Magma mass increase under Sakurajima Volcano, Japan, inferred from campaign relative gravity and leveling data from 1975 to 1992: an interpretation from volcanic gas studies

Abstract Temporal variations of volume and mass in the magma chambers of Sakurajima Volcano were modeled using leveling and relative gravity data collected around the volcano during the eruptive period from 1975 to 1992, to reveal a physical mechanism for the excessive gravity increase observed at the volcano. The following two deflation sources were estimated from the leveling data: a deeper source of $$(-4.0 \pm 0.3)\times 10^6$$ ( - 4.0 ± 0.3 ) × 10 6 m $$^3$$ 3 /year located at a depth of 7800 ± 400 m beneath Aira Caldera, and a shallower source of $$(-9.25^{\, + \, 1.00}_{\, - \, 0.75}) \times 10^5$$ ( - 9 . 25 - 0.75 + 1.00 ) × 10 5 m $$^3$$ 3 /year located at a depth of 4000 ± 400 m beneath the center of Sakurajima Volcano. These deflation sources cannot fully explain the gravity increase of up to 15.75 µGal/year observed at the volcano, because a gravity increase of only $$