| Project/Area Number |
14540395
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| Research Category |
Grant-in-Aid for Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
固体地球物理学
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| Research Institution | KYOTO UNIVERSITY |
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Principal Investigator |
KUGE Keiko KYOTO UNIVERSITY, Graduate School of Science, Associate Professor, 大学院・理学研究科, 助教授 (50234414)
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| Project Period (FY) |
2002 – 2003
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| Project Status |
Completed (Fiscal Year 2003)
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| Budget Amount *help |
¥2,300,000 (Direct Cost: ¥2,300,000)
Fiscal Year 2003: ¥900,000 (Direct Cost: ¥900,000)
Fiscal Year 2002: ¥1,400,000 (Direct Cost: ¥1,400,000)
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| Keywords | continental lithosphere / East Antarctica / velocity structure / thermal structure / depleted mantle / chemical composition / 南極大陸 / 上部マントル / 地震波速度 / プレート / 温度 / 組成 / 地殻 |
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| Research Abstract |
In broadband seismograms from shallow earthquakes occurring south of New Zealand recorded at the South Pole, we found significant arrivals 40-70 s after the first SH arrivals at distances of 29°-35°and 20-50 s after the first P arrivals at distances of 28°-35°. These waves traversing beneath East Antarctica can be modeled by slightly modifying one-dimensional P and S wave velocity structures of the Canadian shield. In the obtained velocity models, a velocity reduction below the lithosphere forms a deep low-velocity zone. S waves turning below the low-velocity zone explain the SH waveforms observed at 29°-55°. The observed P waveforms, however, suggest that a corresponding reduction in P velocity is smaller. These P and S wave velocity variations are likely to be a manifestation of a depleted continental lithosphere (high concentrations of olivine and Mg#). For a lithospheric composition more depleted than that of the underlying mantle, the temperature profile estimated from our velocity models is smooth from the lithosphere to the underlying mantle. Lithospheric depletion can also explain that the velocity anomaly in the lithosphere is larger for S than for P waves. Were the composition to be assumed uniform throughout the upper mantle, a large temperature gradient would be required at the bottom of the lithosphere, implying a heat sink which is unlikely to be sustainable. Thus, a difference in composition between the lithosphere and underlying mantle leads to a reasonable estimate of temperature profile that is consistent with the observed seismic waveforms.
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