| Project/Area Number |
17K05623
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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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| Research Field |
Solid earth and planetary physics
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| Research Institution | Hokkaido University |
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Principal Investigator |
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| Project Period (FY) |
2017-04-01 – 2020-03-31
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| Project Status |
Completed (Fiscal Year 2019)
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| Budget Amount *help |
¥4,550,000 (Direct Cost: ¥3,500,000、Indirect Cost: ¥1,050,000)
Fiscal Year 2019: ¥1,170,000 (Direct Cost: ¥900,000、Indirect Cost: ¥270,000)
Fiscal Year 2018: ¥1,430,000 (Direct Cost: ¥1,100,000、Indirect Cost: ¥330,000)
Fiscal Year 2017: ¥1,950,000 (Direct Cost: ¥1,500,000、Indirect Cost: ¥450,000)
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| Keywords | 地球内部構造 / 地震波 / 不均質性 / 異方性 / リソスフェア / アセノスフェア / 上部マントル / 表面波 / トモグラフィー / 微細不均質性 |
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| Outline of Final Research Achievements |
The effects of fine-scale quasi-laminate heterogeneity in the upper mantle on surface wave phase speeds are investigated through numerical simulations of seismic wavefields. The results indicated that Rayleigh wave phase speeds could be reduced depending on the horizontal scale of the quasi-laminate heterogeneity and the strength of their velocity fluctuations. This indicates that the quasi-laminate heterogeneity can cause non-negligible apparent anisotropy in the lithosphere. We also developed a new method of trans-dimensional Bayesian inversion for high-resolution imaging of the upper mantle structure, incorporating multi-mode surface waves and P-wave receiver functions. The method has been applied to major permanent seismic stations in the Australian continent, and we could successfully detect multiple discontinuities in the upper mantle, including Mid-Lithosphere Discontinuities, Lithosphere-Asthenosphere Boundary and the Lehmann Discontinuity.
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| Academic Significance and Societal Importance of the Research Achievements |
地球表層における地震や火山活動の原動力となるプレートの進化やその運動を理解する上で，プレート内部やその下面であるリソスフェアーアセノスフェア境界に関する詳細な構造は極めて重要な情報となる．しかし，リソスフェア内部の微細不均質性や不連続面の空間分布とその成因，移動する大陸プレートの下面の状態などは未だ十分に明らかになっていない．ラミナ状不均質性が長周期の表面波伝播に与える影響は，トモグラフィーモデルの解釈の上で重要な情報であり，また，新たに開発した種々の地震波情報を統合したベイズ推定よる構造解析法は，上部マントルの高精度なイメージング研究の更なる発展の礎となる．
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