[S-EM14] Electromagnetic Induction in the Earth and Planetary Interiors, and Tectono-Electromagnetism

[SEM14-P04] Repeated aeromagnetic survey of Tarumae volcano using an unmanned autonomous helicopter

*Keiichi Shibuya¹, Takeshi Hashimoto², Tomoya Hayakawa³, Keitaro Yoshikawa⁴ (1.Graduate School of Science, Hokkaido University, 2.Faculty of Science, Hokkaido University, 3.Nippon Koei Co., Ltd., 4.Hokkaido Regional Development Bureau)

Aeromagnetic surveys using an unmanned autonomous helicopter have been conducted at active volcanoes in Hokkaido. In October 2020, we performed the fourth survey at Mt. Tarumae following the previous ones in 2011, 2012 and 2013. In this study, we analyzed the aeromagnetic data in 2020 and compared to the previous surveys in 2011 and 2013. Following the manual correction of the time stamp of the magnetometer for the 2020 data to maximize the correlation with the 2013 data, we obtained the temporal changes between them. The accuracy of the repeated flight was satisfactory as gaps between the actual flight trajectories were mostly within 5m. Then we obtained the temporal changes in the total magnetic field by taking the simple differences of the selected nearest points between the two surveys. We also calculated the temporal changes for the pair between 2011 and 2013 through the same procedure. Both the pairs showed a systematic field pattern suggesting a magnetizing trend beneath the summit lava dome. We accounted for the magnetic field changes in terms of a single dipole source beneath the lave dome with magnetic moment changes of 7.9×10⁶ Am² and 8.0×10⁶ Am², respectively for the 2011-2013 and the 2013-2020 pairs. The source depth was almost the same (c.a. 400 m deep from the lava dome surface), but the horizontal location of the latter source shifted slightly southeast from the former. The almost same amount of the magnetic moment for the two periods suggested a slowdown in the magnetization rate after 2013. This result was consistent with the ground-based monitoring that was annually performed by the Japan Meteorological Agency and Hokkaido University (Hashimoto et al., 2018).