Permalink : http://hdl.handle.net/2115/20430

JaLCDOI : 10.14943/gbhu.70.145

Mt. Hokkaido-Komagatake is located at the southwestern part of Hokkaido and one of the most active volcanoes in Japan. The volcano had made one of the largest eruptions in the 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 and 2000. Wide area and long range geodetic measurements, therefore, are important to infer the long term activity of the volcano. The first order leveling survey, which is administered by Geographical Survey Institute Japan, is the only one geodetic method having the good accuracy and the long term data enough to investigate the long term volcanic activity. In Hokkaido, the distribution of the first order leveling routes is sparse compared with that in the other part of Japan. Mt. Hokkaido-Komagatake and Mt. Usu are the only two volcanoes, which were passed by the first order leveling routes at the foot of them, and the leveling 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 the center of the deformation. The location of the wide area deformation center estimated by the isotropic pressure source (Mogi’s model) is situated at the southwestern foot of Mt. Hokkaido-Komagatake. Its horizontal distance from the central crater of the volcano is about 7km and its depth ranges from 15 to 24km. The rate of magma accumulation is supposed 1.4～2.6×10６㎥／year.