広域水準測量から見た北海道駒ケ岳の深部マグマ溜まり

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Mt. Hokkaido-Komagatake is located at the southwestern part of Hokkaido and one ofthe most active volcanoes in Japan. The volcano had made one of the largest eruptions inthe 20th century in Japan. But the usual seismic activity of the volcano is extremely low,and only few earthquakes observed before the each small phreatic eruption in 1996, 1998 and2000. Wide area and long range geodetic measurements, therefore, are important to inferthe long term activity of the volcano.The first order leveling survey, which is administered by Geographical Survey InstituteJapan, is the only one geodetic method having the good accuracy and the long term dataenough to investigate the long term volcanic activity.In Hokkaido, the distribution of the first order leveling routes is sparse compared withthat in the other part of Japan. Mt. Hokkaido-Komagatake and Mt. Usu are the only twovolcanoes, which were passed by the first order leveling routes at the foot of them, and theleveling routes extended in more than two directions.The trend of regional deformation is found in the leveling results, and that is corrected.After this correction, the area of volcanic deformation is extended to about 50km far from thecenter of the deformation.The location of the wide area deformation center estimated by the isotropic pressuresource (Mogi’s model) is situated at the southwestern foot of Mt. Hokkaido-Komagatake. Itshorizontal distance from the central crater of the volcano is about 7km and its depth rangesfrom 15 to 24km. The rate of magma accumulation is supposed 1.4～2.6×10６㎥／year.
北海道大学大学院理学研究院自然史科学部門（地球物理学）の論文

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森済
北海道大学地震火山研究観測センター

広域水準測量から見た北海道駒ケ岳の深部マグマ溜まり

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