Laboratory Study of Fault Healing and Frictional Properties: Role of Fluids

这个奖项是根据2009年美国复苏和再投资法案(公法111-5)资助的。这个项目将调查构造断层的滑动和地震期间发生的重要过程。我们将重点讨论断层的摩擦强度和地下流体在改变断层强度中的作用。破坏性地震发生在主要构造断层上，其顺序通常相隔50至100年或更长时间。地震危险性分析的一个重要问题是如何在地震之间恢复断层强度？也就是所谓的断层修复。该项目将通过结合详细的实验室实验、计算机建模和基于显微镜的断裂带纹理研究来研究故障修复。地壳中的断层经历了一系列的滑动行为，包括地震和非破坏性的蠕变事件，在这些事件中，滑动发生时不会释放破坏性的地震波。这个项目的目标之一是确定导致每种类型滑移行为的微观和更大范围的因素。这些信息将帮助我们在全国范围内建立更现实的地震危险模型。该项目的结果预计将对理解断层和地震产生重大影响，包括地震和非地震断层滑动的触发、断层相互作用和地震危险性评估。在从构造到弹性动力学的时间尺度上，断层愈合在地震破裂过程中起着核心作用。摩擦愈合(在准静态接触过程中增加静摩擦)被认为是地震间和动态断层强化的最可能机制，在某些情况下，基于实验室的摩擦定律与现场观察的断层愈合有很好的一致性。然而，实验室数据在数量和范围上都是有限的。现有的实验室数据不能对通过重复地震观察到的断层愈合提供一致的解释，这表明地震矩作为连续事件之间的时间函数而增加和减少。此外，故障修复的物理过程以及更广泛地说，摩擦率/状态效应的微观机制还知之甚少。该项目将支持故障修复的多学科调查。这项工作包括两项一般任务。1)在一系列条件(剪切速率、断层泥材料、法向应力、流体性质、温度)下的摩擦愈合和断裂带传输特性的实验室研究。实验将在真三轴应力条件下进行，使用双直接剪切配置，并控制孔隙流体压力和流过。我们将通过摩擦强度、断裂带的弹性性质和剪切过程中的水力传导率来测量愈合程度。将使用变形样本的详细显微结构研究来确定愈合过程。2)数值、实验室和微观结构相结合的研究，旨在确定决定断层愈合、蠕变固结和随时间变化的断层弱化的物理化学过程。拟议研究的每个领域都有初步数据。

This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5).This project will investigate slip on tectonic faults and important processes that occur during earthquakes. We will focus on the frictional strength of faults and the role of underground fluids in modifying fault strength. Damaging earthquakes occur on major tectonic faults in a sequence that is often separated by 50 to 100 years or more. One important question for seismic hazard analysis is that of how fault strength is regained between earthquakes ?so called fault healing. This project will investigate fault healing via a combination of detailed laboratory experiments coupled with computational modeling and microscope-based studies of the fault zone textures. Faults in Earth's crust undergo a range of slip behaviors including earthquakes and non-damaging 'creep' events in which slip occurs without releasing damaging seismic waves. One of the goals of this project is to determine the microscopic and larger-scale factors that cause each type of slip behavior. This information will help us build more realistic models for seismic hazard around the country. Results of the project are expected to have significant impact on understanding faults and earthquakes including triggering of seismic and aseismic fault slip, fault interaction, and seismic hazard assessment. Fault healing plays a central role in earthquake rupture processes at time scales ranging from tectonic to elastodynamic. Frictional healing (as evidenced by increasing static friction during quasi-stationary contact) is considered the most likely mechanism of interseismic and dynamic fault strengthening, and there is good agreement between laboratory-based friction laws and field observations of fault healing in some cases. However, laboratory data are limited in quantity and scope. Existing lab data do not provide a consistent explanation of fault healing as observed via repeating earthquakes, which indicate both increases and decreases in seismic moment as a function of time between successive events. Moreover, the physical processes of fault healing and, more generally, the micro-mechanisms of frictional rate/state effects are poorly understood. This project will support a multidisciplinary investigation of fault healing. The work includes two general tasks. 1) Laboratory study of frictional healing and fault zone transport properties for a range of conditions (shearing rate, gouge material, normal stress, fluid properties, temperature). Experiments will be conducted under true-triaxial stress conditions using the double-direct shear configuration with controlled pore fluid pressure and flow through. We will measure healing via frictional strength, elastic properties of the fault zone, and hydraulic transmissivity during shear. Detailed microstructural studies of the deformed samples will be used to identify processes responsible for healing. 2) Coupled numerical, laboratory, and microstructural studies aimed at identifying the physico-chemical processes that determine fault healing, creep consolidation, and time-dependent fault weakening. Preliminary data are available in each area of proposed study