2004年の浅間山噴火前の地震活動と噴火前に観測された傾斜変化

概要

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A medium-sized eruption occurred at Asama Volcano on September 1, 2004 after a 21-year dormancy following the eruption in April 1983. Before the eruption, the number of volcanic earthquakes had increased beginning late 2002. A prominent feature of this seismicity was the appearance of high-frequency BH-type earthquakes beginning in mid-August, 2004, approximately a half-month before the first eruption. Eruptions of similar size occurred on September 23, September 29 and November 14. Preceding these eruptions, changes in ground tilt were recorded on the EW component of a tiltmeter installed 2.5 km NNE of the summit crater. This was the first time that JMA (Japan Meteorological Agency) recorded tilt changes at Asama Volcano before eruptions. Changes in ground tilt were almost simultaneously accompanied with increases in volcanic earthquake occurrence. The increase in volcanic earthquake occurrence and change in ground tilt preceding the eruptions contributed to the precautionary issuance of preparatory volcanic information to the public. In spite of the appearance of preceding phenomena, however, information was insufficient to predict the exact time and size of each eruption. Additional observation and understanding of physical processes may be necessary for the exact assessment of eruptions.
特定非営利活動法人日本火山学会の論文
2006-04-28