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-P09] Finite frequency S wave tomography model beneath the Ontong Java Plateau using data recorded by broadband ocean bottom seismographs

*堀内 美咲3杉岡 裕子3大林 政行1末次 大輔1塩原 肇2伊藤 亜妃1石原 靖1田中 聡1一瀬 建日2利根川 貴志1吉光 淳子1小林 拓史3 (1.国立研究開発法人海洋研究開発機構、2.東京大学地震研究所、3.神戸大学)

キーワード:有限波長トモグラフィー、S波速度構造

We determined three-dimensional S wave model beneath the Ontong Java Plateau (OJP) by finite frequency tomography using data recorded by broadband seismographs deployed at ocean bottom covered the OJP and at neighbor islands (Suetsugu et al., 2018). Our dataset contains absolute and period-depended differential travel time data. The former consists of ~1,100,000 direct S-wave onset times reported by International Seismological Centre (ISC) and ~400 direct S-wave onset times picked up on broadband waveform records around the OJP and the latter is composed of ~3,000 differential traveltimes between two different stations around the OJP measured by waveform cross correlation at 7 different passband of which center periods varies from 5.3 sec to 42 sec. We used adaptive stacking method (Rawlinson and Kennett, 2004) to measure absolute travel time data near the OJP. These data were inverted based on the infinite frequency travel time tomography method for the absolute travel time data (Inoue et al., 1990; Fukao et al., 1992; Obayashi et al., 2013) and the finite frequency travel time method for the relative travel time data (Dahlen et al., 2000; Obayashi et al., 2013). We obtained a well resolved S wave velocity model beneath the OJP. It shows significant high velocity anomalies in the mantle transition zone, which are considered as stagnant Pacific slabs related to the trench retreating as well as seafloor spreading in the Santa Cruz Basin and Melanesia Basin during the Eocene and Oligocene. It also reveals that S wave velocity just below the OJP is a little higher than the surrounding strong slow anomalies in the mantle shallower than 200 km. We will discuss these remarkable features beneath the OJP in comparison with P wave tomographic model (Obayashi et al., 2018) in this presentation.