桜島火山における繰り返し相対重力測定 (2017年5月～2018年2月)

Abstract

Relative gravity values were measured at 19 gravity points in and around Sakurajima Volcano in May, July, September and October 2017, and February 2018, to monitor spatiotemporal mass variations associated with volcanism. The gravity values observed from 2006 to 2018 showed a clear increase in the central part of the volcano by up to +6.3 μGal/yr. The gravity increase suggests the existence of mass increase under the central Sakurajima without volume inflation, because the gravity increase cannot be fully explained by the ground subsidence which have been measured with leveling surveys. The mass increase value is calculated to be about 1-3 × 1010 kg/yr, assuming that the point mass is located just under the S423 gravity point at the depth of 3-5 km below sea level. In order to more precisely model the mass increase and its spatiotemporal variation, the effects of hydrology and crustal deformation should be corrected from the observed gravity data.