Abstract. We report the results of friction experiments on brucite under both dry and water-saturated (wet) conditions under various normal stresses (10–60 MPa). The steady-state friction coefficients of brucite were determined to be 0.40 and 0.26 for the dry and wet cases, respectively, independent of the normal stress. Under dry conditions, velocity-weakening behavior was observed in all experiments at various normal stresses. Under wet conditions, velocity weakening was observed at low normal stress (10 and 20 MPa), whereas velocity strengthening was determined at a higher applied normal stress. The microstructural observations on recovered experimental samples indicate localized deformation within the narrow shear band, implying that a small volume of brucite can control the bulk strength in an ultramafic setting and significantly change the frictional properties. Brucite is found to be the only mineral that has a low friction coefficient and exhibits unstable frictional behavior under hydrated mantle wedge conditions, explaining the occurrence of slow earthquakes in the mantle wedge.

中文翻译：

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正应力对水镁石摩擦的影响：在地幔楔缓震中的应用

摘要。我们报告了在各种法向应力（10-60 MPa）下在干和水饱和（湿）条件下水镁石的摩擦实验结果。独立于法向应力，干和湿情况下水镁石的稳态摩擦系数分别确定为0.40和0.26。在干燥条件下，所有实验在不同的正应力下均观察到速度减弱行为。在潮湿条件下，在低法向应力（10和20 MPa）下观察到速度减弱，而在较高的法向应力下确定速度增强。对回收的实验样品的微观结构观察表明，在窄剪切带内局部变形，这意味着少量的水镁石可以控制超镁铁矿环境下的堆积强度，并显着改变摩擦性能。发现水镁石是唯一具有低摩擦系数并且在水合地幔楔条件下表现出不稳定摩擦行为的矿物，这解释了在地幔楔中发生缓慢地震的原因。