地震活動と地下からの水素の放出との関係
地震発生機構における意義
1985 年 38 巻 2 号 p. 183-191
詳細
1985 年 38 巻 2 号 p. 183-191
For the purpose of earthquake prediction, chemical compositions of bubble gases from a mineral spring have been successively measured since 1978. The spring is located close to Median Tectonic Line, the longest active fault in Japan. The gas contains helium as much as 300ppm. This suggests that the gas and the mineral water issuing from a fissure of Tertiary volcanics are derived from depths. Sometimes, hydrogen appears in the bubbles, while earthquake swarm occurs along an active fault which runs from WNW to ESE about 3km to the spring. Successive measurements showed that the period of H2 emission from the mineral spring coincided with that in which the earthquake swarm had been active. Four cases of the coincidence without exception were observed in the last three years. The range of the fluctuation of H2 concentration amounts to almost two orders of magnitude up to 200ppm, while other gases such as He, Ar, N2 and CH4 do not much fluctuate. The concentration of H2 correlates with the energy released by the seismic activity. This field evidence and laboratory experiments infer that H2 observed at the mineral spring is produced by a reaction between groundwater and rock fractured by seismic activities. Temporally, the H2 emission preceds the occurrence of the earthquake swarm. This suggests that microcracks in rocks occur prior to earthquakes and H2 is produced by the chemical reaction in the microcracks. This precursory emission of H2 may be useful for the prediction of earthquakes.
