A study of fault gouge from Japan’s Atotsugawa Fault System has identified naturally occurring graphene oxide as a potential ultra-low-friction phase, offering a new explanation for why part of the fault appears to slip aseismically despite lying in an active tectonic setting.
The study builds on earlier suggestions that graphite may help reduce friction along the Atotsugawa Fault System, but points to an even lower-friction carbon phase in the fault gouge. To investigate that possibility, the Tohoku University team analyzed fault gouge and surrounding rocks collected from multiple sites along the Atotsugawa and Mozumi–Sukenobe faults. Their workflow combined Raman spectroscopy, X-ray photoelectron spectroscopy, and transmission electron microscopy to identify carbonaceous material, determine its bonding state and oxidation chemistry, and resolve its nanoscale structure within the gouge.
“We believe that when faults move, they trigger chemical reactions that create graphene oxide,” said co-author Hiroyuki Nagahama in a recent press release. “In other words, the more a fault slips, the more it generates its own ‘nano-lubricant,’ which helps the fault move even more easily.”
Across several gouge samples, Raman spectroscopy suggested that the fault gouge contained graphene oxide-like carbonaceous material rather than graphite alone. XPS analysis showed that the material was rich in oxygen-bearing functional groups – especially hydroxyl groups – and that oxygen-functionalized sp2 carbon was concentrated within microcracks in the Active Fault Survey Tunnel gouge. TEM observations then confirmed the presence of single-layer graphene oxide in those same microcracks.
Graphene oxide has a far lower friction coefficient than either graphite or most rock-forming minerals. In the fault gouge, the authors argue, nanosheets concentrated along microcracks and cleavage surfaces could reduce grain-to-grain contact and promote ultra-low-friction slip. In that interpretation, the material may help account for the fault system’s combination of low seismicity and aseismic creep.
“If graphene oxide can form naturally in faults, it opens up entirely new possibilities not only for understanding earthquake behavior, but also for exploring how faults evolve over time,” said corresponding author Tomoya Shimada.
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