Abstract
Detection of precursory phenomena in observation data is essential to earthquake prediction studies. Continuous monitoring of radon concentration in groundwater in Japan in one case showed a short-term anomaly related to a nearby earthquake. With the exception of the 1978 Izu-Oshimakinkai earthquake (M7.0), however, no abnormal change has been noted. This may be due partially to difficulty in detecting insignificant precursory signals from observation data, which ordinarily contains a noise-induced fluctuations, and partially to lack of understanding of the mechanism controlling the appearance of precursory phenomena. In order to increase our knowledge of the variation pattern of precursory changes in radon concentration of groundwater, hydrologic precursors with significant features are examined in this paper. Complexity of appearance of precursory phenomena and problems in assignment of the specific earthquake are discussed.
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