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Strong ULVZ and Slab Interaction at the Northeastern Edge of the Pacific LLSVP Favors Plume Generation

Lai, Voon Hui and Helmberger, Don V. and Dobrosavljevic, Vasilije V. and Wu, Wenbo and Sun, Daoyuan and Jackson, Jennifer M. and Gurnis, Michael (2022) Strong ULVZ and Slab Interaction at the Northeastern Edge of the Pacific LLSVP Favors Plume Generation. Geochemistry, Geophysics, Geosystems, 23 (2). Art. No. e2021GC010020. ISSN 1525-2027. doi:10.1029/2021gc010020.

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Strong waveform complexities, including multipathing of the S diffracted phase and rapid changes in differential ScS-S times, are observed for multiple deep Fiji earthquakes recorded at the USArray. The complexities occur at the northeastern edge of the Pacific Large Low Shear Velocity Province (LLSVP), about 12 degrees southeast of present-day Hawaiʻi. Waveform modeling of the multipathing provides good constraints on an ultra-low velocity zone (ULVZ) with a width of 5 degree located near the inner edge of the LLSVP. Based on the mineralogical-modeling of the ULVZ as a solid iron-rich magnesiowüstite-bearing assemblage with compatible morphology predicted from geodynamical simulations, a ULVZ model with a thickness of 30 km and a shear wave velocity reduction of 18% is preferred. The rapid change in differential ScS-S travel time is best explained by having both the aforementioned ULVZ and an adjacent high velocity structure near the LLSVP. Furthermore, a low-velocity plume-like structure could potentially explain the observed S travel time delay independent of ScS. These seismic features are proposed to be a ULVZ driven toward the edge of the LLSVP while potentially pushed by a subducted slab. This configuration may trigger plume generation due to strong thermal instabilities and is in the same vicinity where mantle flow models place the present-day Hawaiian plume source. Multiple ScS can potentially be used to verify vertical plume structure in tomographic models but the accuracy of upper mantle structure, which is a key reflection point, needs to be considered.

Item Type:Article
Related URLs:
URLURL TypeDescription data
Lai, Voon Hui0000-0002-0738-0187
Dobrosavljevic, Vasilije V.0000-0002-3710-2188
Wu, Wenbo0000-0002-6249-8065
Sun, Daoyuan0000-0003-4461-4664
Jackson, Jennifer M.0000-0002-8256-6336
Gurnis, Michael0000-0003-1704-597X
Additional Information:© 2022 The Authors. This is an open access article under the terms of the Creative Commons Attribution-NonCommercial License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited and is not used for commercial purposes. Issue Online: 15 February 2022. Version of Record online: 15 February 2022. Accepted manuscript online: 07 February 2022. Manuscript accepted: 29 January 2022. Manuscript revised: 24 January 2022. Manuscript received: 08 July 2021. We thank the editorial team, Jerome Ritsema, Daniel Frost, and two anonymous reviewers for their constructive feedback. The project is supported by grant NSF-CSEDI-EAR-1161046 and 2009935. Data Availability Statement. Waveform data from USArray ( were obtained through Incorporated Research Institutions for Seismology (IRIS). Several plots were made using the Generic Mapping Tools version 4.2.1 (Wessel & Smith, 1998).
Group:Seismological Laboratory
Funding AgencyGrant Number
Subject Keywords:ULVZ; Pacific LLSVP; waveform modeling; body waves; magnesiowüstite; lowermost mantle
Issue or Number:2
Record Number:CaltechAUTHORS:20220309-676533000
Persistent URL:
Official Citation:Lai, V. H., Helmberger, D. V., Dobrosavljevic, V. V., Wu, W., Sun, D., Jackson, J. M., & Gurnis, M. (2022). Strong ULVZ and slab interaction at the northeastern edge of the Pacific LLSVP favors plume generation. Geochemistry, Geophysics, Geosystems, 23, e2021GC010020.
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:113822
Deposited By: George Porter
Deposited On:11 Mar 2022 20:35
Last Modified:11 Mar 2022 20:35

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