Geological observations show that fault zone composition varies and often accommodates a mixture of brittle and ductile deformation. There is growing evidence that the nature of this mixture may play an important role in determining whether the fault creeps steadily or slides in slow slip events (SSEs) and/or fast earthquakes. Using numerical experiments of slip events in a fault zone of finite thickness, we explore how the ratio of brittle to ductile material and the absolute friction change resulting from a variation in slip velocity, affect energy partitioning and slip behavior in brittle‐ductile mixtures. We treat brittle material as Mohr‐Coulomb elastoplastic and ductile material as Maxwell viscoelastic. We simulate velocity‐weakening () behavior in the brittle part of the mixture and velocity‐strengthening () behavior in the ductile part using a rate‐and‐state formulation dependent on plastic strain accumulation. We show that: (1) mixtures can exhibit multiple slip behaviors including earthquakes and slow slip, (2) highly brittle mixtures do not tend to generate SSEs while weakly brittle mixtures can generate slow slip over a wider range of compositions, (3) structural features formed during simulated creep, SSEs, and earthquakes share notable similarities with structures observed in natural fault zones. We find that slip‐synchronous strengthening in the ductile portion of the mixture controls whether a rupture propagates as SSEs of yearlong durations. Shorter duration SSEs occur when the length of the plastic shear segments formed during slip is similar to the characteristic weakening distance for an earthquake.

中文翻译：

---

混合脆性-韧性断裂带的蠕变，滑移事件和地震的力学

地质观测表明，断层带的组成各不相同，并且经常兼有脆性和延性变形的混合作用。越来越多的证据表明，这种混合物的性质在确定断层是平稳地蠕动还是在缓慢滑动事件（SSE）和/或快速地震中滑动时起着重要作用。通过在有限厚度的断层带中进行滑动事件的数值实验，我们探索了脆性与延性材料的比率以及滑动速度变化导致的绝对摩擦力变化如何影响脆性-延性混合物中的能量分配和滑动行为。我们将脆性材料视为Mohr-Coulomb弹塑性，将易延性材料视为Maxwell粘弹性。我们模拟速度弱化（）混合物脆性部分的行为和速度强化（）使用取决于塑性应变累积的速率和状态公式在延性部分中的行为。我们表明：（1）混合物可能表现出多种滑动特性，包括地震和缓慢滑动；（2）高脆性混合物不会产生SSE，而弱脆性混合物则可以在更广泛的组成范围内产生缓慢滑动；（3）结构在模拟蠕变，SSE和地震过程中形成的特征与在天然断层带中观察到的结构有着显着的相似性。我们发现，混合物延性部分中的滑移同步加强控制破裂是否随着长达一年的SSE传播。当滑移过程中形成的塑性剪切段的长度与地震的特征减弱距离相似时，会发生持续时间较短的SSE。