Unraveling the San Gorgonio Knot: Numerical and Analog Investigations

尽管在加利福尼亚州的许多地区结构简单，但加利福尼亚州南部圣戈戈尼奥山口内的圣安德烈亚斯活动断层沿着几个不平行的走滑、逆冲和倾斜断层滑动。圣戈戈尼奥山口地区的今天的复杂性是在过去数百万年里发展起来的，以应对新的活跃股的繁殖、旧股的废弃和其他旧股的重新激活。圣安德烈亚斯断层的许多地球物理模型将系统简化为通过圣戈戈尼奥山口的垂直和连续的系统。这类模型不能反映现今的形变，因为它们低估了断层拓扑的重要性以及与次级断层构造的相互作用。为了解决这一问题，本研究使用圣安德烈亚斯断层通过所谓的圣戈尔戈尼奥结的演化的三维模拟和数值模拟来探索与放弃和发展新的断裂链相关的机械效率的变化。通过在模拟和数值模型中模拟圣安德烈亚斯断层南部的变形，可以观察到一些断层链在机械上变得低效，并被抛弃，转而支持其他更有效的断层链。与活动断裂系统构型变化相关的隆升模式和滑动速率与地质数据进行比较，以约束断裂演化的性质。这项研究的目标是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)解决不同地质和大地测量变形计算之间的差异，这可能是由于不同的测量时间尺度所致，4)测试创新的实验室和数值技术，以更好地解释走滑构造。本研究的结果将通过研究过去50万年来断裂系统的演化，帮助约束这一南加州圣安德烈亚斯断层的现今活动断裂面形态。通过了解这一断层复杂性区域是如何发展的，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。南加州走滑断层模拟和数值模型的结合很好地补充了其他国际工作人员正在进行的努力，即比较其他类型断层系统的模拟和数值模型结果。这项研究还让全国各地聋人高中的学生参与研究，方法是改进现有的课堂模拟建模活动，并在研究团队和教室之间举行视频会议。这些活动加强了学生的学习，并使教师在其地球系统课程中介绍岩石圈科学变得活跃起来。

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.