[S-VC31] Active Volcanism

[SVC31-10] Vertical ground deformation of Sakurajima volcano measured by precise leveling survey (results of the Nov. 2022 survey)

*Keigo Yamamoto¹, Takeshi Matsushima², Shin Yoshikawa³, Kazunari Uchida², Hiroyuki Inoue³, Tadaomi Sonoda¹, Yuusuke Takenaka¹, Kazumi Okada⁴, Ryo Oyanagi³, Ayuka Joudoi², Tatsunosuke Shimeno², Taisuke Kouno⁵, Masaomi Tsukaguchi⁵, Daisuke Mitsunaga⁵, Yuki Tamachi⁵, Atsushi Inoue⁵, Akira Nishijo⁵, Takeshi Kubo⁵, Takahiro Ohkura³ (1.Disaster Prevention Research Institute, Kyoto University, 2.Faculty of Sciences, Kyushu University, 3.Graduate School of Science, Kyoto University, 4.Faculty of Science, Hokkaido University, 5.Japan Meteorological Agency)

Keywords:Sakurajima volcano, precise leveling survey, vertical ground deformation

We conducted the precise leveling survey in Sakurajima volcano, southwest Japan in November 2022. The leveling routes measured in this survey are about 23 km long in total, including Sakurajima western flank route and Sakurajima northern flank route. These leveling routes were measured during the period from November 7 to 18. Mean square errors of the conducted survey were achieved with a good accuracy ranging from ±0.25 to ±0.26 mm/km.
From the measured data, we calculated the relative height of each benchmark referring to the reference benchmark BM.S.17 which is located at the western coast of Sakurajima. The calculated relative heights of the benchmarks were then compared with those of the previous survey conducted in November 2021 (Yamamoto et al., 2022), resulting in the relative vertical displacements of the benchmarks during the period from November 2021 to November 2022.
The resultant displacements indicate the ground subsidence (-3.6 mm at maximum) at benchmarks around the central part of Sakurajima. On the other hand, the ground deformation at benchmarks near the northern part of Sakurajima is minor, suggesting that the magma storage at the magma reservoir beneath Aira caldera was not remarkable during the period between November 2021 and November 2022. From the preliminary analysis based on a spherical source model (Mogi, 1958), the deflation source is located beneath the central part of Sakurajima. The results indicate that the pressure decrease is suggested at the magma reservoir beneath Minamidake.