[S-CG63] 変動帯ダイナミクス

[SCG63-16] The Quaternary tectonics of central Kyushu and the 2016 Kumamoto earthquake: from a multifaceted viewpoint of geology, seismology, and geodesy

★Invited Papers

*大橋 聖和¹、大坪 誠²、松本 聡³、小林 健太⁴、佐藤 活志⁵、西村 卓也⁶ (1.山口大学大学院創成科学研究科、2.産業技術総合研究所　活断層・火山研究部門、3.九州大学大学院理学研究院、4.新潟大学理学部地質科学教室、5.京都大学大学院理学研究科、6.京都大学防災研究所)

キーワード：布田川・日奈久断層帯、別府-島原地溝、沖縄トラフ、中央構造線、フィリピン海プレート、横ずれ引張テクトニクス

The 2016 Kumamoto earthquake occurred in the tectonically complex central Kyushu area where several forcing factors such as the subducting Philippine sea plate, the Median Tectonic Line and the Nankai forearc sliver, the spreading Ryukyu trough, and the migrating volcanic front are involved. In this paper, we revisit the Neogene–Quaternary tectonics of central Kyushu through the integration of geological, seismological, and geodetical approaches. Also, we establish deformation histories of the Futagawa and Hinagu fault zones, source faults of the Kumamoto earthquake, in an attempt to explain the relationship between geologic structures and rupture processes of the earthquakes. Results show that the present-day tectonics surrounding central Kyushu is considered to have been originated in the last 1 Ma or younger, as a transtensional tectonic zone (the Central Kyushu Shear Zone) characterized by combined dextral faults and rift zones (or volcanoes). Reflecting the spatiotemporal variation of the crustal stress field and rift activity, the Futagawa and Hinagu fault zones show a multi-stage deformation throughout the Neogene–Quaternary periods; normal faulting to dextral faulting for the Futagawa fault zone and sinistral to dextral faulting for the Hinagu fault zone. Those diverse histories on stress and strain fields in central Kyushu possibly lead to the complexities of fault geometry and rupture process of the Kumamoto earthquake.