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

地震破裂与理想断层不均匀性的相互作用：对破裂速度、滑移和地震辐射的影响

• 批准号: 1321655
• 负责人: Ares Rosakis
• 金额: $ 40万
• 依托单位: California Institute of Technology
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2013
• 资助国家: 美国
• 起止时间: 2013-07-15 至 2016-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1321655&HistoricalAwards=false
• 关键词: Interaction; earthquake; rupture; idealized; fault

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.

这项研究将促进我们对发震断层的动力学和物理学的基本理解，重点是断层特征与地震辐射之间的关系，以及在地震减灾中的应用。该项目致力于回答的一个关键问题是，断层不均质性的存在是否会导致地震破裂以超剪切速度加速和传播。理解发生超剪切地震的条件是很重要的，因为超剪切破裂在距离断层更远的地方会引起比亚剪切破裂更强烈的震动。这样的破坏性地震会发生在美国的断层上吗？例如，圣安德烈亚斯断层的某些部分已被锁定并加载到新的大断层上？根据公认的理论，均质断层需要高水平的剪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，这些断层在总体剪切预应力水平较低的情况下运行。最近，数值模拟表明，与均匀强度模型相比，具有高应力或低强度斑块的非均质断层在更宽的预应力范围内可以过渡到超剪切速度。在这些发现的推动下，我们计划开展一项实验室和数值相结合的研究，研究地震破裂的速度及其累积滑动和由此产生的地震辐射如何受到天然断层上可能存在的几个断层不均匀特征的影响。我们还将研究辐射波场可以告诉我们有关故障性质变化的补充问题。除了阐明地震的动力学和物理学外，针对具有非均质性的断层开发的具有良好特性的实验还可以作为验证运动学反演模型和动态破裂代码的基准。新提出的通过数字图像相关和高速摄影相结合来增强动态破裂过程表征的实验技术可以成为研究地震科学和固体力学中的瞬变现象的宝贵工具。