3-D synthetic modelling and observations of anisotropy effects on SS precursors: implications for mantle deformation in the transition zone

Huang, Quancheng, Schmerr, Nicholas C., Beghein, Caroline, Waszek, Lauren, and Maguire, Ross (2022) 3-D synthetic modelling and observations of anisotropy effects on SS precursors: implications for mantle deformation in the transition zone. Geophysical Journal International, 229 (2). pp. 1212-1231.

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Abstract

The Earth's mantle transition zone (MTZ) plays a key role in the thermal and compositional interactions between the upper and lower mantle. Seismic anisotropy provides useful information about mantle deformation and dynamics across the MTZ. However, seismic anisotropy in the MTZ is difficult to constrain from surface wave or shear wave splitting measurements. Here, we investigate the sensitivity to anisotropy of a body wave method, SS precursors, through 3-D synthetic modelling and apply it to real data. Our study shows that the SS precursors can distinguish the anisotropy originating from three depths: shallow upper mantle (80–220 km), deep upper mantle above 410 km, and MTZ (410–660 km). Synthetic resolution tests indicate that SS precursors can resolve ≥3 per cent azimuthal anisotropy where data have an average signal-to-noise ratio (SNR = 7) and sufficient azimuthal coverage. To investigate regional sensitivity, we apply the stacking and inversion methods to two densely sampled areas: the Japan subduction zone and a central Pacific region around the Hawaiian hotspot. We find evidence for significant VS anisotropy (15.3 ± 9.2 per cent) with a trench-perpendicular fast direction (93° ± 5°) in the MTZ near the Japan subduction zone. We attribute the azimuthal anisotropy to the grain-scale shape-preferred orientation of basaltic materials induced by the shear deformation within the subducting slab beneath NE China. In the central Pacific study region, there is a non-detection of MTZ anisotropy, although modelling suggests the data coverage should allow us to resolve at least 3 per cent anisotropy. Therefore, the Hawaiian mantle plume has not produced detectable azimuthal anisotropy in the MTZ.

Item ID: 73229
Item Type: Article (Research - C1)
ISSN: 1365-246X
Keywords: Composition and structure of the mantle; Numerical modelling; Body waves; Seismic anisotropy; Hotspots; Subduction zone processes
Copyright Information: This article has been accepted for publication in Geophysical Journal International ©: 2022 the Author(s) Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved. https://academic.oup.com/pages/self_archiving_policy_p
Funders: Australian Research Council (ARC)
Projects and Grants: ARC DE170100329
Research Data: https://doi.org/10.13016/3ecr-1hsu
Date Deposited: 21 Sep 2022 04:13
FoR Codes: 37 EARTH SCIENCES > 3706 Geophysics > 370609 Seismology and seismic exploration @ 100%
SEO Codes: 28 EXPANDING KNOWLEDGE > 2801 Expanding knowledge > 280107 Expanding knowledge in the earth sciences @ 100%
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