火山性地殻変動(1) ―最近の桜島火山における垂直変動と火山活動との関係―

Abstract

The vertical deformations of the earth's crust in the vicinity of Volcano Sakura-jimaaccompanied with the recent volcanic activity are studied from the results of precise levellingsurveys.The vertical displacements of the ground surface at Volcano Sakura-jima were roughlyexplained as the elastic deforivations which are caused by the increase or decrease of hydrostaticpressure of two spherical internal pressure sources or magma reservoirs. Those pressuresources were supposed to exist under the center of Aira Caldera and under the center of VolcanoSakura-jima. Contours of change in elevation between the time of the two successive surveysshow the character of those crustal deformations.As useful parameters of volcanic activity, yearly total number of explosions at Minami-dake crater and the yearly total sum of the square o maximum amplitude of explosion-earthquakes recorded by S-SO seismograph at the Higashi-sakurajima station, were comparedwith the elevation change of B.M. 29 and B.M. 111. There were fairly close relations betweenthe elevation change and the recent volcanic activity at Volcano Sakura-jima.