日本地球惑星科学連合2018年大会

講演情報

[EJ] ポスター発表

セッション記号 S (固体地球科学) » S-CG 固体地球科学複合領域・一般

[S-CG59] 日本列島の構造と進化: 島弧の形成から巨大地震サイクルまで

2018年5月22日(火) 13:45 〜 15:15 ポスター会場 (幕張メッセ国際展示場 7ホール)

コンビーナ:佐藤 比呂志(東京大学地震研究所地震予知研究センター)、篠原 雅尚(東京大学地震研究所)、石川 正弘(横浜国立大学大学院環境情報研究院、共同)、松原 誠(防災科学技術研究所)

[SCG59-P01] Scattered wavefield imaging of the Japan subduction structure using Hi-net array data

*Younghee Kim1Hitoshi Kawakatsu2 (1.Seoul National University、2.Earthquake Research Institute, University of Tokyo)

キーワード:Teleseismic migration, Subduction-zone geometry, Hi-net data

The Japan arcs exhibit significant along-arc transition in slab geometry, subduction-driven magmatic activity, and plate coupling state. We exploit teleseismic data from dense Hi-net array to define the present-day subduction-zone geometry and to constrain the plate boundary dynamics in response to variable slab geometries and physical properties of the subducting material. We retrieve backscattered (or reverberated) body-wave phases in addition to direct Ps (incident P wave forward-scattered as an S wave) and apply the teleseismic migration method based on the Generalized Radon Transform (Bostock et al., 2001) to accurately define both Pacific and Philippine Sea plate subduction structures. This method inverts the scattered waves for sharp variations in the Earth’s elastic properties beneath the high-density array using analytical expressions for their travel-times and amplitudes (Bostock et al., 2001). The four scattering modes (Ps, PpPs, PpSs|v, and PpSs|h) are sensitive to S-wave velocity perturbations (dVs/Vs) and are combined to form a single composite image. As more migrated phases are stacked in, the artifacts due to cross-mode contamination (i.e., parallel echoes of the real structure) become attenuated while energy mapped to its correct depth is sharply imaged. Preliminary images show complex slab structures down to a depth of 200 km with significant along-arc velocity variations at the top of the plate. Such differences in the velocity structures may indicate different hydration state due to slab age and/or presence of low-strength materials.