Decades of geophysical monitoring have revealed the importance of slow aseismic fault slip in the release of tectonic energy. Although significant progress have been made in imaging aseismic slip on natural faults, many questions remain concerning its physical control. Here we present an attempt to study the evolution of aseismic slip in the controlled environment of the laboratory. We develop a kinematic inversion method, to image slip during the nucleation phase of a dynamic rupture within a saw-cut sample loaded in a tri-axial cell. We use the measurements from a strain gauge array placed in the vicinity of the fault, and the observed shortening of the sample, to invert the fault slip distribution in space and time. The inversion approach relies both on a deterministic optimization step followed by a Bayesian analysis. The Bayesian inversion is initiated with the best model reached by the deterministic step, and allows to quantify the uncertainties on the inferred slip history. We show that the nucleation consists of quasi-static aseismic slip event expanding along the fault at a speed of the order of 200 m.${\mathrm{d}\mathrm{a}\mathrm{y}}^{-1}$, before degenerating into a dynamic rupture. The total amount of aseismic slip accumulated during this nucleation phase reaches $7\pm 2\mu$m locally, about 8%–15 % of the coseismic slip. The resolution of the method is evaluated, indicating that the main limitation is related to the impossibility of measuring strain inside the rock sample. The results obtained however show that the method could improve our understanding of earthquake nucleation.

中文翻译：

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实验室地震成核过程中地震断层滑移的运动学反演


数十年的地球物理监测揭示了缓慢地震断层滑移在构造能量释放中的重要性。尽管在自然断层的地震滑移成像方面取得了重大进展，但关于其物理控制仍然存在许多问题。在这里，我们尝试研究实验室受控环境中地震滑移的演变。我们开发了一种运动学反演方法，用于对加载在三轴单元中的锯切样品内动态破裂的成核阶段的滑移进行成像。我们使用放置在断层附近的应变片阵列的测量值，以及观察到的样品缩短，来反转断层滑移在空间和时间上的分布。反转方法依赖于确定性优化步骤，然后是贝叶斯分析。贝叶斯反转由确定性步骤达到的最佳模型启动，并允许量化推断滑移历史的不确定性。我们表明，成核作用由准静态地震滑移事件组成，以 200 ${\mathrm{m.d}\mathrm{}\mathrm{}ay-1}^{\mathrm{}}$ 的速度沿断层扩展，然后退化为动态破裂。在这个成核阶段积累的地震滑移总量达到 $7\pm 2\mu$m，约占同震滑移的 8%–15%。 评估了该方法的分辨率，表明主要限制与无法测量岩石样品内部的应变有关。然而，获得的结果表明，该方法可以提高我们对地震成核的理解。