Constraints on Seismic Anisotropy in the Mantle Transition Zone from Long-Period SS Precursors

dc.contributor.advisorSchmerr, Nicholas
dc.contributor.authorHuang, Quancheng
dc.contributor.authorSchmerr, Nicholas
dc.contributor.authorWaszek, Lauren
dc.contributor.authorBeghein, Caroline
dc.date.accessioned2019-05-02T15:20:49Z
dc.date.available2019-05-02T15:20:49Z
dc.date.issued2019
dc.description.abstractThe mantle transition zone (MTZ) of Earth is demarcated by solid-to-solid phase changes of the mineral olivine that produce seismic discontinuities at 410 and 660 km depths. Mineral physics experiments predict that wadsleyite can have strong single-crystal anisotropy at the pressure and temperature conditions of the MTZ. Thus, significant seismic anisotropy is possible in the upper MTZ where lattice preferred orientation (LPO) of wadsleyite is produced by mantle flow. Here, we use a body wave method, SS precursors, to study the topography change and seismic anisotropy near the MTZ discontinuities. We stack the data to explore the azimuthal dependence of travel times and amplitudes of SS precursors, and constrain the azimuthal anisotropy in the MTZ. Beneath the central Pacific, we find evidence for ~4% anisotropy with a SE fast direction in the upper mantle, and no significant anisotropy in the MTZ. In subduction zones, we observe ~4% anisotropy with a trench-parallel fast direction in the upper mantle, and ~3% anisotropy with a trench-perpendicular fast direction in the MTZ. The transition of fast directions indicates that the LPO of wadsleyite induced by MTZ flow is organized separately from the flow in the upper mantle. Global azimuthal stacking reveals ~1% azimuthal anisotropy in the upper mantle, but negligible anisotropy (< 1%) in the MTZ. Finally, we correct for the upper mantle and MTZ anisotropy structures to obtain a new MTZ topography model. The anisotropy correction produces ±3 km difference, and therefore has minor overall effects on global MTZ topography.en_US
dc.description.sponsorshipNational Science Fundation (NSF) grant EAR-1447041en_US
dc.identifierhttps://doi.org/10.13016/3ecr-1hsu
dc.identifier.urihttp://hdl.handle.net/1903/21819
dc.language.isoen_USen_US
dc.relation.isAvailableAtDigital Repository at the University of Maryland
dc.relation.isAvailableAtUniversity of Maryland (College Park, Md)
dc.subjectMantle Transition Zoneen_US
dc.subjectSeismic Anisotropyen_US
dc.subjectMantle Flowen_US
dc.subjectTopographyen_US
dc.subjectSS Precursorsen_US
dc.titleConstraints on Seismic Anisotropy in the Mantle Transition Zone from Long-Period SS Precursorsen_US
dc.typeArticleen_US

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MTZ_410_depth.txt
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Depth of 410 km discontinuity
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MTZ_660_depth.txt
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Depth of 660 km discontinuity
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MTZ_thickness.txt
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The thickness of mantle transition zone
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SKS_MTZ_YB13SVani.txt
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MTZ anisotropy model calculated from YB13SVani model
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SKS_UUM_YB13SVani.txt
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Upper mantle anisotropy model calculated from YB13SVani model