The Work Budget of Fault Birth within Accretionary Systems

地球上大多数构造板块的边界都包含复杂的活动断层网络。更好地了解地质断层是如何形成的，将有助于更好地了解板块边界的变形。该项目通过调查故障系统的功/能量预算来探索故障的演变。一个变形的断层系统会产生或消耗不同类型的能量，包括抬升地球部分的工作？美国地壳和地震释放的能量作为地面震动。了解完整的工作预算可以帮助预测新的故障发展。例如，当系统内存在新故障所节省的能量大于产生新故障面的能量成本时，就会产生新的故障。本研究考察了1)理论、2)模拟桌面实验和3)地球自然增生楔的断层诞生。增生楔发育在俯冲带板块边界，沉积物从下沉的大洋板块上刮下来。刮掉的沉积物堆积在一个增生的楔形物中，就像在俄勒冈和智利海岸发现的那样。增生楔非常适合研究断层生长，因为新的断层在系统的前端，在以前从未断裂过的年轻物质中发育。在其他类型的板块边界，如圣安德烈亚斯断层，岩石有数百万年的历史，活动断层系统受到岩石先前变形的影响。该研究使用数值模型来探索各种尺度的增生楔内的工作预算。模型将测试吸积楔生长的理论公式，模拟桌面沙盒实验，并模拟日本南开槽吸积楔，这些数据来自最近和正在进行的研究。这项研究的结果将通过揭示在地球上形成新断层所需的能量来完善对断层生命周期的理解。并重新激活旧断层。虽然该项目的重点是增生楔，但由于这些环境中的物质性质相对简单，因此结果应该适用于任何构造板块边界内的断层生长。了解新的断层是如何以及何时形成的，将有助于预测断层的行为，并为活跃断层系统沿线的地震事件做好准备。此外，对南开增生系统的数值模拟可能有助于了解该断裂带的未来行为，该断裂带过去曾发生过强烈的地震和毁灭性的海啸。该提案的延伸部分将促进在初中和高中教室中使用桌面沙盒实验。变形沙盒实验将板块构造学带入学生的生活中，活动的动手和视觉性质激发学生探索地球科学的过程。

Most boundaries of tectonic plates in the Earth contain complex networks of active faults. Better understanding of how geologic faults develop would lead to improved understanding of deformation at plate boundaries. This project explores the evolution of faults by investigating the work/energy budget of the fault system. A deforming fault system will produce or consume different types of energy including the work of uplifting parts of the Earth?s crust and the energy released by earthquakes as ground shaking. Understanding the complete work budget can help predict new fault development. For example, new faults will develop when the energy savings of having the new fault within the system is greater than the energy cost of creating the new fault surface. This study examines the birth of faults within 1) theoretical, 2) analog table top experiments and 3) natural accretionary wedges in the Earth. Accretionary wedges develop at subduction zone plate boundaries where sediments are scraped off of the down-going oceanic plate. The scraped off sediments accumulate within an accretionary wedge, such as found off the coast of Oregon and Chile. Accretionary wedges are well-suited for the study of fault growth because new faults develop at the front of the system within young material that has never before been faulted. At other types of plate boundaries, such as the San Andreas Fault, the rocks are millions of years old and the active fault system is influenced by previous deformation of the rocks. The study uses numerical models to explore the work budget within accretionary wedges of a variety of scales. Models will test theoretical formulations for accretionary wedge growth, simulate table-top sandbox experiments performed, and simulate the Nankai trough accretionary wedge off Japan, for which a wealth of data is available from recent and on-going investigations. The results of the study will refine the understanding of the fault life-cycle by revealing the energy required to both grow new faults in the Earth?s crust and reactivate old faults. While the project focuses on accretionary wedges, because the material properties are relatively simple in these settings, the results should be applicable to fault growth within any tectonic plate boundary. Understanding how and when new faults grow will aid in efforts to predict fault behavior and prepare for earthquake events along active fault systems. Furthermore, the numerical simulation of the Nankai accretionary system may yield insights the future behavior of that fault zone, which has generated strong earthquakes and devastating tsunamis in the past. An outreach component of this proposal will promote the use of table-top sandbox experiments within middle and high school classrooms. The deformational sandbox experiments help bring plate tectonics to life for students and the hands-on and visual nature of the activity inspires students to investigate earth science processes.