Mechanoradical H2 generation during simulated faulting: Implications for an earthquake-driven subsurface biosphere

Molecular hydrogen, H-2, is the key component to link the inorganic lithosphere with the subsurface biosphere. Geochemical and microbiological characterizations of natural hydrothermal fields strongly suggested that H-2 is an important energy source in subsurface microbial ecosystems because of its metabolic versatility. One of the possible sources of H-2 has been considered as earthquakes: mechanoradical reactions on fault surfaces generate H-2 during earthquake faulting. However it is unclear whether faulting can generate abundant H-2 to sustain subsurface chemolithoautotrophic microorganisms, such as methanogens. Here we present the result of high velocity friction experiments aimed to estimate the amount of H-2 generated during earthquakes. Our results show that H-2 generation increases with frictional work (i.e., earthquake magnitude) and that a H-2 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 H-2 concentration is sufficiently high to sustain a H-2-based subsurface lithoautotrophic microbial ecosystem. Furthermore, earthquakes have initiated on the Earth at least since tectonic plate movement began similar to 3.8 Ga, implying the possible existence of ancient earthquake-driven ecosystems. Seismic H-2 based subsurface ecosystems might exist not only over the Earth but also other planets. Citation: Hirose, T., S. Kawagucci, and K. Suzuki (2011), Mechanoradical H-2 generation during simulated faulting: Implications for an earthquake-driven subsurface biosphere, Geophys. Res. Lett., 38, L17303, doi:10.1029/2011GL048850.