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Mantle flow geometry from ridge to trench beneath the Gorda–Juan de Fuca plate system

Nature Geoscience volume 8, pages 965–968 (2015)Cite this article

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Abstract

Tectonic plates are underlain by a low-viscosity mantle layer, the asthenosphere. Asthenospheric flow may be induced by the overriding plate or by deeper mantle convection1. Shear strain due to this flow can be inferred using the directional dependence of seismic wave speeds—seismic anisotropy. However, isolation of asthenospheric signals is challenging; most seismometers are located on continents, whose complex structure influences the seismic waves en route to the surface. The Cascadia Initiative, an offshore seismometer deployment in the US Pacific Northwest, offers the opportunity to analyse seismic data recorded on simpler oceanic lithosphere2. Here we use measurements of seismic anisotropy across the Juan de Fuca and Gorda plates to reconstruct patterns of asthenospheric mantle shear flow from the Juan de Fuca mid-ocean ridge to the Cascadia subduction zone trench. We find that the direction of fastest seismic wave motion rotates with increasing distance from the mid-ocean ridge to become aligned with the direction of motion of the Juan de Fuca Plate, implying that this plate influences mantle flow. In contrast, asthenospheric mantle flow beneath the Gorda Plate does not align with Gorda Plate motion and instead aligns with the neighbouring Pacific Plate motion. These results show that asthenospheric flow beneath the small, slow-moving Gorda Plate is controlled largely by advection due to the much larger, faster-moving Pacific Plate.

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Figure 1: Stacked splitting results determined by this study (red bars) and previous work (black bars; from refs 4,28).
Figure 2: Two distinct patterns in the variation of FSDs with distance from the trench.
Figure 3: Two-dimensional modelling to simulate mantle flow below the Gorda Plate as induced by motion of the Pacific Plate.

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Acknowledgements

Support for this work was provided by the National Science Foundation (OCE-1139701) to R.M.-S. and R.M.A. The data used in this research were provided by instruments from the Ocean Bottom Seismograph Instrument Pool (http://www.obsip.org), which is funded by the National Science Foundation under cooperative agreement OCE-1112722. The work benefited from discussions with J. Lodewyk, A. Frassetto and C. Eakin. GMT (Wessel and Smith27) and MATLAB were used to create the figures.

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Authors and Affiliations

  1. Department of Earth and Planetary Science, McCone Hall, UC Berkeley, California 94720, USA

    Robert Martin-Short, Richard M. Allen, Eoghan Totten & Mark A. Richards

  2. Department of Earth Science and Engineering, Royal School of Mines, Prince Consort Road, Imperial College London, London SW7 2BP, UK

    Ian D. Bastow & Eoghan Totten

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  1. Robert Martin-Short
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Contributions

This study was carried out and written up by R.M.-S., under supervision of R.M.A. I.D.B. assisted with data analysis and helped write the paper. E.T. and M.A.R. provided advice and minor modifications to the text.

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Correspondence to Robert Martin-Short.

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Martin-Short, R., Allen, R., Bastow, I. et al. Mantle flow geometry from ridge to trench beneath the Gorda–Juan de Fuca plate system. Nature Geosci 8, 965–968 (2015). https://doi.org/10.1038/ngeo2569

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