[S-CG52] Inter-segment Tectonics: Interdisciplinary Research on Responses to Plate Subduction

[SCG52-12] Mechanism of Upper-plate Deformations Controlled by the Geometry of Subduction Plate Interfaces

*安藤 亮輔¹、松嶋 亮弥² (1.東京大学大学院理学系研究科、2.公益財団法人　鉄道総合技術研究所)

キーワード：プレート境界形状、応力場、地震、熱構造

The angles of the subducting slab vary worldwide in different subduction zones. By noticing the variation in the cecum pacific scale, the subduction angles have been believed to control the inter-plate coupling (e.g., Lay and Kanamori, 1981) and upperplate processes of the stress loading and volcanisms (e.g., Uyeda, 1984). However, the recent development of the observations unveils the spatial variations on a regional scale, such as the stress field exhibiting the extension near the trenches and compression away from them in the area, including central Chili and Tohoku, Japan. In this study, we focus on developing a mechanical model that can quantitatively explain the temporal and perpendicular-to-ark variation of the upper plate stress field. In our mechanical model, we incorporate the non-planar geometry of the subduction interface and the base of the continental lithosphere, reflecting the thermal structure. Our model successfully reproduces the perpendicular-to-ark variation of the extension to compression, as generally found earlier (Fukahata and Matsu’ura, 2016). Our parameter study confirms the importance of the shallowering of the lithospheric depth along the volcanic front to have sufficient compressional stress in land by modeling the Tohoku case quantitatively, given the stressing rate becomes smaller apart from the subduction interface. The simulated temporal change in the stress field explains the seismic activity before and after the 2011 Tohoku-oki earthquake. By changing the plate interface geometry for the Kyushu, Japan, region with the higher subduction angle, we successfully reproduce the general extensional stress in the land, where the extensional stress regime controls the faulting and volcanism. This study demonstrates the importance of understanding the tectonic variation in the regional scales, which could originate from the segmentation of the plate interfaces.