Why do many inland earthquakes occur in the San-in shear zone where a few active faults exist.

2023 Fiscal Year Final Research Report

• Project/Area Number: 19H02000
• Research Category: Grant-in-Aid for Scientific Research (B)
• Allocation Type: Single-year Grants
• Section: 一般
• Review Section: Basic Section 17040:Solid earth sciences-related
• Research Institution: Kyoto University
• Principal Investigator: Nishimura Takuya 京都大学, 防災研究所, 教授 (90370808)
• Project Period (FY): 2019-04-01 – 2024-03-31
• Keywords: GNSS / 山陰地方 / ひずみ集中帯 / 地震 / テクトニクス / ひずみ分配 / 粘弾性緩和

Outline of Final Research Achievements

The detailed crustal deformation distribution around southwestern Japan centering on the San-in shear zone has been clarified through the installment of new GNSS stations and the integrated analysis of new and existing stations. The regional crustal deformation analysis reveals that the San-in shear zone is a block boundary that accommodates a part of the relative motion of the Amurian Plate and the Philippine Sea Plate, while the concentrated area of strain rate that is prominent in Tottori Prefecture is less prominent in western Shimane Prefecture. It suggests that the block boundary is offshore in this region. This suggests that the block boundary exists offshore in this region. Simulations of crustal deformation associated with the Nankai Trough earthquake cycle indicate that the effect of viscoelastic relaxation in the mantle is small in the latter half of the earthquake cycle because the effects of past large earthquakes and interplate locking cancel out each other.

Free Research Field

測地学

Academic Significance and Societal Importance of the Research Achievements

本研究の成果により、山陰ひずみ集中帯がアムールプレート安定部と西南日本の日本海側地域との間の運動学的なブロック境界であることがはっきりし、アムールプレートとフィリピン海プレートの相対運動の一部をまかなう変形帯であることが明らかになった。そのため、山陰ひずみ集中帯は、長期的にも内陸地震が多発する地帯であることがわかった。また、南海トラフ地震のプレート間固着の推定に、1990年代から現在までのGNSSによって観測された地殻変動を使う場合は、地下の媒質を弾性体と近似できることを示した。