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Judith Chester和Frederick Chester、犹他州立大学的James Evans和圣路易斯大学的David Kirschner正在合作分析SAFOD第三阶段侧钻所取的岩心，以表征圣安德烈亚斯断裂带的组成、结构和变形机制。这项工作解决了有关矿物学转化、流体-岩石相互作用、物理性质和断层力学的关键问题。本研究主要针对以下四种假设：1)断裂带的构造；2)地震和地震变形的过程；3)断层的绝对强度；4)地震的能量收支。许多技术被用来检验这些假设。绘制地核的介观结构和岩性图提供了有关断裂带结构的信息，这些信息正在传递给科学界，以便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、XRD和稳定同位素分析被用于表征在圣安德烈亚斯断裂带地震和地震断层变形中重要的微观结构、矿物反应和流体-岩石相互作用。断层、裂缝和脉的细观和微观结构分析确定了相对于断裂带的主应力的平均方向，从而限制了断裂带的长期强度。光学和电子显微镜被用来描述断裂带地震活跃部分的颗粒尺寸减小和新断裂面形成的特征，从而有助于限制地震事件的能量收支。该研究项目与其他safod相关项目的成果相结合，正在努力记录发生地震的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的生命损失和财产损失。该项目为国家利益的更广泛的研究计划和活动做出了贡献，包括国家减少地震危害计划（NEHRP）和南加州地震中心（SCEC）。至少有三名研究生和两名本科生作为论文研究的一部分参与了该项目，并在科学钻探和众多实验室技术方面获得了宝贵的经验。pi继续通过专门的网络演示、媒体采访和外行演示，向公众宣传EarthScope SAFOD项目和地震。

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.