| Project/Area Number |
63540298
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| Research Category |
Grant-in-Aid for General Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Research Field |
固体地球物理学
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| Research Institution | University of Toyama |
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Principal Investigator |
KAWASAKI Ichiro Toyama Univ., Earth Sci., Assoc. Prof., 理学部, 助教授 (60115136)
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| Co-Investigator(Kenkyū-buntansha) |
MATSUMURA Isamu Kanazawa Univ. of Economics, Lecturer, 経済学部, 講師 (70173862)
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| Project Period (FY) |
1988 – 1990
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| Project Status |
Completed (Fiscal Year 1991)
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| Budget Amount *help |
¥2,000,000 (Direct Cost: ¥2,000,000)
Fiscal Year 1990: ¥500,000 (Direct Cost: ¥500,000)
Fiscal Year 1989: ¥500,000 (Direct Cost: ¥500,000)
Fiscal Year 1988: ¥1,000,000 (Direct Cost: ¥1,000,000)
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| Keywords | Surface waves / Dispersion curve / Rayleigh-Love wave coupling / Pacific ocean / Upper mantle / Low velocity zone / Tomography / Azimuthal anisotropy / 位相速度 / 海洋マントル / 2点法 / トモグラフィ / レ-リ-・ラブカップリング / 表面波 / 異方性 |
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| Research Abstract |
Azimuthal anisotropy of seismic wave propagation velocity in the oceanic mantle has been supposed to be a fossil tracer of paleo-plate spreading direction and an indication of mechansim of the upper mantle low velocity zone (Kawasaki et al., 1989). We have taken following steps to investigate this issue by an analysis of seismic surface waves.
We have rewritten the equations of motion and Hookean low of an elastic body in an orthogonal curvilinear coordinates. With this representation, we have become to be able to obtain eigenvalues (phase velocities) of surface waves in an azimuthally anisotropic medium by conventional integration method (called y-method in seismology). Based on this new method, we have first demonstrated how Rayleigh-Love wave coupling takes place on the GDSN degital long period seismic records of surface waves propagating in the eastern Pacific ocean due to the anisotropy. This seems to be the first direct observation of seismic nature of upper mantle anisotropy.
Sakai and Kawasaki (1990) investigated how seismic anisotropy effect travel times and amplitudes of body waves and how surface wave velocities are related with those of body waves propagating in an anisotropic media. Yoshida and Kawasaki (1991) checked the trade-off relation between seismic wave velocity and density in the surface wave inversions. They suggested a possibility that density in the middle part of the low velocity zone around 100 km depth could be larger than that of oceanic plate.
In Kawasaki et al. (1989) and Kawasaki (1991), we presented our results excluding theoretical part of this research project on wave propagation and discussed future perspectives along the line of this study.
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