雲仙岳の火砕流に伴う震動波形と空振波形の解析

概要

論文の詳細を見る
Small pyroclastic flows have been generated by collapses of lava domes at Unzendake volcano, Japan. Seismic and acoustic waves were analyzed that were excited by the pyroclastic flows. Minor seismic waves are excited at the time of lava dome collapse and low frequency seismic signals with larger amplitude follow them as the blocks of lava fall onto the slope. The low frequency seismic waves are interpreted as a result of the dome collapses and their amplitudes are correlative to the volumes of the collapsed lava blocks. While the pyroclastic flows descend along the mountain slope, high frequency seismic waves are emitted and they die out as the pyrociastics cease to flow. The variation of amplitude ratio among the seismic waves recorded at different stations indicates that the source of seismic signals runs down along the slope. By analyzing the acoustic waves observed by low frequency microphones, the precise locations of the dome collapses were determined. Acoustic signals intermittently observed during the flow of pyroclastics are inferred to be excited from sources moving with the pyroclastic flow front. Excitation of seismic and acoustic waves are sensitive to topographic singularities and their amplitudes and frequencies vary with time.
特定非営利活動法人日本火山学会の論文
1993-08-15