Comparison of Microscale Fault Fabrics Formed in Creeping and Stick-Slip Faults

这项研究应用了一种创新技术，断层沉积物的微观结构分析，以更准确地评估与蠕动断层相关的危险。 该项目扩展了正在进行的粘滑断层断层沉积物结构的微观结构研究（Cashman和Cashman，2000年; Baldwin等人，2001年，在审查）的一个选定的研究地点的蠕变部分的圣安德烈亚斯断层。 研究的目标是发展微结构标准，使古地震学家区分剪切带所产生的地震蠕变从那些所形成的coselsmic断层破裂。数字图像采集和分析，使研究人员能够量化的特点ofrock fabric，如晶粒尺寸和晶粒取向，以测试有关过程的假设控制岩石结构的发展。 例如，基于计算机的图像分析已被用于测量火山岩中的晶体尺寸分布（例如Cashman和Marsh，1988）和囊泡尺寸分布（例如Cashman等人，1994），目的是约束结晶和囊泡形成的动态速率。 这种方法也被证明可用于测量邻近活动麦金莱维尔断层（加州，Cashman和Cashman，2000年）和密苏里州新马德里北断层（Baldwin等人，2001，综述），其目的是评估压实、颗粒破碎和颗粒旋转在剪切带发展中的相对重要性。 这两个粘滑断层的断层带沉积物有几个共同的结构特征，包括压实，明显的粒度减小，优选的颗粒取向，和发展的微尺度剪切带。 特别令人感兴趣的是在未固结的saw.This研究是一个网站上的圣安德烈亚斯断层蠕动部分断层带沉积物的显微结构分析的颗粒破碎的高度。 初步数据表明，粘滑断层作用下的松散砂和ascendroceper作用下的松散砂之间的颗粒破碎程度存在显著的可量化差异。 断层带沉积物的图像分析，从一个有据可查的蠕动断层网站将提供数据的颗粒破碎和其他纹理的变化所产生的蠕变。 这些数据将被用来评估相对重要性的颗粒破碎，颗粒旋转，压实的沉积物defon-ned稳定断层蠕动，并确定是否特定的纹理标准是唯一的粘滑或蠕动断层。

This research applies an innovative technique, microstructural analysis of faultedsediments, to evaluate more accurately the hazard associated with creeping faults. This project extends ongoing microstructural studies of faulted sediment texture from stick-slip faults (Cashman and Cashman, 2000; Baldwin et al., 2001, in review) to a selected study site on the creeping portion of the San Andreas Fault. The research goal is to develop microstructural criteria that will allow paleoselsmologists to differentiate shear zones produced by aseismic creep from those formed by coselsmic fault rupture.Digital image acquisition and analysis enable researchers to quantify characteristics ofrock fabrics such as grain dimensions and grain orientations in order to test hypotheses about processes governing the development of rock texture. For example, computer-based image analysis has been used to measure crystal size distribution (e.g. Cashman and Marsh, 1988) and vesicle size distribution (e.g. Cashman et al. 1994) in volcanic rocks with the goal of constraining dynamic rates of crystallization and vesiculation. This approach has also proved useful for measuring particle size distribution, grain shape, and grain orientation in shear zones in unconsolidated sand adjacent to the active McKinleyville fault, California, (Cashman and Cashman, 2000) and New Madrid North fault, Missouri, (Baldwin et al., 2001, in review) with the goal of assessing the relative importance of compaction, grain breakage, and grain rotation in shear zone development. Fault zone sediments from these two stick-slip faults have several textural features in common, including compaction, pronounced grain size reduction, preferred grain orientation, and development of anastomosing micro-scale shear zones. Of particular interest is the high degree of grain breakage in the unconsolidated sand.This study is a microstructural analysis of fault zone sediments from a site on the creeping portion of the San Andreas Fault. Preliminary data indicate significant quantifiable differences in the degree of grain breakage between unconsolidated sand subjected to stick-slip faulting and that defon-ned by ascismic creep. Image analysis of fault zone sediment from a well-documented creeping fault site will provide data on grain breakage and other textural changes produced by creep. These data will be used to evaluate the relative importance of grain breakage, grain rotation, and compaction in sediment defon-ned by stable fault creep, and to determine if specific textural criteria are unique to stick-slip or to creeping faults.