日本地球惑星科学連合2019年大会

講演情報

[E] ポスター発表

セッション記号 S (固体地球科学) » S-IT 地球内部科学・地球惑星テクトニクス

[S-IT23] Structure and Dynamics of Earth and Planetary Mantles

2019年5月26日(日) 10:45 〜 12:15 ポスター会場 (幕張メッセ国際展示場 8ホール)

コンビーナ:中川 貴司(香港大学地球科学専攻)、芳野 極(岡山大学惑星物質研究所)、趙 大鵬(東北大学大学院理学研究科附属地震・噴火予知研究観測センター)

[SIT23-P10] Shear wave structure of the upper mantle beneath the Ontong Java Plateau

*一瀬 建日1末次 大輔2塩原 肇1杉岡 裕子3伊藤 亜妃2石原 靖2田中 聡2大林 政行2利根川 貴志2吉光 淳子2小林 拓史3吉澤 和範4 (1.東京大学地震研究所、2.海洋研究開発機構、3.神戸大学、4.北海道大学大学院理学研究院)

キーワード:上部マントル、オントンジャワ、表面波トモグラフィー、広帯域海底地震計

Ontong Java Plateau (OJP) is the vastest Large Igneous Provinces (LIPs) in the oceanic region of the Earth. The OJP was emplaced at 122 and 90 Ma by massive volcanism, but the origin of this volcanism is still under discussion.
Richardson et al. (2000) obtained a large low-velocity root of the OJP extending as deep as 300km, though its existence and cause are still in debating.
One reason for poor understanding of the OJP is the insufficient information about the crust and mantle structure beneath the OJP because of the lack of long-term seafloor observation. Between 2014 and 2017, we conducted the first seismological and electromagnetic observations on the seafloor and islands in the OJP, named "OJP array", to clarify the origin of the OJP.
Using the broadband data from the OJP array as well as those from stations on land and seafloor in the western Pacific Ocean, we constructed three-dimensional shear wave speed structure beneath the OJP by surface wave tomography. using phase speed dispersions of Love and Rayleigh waves up to the 4th higher modes. Checkerboard resolution tests suggests that the spatial resolution of the obtained model is ~300km, which is higher than previous studies.

Obtained shear wave speed structure down to the depth of 300 km shows the following new features:
(1) In the center of the OJP at depths between 70–150 km, about 2% fast anomalies exists;
(2) No strong slow anomaly is found beneath the OJP at depths down to 300 km;
(3) Beneath the Caroline Islands, in the north of the OJP, 2 % slow anomalies exist, which may be associated with the Caroline hotspot activity.

These newly found features suggest that further investigation to reveal the origin of the OJP is necessary.