九重火山地域での重力測定結果と九重カルデラについて

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Gravity survey was made over the Aso and Kuju volcanic region occupying central part of Kyushu Island of Japan by use of Worden and LaCoste and Romberg geodetic gravimeters from 1965 to 1966. In this paper, the gravimetric feature of the Kuju volcanic region was discussed. About 20km north-east of the Aso caldera, is situated Kuju volcano group consisting of more than ten cones or domes and covering an area of 20km (EW)×15 km (NS). The number of the observed gravity stations is 146 over the Kuju volcanic region and an average station density was one station per 9.6 km^2. The Bouguer anomalies are characterized by a circular negative anomaly over the Kuju volcanic region. The negative anomaly extends over the Kuju volcanic group. The contours show concentric circular patterns. The Bouguer anomaly at the center relatively lowers to 26 mgal as compared with surrounding area. Gravimetric view thus favors to suppose the "low anomaly type caldera" in this region such as Aso and Aira though topography does not show it up clearly. From the detailed geological survey in this area, T. Matumoto proposed the buried caldera which he named Kuju caldera, formed by gigantic eruptions of tremendous amount of pumice. The eruption of large amount of pyroclastic materials are usually supposed to be related with the formation of calderas. The above mentioned proposal of T. Matumoto is based mainly on the distribution of the Kuju ignimbrites found in the surrounding area of the Kuju volcano group. From above comparative study of gravity and geology, the existence of buried Kuju caldera is reasonably supported. The underground structure over the Kuju volcanic region was computed from the gravity data by use of sin x/x method under the several reasonable assumptions.
特定非営利活動法人日本火山学会の論文
1968-12-01

九重火山地域での重力測定結果と九重カルデラについて

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