In the paper “Mechanoradical H2generation during simulated faulting: Implications for an earthquake-driven subsurface biosphere” by Takehiro Hirose et al. (Geophysical Research Letters, 38, L17303, doi:10.1029/2011GL048850, 2011), we found an error in unit conversion of an amount of H2 gas generation from H2 mixing ratio in the sample chamber measured by a gas chromatograph in the friction experiments. As a result, we incorrectly indicated a unit of H2 generation in the original publication. The correct unit of H2 generation in Figures 1 and 2 and Table A2 is μmol, not mmol. The correct units of calculated H2 generation, cumulative H2 flux and H2 concentration as a function of earthquake magnitude in Figure 4 are mmol, mmol/m2yr and mmol/kg, respectively. The original data for H2 mixing ratio in the chamber (in ppmv) indicated in Table A2 are correct.
 We stated in the original paper that (1) the calculated earthquake-derived H2 flux of 2.3 × 105 mol/m2yr is much higher than H2 flux due to other H2 generation processes on the earth (i.e., 3 × 10−4 mol/m2yr in water—rock redox reaction [Sleep and Zoback, 2007] and 8 × 10−6 mol/m2yr in water radiolysis [Lin et al., 2005]) and (2) the estimated earthquake-derived H2 concentration in a fault zone just after an earthquake is sufficient to sustain a H2-based subsurface lithoautotrophic microbial ecosystem. After correction of the error in unit conversion, the estimated earthquake-derived H2 flux changed from 2.3 × 105 to 2.3 × 102 mol/m2yr, that is seven orders of magnitude higher than the other two sources of H2 flux. In addition, the estimated H2 concentration in a fault zone is still the order of mmol/kg of fluid, in the case that porosity of the fault zone is less than 0.1. The estimated value is enough for sustaining the H2-based microbial ecosystem, as geochemical and microbiological observations of hydrothermal fields suggest that the concentration of the order of mmol/kg is required [Takai et al., 2006]. Therefore, the conclusions of our study are not altered by the errors found this time.