[S-IT24] Probing the Earth's interior with geophysical observation on seafloor

[SIT24-P01] The OJP array: seismological and electromagnetic observation on seafloor and islands in the Ontong Java Plateau

*末次 大輔¹、塩原 肇²、杉岡 裕子⁴、多田 訓子¹、伊藤 亜妃¹、一瀬 建日²、馬場 聖至²、市原 寛³、太田 豊宣⁵、石原 靖¹、田中 聡¹、大林 政行¹、利根川 貴志¹、吉光 淳子¹、小林 拓史⁴、歌田 久司² (1.海洋研究開発機構　地球深部ダイナミクス研究分野、2.東京大学　地震研究所、3.名古屋大学　地震火山研究センター、4.神戸大学大学院　理学研究科、5.有限会社　テラテクニカ)

キーワード：オントンジャワ海台、巨大火成岩区、広帯域海底地震計、海底電位差磁力計

We conducted geophysical observations on the Ontong Java Plateau (OJP) and its vicinity from late 2014 to early 2017 to determine the underlying crust and upper mantle structure beneath the OJP. The OJP was emplaced in the present South Pacific region at 120 and 90 Ma by massive volcanism, but the causes of this volcanism are still debated. Previous studies have suggested that seismic velocity beneath the OJP is anomalously slow, thus could represent thermal or chemical remnants of the volcanism. However, the seismic resolution of the slow anomalies is poor due to lack of seafloor observations. The observation network named “the OJP array” is composed of seafloor and island stations. The seafloor stations have broadband ocean bottom seismographs and ocean bottom electromagnetometers. The island stations have broadband seismographs. The OJP array is designed to obtain seismic and electrical conductivity structures of the mantle beneath the OJP with better resolution than that of previous studies. Joint analysis and interpretation of seismological and electromagnetic data should provide tight constraints to thermal and chemical structures and clarify the cause of OJP emplacement.