Low-velocity zone atop the 410-km seismic discontinuity in the northwestern United States


The seismic discontinuity at 410 km depth in the Earth's mantle is generally attributed to the phase transition of (Mg,Fe)2SiO4 (refs 1, 2) from the olivine to wadsleyite structure. Variation in the depth of this discontinuity is often taken as a proxy for mantle temperature owing to its response to thermal perturbations. For example, a cold anomaly would elevate the 410-km discontinuity, because of its positive Clapeyron slope, whereas a warm anomaly would depress the discontinuity. But trade-offs between seismic wave-speed heterogeneity and discontinuity topography often inhibit detailed analysis of these discontinuities, and structure often appears very complicated. Here we simultaneously model seismic refracted waves and scattered waves from the 410-km discontinuity in the western United States to constrain structure in the region. We find a low-velocity zone, with a shear-wave velocity drop of 5%, on top of the 410-km discontinuity beneath the northwestern United States, extending from southwestern Oregon to the northern Basin and Range province. This low-velocity zone has a thickness that varies from 20 to 90 km with rapid lateral variations. Its spatial extent coincides with both an anomalous composition of overlying volcanism and seismic ‘receiver-function’ observations observed above the region. We interpret the low-velocity zone as a compositional anomaly, possibly due to a dense partial-melt layer, which may be linked to prior subduction of the Farallon plate and back-arc extension. The existence of such a layer could be indicative of high water content in the Earth's transition zone.

Access options

Rent or Buy article

Get time limited or full article access on ReadCube.


All prices are NET prices.

Figure 1: Map of western US displaying samples of fine structure near the 410-km seismic discontinuity.
Figure 2: Modelled displacement waveforms (14–17°) with corresponding ray-paths and travel-time triplications.
Figure 3: Modelled velocity waveforms (21–24°) and receiver function profiles.


  1. 1

    Helffrich, G. Topography of the transition zone seismic discontinuity. Rev. Geophys. 38, 141–158 (2000)

    ADS  Article  Google Scholar 

  2. 2

    Shearer, P. M. et al. in Earth's Deep Interior: Mineral Physics and Tomography from the Atomic to the Global Scale (ed. Karato, S.-I.) 115 (AGU Geophys. Monogr, Vol. 117, Washington DC, 2000)

    Google Scholar 

  3. 3

    Gu, Y., Dziwonski, A. M. & Ekstrom, G. Simultaneous inversion for mantle velocity and topography of transition zone discontinuities. Geophys. J. Int. 154, 559–583 (2003)

    ADS  Article  Google Scholar 

  4. 4

    Flanagan, M. P. & Shearer, P. M. Global mapping of topography on transition zone velocity discontinuities by stacking SS precursors. J. Geophys. Res. 103, 2673–2692 (1998)

    ADS  Article  Google Scholar 

  5. 5

    Flanagan, M. P. & Shearer, P. M. Topography on the 410 km seismic velocity discontinuity near subduction zones from stacking of sS, sP, and pP precursors. J. Geophys. Res. 103, 21165–21182 (1998)

    ADS  Article  Google Scholar 

  6. 6

    Ramesh, D. S., Kind, R. & Yuan, X. Receiver function analysis of the North America crust and upper mantle. Geophys. J. Int. 150, 91–108 (2002)

    ADS  Article  Google Scholar 

  7. 7

    Gilbert, H. J., Sheehan, A. F., Dueker, K. G. & Molnar, P. Receiver functions in the western United States, with implications for upper mantle structure and dynamics. J. Geophys. Res. 109(B5), doi:10.1029/2001JB001194 (2003)

  8. 8

    Dueker, K. G. & Sheehan, A. F. Mantle discontinuity structure from midpoint stacks of converted P to S waves across the Yellowstone hotspot track. J. Geophys. Res. 102, 8313–8327 (1997)

    ADS  Article  Google Scholar 

  9. 9

    Saikia, C. K. Modified frequency-wave-number algorithm for regional seismograms using Filons quadrature-modeling of Lg waves in eastern North America. Geophys. J. Int. 118, 142–158 (1994)

    ADS  Article  Google Scholar 

  10. 10

    Grand, S. P. & Helmberger, D. V. Upper mantle shear structure of North America. Geophys. J. R. Astron. Soc. 76, 399–438 (1984)

    ADS  Article  Google Scholar 

  11. 11

    Kennett, B. L. N. & Bowman, J. R. The velocity structure and heterogeneity of the upper mantle. Phys. Earth Planet. Inter. 59, 134–144 (1990)

    ADS  Article  Google Scholar 

  12. 12

    Van der Lee, S. High-resolution estimates of lithospheric thickness from Missouri to Massachusetts, USA. Earth Planet. Sci. Lett. 203, 15–23 (2002)

    ADS  CAS  Article  Google Scholar 

  13. 13

    Hart, W. K., Aronson, J. L. & Mertzman, S. A. Areal distribution and age of low-K, high-alumina olivine tholeiite magmatism in the northwestern Great Basin. Geol. Soc. Am. Bull. 95, 186–195 (1984)

    ADS  CAS  Article  Google Scholar 

  14. 14

    Hart, W. K. Chemical and isotopic evidence for mixing between depleted and enriched mantle, northwestern USA. Geochim. Cosmochim. Acta 49, 131–144 (1985)

    ADS  CAS  Article  Google Scholar 

  15. 15

    Fitton, J. G., James, D. & Leeman, W. P. Basic magmatism associated with late Cenozoic extension in the western United States: Compositional variations in space and time. J. Geophys. Res. 96, 13693–13711 (1991)

    ADS  CAS  Article  Google Scholar 

  16. 16

    Kempton, P. D., Fitton, J. G., Hawkesworth, C. J. & Ormerod, D. S. Isotopic and trace element constraints on the composition and evolution of the lithosphere beneath the southwestern United States. J. Geophys. Res. 96, 13713–13735 (1991)

    ADS  CAS  Article  Google Scholar 

  17. 17

    Awater, T. & Stock, J. Pacific North America plate tectonics of the Neogene southwestern United States. Int. Geol. Rev. 40, 375–402 (1998)

    Article  Google Scholar 

  18. 18

    Sacks, I. S. & Snoke, J. A. The use of converted phases to infer the depth of the lithosphere-asthenosphere boundary beneath South America. J. Geophys. Res. 82, 2011–2017 (1977)

    ADS  Article  Google Scholar 

  19. 19

    Revenaugh, J. & Sipkin, S. A. Seismic evidence for silicate melt atop the 410-km mantle discontinuity. Nature 369, 474–476 (1994)

    ADS  CAS  Article  Google Scholar 

  20. 20

    Nolet, G. & Zielhuis, A. Low S velocities under the Tornquist-Teisseyre zone: evidence for water injection into the transition zone by subduction. J. Geophys. Res. 99, 15813–15820 (1994)

    ADS  Article  Google Scholar 

  21. 21

    Vinnik, L., Kumar, M. R., Kind, R. & Farra, V. Super-deep low-velocity layer beneath the Arabian plate. Geophys. Res. Lett. 30(1415), doi:10.1029/2002GL016590 (2003)

  22. 22

    Hammond, W. C. & Humphreys, E. D. Upper mantle seismic wave velocity: Effects of realistic partial melt geometries. J. Geophys. Res. 105, 10975–10986 (2000)

    ADS  Article  Google Scholar 

  23. 23

    Williams, Q. & Hemley, R. J. Hydrogen in the deep Earth. Annu. Rev. Earth Planet. Sci. 29, 365–418 (2001)

    ADS  CAS  Article  Google Scholar 

  24. 24

    Dixon, J. E., Leist, L., Langmuir, J. & Schilling, J.-G. Recycled dehydrated lithosphere observed in plume-influenced mid-ocean-ridge basalt. Nature 420, 385–389 (2002)

    ADS  CAS  Article  Google Scholar 

  25. 25

    Bercovici, D. & Karato, S. Whole-mantle convection and the transition-zone water-filter. Nature 425, 39–44 (2003)

    ADS  CAS  Article  Google Scholar 

  26. 26

    Stolper, E. M., Walker, D., Hager, B. H. & Hays, J. F. Melt segregation from partially molten source regions: the importance of melt density and source region size. J. Geophys. Res. 86, 6261–6271 (1981)

    ADS  CAS  Article  Google Scholar 

  27. 27

    Rigden, S. M., Ahrens, T. J. & Stolper, E. M. Densities of liquid silicates at high pressure. Science 226, 1071–1074 (1984)

    ADS  CAS  Article  Google Scholar 

  28. 28

    Agee, C. B. Crystal-liquid density inversions in terrestrial and lunar magmas. Phys. Earth Planet. Inter. 107, 63–74 (1998)

    ADS  CAS  Article  Google Scholar 

  29. 29

    Chen, G. Q., Ahrens, T. J. & Stolper, E. M. Shock-wave equation of state of molten and solid fayalite. Phys. Earth Planet. Inter. 134, 35–52 (2002)

    ADS  CAS  Article  Google Scholar 

  30. 30

    Angel, R. J., Frost, D. J., Ross, N. L. & Hemley, R. Stabilities and equations of state of dense hydrous magnesium silicates. Phys. Earth Planet. Inter. 127, 181–196 (2001)

    ADS  CAS  Article  Google Scholar 

Download references


We thank J. Ni, R. Aster, and the rest of the RISTRA team for the use of their data set, and we acknowledge all who have contributed to the PASSCAL arrays and IRIS DMC. We also thank H. Gilbert for providing receiver-function profiles. Reviews from D. Anderson, P. Asimow, T. Ahrens, B. Savage and M. Simons also helped to clarify early versions of this paper. We benefited from discussions with H. Gilbert, D. Anderson, H. Kanamori, Y. Tan, S. Ni and M. Gurnis. We thank L. Zhu for sharing his receiver function modelling code. This study was supported by the NSF and is a contribution to Division of Geological and Planetary Science, Caltech.

Author information



Corresponding author

Correspondence to Teh-Ru Alex Song.

Ethics declarations

Competing interests

The authors declare that they have no competing financial interests.

Supplementary information

Rights and permissions

Reprints and Permissions

About this article

Cite this article

Alex Song, T., Helmberger, D. & Grand, S. Low-velocity zone atop the 410-km seismic discontinuity in the northwestern United States. Nature 427, 530–533 (2004). https://doi.org/10.1038/nature02231

Download citation

Further reading


By submitting a comment you agree to abide by our Terms and Community Guidelines. If you find something abusive or that does not comply with our terms or guidelines please flag it as inappropriate.