浅間火山2004年9月1日噴火前後の重力変化(<特集>2004年浅間山噴火(1))

概要

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Asama volcano, one of the most active andesitic volcanoes in central Japan, started a series of eruptions on September 1, 2004 and the eruptive activity lasted about three months. We have carried out microgravity measurements at the volcano three times; one year before, immediately after the eruption and one and a half months later. "Hybrid measurement", combining relative measurements over an area and an absolute measurement at a reference station, was employed to observe temporal changes in absolute gravity value. The data obtained before and after the eruption shows that the gravity changes preceding the eruption are from -6 to +9 microgals, which are of the nearly same value as that of the accuracy of observations. The gravity changes predicted from the tensile fault models and Mogi models proposed for the ground deformations are always less than 1 microgal at any gravity station. The observational fact that gravity changes did not exceed 10 microgals gives some constraints on the magma accumulation in the conduit. A numerical examination suggests that the volume of the magma accumulated in one year preceding the eruption may be less than 2×10^7m^3.
特定非営利活動法人日本火山学会の論文
2005-10-31