Ultra-low friction graphene oxide in the Atotsugawa Fault System

The active Atotsugawa Fault System in central Japan exhibits low levels of seismicity and creep to depths of 7-8 km. Low-friction graphite (friction coefficient, μ ~ 0.1) in fault rocks has previously been proposed as a mechanism for reducing fault strength and contributing to aseismic creep. Here, we use state-of-the-art Raman spectroscopy, X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM) to document for the first time the discovery of graphene oxide in natural fault gouge, a material characterized by an ultra-low coefficient of friction (μ ~ 0.01) and possible superlubricity. Graphene oxide is concentrated within microcracks in fault gouge and occurs as single-layer sheets with particle sizes of 3-10 nm. Analysis of hydroxyl groups and the degree of oxidation indicate that the graphene oxide has the most effective chemical composition for fault weakening. We suggest that graphene oxide in fault rocks could dramatically reduce fault frictional strength and promote fault creep.