[S07]PM-2

[S07-01] 多重ScS波解析によるオントンジャワ海台マントルのS波速度と減衰の推定

*末次 大輔¹、塩原 肇²、杉岡 裕子³、伊藤 亜妃¹、一瀬 建日²、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. 神戸大学大学院理学研究科)

The Ontong Java Plateau (OJP) in the southwest Pacific is the largest oceanic Large Igneous Provinces (LIP) on Earth. Detailed seismic structure of the plateau has not been understood well because of sparse seismic stations. We investigated seismic attenuation of the mantle beneath the plateau by analyzing temporary seismic stations on the seafloor and islands in and around the plateau. We analyzed the spectra of multiple ScS waves to determine the average attenuation of the mantle (Q_ScS) beneath the plateau. We estimated the average Q_ScS values for the paths with bounce points located in the plateau to be 309, which is significantly higher than the average (i.e., weaker attenuation than average) estimated in the western Pacific and is close to that of stable continents. We obtained positive residuals of 6 s for travel times of multiple ScS waves, which indicate that the average S velocity in the entire mantle beneath the OJP is low. While the positive residuals is at least partially attributable to the Pacific Large Low Shear Velocity Province (Pacific LLSVP), it is difficult to conclude whether low-velocity anomalies are required in the OJP upper mantle to explain the residuals from the multiple ScS analysis.