Unbending Hypothesis for Water Upwelling at the Subduction Zone

2023 Fiscal Year Final Research Report

• Project/Area Number: 19K21892
• Research Category: Grant-in-Aid for Challenging Research (Exploratory)
• Allocation Type: Multi-year Fund
• Review Section: Medium-sized Section 17:Earth and planetary science and related fields
• Research Institution: The University of Tokyo
• Principal Investigator: KAWAKATSU Hitoshi 東京大学, 地震研究所, 名誉教授 (60242153)
• Co-Investigator(Kenkyū-buntansha): 悪原 岳 東京大学, 地震研究所, 助教 (30802954)
• Project Period (FY): 2019-06-28 – 2024-03-31
• Keywords: 沈み込み / スラブ / 海底地震観測 / レシーバー関数 / 地震波トモグラフィー / 海洋堆積層

Outline of Final Research Achievements

By focusing on the dynamics of the lower half of the oceanic plate (slab) with a thickness of ~80 km and the mantle beneath the slab, we determined the seismic wave velocity structure of the oceanic plate subducting beneath the Tohoku Japan Arc from the vicinity of the Japan Trench. This was achieved by analyzing data from a dense seismic observation network deployed on both land and sea bottom. As a result, we succeeded in continuously imaging the oceanic Moho surface in the upper part of the slab, extending from beneath the seafloor to beneath the land. On the other hand, we were unable to elucidate the structure of the lower part of the slab. We identified the cause as multiple reflections within the oceanic sedimentary layer and developed a method to determine the fine structure of the sedimentary layer using seafloor seismic observations. By incorporating these results into future analyses, it is anticipated that the originally intended deeper structure will be elucidated.

Free Research Field

固体地球科学

Academic Significance and Societal Importance of the Research Achievements

日本列島太平洋岸を含む沈み込み帯浅部では，海溝型の巨大地震が発生することが知られている．ひとが生活する陸域から地震の発生する海洋下までの地球内部の地震学的構造を連続的に解明することは，地震動伝搬の予測にもつながる社会的にも意義がある基本的な学術課題である．海洋堆積層は，海底地震計を設置する海洋底ではどこにも存在し，構造推定への影響を明らかにし補正手法を提示したこと，また海洋堆積層の微細構造を決定する手法を開発したことは，今後の当該学術分野の発展の基盤になることが期待される．