桜島昭和火口噴火の規模について

Abstract

2006年6月から桜島の昭和火口における噴火活動が再開した。2008年および2009年の爆発的噴火の規模を，爆発地震，空気振動，地盤変動量，火山灰放出量の4つのパラメータについて南岳において発生した爆発的噴火と比較した。いずれの項目についても昭和火口における爆発は1-2桁小さいことが分かった。

Eruptive activity at Showa crater of Sakurajima volcano resumed in June 2006 after 58 years dormancy of the crater. The annual number of explosive eruptions at the Showa crater reached 578 in 2009, exceeding the maximum annual number of explosive eruptions at the summit crater, Minamidake. The following parameters of explosive eruptions at Showa crater were compared with those at the summit crater; 1) moment of LP phase of explosion earthquake, 2) amplitude of air-shock at the station 2-3km apart from the crater, 3) volume change of pressure source causing deflating ground deformation associated with explosive eruption, 4) estimated weight of volcanic ash ejected from the crater. All the parameters associated with explosive eruptions at the summit crater are larger by 1-2 orders than those at Showa crater. Smaller scale of explosive eruptions at Showa crater may be related to smaller-size of conduit connecting to the Showa crater.