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The depth distribution of azimuthal anisotropy in the continental upper mantle


The most likely cause of seismic anisotropy in the Earth’s upper mantle is the lattice preferred orientation of anisotropic minerals such as olivine1,2. Its presence reflects dynamic processes related to formation of the lithosphere as well as to present-day tectonic motions. A powerful tool for detecting and characterizing upper-mantle anisotropy is the analysis of shear-wave splitting measurements. Because of the poor vertical resolution afforded by this type of data, however, it has remained controversial whether the splitting has a lithospheric origin that is ‘frozen-in’ at the time of formation of the craton3, or whether the anisotropy originates primarily in the asthenosphere, and is induced by shear owing to present-day absolute plate motions4. In addition, predictions from surface-wave-derived models are largely incompatible with shear-wave splitting observations5,6. Here we show that this disagreement can be resolved by simultaneously inverting surface waveforms and shear-wave splitting data. We present evidence for the presence of two layers of anisotropy with different fast-axis orientations in the cratonic part of the North American upper mantle. At asthenospheric depths (200–400 km) the fast axis is sub-parallel to the absolute plate motion, confirming the presence of shear related to current tectonic processes, whereas in the lithosphere (80–200 km), the orientation is significantly more northerly. In the western, tectonically active, part of North America, the fast-axis direction is consistent with the absolute plate motion throughout the depth range considered, in agreement with a much thinner lithosphere.

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Figure 1: Horizontal slices at three different depths showing azimuthal anisotropy in the North American upper mantle.
Figure 2: Difference in azimuth between the axis of fast propagation in model B and the present-day APM direction.
Figure 3: Comparison of observed and predicted SKS splitting measurements.
Figure 4: Results of four resolution tests designed to assess the ability of our data set to resolve several anisotropic layers.


  1. Nicolas, A. & Christensen, N. I. in Composition, Structure and Dynamics of the Lithosphere/Asthenosphere System (eds Fuchs, K. & Froidevaux, C.) Geodyn. Ser. 16, 111–123 (AGU, Washington DC, 1987)

    Book  Google Scholar 

  2. Babuška, V. & Cara, M. Seismic Anisotropy in the Earth (Kluwer Academic, Dordrecht, 1991)

    Book  Google Scholar 

  3. Silver, P. G. Seismic anisotropy beneath continents: probing the depth of geology. Annu. Rev. Earth Planet. Sci. 24, 385–421 (1996)

    ADS  CAS  Article  Google Scholar 

  4. Vinnik, L. P., Makeyeva, L. I., Milev, A. Y. & Usenko, A. Y. Global patterns of azimuthal anisotropy and deformations in the continental mantle. Geophys. J. Int. 111, 433–447 (1992)

    ADS  Article  Google Scholar 

  5. Montagner, J.-P., Griot-Pommera, D.-A. & Lavé, J. How to relate body wave and surface wave anisotropy? J. Geophys. Res. 105, 19015–19027 (2000)

    ADS  Article  Google Scholar 

  6. Debayle, E., Kennett, B. L. N. & Priestley, K. Global azimuthal seismic anisotropy and the unique plate-motion deformation of Australia. Science 433, 509–512 (2005)

    CAS  Google Scholar 

  7. Vinnik, L. P., Kosarev, G. L. & Makeyeva, L. I. Anisotropy of the lithosphere from the observations of SKS and SKKS. Proc. Acad. Sci. USSR [in Russian]. 278, 1335–1339 (1984)

  8. Montagner, J.-P. Upper mantle structure: global isotropic and anisotropic elastic tomography. Treat. Geophys. 1, (in the press).

  9. Gung, Y., Panning, M. & Romanowicz, B. Global anisotropy and the thickness of continents. Nature 422, 707–711 (2003)

    ADS  CAS  Article  Google Scholar 

  10. Marone, F., Gung, Y. & Romanowicz, B. 3D radial anisotropic structure of the North American upper mantle from inversion of surface waveform data. Geophys. J. Int. (submitted).

  11. Gripp, A. E. & Gordon, R. G. Young tracks of hotspots and current plate velocities. Geophys. J. Int. 150, 321–361 (2002)

    ADS  Article  Google Scholar 

  12. Smith, D. B., Ritzwoller, M. H. & Shapiro, N. M. Stratification of anisotropy in the Pacific upper mantle. J. Geophys. Res. 109 B11309 doi: 10.1029/2004JB003200 (2004)

    ADS  Article  Google Scholar 

  13. Tanimoto, T. & Anderson, D. L. Lateral heterogeneity and azimuthal anisotropy of the upper mantle: Love and Rayleigh waves 100–250 s. J. Geophys. Res. 90, 1842–1858 (1985)

    ADS  Article  Google Scholar 

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

    ADS  Article  Google Scholar 

  15. Simons, F., Van der Hilst, R., Montagner, J.-P. & Zielhuis, A. Multimode Rayleigh wave inversion for heterogeneity and azimuthal anisotropy of the Australian upper mantle. Geophys. J. Int. 151, 738–754 (2002)

    ADS  Article  Google Scholar 

  16. Fouch, M. J., Fischer, K. M., Parmentier, E. M., Wysession, M. E. & Clarke, T. J. Shear wave splitting, continental keels, and pattern of mantle flow. J. Geophys. Res. 105, 6255–6275 (2000)

    ADS  Article  Google Scholar 

  17. Rondenay, S., Bostock, M. G., Hearn, T. M., White, D. J. & Ellis, R. M. Lithospheric assembly and modification of the SE Canadian Shield: Abitibi-Grenville teleseismic experiment. J. Geophys. Res. 105, 13735–13754 (2000)

    ADS  Article  Google Scholar 

  18. Eaton, D., Frederiksen, A. & Miong, S.-K. Shear-wave splitting observations in the lower Great Lakes region: Evidence for regional anisotropic domains and keel-modified asthenospheric flow. Geophys. J. Lett. 31 L07610 doi: 10.1029/2004GL019438 (2004)

    ADS  Article  Google Scholar 

  19. Babuška, V., Montagner, J.-P., Plomerová, J. & Girardin, N. Age-dependent large-scale fabric of the mantle lithosphere as derived from surface-wave velocity anisotropy. Pure Appl. Geophys. 151, 257–280 (1998)

    ADS  Article  Google Scholar 

  20. Kay, I. et al. Shear wave splitting observations in the Archean Craton of Western Superior. Geophys. Res. Lett. 26, 2669–2672 (1999)

    ADS  Article  Google Scholar 

  21. Levin, V., Menke, W. & Park, J. No regional anisotropic domains in the northeastern U.S. Appalachians. J. Geophys. Res. 105, 19029–19042 (2000)

    ADS  Article  Google Scholar 

  22. Bokelmann, G. H. R. & Silver, P. G. Mantle variation within the Canadian Shield: travel times from the portable broadband Archean-Proterozoic transect 1989. J. Geophys. Res. 105, 579–605 (2000)

    ADS  Article  Google Scholar 

  23. Currie, C. A., Cassidy, J. F., Hyndman, R. D. & Bostock, M. G. Shear wave anisotropy beneath the Cascadia subduction zone and western North American craton. Geophys. J. Int. 157, 341–353 (2004)

    ADS  Article  Google Scholar 

  24. Gaherty, J. B. A surface wave analysis of seismic anisotropy beneath eastern North America. Geophys. J. Int. 158, 1053–1066 (2004)

    ADS  Article  Google Scholar 

  25. Li, X.-D. & Romanowicz, B. Comparison of global waveform inversions with and without considering cross branch coupling. Geophys. J. Int. 121, 695–709 (1995)

    ADS  Article  Google Scholar 

  26. Smith, M. L. & Dahlen, F. A. The azimuthal dependence of Love and Rayleigh waves propagation in a slightly anisotropic medium. J. Geophys. Res. 78, 3321–3333 (1973); correction. 80, 1923 (1975)

  27. Romanowicz, B. & Snieder, R. A new formalism for the effect of lateral heterogeneity on normal modes and surface waves, II. General anisotropic perturbations. Geophys. J. R. Astron. Soc. 93, 91–99 (1988)

    Article  Google Scholar 

  28. Larsen, E. W. F., Tromp, J. & Ekström, G. Effects of slight anisotropy on surface waves. Geophys. J. Int. 132, 654–666 (1998)

    ADS  Article  Google Scholar 

  29. Montagner, J.-P. & Nataf, H.-C. A simple method for inverting the azimuthal anisotropy of surface waves. J. Geophys. Res. 91, 511–520 (1986)

    ADS  Article  Google Scholar 

  30. Love, A. E. H. A Treatise on the Mathematical Theory of Elasticity (Cambridge Univ. Press, Cambridge, 1927)

    MATH  Google Scholar 

  31. Montagner, J.-P. & Anderson, D. L. Petrological constraints on seismic anisotropy. Phys. Earth Planet. Inter. 54, 82–105 (1989)

    ADS  Article  Google Scholar 

  32. Silver, P. G. & Savage, M. K. The interpretation of shear-wave splitting parameters in the presence of two anisotropic layers. Geophys. J. Int. 119, 949–963 (1994)

    ADS  Article  Google Scholar 

  33. Wolfe, J. W. & Silver, P. G. Seismic anisotropy of oceanic upper mantle: Shear wave splitting methodologies and observations. J. Geophys. Res. 103, 749–771 (1998)

    ADS  Article  Google Scholar 

  34. Rümpker, G. & Silver, P. G. Apparent shear-wave splitting parameters in the presence of vertically varying anisotropy. Geophys. J. Int. 135, 790–800 (1998)

    ADS  Article  Google Scholar 

  35. Panning, M. P. & Romanowicz, B. A three dimensional radially anisotropic model of shear velocity in the whole mantle. Geophys. J. Int. 167, 361–379 (2006)

    ADS  Article  Google Scholar 

  36. Mooney, W. D., Laske, G. & Masters, T. G. CRUST5.1: a global crustal model at 5°x 5°. J. Geophys. Res. 103, 727–747 (1998)

    ADS  CAS  Article  Google Scholar 

  37. Mégnin, C. & Romanowicz, B. The 3D shear velocity structure of the mantle from the inversion of body, surface and higher mode waveforms. Geophys. J. Int. 143, 709–728 (2000)

    ADS  Article  Google Scholar 

  38. Tarantola, A. & Valette, B. Generalized nonlinear inverse problems solved using the least squares criterion. Rev. Geophys. Space Phys. 20, 219–232 (1982)

    ADS  MathSciNet  Article  Google Scholar 

  39. Wang, Z. & Dahlen, F. A. Spherical-spline parameterization of three-dimensional Earth models. Geophys. Res. Lett. 22, 3099–3102 (1995)

    ADS  Article  Google Scholar 

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We thank IRIS-DMC, the Geological Survey of Canada and the Northern California Earthquake Data Center for distributing the data used in this study. This work was partially supported through an NSF grant and a grant from the Stefano Franscini Foundation (Switzerland).

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Correspondence to Barbara Romanowicz.

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This file contains Supplementary Data, Supplementary Methods, Supplementary Figures 1-8 with Legends, Supplementary Table 1 and additional references. (PDF 2555 kb)

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Marone, F., Romanowicz, B. The depth distribution of azimuthal anisotropy in the continental upper mantle. Nature 447, 198–201 (2007).

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