Collaborative Research: Comparison of Numerical, Physical and Natural Extensional Fault Systems

两种基本的断层模式适应了脆性上地壳的伸展：地垒-地堑几何形状和书架几何形状。 在地垒地堑几何学中，相邻的正断层向相反的方向倾斜;在书架几何学中，相邻的断层向相同的方向倾斜。 数值模型和比例物理模型与干砂通常产生地垒和地堑的几何形状。 书架的几何形状只有在特定的、不对称的边界条件下才能发展。 然而，湿粘土的比例物理模型产生了具有对称或不对称边界条件的书架几何形状。 这些意见提出了以下问题。 书架的几何形状在自然界中是否是基本上不对称的应力模式的结果？ 砂和粘土的力学行为有哪些显著差异？ 数值模型能再现更多类似粘土的行为吗？ 自然界中许多岩石的力学行为是否更像粘土而不是沙子？数值，沙子和粘土模型，一系列的边界条件，正在进行中，以解决这些问题。 这些模型的分析有几个目标：（1）确定哪些数值参数最好地再现了在砂土和粘土模型中观察到的断层模式;（2）检查砂土和粘土模型中变形随深度的传递;（3）数值模拟低粘度行为、各向异性行为和断层附近的孔隙压力变化，以更好地理解粘土模型的结果。 这种合作的数值/实验研究的最终目标是量化和理解的地质条件和材料的行为，可以产生的几何形状的断层观察到的自然区域的大陆延伸的范围。 该项目具有经济影响，因为伸展断层系统通常与产烃区有关。 此外，约束断层和岩石圈属性可能会提高对地震动力学的理解。

Two fundamental fault patterns accommodate extension in the brittle, upper crust: horst-and-graben geometry and book-shelf geometry. With a horst-and-graben geomety, neighboring normal faults are inclined in opposite directions; with a book-shelf geometry, neighboring faults are inclined in the same direction. Numerical models and scaled physical models with dry sand commonly produce a horst-and-graben geometry. The book-shelf geometry only develops under specific, asymmetric boundary conditions. Scaled physical models with wet clay, however, produce a book-shelf geometry with either symmetric or asymmetric boundary conditions. These observations raise the following questions. Is the book-shelf geometry in nature generally the result of fundamentally asymmetric stress patterns? What are the significant differences in the mechanical behavior of sand and clay? Can numerical models reproduce more clay-like behavior? Is the mechanical behavior of many rocks in nature more clay-like than sand-like?Numerical, sand, and clay models, with a range of boundary conditions, are underway to address these questions. The analyses of these models has several objectives: (1) to define which numerical parameters best reproduce the fault patterns observed in sand and clay models; (2) to examine the transfer of deformation with depth in the sand and clay models; and (3) to numerically simulate low-viscosity behavior, anisotropic behavior, and pore-pressure changes near faults to better understand the results of the clay models. The ultimate goal of this collaborative numerical/experimental research is to quantify and understand the ranges of geologic conditions and material behaviors that can produce the geometries of faults observed in natural zones of continental extension. The project has economic impact because extensional fault systems are commonly associated with hydrocarbon-producing regions. Also, constraining fault and lithospheric properties may improve the understanding of earthquake dynamics.