addition to clarifying the dynamics and physics of earthquakes, the developed well-characterized experiments on faults with inhomogeneity can serve as benchmarks for validation of kinematic inversion models and dynamic rupture codes. The new proposed experimental technique for the enhanced characterization of dynamic rupture processes by coupling digital image correlation and high speed photography can become an invaluable tool for studies of transient phenomena in earthquake science and solid mechanics.