Iron redox change in simulated olivine fault zones by earthquake faulting: its implication for an earthquake-driven subsurface biosphere

Abstract

Frictional heat during a coseismic faulting facilitates physico-chemical reactions along the fault and eventually changes in redox conditions in the earth. In order to explore a hypothesis that the redox reactions associated with an earthquake could provide a potential metabolic energy source for subsurface life, we have conducted high-velocity friction experiments on olivine and determined redox change within olivine fault zones by X-ray absorption near edge structure (XANES) analysis. We confirm that (1) the rapid Fe oxidation reaction takes place due to the combination of the formation of nano-scale olivine grains with fresh reactive surfaces and the transformation of liquid water into supercritical state by frictional heat, and (2) the Fe oxidation reaction progresses with increasing input shear energy. If seismic observation data could be available, the proposed correlation between the shear energy (equivalent to quake magnitude) and the oxidation progress enables us to estimate the earthquake-driven redox change that could be utilized as energy for subsurface biosphere.