[S-VC47] [JJ] 活動的火山

[SVC47-07] Brief overview of landing survey and seisimic observation at Nishinoshima

*武尾 実¹、大湊 隆雄¹、市原 美恵¹、前野 深¹、金子 隆之¹、篠原 雅尚¹、馬場 聖至¹、西田 究¹、安田 敦¹、渡邊 篤志¹、杉岡 裕子⁸、浜野 洋三²、多田 訓子²、中野 俊³、吉本 充宏⁴、川上 和人⁵、千田 智基⁶、高木 朗充⁷、長岡 優⁷ (1.東京大学地震研究所、2.海洋研究開発機構、3.産業技術総合研究所地質調査総合センター、4.山梨県富士山科学研究所、5.森林総合研究所、6.環境省関東地方環境事務所、7.気象研究所、8.神戸大学)

キーワード：西之島、火山島、噴火

A new volcanic islet had been growing up with lava effusion and Strombolian acitivities at Nishinosima, Izu-Bonin arc from November 2013 to November 2015. The morophological evolution of Nishinoshima had been revealed based on airbone observtions and satellite images. The eruption activity has been monitored continuously using ocean bottom seismograph observation; the number of eruptions had registered a decline gradually, the eruption having stoped by the end of November 2015. After the volcanic activity falling to a low level, we had promoted a research survey of volcanology and bionomy at Nishinoshima from October 16^th to 25^th, 2016, using an academic investigation ship “Shinsei-maru” managed by AORI, University of Tokyo. The investigation item of the landing team were geological survey, installation of seismic station, and survey on nidification of seabirds. OBSs and OBEMs had been installed around Nishinoshima, pre-installed OBSs having recoverd. A monitoring system of remote volcanic island using WaveGlider was operated around Nishinoshima on a trial basis. An analysis of whole rock chemical composition of volcanic products in 2013-2015 eruption reveals that all samples are composed of andesite with SiO₂ content of 59.5-59.9wt%, falling on middle content between the eruption products in 1973-1974 eruption and the laval of the old islet. The telemetric seismic monitoring system in Nishinoshima is on couse to operate; the seismic data occasionally include long-lasting high-frequency tremors which seem to be related with some sort of Nishinoshima activity. We will make clear the growing process of volcanic islet together with geological and geophysical knowledges based on futher analyses of volcanic products and those of OBS and OBEM data which will be recovered on June 2017.