Fluids are pervasive in fault zones cutting the Earth's crust; however, the effect of fluid viscosity on fault mechanics is mainly conjectured by theoretical models. We present friction experiments performed on both dry and fluid-permeated silicate and carbonate bearing-rocks, at normal effective stresses up to 20 MPa, with a slip-rate ranging between 10 μm/s and 1 m/s. Four different fluid viscosities were tested. We show that both static and dynamic friction coefficients decrease with viscosity and that dynamic friction depends on the dimensionless Sommerfeld number (S) as predicted by the elastohydrodynamic-lubrication theory (EHD).Under favourable conditions (depending on the fluid viscosity (η), co-seismic slip-rate (V), fault geometry (L/H₀²) and earthquake nucleation depth (∝σ_eff)), EHD might be an effective weakening mechanism during natural and induced earthquakes. However, at seismic slip-rate, the slip weakening distance (D_c) increases markedly for a range of fluid viscosities expected in the Earth, potentially favouring slow-slip rather than rupture propagation for small to moderate earthquakes.

流体渗透到切割地壳的断层带。然而，流体粘度对断层力学的影响主要是通过理论模型来推测的。我们介绍了在干态和流体渗透的硅酸盐和碳酸盐轴承岩上进行的摩擦实验，其正常有效应力高达20 MPa，滑移率介于10μm/ s和1 m / s之间。测试了四种不同的流体粘度。我们发现静摩擦系数和动摩擦系数都随粘度而降低，并且动摩擦取决于弹性流体动力润滑理论（EHD）预测的无量纲索默菲尔德数（S）。在有利条件下（取决于流体粘度（η），同震滑移率（V），断层几何特征（L/ ħ ₀ ²）和地震成核深度（α σ _EFF）），EHD可能是在自然和诱发地震的有效减弱机构。但是，在地震滑移率下，对于地球上预期的一定范围的流体粘度，滑移弱化距离（D _c）会显着增加，对于中小地震，可能更倾向于缓慢滑动而不是破裂传播。