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

最近用模拟断层泥进行的大位移实验表明，断层泥摩擦力的速度依赖性演化为速度弱化行为，或退出速度弱化行为，取决于累积滑动历史。这种速率依赖的转变似乎与某些剪切局域化和离域微观结构相一致。微结构是否随着累积位移而系统地出现和消失？PI建议通过具有剪切局部化和反复离域化倾向的特定模型来研究这一问题。在一个模型中，断层泥的状态是由剪切带和表面在断层厚度尺度上的相互作用决定的，而在另一个模型中，观察到的速率相关的转变直接来自于颗粒尺度的过程。他们将研究这些模型在模拟断层泥和天然断层泥中的有效性。模拟的断层泥样本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过的加州南部的圣加布里埃尔和彭奇堡断层露头中收集。与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破裂、愈合和发展过程的经验表达。已知的控制这些过程的微观结构参数包括颗粒大小、颗粒大小分布、刨削层厚度、孔隙率和刨削织物。由于难以处理脆性变形微结构固有的随机性、变异性和不连续性，微观结构分析和力学分析之间的耦合很弱。碎裂微结构是否提供了比传统方法所获得的更多的信息？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类型的操作，并应用统计、海量和顺序数据分析。他们认为，该项目对摩擦本构方程中演化规律的物理定义、实验室到现场的比例关系以及刨削演化的计算机模拟具有明显的影响。此外，预计大型断层力学调查(如SAFOD)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.