Collaborative Research: Brittle fracture, deformability, permeability, and seismic anisotropy adjacent to and inside the San Andreas Fault Zone through SAFOD

威斯康星大学麦迪逊分校和纽约州立大学石溪分校正在进行一个合作研究项目，其主要目标是调查圣安德烈亚斯断层带附近和内部的脆性断裂、变形性、渗透性和地震各向异性，这是地球镜科学方案的一部分。这项实验室研究是在从圣安德烈亚斯断层观测站（SAFOD）孔中提取的岩心上进行的。通过这项研究的地球物理特性的特点是基本的努力，以了解机制，使地震沿着圣安德烈亚斯断层。 麦迪逊实验室提供的一种独特的真三轴仪器用于获得圣安德烈亚斯断层内和附近岩石的经验强度标准，当与沿沿着记录的钻孔崩落尺寸结合使用时，这些信息对于评估构造应力条件至关重要。 真三轴试验还提供了必要的信息，力学性能，如弹性模量，体积应变，屈服起始，和脆性断裂的折返断层和围岩。 该研究旨在回答一些问题，如这些属性如何在断层带内外变化;它们如何取决于环境因素，如原地应力，矿物学，孔隙压力和温度;如何将岩心样品测量的机械性能与从钻孔日志和地面地球物理观测推断的性能进行比较。 渗透率和地震各向异性测量在斯托尼布鲁克实验室进行。 在断裂带附近的岩心样品的检索和渗透率作为应力的函数的系统测量提供了重要的背景数据的圣安德烈亚斯断层结构，以及关键的限制，孔隙压力过剩和断层弱化的某些机制是否可以操作。 以往对断层岩心地震各向异性的系统研究尚未见报道。 虽然相当复杂的理论模型有关的应力引起的损伤和速度各向异性是可用的，实验室测量的控制应力和孔隙压力条件下的速度，以及定量表征的损害是必要的，以阐明这种现象的力学。对圣安德烈亚斯断层带中断层物质和围岩的某些力学和水力性质的全面研究是实现SAFOD了解断层带过程和地震物理学的总体目标的先决条件。

A collaborative research project is underway at the University of Wisconsin-Madison and the State University of New York-Stony Brook, the principal objective of which is to investigate brittle fracture, deformability, permeability and seismic anisotropy adjacent to and inside the San Andreas Fault Zone, as part of the EarthScope science program. This laboratory study is being carried out on core extracted from the San Andreas Fault Observatory at Depth (SAFOD) hole. The geophysical properties that are characterized through this study are fundamental in efforts to understand the mechanisms that bring about earthquakes along the San Andreas Fault. A unique true-triaxial apparatus available in the Madison laboratory is used to obtain empirical strength criteria for the rocks in and adjacent to the San Andreas Fault, information that is crucial to assessing the tectonic stress conditions when used in conjunction with the dimensions of borehole breakouts logged along the hole. The true triaxial tests also provide necessary information on mechanical properties like the elastic moduli, volumetric strain, dilatancy onset, and brittle fracture of the exhumed fault and country rocks. The study seeks to answer questions such as how these properties vary across the fault zone and beyond; how they depend on environmental factors like situ stress, mineralogy, pore pressure, and temperature; how mechanical properties measured on core samples compare with properties inferred from borehole logs and surface-based geophysical observations. Permeability and seismic anisotropy measurements are conducted in the Stony Brook laboratory. The retrieval of core samples in the vicinity of the fault zone and the systematic measurement of permeability as a function of stress provide significant background data on the San Andreas Fault architecture, as well as critical constraints on whether certain mechanisms for pore pressure excess and fault weakening can be operative. No previous systematic studies of seismic anisotropy on fault cores have been conducted. While fairly sophisticated theoretical models relating stress-induced damage and velocity anisotropy are available, laboratory measurements of such velocities under controlled stress and pore pressure conditions as well as quantitative characterization of the damage are necessary to elucidate the mechanics of such phenomena. This comprehensive study of some mechanical and hydraulic properties of the fault material and country rock in the San Andreas Fault Zone is a prerequisite in accomplishing the SAFOD general goal of understanding fault zone processes and earthquake physics.