Collaborative Research: The Southern San Andreas Fault Zone Experiment

加利福尼亚州的圣安德烈亚斯断层（SAF）是一个成熟的板块边界断层，能够发生大地震（8级或更大）。SAF的南段在历史上（在过去的300年里）没有发生过大地震，目前被认为是加州最大的地震风险。该项目将使用新的地震和大地测量观测来调查南圣安德烈亚斯断层（SSAF）的地下结构和几何形状。特别是，该项目将测试一个假设，即SSAF可能不是垂直的，可能向东倾斜。如果得到证实，非垂直断层倾角将对SSAF的力学和长期构造演化具有重要意义。更好地了解SSAF的地下几何结构也将改进对地震辐射模式和未来SSAF上大地震引起的地面震动强度的预测。这项工作的更广泛影响将是对南加州和墨西哥人口稠密地区地震危险性的精确估计，以及为两名研究生的教育提供支持。来自加州大学圣地亚哥分校、斯克里普斯海洋研究所和南加州大学联合项目的研究人员将通过对上地壳中与SSAF相关的低刚性损伤区和/或双材料界面进行成像，深入研究断层的产状。这将通过在SSAF上部署密集的地震阵列来实现。来自部署的地震阵列和区域地震台网的数据将用于生成整个发震层的断裂带的高分辨率层析成像。地震数据将与高分辨率大地测量观测相结合，包括干涉合成孔径雷达（InSAR）和全球导航卫星系统（GNSS）。对地震和大地测量数据的联合分析将提供对成熟板块边界断层周围的空间范围和破坏程度的新见解，并使其能够与加利福尼亚和其他地方的其他断层的观测结果进行比较，以检查破坏的分布和数量如何取决于断层年龄、地震潜力和几何复杂性。同时部署密集的地震和大地测量阵列将为未来测量由外部应力扰动引起的断裂带岩石力学特性的可能随时间变化建立基线，这可能有助于限制发震深度的绝对应力大小。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

The San Andreas Fault (SAF) in California is a mature plate boundary fault capable of great (magnitude 8 or greater) earthquakes. The southern section of the SAF has not produced a major earthquake in historic times (over the last 300 years), and is currently believed to pose the largest seismic risk in California. This project will use new seismic and geodetic observations to investigate the sub-surface structure and geometry of the Southern San Andreas Fault (SSAF). In particular, the project will test a hypothesis that the SSAF may not be vertical and may substantial dip to the East. If confirmed, a non-vertical fault dip would have important implications for the mechanics and the long-term tectonic evolution of the SSAF. Better knowledge of the sub-surface geometry of the SSAF will also improve predictions of seismic radiation patterns and the intensity of ground shaking due to future large earthquakes on the SSAF. The broader impacts of this work will be refined estimates of seismic hazard in densely populated areas in Southern California and Mexico as well as support for the education of two graduate students.The researchers from this joint project between the University of California San Diego, Scripps Institution of Oceanography and the University of Southern California, will investigate the fault attitude at depth by imaging a low-rigidity damage zone and/or a bi-material interface associated with the SSAF in the upper crust. This will be accomplished by deploying a dense seismic array spanning the SSAF. Data from the deployed seismic array and regional seismic networks will be used to generate high-resolution tomographic images of the fault zone throughout the seismogenic layer. Seismic data will be combined with high-resolution geodetic observations, including Interferometric Synthetic Aperture Radar (InSAR) and Global Navigation Satellite System (GNSS). A joint analysis of seismic and geodetic data will provide new insights into the spatial extent and degree of damage around a mature plate boundary fault and enable comparisons with observations from other faults in California and elsewhere to examine how the distribution and amount of damage might depend on the fault age, seismic potential, and geometric complexity. The deployment of co-located dense seismic and geodetic arrays will establish a baseline for future measurements of possible time-dependent variations in mechanical properties of rocks comprising the fault zone due to external stress perturbations, which may help constrain the magnitude of absolute stress at seismogenic depth.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.