[S-IT06] Interaction and Coevolution of the Core and Mantle

[SIT06-11] 波形インバージョンによる北部太平洋及びアラスカ下のD"の3次元S波速度構造推定

*鈴木 裕輝¹、河合 研志²、ゲラー ロバート¹、小西 健介³ (1.東京大学大学院理学系研究科地球惑星科学専攻、2.東京大学大学院総合文化研究科広域科学専攻、3.台湾中央研究院)

キーワード：S波速度構造、D"領域、波形インバージョン

We conduct waveform inversion to infer the 3-D shear wave velocity structure within D” beneath the Northern Pacific and Alaska (Fig. 1a). This region is suitable as the target for waveform inversion, since we are able to use data that densely sample the target region (the lowermost 400 km of the mantle beneath the Northern Pacific and Alaska). Our dataset consists of ~20,000 transverse components of broadband body-wave seismograms observed at North American stations (from dense receiver networks such as the USArray). We use 114 intermediate and deep events that are widely distributed throughout the western Pacific (Japan and Izu Bonin) region. We use S, ScS and other phases that arrive between them. Our dataset is homogeneous in terms of epicentral distance (Fig.1b). Resolution tests indicate that our method and data can resolve the lateral and vertical velocity profile within D” in the target region. We use two different one dimensional shear wave velocity models (Fig. 1c) as the starting model for the inversion: PREM, and a model based on mineral physics, which includes a thermal boundary layer of 100 km effective thickness. The 3-D models obtained by our inversion show that there is a high velocity area that can be interpreted as subducted paleoslabs down to about 200 km above the core-mantle boundary (CMB), a plume like low-velocity structure, and also lateral and vertical complexity that may come from interaction between the subducted paleoslabs and development of plumes within D”.