Mechanoradical H2generation during simulated faulting: Implications for an earthquake-driven subsurface biosphere

Abstract

[1] Molecular hydrogen, H2, is the key component to link the inorganic lithosphere with the subsurface biosphere. Geochemical and microbiological characterizations of natural hydrothermal fields strongly suggested that H2 is an important energy source in subsurface microbial ecosystems because of its metabolic versatility. One of the possible sources of H2 has been considered as earthquakes: mechanoradical reactions on fault surfaces generate H2 during earthquake faulting. However it is unclear whether faulting can generate abundant H2 to sustain subsurface chemolithoautotrophic microorganisms, such as methanogens. Here we present the result of high velocity friction experiments aimed to estimate the amount of H2 generated during earthquakes. Our results show that H2 generation increases with frictional work (i.e., earthquake magnitude) and that a H2 concentration of more than 1.1 mol/kg of fluid can be achieved in a fault zone after earthquakes of even small magnitudes. The estimated earthquake-derived H2 concentration is sufficiently high to sustain a H2-based subsurface lithoautotrophic microbial ecosystem. Furthermore, earthquakes have initiated on the Earth at least since tectonic plate movement began ∼3.8 Ga, implying the possible existence of ancient earthquake-driven ecosystems. Seismic H2 based subsurface ecosystems might exist not only over the Earth but also other planets.