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.

这项研究将增进我们对地震断层动力学和物理学的基本理解，重点关注断层特征与地震辐射之间的关系，并应用于减轻地震灾害。 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可能导致地震破裂加速并以超剪切速度传播。了解超剪切地震发生的条件很重要，因为超剪切破裂会比亚剪切破裂引起更远离断层的强烈震动。这种破坏性地震是否会发生在美国的断层上，例如圣安德烈亚斯断层，其某些部分被锁定并为新的大断层加载？根据成熟的理论，同质断层需要高水平的剪应力以超剪切速度传播。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，具有较高应力或较低强度的异质断层可以在比具有均匀强度的模型中获得的预应力条件范围更广的预应力条件下过渡到超剪切速度。受这些发现的启发，我们计划进行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的滑移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种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断层属性变化的补充问题。除了阐明地震的动力学和物理原理之外，所开发的针对不均匀断层的良好表征实验还可以作为验证运动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耦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瞬态现象的宝贵工具。