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、犹他州州立大学的詹姆斯·埃文斯和圣刘易斯大学的大卫·基尔施纳正在合作分析SAFOD第三阶段侧钻期间采集的岩心，以表征圣安德烈亚斯断层带的成分、结构和变形机制。这项工作正在解决有关矿物学转换，流体-岩石相互作用，物理性质和断层力学的关键问题。这项研究涉及四个一般性假设，涉及1）断裂带的结构，2）地震和地震变形的过程，3）断层的绝对强度，和4）地震的能量收支。目前正在使用一些技术来检验这些假设。绘制岩芯的中观结构和岩性图提供了关于断层带结构的信息，这些信息正在传达给科学界，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，XRD和稳定同位素分析正在被用来表征的微观结构，矿物反应，流体-岩石的相互作用，在圣安德烈亚斯断层带的地震和地震断层的变形是重要的。断层、裂缝和矿脉的中观和微观组构分析界定了主应力相对于断层带的平均方向，从而限制了断层带的长期强度。光学显微镜和电子显微镜正被用来描述断层带地震活跃部分的晶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相关项目的结果相结合，正在努力记录在地震孕育深度的物理和化学过程，这些过程在产生地震中最重要，从而减少地震在美国和世界造成的毁灭性生命损失和财产损失。该项目正在促进更广泛的研究计划和国家利益的活动，包括国家地震减灾计划（NEHRP）和南加州地震中心（SCEC）。至少有三名研究生和两名本科生参加了该项目，作为他们论文研究的一部分，并在科学钻探和许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、媒体采访和向非专业观众的演示，教育公众了解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.