日本地球惑星科学連合2015年大会

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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-CG57] 変動帯の構造・進化とダイナミクス

2015年5月27日(水) 18:15 〜 19:30 コンベンションホール (2F)

コンビーナ:*竹下 徹(北海道大学大学院理学院自然史科学専攻)、佐藤 比呂志(東京大学地震研究所地震予知研究センター)、尾鼻 浩一郎(海洋研究開発機構 地震津波海域観測研究開発センター)、西村 卓也(京都大学防災研究所)、深畑 幸俊(京都大学防災研究所)、加藤 愛太郎(名古屋大学大学院環境学研究科)、武藤 潤(東北大学大学院理学研究科地学専攻)、佐藤 活志(京都大学大学院理学研究科地球惑星科学専攻)、小平 秀一(海洋研究開発機構 地球内部ダイナミクス領域)、鷺谷 威(名古屋大学減災連携研究センター)、石山 達也(東京大学地震研究所)、松原 誠(防災科学技術研究所)、池田 安隆(東京大学大学院理学系研究科地球惑星科学専攻)

18:15 〜 19:30

[SCG57-P28] プレートの定常沈み込みに伴う島弧の変形とその特徴

*深畑 幸俊1松浦 充宏2 (1.京都大学防災研究所、2.統計数理研究所)

キーワード:島弧, 地殻変動, 粘弾性, 重力異常

Steady plate subduction elastically brings about permanent lithospheric deformation in island arcs, though this effect has been neglected in most studies based on dislocation theory. We investigate the characteristics of the permanent lithospheric deformation using a kinematic model, in which steady slip motion is given along a plate interface in the elastic lithosphere overlying the viscoelastic asthenosphere under gravity. As a rule of thumb, long-term lithospheric deformation can be understood as a bending of an elastic plate floating on non-viscous fluid, because the asthenosphere behaves like water in a long term. The steady slip below the lithosphere-asthenosphere boundary does not contribute to long-term lithospheric deformation. Hence, the key parameters that control the lithospheric deformation are only the thickness of the lithosphere and the geometry of the plate interface. Slip on a plate interface generally causes substantial vertical displacement, and the gravity always tries to retrieve the original gravitational equilibrium. For a curved plate interface gravity causes upward bending of the island arc lithosphere, while for a planar plate interface gravity causes downward bending. Larger curvature and thicker lithosphere generally causes larger deformation. When the curvature changes along the plate interface, internal deformation is also involved intrinsically, which modifies the deformation field due to gravity. Because the plate interface generally has some curvature, at least near the trench, upward bending of the island arc lithosphere, which involves uplift of island arc and subsidence around the trench, is always realized. On the other hand, the deformation field of the island arc lithosphere sensitively depends on lithospheric thickness and plate interface geometry. These characteristics obtained by the numerical simulation are well consistent with observed topography and free-air gravity anomalies in subduction zones, where a pair of topography and gravity anomaly, high in the arc and low around the trench, exists without exceptions all over the world, while there are large variety in the amplitude and horizontal scale.