A Microstructural Study of Simulated and Natural Fault Gouge Using Digital Image Techniques

最近的大位移实验与模拟断层泥表明，速度依赖性断层泥摩擦演变，并出速度弱化行为，依赖于累积的滑动历史。这种速率依赖性的转变似乎与某些剪切局部化和离域微观结构相吻合。微结构的出现和消失是否随位移的累积而有系统地进行？PI建议通过具有剪切局部化和经常性离域化的内置趋势的特定模型来研究这个问题。在一个模型中，断层泥的状态是由断层泥厚度尺度上的剪切带和表面的相互作用决定的，在另一个模型中，所观察到的速率依赖性转变直接来自于晶粒尺度过程。他们将研究模型在模拟和天然断层泥中的有效性。模拟断层泥样品将通过一系列旋转剪切实验产生;天然断层泥将从先前研究的加州南部的圣盖博和潘奇鲍尔断层露头中收集。速率和状态相关的摩擦定律在很大程度上是断层泥内部结构碎裂、愈合和发展过程的经验表达式。已知控制这些过程的微观结构参数包括粒度、粒度分布、凿层厚度、孔隙率和凿组构。微观结构和力学分析之间的耦合是薄弱的，由于工作的随机性，可变性和不连续性，这是固有的脆性变形微观结构的困难。碎裂岩显微构造是否比传统方法提供了更多的信息？PI建议使用数字图像技术，该技术允许对图像数据进行矩阵式操作，并应用统计、海量和连续数据分析。他们认为，该项目具有明确的含义，在摩擦本构方程的演化规律的物理定义，实验室到现场的比例关系，和计算机模拟的断层演变。此外，大规模断层力学研究（例如SAFOD）预计将受益于该项目将开发的数字图像技术的便携性和效率。

Recent large-displacement experiments with simulated gouge indicate that velocity-dependence of gouge friction evolves to, and out of velocity weakening behavior, dependent upon cumulative slip history. Such rate-dependence transitions appear to coincide with certain shear localization and delocalization microstructures. Do the microstructures appear and disappear in a systematic way with cumulative displacement? The PI's propose to investigate the question through specific models with built-in tendency for shear localization and recurrent delocalization. In one model the state of gouge is determined by interaction of shear bands and surfaces at the scale of gouge thickness, in another the observed rate-dependence transitions result directly from grain-scale processes. They will investigate the validity of the models in both simulated and natural fault gouge. Simulated gouge samples will be produced by a series of rotary shear experiments; natural gouges will be collected from previously studied San Gabriel andPunchbowl fault outcrops in southern California. The rate-and state-dependent friction laws are to a large extent empirical expressions of the processes of cataclasis, healing, and development of internal structures in gouge. Microstructural parameters known to control these processes include particle size, particle size distribution, gouge layer thickness, porosity, and gouge fabrics. The coupling between microstructural and mechanical analysis is weak due to difficulties in working with randomness, variability, and discontinuity that is inherent in brittle deformation microstructures. Do cataclasticmicrostructures offer significantly more information than have been acquired so far by traditional methods? The PI's propose to use digital image techniques, which allow matrix-type manipulations of image data and application of statistical, massive and sequential data analyses. They believe that the project has clear implications for the physical definition of the evolution laws in friction constitutive equations, laboratory-to-field scaling relations, and computer simulation of gouge evolution. Furthermore, large-scale fault mechanics investigations (e.g. SAFOD) are expected to benefit from the portability and efficiency of digital image techniques that will be developed by this project.