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Hydrothermal friction experiments on simulated basaltic fault gouge and implications for megathrust earthquakes
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  • Hanaya Okuda,
  • André R. Niemeijer,
  • Miki Takahashi,
  • Asuka Yamaguchi,
  • Christopher J. Spiers
Hanaya Okuda
Atmosphere and Ocean Research Institute, University of Tokyo

Corresponding Author:[email protected]

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André R. Niemeijer
Utrecht University
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Miki Takahashi
Geological Survey of Japan
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Asuka Yamaguchi
Atmosphere and Ocean Research Institute, University of Tokyo
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Christopher J. Spiers
Utrecht University
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Abstract

Nucleation of earthquake slip at the plate boundary fault (décollement) in subduction zones has been widely linked to the frictional properties of subducting sedimentary facies. However, recent seismological and geological observations suggest that the décollement develops in the subducting oceanic crust in the depth range of the seismogenic zone, at least in some cases. To understand the frictional properties of oceanic crustal material and their influence on seismogenesis, we performed hydrothermal friction experiments on simulated fault gouges of altered basalt, at temperatures of 100-550 ℃. The friction coefficient (μ) lies around 0.6 at most temperature conditions but a low μ down to 0.3 was observed at the highest temperature and lowest velocity condition. The velocity dependence of μ, a−b, changes with increasing temperature from positive to negative at 100-200 ºC and from negative to positive at 450-500 ºC. Compared to gouges derived from sedimentary facies, the altered basalt gouge showed potentially unstable velocity weakening over a wider temperature range. Microstructural observations and microphysical interpretation infer that competition between dilatant granular flow and viscous compaction through pressure-solution creep of albite contributed to the observed transition in a−b. Alteration of oceanic crust during subduction produces fine grains of albite and chlorite through interactions with interstitial water, leading to reduction in its frictional strength and an increase in its seismogenic potential. Therefore, shear deformation possibly localizes within the altered oceanic crust leading to a larger potential for the nucleation of a megathrust earthquake in the depth range of the seismogenic zone.
21 Dec 2022Published in Journal of Geophysical Research: Solid Earth. 10.1029/2022JB025072