地中ガスの挙動から見た日本の地体構造

―γ線リモートセンシング―

抄録

Bed gases (radon and thoron) behaviors of the following geotectonic lines were clarified by the airborne gamma ray remote sensing with a helicopter; Tanakura line dividing the Japanese Islands into southwest and northeast, Itoigawa-Shizuoka line traversing the Islands from north to south, and Median Tectonic line dividing Southwest Japan into inner zone and outer zone. As the results of closer investigations, some excellent relations were recognized, as followings;
(1) For non seismic zone: Thoron, thoron/potassium and thoron/radon in Abukuma mountainland (mainly andesite and metamorphic rock) are rare.
(2) For collapsed zone: Radon and thoron in great land failure zone (Shimanto group) on Mt. Shichimenzan are plenty.
(3) For bed water (in Shimanto group) : In case of lower pressure of pore water in the bed, radon increases but thoron/radon decreases.
(4) For geotectonic lines and diastrophism: Thoron, thoron/potassium, and thoron/radon increase in order of Tanakura line, Itoigawa-Shizuoka line, and Median Tectonic line in proportion to the scales of tectonic movement.
In conclusion, in Abukuma mountainland where bed gases are unactive, no evidence of the active faults and the distructive earthquakes shows. However, on Median Tectonic line where bed gases are active, some large scale earthquakes had occurred in the geological age.