Unraveling the San Gorgonio Knot: Numerical and Analog Investigations

虽然加州许多地区的构造简单，但位于加州南部圣戈尔尼奥山口的活跃的圣安德烈亚斯断层沿着几条非平行的走滑、逆冲和斜断层滑动。今天的圣戈尼奥山口地区的复杂性是在过去的几百万年里随着新的活跃山带的繁殖、旧山带的废弃和其他旧山带的重新激活而发展起来的。许多圣安地列斯断层的地球物理模型将其简化为垂直和连续的圣戈尔尼奥山口。这样的模型无法捕捉到现今的变形，因为它们低估了断层拓扑结构以及与次级断层结构相互作用的重要性。为了解决这个问题，本研究通过所谓的San Gorgonio结对San Andreas断层的演化进行了三维模拟和数值模拟，以探索与新断层链的放弃和发展相关的机械效率变化。通过模拟和数值模型模拟南圣安德烈亚斯断层的变形，可以观察到一些断层链变得机械效率低下，并被其他更有效的断层链所取代。与活动断层系统结构变化相关的隆升模式和滑动速率与地质数据进行了比较，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来约束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来评估断层演化的机制；3)解决可能由于测量时间尺度不同而导致的不同地质和大地测量变形计算之间的差异；4)测试创新的实验室和数值技术，以更好地解释走滑构造。这项研究的结果将通过检查断层系统在过去50万年中的演变，帮助限制南加州圣安德烈亚斯断层目前的活动断层表面结构。通过了解该地区的断层复杂性如何发展，将有助于更好地了解该地区现今的滑动分布和地震危险性。这项研究采用了模拟和数值模型的创新结合。因此，除了为该地区的地震危险性分析提供信息外，该项目还允许对断层系统长期变形的模拟模型和数值模型进行比较。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比较其他类型断层系统的模拟和数值模型结果的努力。这项研究还通过改进现有的教室模拟建模活动和研究小组与教室之间的视频会议，让全国聋人高中的学生参与研究。这些活动促进了学生的学习，并使教师在地球系统课程中对岩石圈科学的介绍更加生动。

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.