Abstract
Seismicity is active around the Izu Peninsula. For the purpose of earthquake prediction, chemical compositions of bubble gas from a hot spring have been continually observed since April 1983 at Atagawa on the east shore of the Izu Peninsula. Variations of gas compositions at the spring were observed before the earthquake swarms which occurred off the east coast of the Izu Peninsula. He/Ar ratios of the spring gas remarkably decreased six months before the occurrence of earthquake swarms and H2/Ar ratio increased along with He/Ar variations. The variations of these ratios range in two orders of magnitude. Since deep seated gases with high ratio of He/Ar may be driven out of depth under a high pore pressure, the decrease of He/Ar ratio may be caused by the decrease of the pore pressure which is due to the microcrack opening by tectonic activities eventually resulted in earthquakes. Whereas the increase of H2/Ar ratio may be due to the production of H2 by the chemical reaction between groundwater and fractured rock in microcracks. The relationship between N2/Ar ratio and He/Ar ratio supports this interpretation. The continual observation of chemical compositions of spring gas which are subjected to tectonic activities can thus be regarded as a useful tool for earthquake prediction.
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Schedule a callMore From: Zisin (Journal of the Seismological Society of Japan. 2nd ser.)
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