Collaborative Research: Influence of Structure, Composition and Fluid-Rock Chemistry on Mode of Slip in the San Andreas Fault Zone at SAFOD

德克萨斯农工大学的朱迪思·切斯特和弗雷德里克·切斯特、犹他州立大学的詹姆斯·埃文斯和圣路易斯大学的大卫·基尔施纳正在合作分析SAFOD第三阶段侧钻钻探期间采集的岩心，以表征圣安德烈亚斯断裂带的成分、结构和变形机制。这项工作正在解决与矿物学转换、流体-岩石相互作用、断层的物理性质和力学有关的关键问题。这项研究涉及四个基本假设：1)断裂带的结构，2)地震和非地震形变的过程，3)断层的绝对强度，4)地震的能量收支。许多技术正被用来检验这些假说。绘制岩心的介观结构和岩性图提供了有关断裂带结构的信息，目前正在向科学界传达这些信息，以指导其他研究小组正在进行的调查和取样。光学和电子显微镜、XRF、X射线衍射仪和稳定同位素分析被用来表征微结构、矿物反应和流体-岩石相互作用，这些在圣安德烈亚斯断裂带的地震和非地震断裂的变形中是重要的。对断层、裂缝和矿脉的中观和微观组构分析正在划定相对于断裂带的主应力的平均方向，从而对断裂带的长期强度施加约束。光学和电子显微镜被用来表征断裂带地震活跃部分的颗粒尺寸减小和新断裂面的形成，从而将有助于限制地震事件的能量收支。这一研究项目与其他SAFOD相关项目的结果相结合，致力于在孕震深度记录在地震发生中最重要的物理和化学过程，从而减少地震在美国和世界造成的毁灭性生命和财产损失。该项目正在为更广泛的国家利益研究计划和活动做出贡献，包括国家减少地震灾害计划(NEHRP)和南加州地震中心(SCEC)。作为论文研究的一部分，至少有三名研究生和两名本科生参与了该项目，并在科学钻探和众多实验室技术方面获得了宝贵的经验。私人投资机构继续通过专门的网络演示、媒体采访和面向非专业受众的演示，教育普通公众关于地球范围SAFOD项目和地震的知识。

In collaboration, Judith Chester and Frederick Chester of Texas A&M University, James Evans of Utah State University, and David Kirschner of Saint Louis University are analyzing the cores taken during phase 3 sidetrack drilling at SAFOD to characterize the composition, structure, and deformation mechanisms of the San Andreas fault zone. The work is addressing key questions regarding mineralogic transformations, fluid-rock interactions, physical properties, and mechanics of the fault. This study is addressing four general hypotheses that relate to the 1) architecture of the fault zone, 2) processes involved in seismic and aseismic deformation, 3) absolute strength of the fault, and 4) energy budget of earthquakes. A number of techniques are being used to test the hypotheses. Mapping the mesoscopic structure and lithology of the core is providing information on the fault-zone architecture, which is being conveyed to the scientific community in order to guide the ongoing investigations and sampling by other research groups. Optical and electron microscopy, XRF, XRD, and stable isotope analyses are being used to characterize the microstructures, mineral reactions, and fluid-rock interactions that are important in the deformation of seismic and aseismic faults in the San Andreas fault zone. Mesoscopic and microscopic fabric analyses of faults, fractures, and veins are delimiting the average orientations of principal stresses relative to the fault zone, and thus place constraints on the long-term strength of the fault zone. Optical and electron microscopy is being used to characterize the reduction in grain size and formation of new fracture surfaces in seismically active portions of the fault zone, and thus will help place constraints on the energy budget of seismic events. This research project, in combination with the results of other SAFOD-related projects, is working to document at seismogenic depths the physical and chemical processes that are most important in generating earthquakes, and thus to reduce the devastating loss of life and property damage that earthquakes cause in the U.S. and world. The project is contributing to broader research programs and activities of national interest including the National Earthquake Hazard Reduction Program (NEHRP) and the Southern California Earthquake Center (SCEC). At least three graduate and two undergraduate students are participating in the project as part of their thesis research, and are gaining valuable experience in scientific drilling and numerous laboratory techniques. The PIs are continuing to educate the general public on the EarthScope SAFOD project and earthquakes through dedicated web presentations, media interviews and presentations to lay audiences.