Ward, J, Nowacki, A orcid.org/0000-0001-7669-7383 and Rost, S orcid.org/0000-0003-0218-247X (2020) Lateral Velocity Gradients in the African Lower Mantle Inferred From Slowness Space Observations of Multipathing. Geochemistry, Geophysics, Geosystems, 21 (8). e2020GC009. ISSN 1525-2027
Abstract
Large low‐velocity provinces (LLVPs) are hypothesized to be purely thermal features or possess some chemical heterogeneity but which exactly remains ambiguous. Regional seismology studies typically use travel time residuals and multipathing identification in the waveforms to infer properties of LLVPs. These studies have not fully analyzed all available information such as measuring the direction and inclination of the arrivals. These measurements would provide more constraints of LLVP properties such as the boundary velocity gradient and help determine their nature. Here, we use array seismology to measure backazimuth (direction) and horizontal slowness (inclination) of arriving waves to identify structures causing multipathing and wavefield perturbation. Following this, we use full‐wavefield forward modeling to estimate the gradients required to produce the observed multipathing. We use SKS and SKKS data from 83 events sampling the African LLVP, which has been extensively studied providing a good comparison to our observations. We find evidence for structures at heights of up to 600 km above the core‐mantle boundary causing multipathing and wavefield perturbation. Forward modeling shows gradients of up to 0.7% δ V s per 100 km (0.0005 km s−1 km−1) can produce multipathing with similar backazimuth and horizontal slowness to our observations. This is an order of magnitude lower than the previous strongest estimates of −3% δ V s per 50 km (0.0044 km s−1 km−1). As this is lower than that predicted for both thermal and thermochemical structures, lateral velocity gradients capable of producing multipathing are not necessarily evidence for a thermochemical nature.
Metadata
Item Type: | Article |
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Authors/Creators: |
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Copyright, Publisher and Additional Information: | © 2020, The Authors. This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.To view a copy of this license, visit http://creativecommons.org/licenses/by/4.0/. |
Keywords: | Lower mantle; Array seismology; Multipathing |
Dates: |
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Institution: | The University of Leeds |
Academic Units: | The University of Leeds > Faculty of Environment (Leeds) > School of Earth and Environment (Leeds) > Inst of Geophysics and Tectonics (IGT) (Leeds) |
Funding Information: | Funder Grant number NERC (Natural Environment Research Council) NE/R001154/1 |
Depositing User: | Symplectic Publications |
Date Deposited: | 21 Jul 2020 14:10 |
Last Modified: | 11 Aug 2020 11:20 |
Status: | Published |
Publisher: | American Geophysical Union |
Identification Number: | 10.1029/2020GC009025 |
Open Archives Initiative ID (OAI ID): | oai:eprints.whiterose.ac.uk:163480 |