The recognition of slow earthquakes in geodetic and seismological data has transformed the understanding of how plate motions are accommodated at major plate boundaries. Slow earthquakes, which slip more slowly than regular earthquakes but faster than plate motion velocities, occur in a range of tectonic and metamorphic settings. They exhibit spatiotemporal associations with large seismic events that indicate a causal relation between modes of slip at different slip rates. Defining the physical controls on slow earthquakes is, therefore, critical for understanding fault and shear zone mechanics. In this Review, we synthesize geological observations of a suite of ancient structures that were active in tectonic settings comparable to where slow earthquakes are observed today. At inferred slow earthquake regions, a range of grain-scale deformation mechanisms accommodated slip at low effective stresses. Material heterogeneity and the geometric complexity of structures that formed at different inferred strain rates are common to faults and shear zones in multiple tectonic environments, and might represent key limiting factors of slow earthquake slip rates. Further geological work is needed to resolve how the spectrum of slow earthquake slip rates can arise from different grain-scale deformation mechanisms and whether there is one universal rate-limiting mechanism that defines slow earthquake slip.

大地测量和地震数据中对慢地震的认识改变了人们对如何在主要板块边界处适应板块运动的认识。慢地震发生在一定的构造和变质环境中，其滑动速度比常规地震慢，但比板块运动速度快。它们表现出与大地震事件的时空关联，表明在不同滑移率下滑移模式之间存在因果关系。因此，定义慢地震的物理控制对于理解断层和剪切带力学至关重要。在这篇评论中，我们综合了一套在构造环境中活跃的古代结构的地质观测结果，这些构造与今天观察到的慢地震相当。在推断的慢地震地区，一系列的晶粒尺寸变形机制在低有效应力下适应了滑移。在多个构造环境中，断层和剪切带的材料异质性和以不同推断应变率形成的结构的几何复杂性是常见的，并且可能代表了缓慢的地震滑移率的关键限制因素。需要进一步的地质工作来解决慢地震滑移率的频谱是如何由不同的晶粒尺度变形机制产生的，以及是否存在一种定义慢地震滑移的通用限速机制。并可能代表了缓慢的地震滑移率的关键限制因素。需要进一步的地质工作来解决慢地震滑移率的频谱是如何由不同的晶粒尺度变形机制产生的，以及是否存在一种定义慢地震滑移的通用限速机制。并可能代表了缓慢的地震滑移率的关键限制因素。需要进一步的地质工作来解决慢地震滑移率的频谱是如何由不同的晶粒尺度变形机制产生的，以及是否存在一种定义慢地震滑移的通用限速机制。