Unraveling the San Gorgonio Knot: Numerical and Analog Investigations

虽然加州的许多地方结构简单，但加州南部圣戈尔戈尼奥山口内的活动圣安德烈亚斯断层沿着几个不平行的走滑、逆冲和斜断层滑动。 在过去的几百万年里，圣戈尔戈尼奥山口地区的复杂性随着新的活跃链的繁殖、旧链的放弃和其他旧链的重新激活而发展。圣安德烈亚斯断层的许多地球物理模型将该系统简化为垂直和连续通过圣戈尔戈尼奥山口。这种模型不能捕捉到现今的变形，因为它们低估了断层拓扑结构和与次级断层结构相互作用的重要性。为了解决这个问题，本研究使用三维模拟和数值模拟的圣安德烈亚斯断层的演变，通过所谓的圣戈尔戈尼奥结探索机械效率的变化与放弃和新的故障链的发展。通过在模拟和数值模型中模拟圣安德烈亚斯断层南部沿着的变形，将有可能观察到一些断层链变得机械效率低下，并被其他更有效的链所抛弃。与活动断层系统配置的变化相关的隆起模式和滑动速率与地质数据进行比较，以约束断层演化的性质。本研究的目标是：1）通过与现有地质数据的比较，限制圣安德烈亚斯断层的三维演化，2）根据演化系统的工作预算评估断层演化的力学，3）解决不同的地质和大地测量变形计算之间的差异，这些差异可能是由于不同的测量时间尺度造成的;测试创新的实验室和数值技术，以更好地解释走滑构造。这项研究的结果将有助于通过检查过去50万年来断层系统的演变来限制加州南部圣安德烈亚斯断层现今的活动断层表面结构。通过了解这一地区的断层复杂性如何发展，将导致更好地了解当今的滑动分布和地震灾害的地区。该研究采用了模拟和数值模型的创新组合。因此，除了为该地区的地震危险性分析提供信息外，该项目还可以比较断层系统长期变形的模拟和数字模型。这种在南加州走滑断层的模拟和数值模型的结合很好地补充了其他国际工作者正在进行的努力，比较模拟和数值模型的结果在其他类型的断层系统。该研究还涉及全国聋人高中的学生，通过改进现有的课堂模拟建模活动和研究团队与教室之间的视频会议进行研究。这些活动促进了学生的学习，并激发了教师在地球系统课程中介绍岩石圈科学的活力。

While structurally simple in many parts of California, the active San Andreas Fault within the San Gorgonio Pass, southern California, slips along several, non-parallel, strike-slip, thrust and oblique faults. The present-day complexity of the San Gorgonio Pass region has developed over the past few million years in response to propagation of new active strands, abandonment of old strands and reactivation of other old strands. Many geophysical models of the San Andreas Fault simplify the system as vertical and continuous through the San Gorgonio Pass. Such models cannot capture the present-day deformation because they underestimate the importance of fault topology and interaction with secondary fault structures. To address this problem, this study uses three-dimensional analog and numerical modeling of the evolution of the San Andreas Fault through the so-called San Gorgonio knot to explore the change in mechanical efficiency associated with abandonment and development of new fault strands. By simulating deformation along the southern San Andreas Fault within both analog and numerical models, it will be possible to observe some fault strands become mechanically inefficient and become abandoned in favor of other, more efficient strands. The uplift pattern and slip rates associated with changes in the active fault system configuration are compared to geologic data to constrain the nature of fault evolution. The goals of this study are to 1) constrain the three-dimensional evolution of the San Andreas fault by comparison to available geologic data, 2) evaluate the mechanics of fault evolution with regard to the work budget of the evolving system, 3) resolve discrepancies between different geologic and geodetic calculations of deformation that may owe to different time scales of measurement and 4) test innovative laboratory and numerical techniques towards better interpreting strike-slip tectonics.The results of this study will help constrain the present-day active fault surface configuration of the San Andreas Fault in this southern California by examining the evolution of the fault system over the past half- million years. By understanding how this region of fault complexity developed will lead to better understanding of the present-day slip distribution and seismic hazards for the region. The study uses an innovative combination of analog and numerical models. Consequently, in addition to providing information for seismic hazard analysis in the region, the project allows comparison of analog and numerical models of long-term deformation of fault systems. This combination of analog and numerical models of strike-slip faulting in southern California nicely complements on going efforts by other international workers to compare analog and numerical model results in other types of fault systems. The study also involves students at high schools for the Deaf around the country in research via refinement of existing classroom analog modeling activities and videoconferences between the research team and the classrooms. These activities enhance the students' learning and invigorate the teachers' presentations of lithospheric science in their earth system courses.