南海トラフ地震発生帯掘削がもたらした沈み込み帯の新しい描像  [in Japanese] A new perspective of the subduction zone derived from the Ocean Drilling Program for the Nankai Trough Seismogenic Zone Experiment (NanTroSEIZE)  [in Japanese]

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Author(s)

    • 木村 学 Kimura Gaku
    • 東京海洋大学海洋資源環境学部 Department of Marine Environment and Resources, Tokyo University of Marine Science and Technology
    • 江口 暢久 Eguchi Nobuhisa
    • 海洋研究開発機構地球深部探査センター Center for Deep Earth Exploration (CDEX), Japan Agency for Marine-Earth Science and Technology
    • Sean Toczko Toczko Sean
    • 海洋研究開発機構地球深部探査センター Center for Deep Earth Exploration (CDEX), Japan Agency for Marine-Earth Science and Technology
    • 木下 正高 Kinoshita Masataka
    • 東京大学地震研究所|海洋研究開発機構海洋掘削科学研究開発センター Earthquake Research Institute, The University of Tokyo|Center for Ocean Drilling Science (ODS), Japan Agency for Marine-Earth Science and Technology
    • 金松 敏也 Kanamatsu Toshiya
    • 海洋研究開発機構地震津波海域観測研究開発センター Center for Earthquake and Tsunami (CEAT), Japan Agency for Marine-Earth Science and Technology
    • 斎藤 実篤 Saito Saneatsu
    • 海洋研究開発機構海洋掘削科学研究開発センター Center for Ocean Drilling Science (ODS), Japan Agency for Marine-Earth Science and Technology
    • 廣瀬 丈洋 Hirose Takehiro
    • 海洋研究開発機構高知コア研究所 Kochi Institute for Core Sample Research, Japan Agency for Marine-Earth Science and Technology
    • 山田 泰広 Yamada Yasuhiro
    • 海洋研究開発機構海洋掘削科学研究開発センター Center for Ocean Drilling Science (ODS), Japan Agency for Marine-Earth Science and Technology
    • 荒木 英一郎 Araki Eiichiro
    • 海洋研究開発機構地震津波海域観測研究開発センター Center for Earthquake and Tsunami (CEAT), Japan Agency for Marine-Earth Science and Technology

Abstract

<p>2007年開始の南海トラフ地震発生帯掘削計画は,プレート境界で起こる地震発生,断層メカニズムの理解を目的に実施,掘削の結果,これまで以下の主要な成果が得られた.</p><p>1)南海前弧域は,~6Ma以降の沈み込み,特に2Ma以降の付加体の急成長によって形成され,プレート境界の上盤を形成することとなった.</p><p>2)プレート境界と分岐断層に沿うすべりは,海底面まで高速ですべり抜けたことがある.</p><p>3)粘土鉱物に富む断層ガウジは静的にも動的にも,絶対的に弱い.</p><p>4)掘削によって応力測定に成功した.多くの地点で最大水平圧縮方向はプレートの収束方向とほぼ平行であり,次の南海地震に向けての応力蓄積の進行が示唆される.</p><p>5)掘削孔設置の観測計が,2016年4月1日に南海プレート境界で72年ぶりに発生した地震による圧力変動を観測した.海底観測網による微小津波観測と同期しており,上盤内の地震時体積収縮を世界で初めて観測した.</p>

<p>The NanTroSEIZE project has been one of the most complex and challenging scientific ocean drilling projects in history, representing a milestone for the Integrated Ocean Drilling Program (2005–2013) and the current International Ocean Discovery Program (2013–013) and the current International Ocean Discovery Program (2013fic ocseismogenesis of the Nankai Trough is now approaching the final stage; i.e., directly sampling, analyzing, and monitoring the plate boundary fault system responsible for historically recurring mega-earthquakes and associated tsunamis. The study area is located southeast of Kii Peninsula and comprises a transect of drill sites extending from the Kumano Basin across the Nankai Trough to the incoming Philippine Sea Plate.</p><p>The drilling of the Nankai seismogenic subduction zone, initiated in 2007, has resulted in the re-evaluation of previously accepted geological models. The main findings are as follows:</p><p>1) The Nankai forearc grew intermittently between ~6 and ~2 Ma due to rapid terrestrial sediment supply, resulting in the formation of a hanging wall wedge as a result of the occurrence of great earthquakes. </p><p>2) Slip along the plate boundary megathrust and along the associated splay fault has previously reached as far as the Nankai trough and ocean floor.</p><p>3) The fault, composed of clay-rich gouge, is weak in both static and dynamic cases.</p><p>4) The in situ stress conditions of the accretionary wedge and incoming Philippine Sea Plate are well constrained, and the horizontal compressional stress, parallel to the direction of plate convergence, suggests tectonic loading of accretionary sediments, implying a possible stress buildup that could result in the next great Nankai earthquake.</p><p>5) Borehole observatories and an ocean floor network recorded the earthquake, tsunami, and slow slips along the megathrust on 1 April 2016, and represent a new and innovative technology for application in the field of ocean floor science.</p>

Journal

  • The Journal of the Geological Society of Japan

    The Journal of the Geological Society of Japan 124(1), 47-65, 2018

    The Geological Society of Japan

Codes

  • NII Article ID (NAID)
    130007377688
  • NII NACSIS-CAT ID (NCID)
    AN00141768
  • Text Lang
    JPN
  • ISSN
    0016-7630
  • NDL Article ID
    028833587
  • NDL Call No.
    Z15-174
  • Data Source
    NDL  J-STAGE 
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