[S-VC28] 活動的⽕⼭

[SVC28-P04] 吾妻山の最近の火山活動における深部圧力源の存在とその挙動

*岡田 純¹、丹原 裕²、宮川 祐司³、関 晋³、山村 卓也²、近澤 心³ (1.気象庁気象研究所火山研究部、2.気象庁仙台管区気象台地域火山監視・警報センター、3.気象庁仙台管区気象台地震火山課)

キーワード：吾妻山、GNSS、地殻変動、深部圧力源、マグマだまり

Recent volcanic activity of Azuma volcano, NE Japan is characterized by the repetitive unrests where the shallow seismic activities coincide with ground deformation attributed to the various depths. In the volcanic activities of 2014-2015 and 2018-2019, there are two types of ground deformation such as (1) months-long inflation at both shallow and deep parts and (2) short-term shallow inflation and deep deflation during the volcanic tremors (Okada et al., 2019, JpGU). This indicates that both shallow and deep parts beneath the volcano are related each other. Regarding (2), the shallow inflation preceded the deep deflation at least for the 2018-2019. The recent studies of Tohoku University (2019) and Seki et al. (2020) pointed out long-period events with the frequency lower than 0.1 Hz exist during the above-mentioned short-term deformation. Their results show the shallow volcanic activities might have affected the deeper parts. The existence of deep inflation sources (BSL 3-4km and/or more) is suggested by Seki et al. (2020) in order to explain the entire activity of the 2018-2019. Similar deep inflation episode exists during 2003-2004, 2006-2007 and 2014-2015, and all these cases resulted in volcanic unrests with intense seismic activities beneath Oana crater. However, the volcanic episodes of the 2008-2012 and the March-October 2020 seem exceptional. The former episode misses a clear deep inflation but shows the significant thermal activity on the surface. The latter episode shows deep inflation but does not lead any clear volcanic unrests hitherto (February 2021). Different behaviors of deep pressure sources may address the feasibility of magma ascent/supply from the depth and provide important constraints on the changeable condition of the shallow hydrothermal system such as wet/dry environments or with/without sealing of the preexisting conduits/vents.

Reference:
1. Okada et al. (2019) Ground deformation associated with the 2014-2015 and the 2018-2019 volcanic activities at Azumayama. SVC38-P02, Japan Geoscience Union Meeting 2019.
2. Seki et al. (2020, accepted) Volcanic activity in 2018-2019 at Azumayama Volcano, Japan. Kenshin-Jiho, 35pp.
3. Tohoku University (2019) Seismic activity of Azumayama, Report of the 144^th Coordinating Committee for Prediction of Volcanic Eruption (No. 5) additional material, 9-10.