1999年南岳山頂噴火活動および2006年昭和火口噴火活動再開に先行する桜島火山の地盤変動源について

Abstract

We analyzed GPS data during 1998-2006 to make clear process of magma accumulation and movement of Sakurajima volcano prior to eruptive activity at the summit crater in 1999 and eruptive activity at Showa crater resumed in 2006. Obtained deformation rate was not constant. Large deformation rate was obtained prior to eruptive activity at the summit crater in 1999 and eruptive activity at Showa crater resumed in 2006, and we obtained pressure source at depths 6-8 km near the northern coast of Sakurajima accurately by assuming a spherical source. In those periods, magma was thought to be moved from Aira caldera to Sakurajima volcano prior to eruptive activity at the summit crater in 1999 and eruptive activity at Showa crater resumed in 2006. In addition, in phases A (Jan-Dec 98), B (Dec98-Sep99), D (Nov04-Mar05) and F (Nov05-Mar06), magma accumulation rates estimated from volume changes of the pressure source and the amount of ash fall thought to be reached to 1×10[7] m[3]/yr, which is average magma accumulation rate at Sakurajima.