Radon concentration in ground water increased for several months before the 1995 southern Hyogo Prefecture (Kobe) earthquake on 17 January 1995. From late October 1994, the beginning of the observation, to the end of December 1994, radon concentration increased about fourfold. On 8 January, 9 days before the earthquake, the radon concentration reached a peak of more than 10 times that at the beginning of the observation, before starting to decrease. These radon changes are likely to be precursory phenomena of the disastrous earthquake.
The third Kurayosi explosion was fired by the Research Group for Explosion Seismology on November 21, 1970 in order to detect the seismic waves reflected from deep crustal boundaries. Very clear reflected waves from the Conrad discontinuity were recorded by the instrument for seismic prospecting (E.T.L. recorder). There was also weak indication of the reflection from the Mohorovicic discontinuity in the records obtained at closely spaced temporary observation points equipped with FM data recorders at the shot distance of about 100km. On the basis of these results, a revision was made for the previous model. The crustal thickness obtained is about 35km and the Pn velocity, about 7.8km/sec.
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