Shear wave anisotropy beneath the volcanic front in South Kyushu area, Japan: Development of C-type olivine CPO under H2O-rich conditions
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Shear wave splitting from local intermediate-depth earthquakes is investigated to detect the anisotropic structure in the mantle wedge beneath the South Kyushu area, Japan. We observed shear wave splitting with NEE-SWW to NWW-SEE polarization directions and delay times of 0.04-0.63 s. Trench-normal shear wave polarization anisotropy with a delay time greater than 0.3 s probably overlaps in the high VP/VS region at a depth of 100-150 km beneath the volcanic front. Model calculations for the cause of the anisotropy suggest that the development of "C-type" olivine crystallographic preferred orientation (CPO) with a trench-parallel b axis concentration and a trench-normal a axis concentration best reproduces observations compared to A-, B-, or E-type olivine CPOs and antigorite CPO. We conclude that a thick anisotropic layer, approximately 50 km, is formed by concentration of interstitial fluid in peridotite. We briefly discuss the mechanism carrying water to the deep mantle wedge. A possible explanation is that interstitial fluids in the mantle wedge are effectively released because of a decrease in dihedral angles of olivine-fluid interfaces at 150 km depth. Our results imply a close relation between the high density of explosive volcanoes in the South Kyushu area and the underlying water-rich mantle. © 2013. American Geophysical Union. All Rights Reserved.
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- Journal of Geophysical Research B: Solid Earth
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Journal of Geophysical Research B: Solid Earth 118 (8), 4253-4264, 2013-01-01
American Geophysical Union (AGU)
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詳細情報 詳細情報について
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- CRID
- 1390857757584881664
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- NII論文ID
- 120005349163
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- NII書誌ID
- AA10522493
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- ISSN
- 01480227
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- Web Site
- http://hdl.handle.net/2297/36262
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- 本文言語コード
- en
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- データソース種別
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- JaLC
- IRDB
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