In order to understand mechanisms of H
2 emanation increase in groundwater or soil gas near active faults before an earthquake, we investigated the variation of H
2 emanation from a Westerly granite specimen under uniaxial compression, using a ceramic sensor with high selectivity and sensitivity to H
2. Creep tests were carried out under 120, 140, 160, 180 and 193MPa stress levels, to clarify relations between H
2 emanation, Rn emanation, stress, acoustic emission and strain.
The experimental results are as follows: (1) H
2 and Rn emanation began to increase in company with generation of acoustic emission, that is, microfracturing; (2) when generation of microfracturing stopped, H
2 emanation stopped whereas Rn emanation was maintained at the same emanation level; (3) before ultimate fracture, H
2 and Rn emanation continuously increased together with increasing volumetric strain; (4) drastic increase of H
2 and Rn emanation appeared after the ultimate fracture, which was caused by the increase of fracture surface.
The results suggest that simultaneous increase of H
2 and Rn near active faults means continuous generation of microfracturing under the ground, and it may possibly act as a precursor of an earthquake.
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