浅間火山に発生した火山性微動 : 1973年及び1982年の噴火活動期の火山性微動の解析と解釈

概要

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Two different types of volcanic tremor originating from Asama Volcano are analyzed. They accompanied with 1) the February, 1973, minor eruption and 2) the October, 1982, minor eruption. Analogue records during the 1973 eruption are digitized, which were obtained at four seismic stations on the eastern slope of the volcano edifice. Digital data on MT are available for the 1982 eruption. Power spectra of the vertical component of the seismic signals as well as some peculier feature of low-sensitivity smoked paper records suggest that: tremor during the 1973 eruption is most probably the successive occurrence of the BL-type earthquakes, On the contrary, the volcanic tremor observed in 1982 has very different waveforms from that of BL-type one. Power spectra have a few distinct peaks with the fundamental frequency of 0.88 Hz and its integer multiple harmonics. The particle motion of the tremor near the summit crater (i.e. the station MAE) exhibits a dominant rajectory only in the horizontal radial direction. At far field distances (i.e. the station SAN) the particle motion has some vertical and transversal components which implies predominance of surface waves. The tremor in October 1982 is explained as due to the vibration of a magma column within the vent.
1992-04-01