Laboratory of Experimental Rock Mechanics (LEMR), École Polytechnique Fédérale de Lausanne (EPFL), Station 18, Lausanne, CH-1015, Switzerland.
Istituto Nazionale di Geofisica e Vuolcanologia (INGV), Via di Vigna Murata, 605, Rome, 00143, Italy.
Nat Commun. 2019 Mar 20;10(1):1274. doi: 10.1038/s41467-019-09293-9.
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/H) and earthquake nucleation depth (∝σ)), EHD might be an effective weakening mechanism during natural and induced earthquakes. However, at seismic slip-rate, the slip weakening distance (D) 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.
流体普遍存在于切割地球地壳的断层带中；然而，流体粘度对断层力学的影响主要是通过理论模型推测的。我们在正常有效应力高达 20 MPa 的条件下，对干燥和渗透有流体的硅酸盐和碳酸盐岩进行了摩擦实验，滑动速率在 10 μm/s 到 1 m/s 之间。我们测试了四种不同的流体粘度。结果表明，静态和动态摩擦系数都随粘度的降低而降低，而动态摩擦系数取决于弹性流体动力润滑理论（EHD）预测的无量纲 Sommerfeld 数（S）。在有利条件下（取决于流体粘度（η）、同震滑移率（V）、断层几何形状（L/H）和地震核形成深度（∝σ）），EHD 可能是自然和诱发地震期间的有效弱化机制。然而，在地震滑移率下，对于地球中预期存在的一系列流体粘度，滑动弱化距离（D）显著增加，这可能有利于小到中等地震的慢滑而不是破裂传播。
