Several regularly recurring moderate-size earthquakes motivated dense instrumentation of the Parkfield section of the San Andreas fault (SAF), providing an invaluable near-fault observatory. We present a seismo-geodetic dynamic inversion of the 2004 Parkfield earthquake, which illuminates the interlinked complexity of faulting across time scales. Using fast-velocity-weakening rate-and-state friction, we jointly model coseismic dynamic rupture and the 90-day evolution of postseismic slip in a 3D domain. We utilize a parallel tempering Markov chain Monte Carlo approach to solve this non-linear high-dimensional inverse problem, constraining spatially varying prestress and fault friction parameters by 30 strong motion and 12 GPS stations. From visiting $>$2 million models, we discern complex coseismic rupture dynamics that transition from a strongly radiating pulse-like phase to a mildly radiating crack-like phase. Both coseismic phases are separated by a shallow strength barrier that nearly arrests rupture and leads to a gap in the afterslip, reflecting the geologic heterogeneity along this segment of the SAF. Coseismic rupture termination involves distinct arrest mechanisms that imprint on afterslip kinematics. A backward propagating afterslip front may drive delayed aftershock activity above the hypocenter. Trade-off analysis of the 10,500 best-fitting models uncovers local correlations between prestress levels and the reference friction coefficient, alongside an anticorrelation between prestress and rate-state parameters $b-a$. We find that a complex, fault-local interplay of dynamic parameters determines the nucleation, propagation, and arrest of both, co- and postseismic faulting. This study demonstrates the potential of inverse physics-based modeling to reveal novel insights and detailed characterizations of well-recorded earthquakes.

中文翻译：

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2004 年帕克菲尔德地震地震大地动力学反演揭示的同震和震后断层的关联复杂性


几次定期重复的中等规模地震促使对圣安德烈亚斯断层 （SAF） 的帕克菲尔德部分进行了密集的仪器测量，提供了一个宝贵的近断层观测站。我们提出了 2004 年帕克菲尔德地震的地震-大地动力学反演，它阐明了跨时间尺度断层的相互关联复杂性。使用快速减弱速率和状态摩擦，我们共同模拟了 3D 域中同震动力破裂和震后滑移的 90 天演变。我们利用平行回火马尔可夫链蒙特卡洛方法来解决这个非线性高维逆问题，通过 30 个强运动和 12 个 GPS 站来约束空间变化的预应力和断层摩擦参数。通过访问价值 $200$ 万美元的模型，我们辨别出复杂的同震破裂动力学，这些动力学从强烈辐射的脉冲状相位转变为轻度辐射的裂纹状相位。两个同震相都由一个较浅的强度屏障隔开，该屏障几乎阻止了破裂并导致后滑中的间隙，反映了沿 SAF 这一部分的地质非均质性。共震破裂终止涉及不同的止动机制，这些机制印在有后滑运动学上。向后传播的余滑锋可能会驱动震源上方的延迟余震活动。对 10,500 个最佳拟合模型的权衡分析揭示了预应力水平和参考摩擦系数之间的局部相关性，以及预应力和速率状态参数 $b-a$ 之间的反相关。 我们发现，动态参数的复杂、断层-局部相互作用决定了同震断层和震后断层的成核、传播和停滞。这项研究展示了基于逆向物理的建模的潜力，可以揭示记录良好的地震的新见解和详细特征。