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

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。这些数值模型从关于物质结构、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(以及由此产生的近源地面运动)。这样的动态模型通常要么使用实验室得出的摩擦定律，要么使用现实中复杂的断层几何，但不能两者兼而有之。研究人员建议，通过将这两个独立的轨道结合起来，使动态地震模拟向前迈出重要的一步：他们将使用实验室得出的摩擦定律来模拟具有真实复杂几何形状的断层上的自发破裂传播和滑动。他们希望在破裂传播、滑动和地面运动方面获得与以前的建模工作不同的一阶效应，从而更好地理解地震过程，并更好地预测断层行为和地面运动。动力地震模型历来遵循两条轨迹：1)研究摩擦参数和应力模式对简单平面断层的影响，2)使用简单的摩擦参数研究断层几何形状对地震过程的影响。PI将把这两条轨道结合起来，产生新一代动态地震模型。高滑动速率下的实验室实验数据和理论模型表明，在地震期间观察到的高滑动速率下，典型的速率和状态摩擦公式必须进行修改，以便在更大的长度尺度上包含更大程度的减弱。此外，对具有复杂、不对称几何结构的断层的研究表明，非平面断层上不可避免的正应力的时间变化可以对破裂动力学产生重大影响。为了正确地模拟这两个方面的断层行为，他们将开发一种现代的摩擦参数化，并使用它来模拟几何上复杂的断层的行为，例如具有断层和分支的系统。新的三维有限元方法将结合一种新的、现实的断层外应力松弛方法，这是避免此类断层系统上病理性应力积累所必需的。地震物理学的这些重要组成部分以前从未被组合在一个单一的建模方法中，这种组合的结果将是对地震物理学建模的最先进工具。研究人员将解决有关断层在荒漠和分支上的行为的重要问题，包括确定是否有关于如何预测分支破裂路径的一般规则，以及破裂跨越荒漠的能力。拟议的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。建模方法的一个关键用途将是深入了解几何复杂断层系统上地震的潜在规模，例如洛杉矶地区的断层系统。许多断层系统受到断层空隙和节段方向变化等几何特征的约束；所提出的数值模型将有助于确定地震破裂可能在什么情况下穿过这些节段边界传播，并产生更大的地震和更大的地面运动。此外，拟议的研究将导致对滑动分布和破裂前沿演化的更好估计，这也对地面运动有很大影响。由此得到的改进的震源模型可以帮助对地震规模和地面运动模式的概率评估，以及随后对地震危险性和建筑规范和设计的潜在影响。

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.