Collaborative Research: Laboratory Study of the Mechanics and Physical Properties of the San Andreas Fault and 3D SAFOD Volume

合作研究：圣安德烈亚斯断层力学和物理特性和 3D SAFOD 体积的实验室研究

• 批准号: 0545548
• 负责人: Harold Tobin
• 金额: $ 7.5万
• 依托单位: New Mexico Institute of Mining and Technology
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2006
• 资助国家: 美国
• 起止时间: 2006-01-01 至 2007-11-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0545548&HistoricalAwards=false
• 关键词: Collaborative; Research; Laboratory; Study; Mechanics

0545548TobinThe principal goal of the SAFOD borehole, and one of the main motivations for the NSF EarthScope initiative, is to gather critical data needed to understand fault mechanics and earthquakes. Through sampling, down-hole measurements, and long-term monitoring, the SAFOD experiment will provide data to test key hypotheses regarding long-term fault strength, earthquake nucleation, and fault slip behavior. However, the borehole itself will penetrate only a small part of the crustal volume surrounding the San Andreas Fault zone, and will sample only a subset of lithologies present in the subsurface. Although SAFOD will provide observations of the shallow seismogenic zone of a major plate bounding fault in unprecedented detail, additional characterization of rock physical properties for the 3-D volume containing SAFOD and the San Andreas Fault are critical for addressing several of the most important outstanding questions in fault mechanics and earthquake physics. These include: 1) What causes spatial variability in fault slip behavior and seismicity? 2) Are elevated fluid pressures within the SAFOD 3-D volume plausible? 3) How are geophysical observations such as low velocity or resistivity linked to in situ conditions of stress and fluid pressure? 4) What do thermal data in the shallow subsurface tell us about the fault energy budget? We are conducting a comprehensive study of the processes and properties that affect mechanical behavior and transport properties of fault zones. The research involves laboratory measurements of SAFOD core and outcrop samples. These measurements are designed to characterize the deformation processes and physical properties of rocks from the 3-D SAFOD volume. This work complements ongoing work on SAFOD samples. The data we collect will inform regional geologic, hydrologic, and thermal models. Our research is designed to address the following key objectives: - Determine the frictional strength and constitutive properties for SAFOD core material and host rock adjacent to the San Andreas Fault. - Test the hypothesis that the upper stability transition from aseismic to seismic faulting is associated with a change in mineralogy of fault gouge and/or host rock. - Develop experimental constraints necessary to test 1) the hypothesis that the San Andreas Fault is weak in an absolute and relative sense, and 2) models of long-term pore pressure generation and dynamic fault weakening. - Provide constraints on processes relevant to the energy budget of faulting: including frictional heat generation, advective heat transport, and thermal refraction. - Investigate the relationship between frictional strength (including healing and steady-state velocity dependence), seismic wave speed, and permeability. - Investigate the stress and pore pressure dependence of P and S wave speeds and their anisotropies in fault zone and wall rock, to evaluate and improve seismic-attribute proxies for pore pressure, effective stress, frictional strength, fluid content, and other properties inferred from borehole log and surface seismic data. This research will provide an understanding of processes that govern the strength and stability of major faults. In addition, we will measure those properties of fault rock that determine remotely sensed geophysical signatures, which is important for better assessment of earthquake hazard and for linking observations of fault behaviors with fundamental physical processes.

0545548Tobin SAFOD 钻孔的主要目标，也是 NSF EarthScope 计划的主要动机之一，是收集了解断层力学和地震所需的关键数据。通过采样、井下测量和长期监测，SAFOD 实验将提供数据来检验有关长期断层强度、地震成核和断层滑移行为的关键假设。然而，钻孔本身将仅穿透圣安德烈亚斯断层带周围地壳体积的一小部分，并且仅对地下存在的岩性子集进行采样。尽管 SAFOD 将以前所未有的细节对主要板块边界断层的浅层地震带进行观测，但包含 SAFOD 和圣安德烈亚斯断层的 3-D 体积的岩石物理性质的附加表征对于解决几个最重要的悬而未决的问题至关重要断层力学和地震物理学。其中包括：1）是什么导致断层滑动行为和地震活动的空间变异？ 2) SAFOD 3-D 体积内的流体压力升高是否合理？ 3) 低速或电阻率等地球物理观测结果如何与应力和流体压力的现场条件联系起来？ 4) 浅层地下热数据告诉我们有关断层能量收支的哪些信息？我们正在对影响断层带机械行为和输运特性的过程和特性进行全面研究。该研究涉及 SAFOD 岩心和露头样本的实验室测量。这些测量旨在表征 3-D SAFOD 体积中岩石的变形过程和物理特性。这项工作补充了正在进行的 SAFOD 样本工作。我们收集的数据将为区域地质、水文和热模型提供信息。我们的研究旨在解决以下关键目标： - 确定 SAFOD 核心材料和圣安德烈亚斯断层附近主岩的摩擦强度和本构特性。 - 检验以下假设：从抗震断层到地震断层的上部稳定性转变与断层泥和/或主岩的矿物学变化有关。 - 开发必要的实验约束来测试 1）圣安德烈亚斯断层在绝对和相对意义上较弱的假设，以及 2）长期孔隙压力生成和动态断层弱化的模型。 - 对与断层能量预算相关的过程提供约束：包括摩擦生热、平流热传输和热折射。 - 研究摩擦强度（包括愈合和稳态速度依赖性）、地震波速度和渗透率之间的关系。 - 研究断层带和围岩中纵波和横波速度的应力和孔隙压力依赖性及其各向异性，以评估和改进孔隙压力、有效应力、摩擦强度、流体含量以及从地震推断的其他属性的地震属性代理钻孔测井和地面地震数据。这项研究将提供对控制主要断层强度和稳定性的过程的理解。此外，我们将测量断层岩石的那些确定遥感地球物理特征的特性，这对于更好地评估地震危险以及将断层行为的观察与基本物理过程联系起来非常重要。