Three-dimensional spontaneous dynamic rupture models on geometrically complex faults with state-of-the-art frictional parameterization

具有最先进摩擦参数化的几何复杂断层的三维自发动态破裂模型

• 批准号: 0838464
• 负责人: David Oglesby
• 金额: $ 17.19万
• 依托单位: University of California-Riverside
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2009
• 资助国家: 美国
• 起止时间: 2009-03-15 至 2012-02-29
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0838464&HistoricalAwards=false
• 关键词: Three; dimensional; spontaneous; dynamic; rupture

Dynamic spontaneous earthquake rupture models have proven themselves to be valuable tools to investigate the physics of earthquakes and to help predict ground motion. These numerical models start from basic assumptions about material structure, frictional behavior, and fault geometry, and calculate the spatiotemporal evolution of fault slip (and often the resultant near-source ground motion). Such dynamic models typically use either laboratory-derived friction laws or realistically complex fault geometry, but not both. The researchers propose to bring dynamic earthquake modeling an important step forward by combining these two separate tracks: they will use laboratory-derived friction laws to model spontaneous rupture propagation and slip on faults with realistically complex geometry. They expect to obtain first-order effects in rupture propagation, slip, and ground motion that will differ from previous modeling efforts, leading to both a better understanding of the earthquake process and better predictions of faulting behavior and ground motion. Dynamic earthquake models have historically followed two tracks: 1) investigations of the effect of frictional parameterization and stress pattern on simple planar faults, and 2) investigations of the effects of fault geometry on the earthquake process, using simple frictional parameterizations. the PIs will combine these two tracks to produce a new generation of dynamic earthquake models. Data from laboratory experiments at high slip rates and theoretical models imply that at the high slip rates observed during earthquakes, the typical rate-and-state frictional formulation must be modified to incorporate a greater degree of weakening over a larger length scale. Additionally, research on faults with complex, asymmetrical geometry shows that temporal variation of normal stress, which is inevitable on non-planar faults, can have a significant effect on rupture dynamics. To correctly model both these aspects of faulting behavior, they will develop a modern frictional parameterization and use it to model the behavior of geometrically complex faults, such as systems with stepovers and branches. The new 3D finite element method that will incorporate a new, realistic method for off-fault stress relaxation, which is necessary to avoid pathological stress buildup on such fault systems. These important ingredients of earthquake physics have never before been combined in a single modeling method, and the result of such a combination will be a state-of-the art tool to model the physics of earthquakes. The researchers will address important questions about the behavior of faults at stepovers and branches, including determining if there are general rules for how to predict rupture path at branches, and the ability of rupture to span stepovers.The proposed research will have important implications for both earthquake science and the broader scientific and educational community. A key use of the modeling method will be to gain insight into the potential size of earthquakes on geometrically complex fault systems, such as those in the Los Angeles region. Many fault systems are bounded by geometrical features such as fault gaps and changes in segment orientation; the proposed numerical models will help determine the circumstances under which earthquake rupture may propagate across these segment boundaries, and generate larger earthquakes with larger ground motion. In addition, the proposed research will lead to better estimates of the slip distribution and rupture front evolution, which also strongly affect ground motion. The resulting improved earthquake source models can help in the probabilistic assessment of earthquake size and ground motion pattern, with subsequent potential impacts on seismic hazard and building code and design.

动态自发地震破裂模型已被证明是研究地震物理和帮助预测地面运动的宝贵工具。 这些数值模型从有关材料结构、摩擦行为和断层几何形状的基本假设出发，计算断层滑动的时空演化（通常还计算由此产生的近源地震动）。 此类动态模型通常使用实验室推导的摩擦定律或实际复杂的断层几何形状，但不能同时使用两者。 研究人员建议通过结合这两个独立的轨道，使动态地震建模向前迈出重要一步：他们将使用实验室导出的摩擦定律来模拟具有实际复杂几何形状的断层上的自发破裂传播和滑动。 他们希望获得破裂传播、滑动和地面运动的一阶效应，这将不同于以前的建模工作，从而更好地了解地震过程并更好地预测断层行为和地面运动。动态地震模型历史上遵循两条轨道：1）研究摩擦参数化和应力模式对简单平面断层的影响，2）使用简单摩擦参数化研究断层几何形状对地震过程的影响。 PI 将结合这两个轨道来生成新一代动态地震模型。高滑移率实验室实验和理论模型的数据表明，在地震期间观察到的高滑移率下，必须修改典型的速率和状态摩擦公式，以在更大的长度范围内纳入更大程度的弱化。 此外，对具有复杂、不对称几何形状的断层的研究表明，在非平面断层上不可避免的正应力的时间变化会对破裂动力学产生重大影响。 为了正确模拟断层行为的这两个方面，他们将开发现代摩擦参数化，并用它来模拟几何复杂断层的行为，例如具有步距和分支的系统。 新的 3D 有限元方法将采用一种新的、现实的断层应力松弛方法，这对于避免此类断层系统上的病态应力积累是必要的。 地震物理学的这些重要组成部分以前从未被结合在单一的建模方法中，这种结合的结果将成为模拟地震物理学的最先进的工具。 研究人员将解决有关跨步和分支断层行为的重要问题，包括确定是否存在预测分支破裂路径的一般规则，以及破裂跨越跨步的能力。这项研究将对地震科学和更广泛的科学和教育界产生重要影响。 该建模方法的一个关键用途是深入了解几何复杂断层系统（例如洛杉矶地区的断层系统）发生地震的潜在规模。 许多断层系统受到断层间隙和断层方向变化等几何特征的限制；所提出的数值模型将有助于确定地震破裂可能跨越这些段边界传播的情况，并产生具有更大地面运动的更大地震。 此外，所提出的研究将有助于更好地估计滑移分布和破裂前沿演化，这也强烈影响地震动。 由此产生的改进的地震源模型可以帮助对地震规模和地面运动模式进行概率评估，从而对地震危害以及建筑规范和设计产生潜在影响。