In recent laboratory experiments, varying nucleation locations of accelerating slip with changing nucleation lengths were observed. Spatial variations in effective normal stress, due to the controlling influence on fault strength and fracture energy, play an important role. We quantitatively explain how spatially heterogeneous effective normal stresses affect earthquake nucleation and slip behavior. We simulate a meter-scale laboratory experiment in a numerical earthquake sequence model with stochastically variable normal stresses. We identify five regimes of earthquake nucleation and slip behaviors, controlled by the ratio of the heterogeneity wavelength $(\lambda )$ to the nucleation length $\left(L_c\right)$. When $\lambda /L_c\ll 1$, full ruptures are observed. Slip rates and recurrence intervals are similar to those on homogeneous faults with comparable averaged normal stress. When $\lambda /L_c\gg 1$, slow slip events and partial ruptures occur frequently and the nucleation length of each earthquake depends on the local stress level. We find locations of nucleation and arrest in both low and high normal stress regions (LSR and HSR, respectively) when $\lambda$ and $L_c$ are of the same magnitude. When $\lambda /L_c\gtrsim 1$, earthquakes nucleate in LSRs, and arrest in HSRs. However, HSRs and LSRs switch these roles when $\lambda /L_c\lesssim 1$. Interestingly, we observe that nucleation migrates from an LSR to its neighboring HSR in one earthquake, when $\lambda$ is between the minimum and maximum local nucleation lengths. We observe a large amount of aseismic slip and associated stress drop in the initial LSR, which might be linked to the migration of foreshocks as documented in natural and laboratory observations. This improved understanding of earthquake nucleation is important in estimating the seismic potential of different fault patches for natural and induced seismicity.

中文翻译：

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随机法向应力异质性改变的地震成核和滑移行为


在最近的实验室实验中，观察到随着成核长度的变化，加速滑移的成核位置发生了变化。由于对断层强度和断裂能量的控制影响，有效法向应力的空间变化起着重要作用。我们定量解释了空间异质有效法向应力如何影响地震成核和滑移行为。我们在具有随机可变法向应力的数值地震序列模型中模拟了米级实验室实验。我们确定了地震成核和滑移行为的五种状态，由异质性波长 $(\lambda )$ 与成核长度 $\left(L_c\right)$ 的比率控制。当 观察到完全破裂时 $\lambda /L_c\ll 1$ 。滑移率和重现间隔与具有可比平均法向应力的均质断层上的滑移率和重现间隔相似。当 $\lambda /L_c\gg 1$ 时，慢滑事件和部分破裂频繁发生，每次地震的成核长度取决于当地的应力水平。当 和 $L_c$ 具有相同的量级时 $\lambda$ ，我们在低和高正常应力区域 （分别为 LSR 和 HSR） 中发现了成核和停滞的位置。当 $\lambda /L_c\gtrsim 1$ 时，地震在 LSR 中成核，在 HSR 中停止。但是，HSR 和 LSR 会在 . $\lambda /L_c\lesssim 1$ 有趣的是，我们观察到，当 介于最小和最大局部成核长度之间时 $\lambda$ ，成核在一次地震中从 LSR 迁移到其相邻的 HSR。我们在初始 LSR 中观察到大量的地震滑移和相关的应力下降，这可能与自然和实验室观测中记录的前震迁移有关。 这种对地震成核的更好理解对于估计不同断层带对自然地震和诱发地震的地震潜力非常重要。