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The unique anisotropy of the Pacific upper mantle

Abstract

The development and interpretation of tomographic models of the Earth's mantle have usually proceeded under the assumption that fast and slow seismic velocity anomalies represent a spatially heterogeneous temperature field associated with mantle convection. Implicit in this approach is an assumption that either the effect of anisotropy on seismic velocities is small in comparison with isotropic thermal or compositional effects, or that the tomographic results represent the average isotropic heterogeneity, even if individual seismic observations are affected by anisotropic structure. For example, velocity anomalies in the upper portions of the oceanic mantle are commonly interpreted in terms of the progressive cooling1,2 (and localized reheating3) of amechanical and thermal boundary layer consisting of rigid oceanic lithosphere and an underlying, less viscous, asthenosphere. Here, however, we present results from a global three-dimensional tomographic model of shear-wave velocity which shows that the uppermost mantle beneath the central Pacific Ocean is considerably more complicated than this simple model. Over a broad area, with its centre near Hawaii, the seismic data reveal a regional anomaly in elastic anisotropy which produces variations of seismic velocities that are at least as large as those due to thermal effects. Because seismic anisotropy is an indicator of strain in Earth materials, our tomographic results canbe used to put constraints on both buoyancy forces (thermal effects) and flow patterns in the upper mantle.

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Figure 1: Maps showing the velocity variations in the model S20A at 50, 100, and 150?km depth.
Figure 2: Velocity profiles of the shear-wave velocities VSV and VSH.
Figure 3: Shear-wave velocity variations beneath the Pacific plate at 150?km depth.

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References

  1. Zhang, Y.-S. & Tanimoto, T. Ridges, hotspots and their interaction as observed in seismic velocity maps. Nature 355, 45–49 (1992).

    Article  ADS  Google Scholar 

  2. Su, W.-J., Woodward, R. L. & Dziewonski, A. M. Deep origin of mid-ocean-ridge seismic velocity anomalies. Nature 359, 149–152 (1992).

    Article  ADS  Google Scholar 

  3. McNutt, M. K. & Superswells. Rev. Geophys. Space Phys. (in the press).

  4. Ekström, G. & Dziewonski, A. M. Improved models of upper mantle S velocity structure. (abstr.) EOS 76(46), F421 (1995).

    Google Scholar 

  5. Su, W.-J., Woodward, R. L. & Dziewonski, A. M. Degree-12 model of shear velocity heterogeneity in the mantle. J. Geophys. Res. 99, 4945–4980 (1994).

    Google Scholar 

  6. Masters, G., Johnson, S., Laske, G. & Bolton, H. Ashear-velocity model of the mantle. Phil. Trans. R. Soc. Lond. A 354, 1385–1411 (1996).

    Article  ADS  Google Scholar 

  7. Li, X.-D. & Romanowicz, B. Global mantle shear velocity model developed using nonlinear asymptotic coupling theory. J. Geophys. Res. 101, 22245–22272 (1996).

    Article  ADS  Google Scholar 

  8. Nataf, H. C., Nakanishi, I. & Anderson, D. L. Anisotropy and shear-velocity heterogeneities in the upper mantle. Geophys. Res. Lett. 11, 109–112 (1984).

    Article  ADS  Google Scholar 

  9. Nataf, H. C., Nakanishi, I. & Anderson, D. L. Measurements of mantle wave velocities and inversion for lateral heterogeneities and anisotropy. J. Geophys. Res. 91, 7261–7307 (1986).

    Article  ADS  Google Scholar 

  10. Montagner, J.-P. & Tanimoto, T. Global anisotropy in the upper mantle inferred from the regionalization of phase velocities. J. Geophys. Res. 95, 4797–4819 (1990).

    Article  ADS  Google Scholar 

  11. Montagner, J.-P. & Tanimoto, T. Global upper mantle tomography of seismic velocities and anisotropies. J. Geophys. Res. 96, 20337–20351 (1991).

    Article  ADS  Google Scholar 

  12. McEvilly, T. V. Central US crust-upper mantle structure from Love and Rayleigh wave phase velocity inversion. Bull. Seismol. Soc. Am. 54, 1997–2015 (1964).

    Google Scholar 

  13. Forsyth, D. W. The early structural evolution and anisotropy of the oceanic upper mantle. Geophys. J. R. Astron. Soc. 43, 103–162 (1975).

    Article  ADS  Google Scholar 

  14. Mitchell, B. J. & Yu, G.-K. Surface wave dispersion, regionalized velocity models, and anisotropy of the Pacific crust and upper mantle. Geophys. J. R. Astron. Soc. 63, 497–514 (1980).

    Article  ADS  Google Scholar 

  15. Gee, L. S. & Jordan, T. H. Polarization anisotropy and fine-scale structure of the Eurasian upper mantle. Geophys. Res. Lett. 15, 824–827 (1988).

    Article  ADS  Google Scholar 

  16. Gaherty, J. B., Jordan, T. H. & Gee, L. S. Seismic structure of the upper mantle in a central Pacific corridor. J. Geophys. Res. 101, 22291–22309 (1996).

    Article  ADS  Google Scholar 

  17. Nishimura, C. E. & Forsyth, D. W. Rayleigh wave phase velocities in the Pacific with implications for azimuthal anisotropy and lateral heterogeneities. Geophys. J. R. Astron. Soc. 94, 479–501 (1988).

    Article  Google Scholar 

  18. Nishimura, C. E. & Forsyth, D. W. The anisotropic structure of the upper mantle in the Pacific. Geophys. J. R. Astron. Soc. 96, 203–229 (1989).

    Article  Google Scholar 

  19. Dziewonski, A. M. & Anderson, D. L. Preliminary reference Earth model. Phys. Earth Planet. Inter. 25, 297–356 (1981).

    Article  ADS  Google Scholar 

  20. Lévêque, J. J. & Cara, M. Long-period Love wave overtone data in North America and the Pacific Ocean: new evidence for upper mantle anisotropy. Phys. Earth Planet. Inter. 33, 164–179 (1983).

    Article  ADS  Google Scholar 

  21. Gaherty, J. B., Kato, M. & Jordan, T. H. Seismological structure of the upper mantle: A regional comparison of seismic layering. Phys. Earth Planet. Inter. (submitted).

  22. Mitchell, B. J. On the inversion of Love and Rayleigh wave dispersion and implications for earth structure and anisotropy. Geophys. J. R. Astron. Soc. 76, 233–241 (1984).

    Article  ADS  Google Scholar 

  23. Regan, J. & Anderson, D. L. Anisotropic models of the upper mantle. Phys. Earth Planet. Inter. 35, 227–263 (1984).

    Article  ADS  Google Scholar 

  24. Birch, F. The velocity of compressional waves in rocks to 10 kilobars. J. Geophys. Res. 65, 1083–1102 (1960).

    Article  ADS  Google Scholar 

  25. Nicolas, A. & Christensen, N. I. in Composition, Structure, and Dynamics of Lithosphere-Asthenosphere System (eds Fuchs, K. & Froidevaux, C.) 111–123 (Geodyn. Ser. Vol. 16, Am. Geophys. Union, Washington DC, (1987)).

    Book  Google Scholar 

  26. Ribe, N. M. Seismic anisotropy and mantle flow. J. Geophys. Res. 94, 4213–4223 (1989).

    Article  ADS  Google Scholar 

  27. Parsons, B. & McKenzie, D. Mantle convection and the thermal structure of the plates. J. Geophys. Res. 83, 4485–4496 (1978).

    Article  ADS  Google Scholar 

  28. Dziewonski, A. M., Ekström, G. & Liu, X.-F. in Monitoring a Comprehensive Test Ban Treaty (eds Husebye, E. S. & Dainty, A. M.) 521–550 (Kluwer Academic, Dordrecht, (1996)).

    Book  Google Scholar 

  29. Woodhouse, J. H. & Dziewonski, A. M. Mapping the upper mantle: Three dimensional modeling of Earth structure by inversion of seismic waveforms. J. Geophys. Res. 89, 5953–5986 (1984).

    Article  ADS  Google Scholar 

  30. Ekström, G., Tromp, J. & Larson, E. W. F. Measurements and global models of surface wave propagation. J. Geophys. Res. 102, 8317–8157 (1997).

    Article  ADS  Google Scholar 

  31. Love, A. E. H. A Treatise on the Theory of Elasticity4th edn (Cambridge Univ., (1927)).

    MATH  Google Scholar 

  32. Takeuchi, H. & Saito, M. Seismic surface waves. Methods Comput. Phys. 11, 217–295 (1972).

    Google Scholar 

  33. Mooney, W. D., Laske, G. & Masters, G. CRUST-5.1: A global crustal model at 5° × 5°. J. Geophys. Res. 103, 727–747 (1998).

    Article  ADS  CAS  Google Scholar 

Download references

Acknowledgements

The data used in this work were obtained from the IRIS, GDSN, IDA, GEOSCOPE, MEDNET, CDSN and GTSN seismograph networks. We thank D. Forsyth, J. Gaherty, J. Phipps Morgan, G. Smith and C. Wolfe for discussions, and X.-F. Liu, S. Sianissian and W.-J. Su for help with collecting and preparing the data sets. This work was supported by the US NSF and the US Air Force Office for Scientific Research.

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Correspondence to Göran Ekström.

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Ekström, G., Dziewonski, A. The unique anisotropy of the Pacific upper mantle. Nature 394, 168–172 (1998). https://doi.org/10.1038/28148

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