桜島における空振アレイ観測

Abstract

桜島昭和火口の噴火を対象とした空振観測を行った。観測された昭和火口噴火の空振は2Hzと0.5Hzにピークを持っており，前者は火口内の地形構造が，後者は噴出噴煙そのものに起因して励起されたものでと考えられる。また，爆発的噴火の観測波形は，噴火開始期に放射される爆発波の位相が，桜島山体や姶良カルデラ地形で回折・反射し，1分以上にわたって断続的に多方向から到来したものであった。

Results of the 2011 infrasound observations at Sakurajima volcano revealed several basic but suggestive facts for the future study of volcanic infrasound. Two peaks, around 2Hz and 0.5Hz, in power spectrum of the infrasound are identified; the former peak would be related to the eigen frequency of the vent of Showa crater, but the latter would be related to dynamics of eruption clouds. The first 10 s duration of the infrasound signal is made by explosion itself. However, after that time, diffraction and reflection waves from characteristic topography around Sakurajima volcano, like a wall-like topography of the Aira caldera, are dominant.