Change in paleo-stress and quantitative comparison between elastic strain and deformation fabrics in seismic cycles in subduction zone(Fostering Joint International Research)

2018 Fiscal Year Final Research Report

• Project/Area Number: 15KK0170
• Research Category: Fund for the Promotion of Joint International Research (Fostering Joint International Research)
• Allocation Type: Multi-year Fund
• Research Field: Geology
• Research Institution: Kochi University
• Principal Investigator: Hashimoto Yoshitaka 高知大学, 教育研究部自然科学系理工学部門, 教授 (40346698)
• Research Collaborator: Stipp Michael GEOMAR, Marine geodynamics, Research position
• Project Period (FY): 2015 – 2018
• Keywords: 沈み込み帯巨大地震 / 古応力

Outline of Final Research Achievements

The purpose of this project is to examine a change in paleo-stress orientation and to constrain a magnitude of paleo stress in oceanic accretionary prism. I conducted laboratory experiment in GEOMAR, Germany for one year to obtain soil mechanical behavior of sediments. Combining the physical property of sediments with the paleo-stress orientations from micro-fault inversions, we succeeded to constrain the magnitude of paleo-stress. We also identified the change in paleo-stress orientations which could be related to seismic cycles in subduction zone. My collaborators in Germany and I prepared the manuscript and submit it last year. Finally the manuscript was accepted in an International journal in the end of the last year. It was published in January this year.

Free Research Field

構造地質学

Academic Significance and Societal Importance of the Research Achievements

南海トラフ巨大地震の前後で変化すると期待される応力の履歴を地質学的に解明した。ドイツGEOMARで堆積物の圧密物性を室内実験で求めた。この圧密物性と古応力の方位を合わせることで、古応力の大きさの制約に成功した。また、古応力方位についても、地震サイクルに伴う変化が記録されていることが明らかとなった。すなわち地震時の逆断層は水平圧縮応力が大きく、地震後に応力が小さくなり、垂直圧縮応力ばに変化した記録が得られた。これは、過去の地震の規模を推定する新たな手法を開発したのみならず、将来の地震への切迫度の指標となりうるデータを提供する意義がある。