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

蠕动断层和粘滑断层形成的微尺度断层组构的比较

• 批准号: 0207672
• 负责人: Susan Cashman
• 金额: $ 4.06万
• 依托单位: Humboldt State University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2002
• 资助国家: 美国
• 起止时间: 2002-06-01 至 2005-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0207672&HistoricalAwards=false
• 关键词: Comparison; Microscale; Fault; Fabrics; Formed

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.

本研究采用了一种创新的技术，断层沉积物的微观结构分析，以更准确地评估与爬行断层相关的危害。该项目将目前对粘滑断层断层沉积物结构的微观结构研究（Cashman and Cashman, 2000; Baldwin et al., 2001，回顾）扩展到选定的圣安德烈亚斯断层爬行部分的研究地点。研究目标是发展微观结构标准，使古自旋学家能够区分由地震蠕变产生的剪切带和由自旋断层破裂形成的剪切带。数字图像采集和分析使研究人员能够量化岩石结构的特征，如颗粒尺寸和颗粒方向，以测试有关控制岩石结构发展过程的假设。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大小分布（例如，Cashman和Marsh， 1988）和囊泡大小分布（例如，Cashman等，1994），目的是限制结晶和囊泡的动态速率。这种方法也被证明对测量剪切带中未固结砂的粒度分布、颗粒形状和颗粒方向非常有用，这些剪切带靠近活跃的加利福尼亚州麦金利维尔断层（Cashman and Cashman, 2000）和密苏里州新马德里北断层（Baldwin et al., 2001，回顾），目的是评估压实作用、颗粒破碎和颗粒旋转在剪切带发育中的相对重要性。这两个粘滑断裂的断裂带沉积物具有压实作用、明显的粒度减小、优先的颗粒取向和吻合的微尺度剪切带发育等共同的结构特征。特别令人感兴趣的是松散砂土中的高度颗粒破碎。本研究是对圣安德烈亚斯断层爬行部分的断裂带沉积物进行微观结构分析。初步数据表明，受粘滑断裂作用的松散砂粒破碎程度与受自滑蠕变作用的松散砂粒破碎程度存在显著的可量化差异。从一个记录良好的蠕变断层位置对断层带沉积物进行图像分析，将提供蠕变产生的颗粒破碎和其他结构变化的数据。这些数据将用于评估稳定断层蠕变所决定的沉积物中颗粒破碎、颗粒旋转和压实的相对重要性，并确定特定的结构标准是粘滑断层还是蠕变断层所特有的。