セオドライト観測による2000年有珠山噴火後の地殻変動(<特集>2000年有珠山噴火 (3))

概要

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The eruption of Mt. Usu started in its north-western part on May 31, 2000. The first eruption occurred at the western flank of Mt. Nishiyama, which was named "Nishiyama vents group", where many small craterlets appeared. In this local area the cryptodome has been growing since the first eruption in 2000. We observed the crustal deformation in this area by a theodolite after the first eruption from May to September, 2000 and June, 2001. The theodolite measurement revealed that the skyline in Nishiyama vents group had risen until July, 2000. The accumulated uplift around N-B (Nishiyama-B) crater could be as high as 5.5 m from May 11 to August 23. The rate of the upheaval was decayed gradually, and turned to a subsidence in August, but subsidence rate became smaller gradually after summer, 2000. We estimated the amounts of inflation volume in three periods, in May, June and July to August, 2000. The inflation rates were 74,000 m^3, 41,000 m^3 and 8,000 m^3 per day, respectively. Their pressure sources are estimated to be located 30(h400 meters beneath N-B crater that is the main crater in Nishiyama vents group.
2002-11-29