2023 Fiscal Year Final Research Report
Estimating the 3-D tectonic stress fields in and around the Japanese Islands
| Project/Area Number |
18K03801
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| Research Category |
Grant-in-Aid for Scientific Research (C)
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| Allocation Type | Multi-year Fund |
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| Section | 一般 |
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| Review Section |
Basic Section 17040:Solid earth sciences-related
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| Research Institution | Nagoya University |
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Principal Investigator |
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| Project Period (FY) |
2018-04-01 – 2024-03-31
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| Keywords | 地震 / 応力場 / 弾性歪エネルギー / 応力インバージョン |
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| Outline of Final Research Achievements |
We investigated the deviatoric stress magnitude of background stress fields before the 2016 Kumamoto earthquake sequence in Japan, based on the temporal changes in elastic strain energies caused by the mainshock (dE) and the coseismic stress rotation.We modelled six components of background stress fields from stress orientation together with the effective friction coefficients (m’ = 0.3, 0.15, 0.1, 0.05, 0.03), using the 3-D Mohr diagram. By combining coseismic stress changes fields with them, we also computed the absolute stress fields after the largest foreshock and the mainshock of the sequence. Considering the energy balance, dE must be larger than the radiated energy. We also examined the compatibility of the focal mechanisms of aftershocks with the stress fields after the mainshock. We concluded that that the effective friction coefficient in the crust is much larger than that estimated in previous studies
(m' < 0.1).
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| Free Research Field |
地震学
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| Academic Significance and Societal Importance of the Research Achievements |
地震は地下に蓄えられた応力を断層運動により解放する物理過程であり，応力状態を把握することは地震の発生を理解するうえで重要である．しかし，応力は，直接測定することの難しい物理量であり，震源域の応力レベルに関しては統一的な見解が得られていない．本研究は，2016年熊本地震震源域を対象に，独自の視点により応力場を実効摩擦係数をパラメータとしてモデル化し，本震前後の様々な物理量の変化のモデル依存性と，観測データから得られる情報を手掛かりに，地震発生域の応力状態を推定することに成功した．推定した実効摩擦係数の値は，従来考えられてきたものより有意に大きいことが分かり，大きな進展をもたらした．
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