Mantle anisotropy beneath the Izu-Bonin and Mariana subduction zones
| Autor: | Li-Chen Hsu, 徐立宸 |
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| Rok vydání: | 2018 |
| Druh dokumentu: | 學位論文 ; thesis |
| Popis: | 106 Understanding the mechanism of plate subduction helps us put together a whole picture of how the mantle works under plate tectonics. The sub-slab seismic anisotropy serves as a direct tool for illuminating subduction dynamics, implying the flow direction and deformation patterns of subducting slabs. We measured source-side shear wave splitting with receiver-side correction for the Izu-Bonin and Mariana subduction zones, and find different fast direction (ϕ) patterns of these two regions. Trench parallel fast splitting directions dominate beneath the Mariana slab except for shallow events, while the fast directions of Izu-Bonin seem to be random with respect to the slab contour. The delay times (δt) of the two regions are ~ 2 seconds in average, maximum value may up to ~ 3 seconds. The variations of splitting parameters with S wave initial polarizations in Izu-Bonin region implies the sub-slab anisotropy materials more complex than a single anisotropic layer. A forward approach shows that a two-layer structure better explains the splitting observations than a single anisotropic layer. In Izu-Bonin, these splitting parameters are mainly at transition zone depths, suggest the presence of anisotropy at transition zone and lower mantle. Combined with the deformation-induced crystallographic preferred orientation (CPO) evidences, the wadsleyite and bridgmanite may cause the two-layer anisotropy at midmantle beneath Izu-Bonin. |
| Databáze: | Networked Digital Library of Theses & Dissertations |
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