SUMMARY Two key parameters control the localization of deformation and seismicity along and surrounding crustal faults: the strength and roughness of the pre-existing fault surface. Using 3-D discrete element method simulations, we investigate how the anisotropy and amplitude of roughness control the mechanical behaviour of healed faults within granite blocks during quasi-static triaxial compression. We focus on models in which the uniaxial compressive strength of the healed faults is about 25 per cent of that strength of the surrounding host rock. These models provide insights into the evolution of fracture network localization, fault roughness, gouge production, fault slip and stress concentrations along initially healed faults of varying roughness. In contrast to expectations, the uniaxial compressive strengths of models that host faults with root-mean-squared roughness amplitudes of 0.2–1.4 mm do not vary more than the change produced by variations in particle packing. To assess if this lack of influence arises from the evolving roughness of the faults, we track the roughness amplitudes parallel and perpendicular to the downdip direction throughout fault failure and slip. The de facto roughness does not provide an explanation for the lack of influence of roughness on compressive strength because the roughness of the faults does not evolve to similar values with slip. Rather, smoother faults remain smoother than rougher faults throughout the simulation. However, the rougher faults produce larger volumes of gouge than the smoother faults. The gouge lubricates the fault and thereby reduces the influence of roughness on compressive strength. These observations suggest that fault topography and the asperities that build this topography do not exert a significant impact on deformation. To quantify the influence of asperities on slip, we calculate correlation coefficients between the fault surface topography and components of the slip vectors. The observed negative correlation coefficients between the fault topography and fault-plane parallel slip quantify the degree to which asperities slow slip in the downdip direction. The observed positive correlation coefficients between the topography and fault-plane perpendicular movement quantify the degree to which asperities promote opening. Thus, this analysis shows how asperities control slip by acting as speed bumps that hinder fault-plane parallel slip and promote fault-plane normal opening as the healed faults slide. The asperities do not significantly control fault movement during the unlocking and failure of the healed faults, but only following the peak axial stress as the faults slide and damage zones develop. These models thus provide unparalleled access to the dynamics of reactivated healed faults.

中文翻译：

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解密愈合断层带：过凿生产如何降低断层粗糙度的影响

总结 控制变形和地震活动沿和周围地壳断层的局部化的两个关键参数：预先存在的断层表面的强度和粗糙度。使用 3-D 离散元方法模拟，我们研究了在准静态三轴压缩过程中，粗糙度的各向异性和幅度如何控制花岗岩块内愈合断层的力学行为。我们专注于修复断层的单轴抗压强度约为周围主岩强度的 25% 的模型。这些模型提供了对裂缝网络定位、断层粗糙度、过凿产生、断层滑动和沿不同粗糙度的初始愈合断层的应力集中的演变的见解。与预期相反，包含均方根粗糙度幅度为 0.2-1.4 mm 的断层模型的单轴抗压强度变化不大于颗粒堆积变化所产生的变化。为了评估这种影响的缺乏是否源于断层的粗糙度，我们在整个断层失效和滑动过程中跟踪平行和垂直于下倾方向的粗糙度幅度。事实上的粗糙度并不能解释粗糙度对抗压强度没有影响，因为断层的粗糙度不会随着滑移而演变为相似的值。相反，在整个模拟过程中，更平滑的断层仍然比粗糙的断层更平滑。然而，较粗糙的断层比较平滑的断层产生更大的过切量。凿子润滑断层，从而减少粗糙度对抗压强度的影响。这些观察表明，断层地形和构成该地形的凹凸不平对变形没有显着影响。为了量化凹凸不平对滑动的影响，我们计算了断层表面地形与滑动矢量分量之间的相关系数。观察到的断层地形和断层平面平行滑动之间的负相关系数量化了凹凸体在下倾方向上减缓滑动的程度。观察到的地形和断层面垂直运动之间的正相关系数量化了凹凸不平促进开放的程度。因此，该分析表明，粗糙体如何通过充当减速带来控制滑动，这些减速带阻碍断层面平行滑动，并在愈合断层滑动时促进断层面正常张开。在愈合断层的解锁和破坏过程中，凹凸不明显地控制断层运动，而只是随着断层滑动和损伤区的发展而跟随峰值轴向应力。因此，这些模型提供了对重新激活的修复断层动态的无与伦比的访问。