<論文>九重硫黄山での地磁気変化による噴気火道の形成推定

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Geothermal changes in the subsurface volcanic and geothermal areas can be inferred from monitoring thegeomagnetic changes. We installed several proton precession magnetometers for continuous observation andset up tens of observation sites for repeated survey in the geothermal area at Kuju-Iwoyama, Kyushu Island,Southwest of Japan, after the vapor eruption (phreatic explosion) event in October of 1995. So far, we carriedout repeated surveys three times - in March to April of 1999, August to September of 1999, and Decemberof 1999 to January of 2000 for more than 30 sites. Geomagnetic changes in the total force close to 40nTjyearwere observed at some observation sites during less than one year. The amounts of changes obtained by therepeated surveys were consistent with those obtained by the continuous observations.In this study we indicate that installing a number of sites for repeated survey made it possible to revealthe shape of cooling or heating bodies to some extent. An inclined and cone-shaped cooling body beneathmajor fumaroles is inferred at Kuju-Iwoyama.