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<p>Slow earthquakes exhibit systematic depth-dependence (i.e., reduced seismic moments and recurrence intervals at greater downdip depths, termed downdip weakening) and diverse moment-duration (<i>M</i>₀-<i>T</i> ) scaling laws. However, our friction experiments on olivine-antigorite gouges—serpentinized mantle wedge analogs—at fixed temperature and effective normal stress (σ<sub>eff</sub>) show that updip-increasing antigorite promotes viscous granular flow (and thus linear scaling, <i>M</i>₀ ∝ <i>T</i> ) but yields smaller, more frequent events, opposing the natural downdip trend. Synthesis with prior laboratory data therefore identifies the downdip reduction of σ<sub>eff</sub> as the first-order, unifying control on the depth-dependence, resolving laboratory contradictions. Within this low-σ<sub>eff</sub> environment, architectural maturity of the fault rock—quantified by the competent fragment-to-shear-zone-width ratio—acts as a second-order selector, determining whether deformation is fracture-dominated (e.g., cubic scaling, <i>M</i>₀ ∝ <i>T</i>³ ) or flow-dominated (linear scaling, <i>M</i>₀ ∝ <i>T</i> ). This hierarchical framework unifies observations across scales and predicts that the spatial distribution of scaling laws correlates with measurable geological structure, offering structurally based criteria for their interpretation.</p>

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A hierarchical framework governs depth-dependence and scaling laws for slow earthquakes

  • 期刊论文

  • 出版模式：

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  • 发表日期：

    2026年7月8日

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  • Tongbin Shao,
  • Lei Zhang,
  • Jie Wu,
  • Maoshuang Song

摘要

Slow earthquakes exhibit systematic depth-dependence (i.e., reduced seismic moments and recurrence intervals at greater downdip depths, termed downdip weakening) and diverse moment-duration (M₀-T ) scaling laws. However, our friction experiments on olivine-antigorite gouges—serpentinized mantle wedge analogs—at fixed temperature and effective normal stress (σeff) show that updip-increasing antigorite promotes viscous granular flow (and thus linear scaling, M₀ ∝ T ) but yields smaller, more frequent events, opposing the natural downdip trend. Synthesis with prior laboratory data therefore identifies the downdip reduction of σeff as the first-order, unifying control on the depth-dependence, resolving laboratory contradictions. Within this low-σeff environment, architectural maturity of the fault rock—quantified by the competent fragment-to-shear-zone-width ratio—acts as a second-order selector, determining whether deformation is fracture-dominated (e.g., cubic scaling, M₀ ∝ T³ ) or flow-dominated (linear scaling, M₀ ∝ T ). This hierarchical framework unifies observations across scales and predicts that the spatial distribution of scaling laws correlates with measurable geological structure, offering structurally based criteria for their interpretation.