Evolving work budget of fault initiation, linkage and growth within accretionary systems

下一次破坏性地震会发生在一个有着长期滑动历史的断层上，还是会发生在一个地质学家还没有认识到的新形成的断层上？新断层的增长对准确评估世界地震活跃区的地震危险性提出了重大挑战。对新断层生长的预测将有助于更好地了解活动断层系统的发展。通过多次地震的积累，每次地震都逐步推进断层系统的发展，最初分布的1厘米裂缝可以演变成100公里长的断层，能够破坏地震。由于断层生长发生在广泛的空间尺度和地下，地质学家无法直接观察新断层的生长。该项目使用物理实验室实验和计算机模型相结合，模拟断层生长，在没有直接观察的情况下探索这个问题。计算机模型建立在新的故障增长的想法，以尽量减少工作，并实现较低的能量状态。计算机预测，将与实验室实验进行比较，将模拟在一个增生楔，日本东京南部的南海海槽前面的新断层的发展。这一非常好的俯冲带成像为检验地壳断层生长模型提供了良好的约束条件。南海海槽已经产生了几次毁灭性的地震，从这个俯冲带中学到的见解将指导我们对其他俯冲带的理解，如西雅图的卡斯卡迪亚边缘和阿拉斯加的阿留申群岛。其他期望的社会成果包括妇女和残疾人充分参与STEM，通过研究生和博士后研究人员培训，国际合作，并通过开发和分发新的计算机建模代码来增强研究基础设施。增生棱镜是研究断层发育的理想位置，因为材料包含在断层的趾部棱镜相对无缺陷。野外观测表明，贯通的棱柱形断层是通过加积系统内较小断裂的相互作用和联系而形成的。这种聚结导致应变从最初沿沿着许多小裂缝的扩散应变沿沿着离散断层的局部化。本计画以比例物理实验与南海棱镜来探讨裂缝聚结至断层形成的演化。增生系统将采用创新的新数值代码GROW进行建模，该代码通过优化外部工作来预测裂缝扩展。将在四个不同的系统中模拟裂纹的合并：（1）双轴和三轴系统，用于在挪威奥斯陆大学进行的类似载荷的实验室试验的验证，该试验使用层析成像来跟踪裂纹合并;（2）在法国Cergy-Ponnés大学进行的吸积的比例物理实验，提供了已知的边界条件，（3）中等复杂性和规模的吸积模拟，提供了（2）和（4）之间的关键步骤，并允许调查越来越现实的参数;（4）南海增生棱柱体熊野断面的模拟，为序列内和序列外地壳逆冲断层的发育提供了一个约束良好的实例。对于后者，将在过去的2 Ma在几个连续的时间间隔模拟拟议的巨型推力发展。所有四套模型都将研究故障发展，考虑到故障增长的前提，以优化系统的总工作。许多模型将从初始分布的种子点开始断层生长和合并，这代表了实验和地壳中的弱非均质性。对于所有的模型套件，系统内不断变化的工作预算揭示了不同变形机制的竞争影响。通过研究每个系统中应变局部化、断裂相互作用和各种能量消耗过程之间的关系，研究人员将能够比较厘米级实验室物理实验模型和公里级自然造山带模型之间这些关系的差异。

Will the next damaging earthquake occur on a fault that has had a long history of slip or will it happen on a newly formed fault that is not yet recognized by geologists? The growth of new faults presents a significant challenge for accurate assessments of earthquake hazards in seismically active regions of the world. Prediction of new fault growth would allow better understanding of the development of active fault systems. Through the accumulation of many earthquakes that each incrementally advance the fault system development, an initial distribution of 1 cm cracks can evolve into a 100-km long fault capable of damaging earthquakes. Because fault growth happens across a wide range of spatial scales and in the subsurface, geologists are unable to directly observe the growth of a new fault. This project uses a combination of physical laboratory experiments and computer models that simulate fault growth to explore this problem in the absence of direct observation. The computer models build on the idea that new faults grow to minimize work and achieve a lower energy state. The computer predictions, which will be compared with laboratory experiments, will simulate the development of new faults in front of an accretionary wedge, the Nankai trough south of Tokyo, Japan. This extremely well imaged subduction zone provides good constraints for testing the crustal fault growth models. The Nankai trough has produced several devastating earthquakes and insights learned from this subduction zone will guide our understanding of other subduction zones such as Cascadia margin off Seattle and the Aleutians in Alaska. Additional desired societal outcomes include full participation of women and persons with disabilities in STEM, development of a diverse competitive STEM workforce through graduate student and post-doctoral researcher training, international collaboration, and enhanced infrastructure for research by development and distribution of new computer modeling code.Accretionary prisms are ideal locations for the study of fault development because the material incorporated at the toe of the prism is relatively un-faulted. Field observations suggest that through-going, prism-scale faults develop via the interaction and linkage of smaller fractures within accretionary systems. This coalescence results in the localization of strain along discrete faults from initially diffuse strain along many small fractures. This project examines the evolution of crack coalescence to fault formation within both scaled physical experiments and the Nankai prism. Accretionary systems will be modeled with an innovative new numerical code, GROW, which predicts fracture propagation through the optimization of external work. Crack coalescence will be simulated within four distinct systems: (1) biaxial and triaxial systems for validation with similarly loaded laboratory tests run at the University of Oslo, Norway, that use tomography to track crack coalescence; (2) scaled physical experiments of accretion run at the University of Cergy-Pontoise, France, that provide known boundary conditions, material properties and detailed quantitative observations of the evolution of faulting and associated deformation; (3) accretion simulations of intermediate complexity and scale that provide a critical step between (2) and (4) and allow investigation of increasingly realistic parameters; and (4) simulation of the Kumano transect across the Nankai accretionary prism, which provides a well-constrained example of the development of in-sequence and out-of-sequence crustal thrusts. For the latter, the proposed megathrust development will be simulated over the past 2 Ma in several successive time intervals. All four suites of models will investigate fault development considering the premise that faults grow to optimize the total work on the system. Many of the models will initiate fault growth and coalescence from initial distributed seed points, that represent weak heterogeneities in the experiment and crust. For all suites of models, the evolving work budget within the systems reveals the competing influences of different deformation mechanisms. By investigating the relationship between strain localization, fracture interaction and various energy consuming processes within each system, the researchers will be able to compare the differences in these relationships between models of cm-scale, laboratory physical experiments and km-scale, natural orogens.