有珠山2000年噴火に伴う空振活動(<特集>2000年有珠山噴火 (3))

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There was intense acoustic activity associated with the eruption of Mount Usu, which began on March 31, 2000. Repetitive phreatic explosions generated many isolated infrasonic signals, which were observed at plural acoustic stations. During the periods when acoustic activity was high, infrasonic pulses as many as 200 were identified every 10 minutes. Source location of infrasonic signals could be well identified from the records of the low frequency microphone network. Two active craters, Nishiyama and Konpirayama craterlets, are clearly distinguished by sound source determination analysis in spite of their proximity (〜1 km). To investigate temporal change in the acoustic activity from April to June, 2000, we developed a method to detect arrival and amplitude of infrasonic signals automatically. The number of automatically identified infrasonic signals exceeds 1.46 million during three months. It seems that there is a good correlation between acoustic activity and seismic signal amplitude. Patterns of acoustic activity and infrasonic pulse shapes observed at Usu volcano are very similar to those observed at Stromboli volcano, Italy. We named the acoustic activity attended with phreatic explosion which scatters a lot of clods, "mud-pool Strombolian type". Phreatic explosion excites not only infrasonic pulses but also seismic signals observed before the arrival of an infrasonic pulse. Existence of a Rayleigh wave phase with a large amplitude suggests that the seismic wave is excited at a shallow part of the crater.
特定非営利活動法人日本火山学会の論文
2002-11-29

有珠山2000年噴火に伴う空振活動(<特集>2000年有珠山噴火 (3))

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