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SUPPLEMENTARY INFORMATIONdoi: 10.1038/ngeo969

nature geoscience | www.nature.com/naturegeoscience 1

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Seismic evidence for a global low velocity layer within the Earth’s

upper mantle

SUPPLEMENTARY MATERIAL

Benoît Tauzin1, Eric Debayle2 & Gérard Wittlinger3

1Department of Earth Sciences, Utrecht University, P.O. Box 80.021, 3508 TA Utrecht,

The Netherlands

2Laboratoire de Sciences de la Terre, Université de Lyon I, CNRS and Ecole Normale

Supérieure de Lyon, UMR5570, F-69622 Villeurbanne, France

3Ecole et Observatoire des Sciences de la Terre, UMR-CNRS 7516, 5 rue René

Descartes, 67084 Strasbourg Cedex, France

2 nature geoscience | www.nature.com/naturegeoscience

SUPPLEMENTARY INFORMATION doi: 10.1038/ngeo969

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Supplementary Figure S1

Global map showing previous observations of a low-velocity layer atop the 410-

km discontinuity. Outlined red stars are data from P-to-S conversions (Ps) at

individual stations1,2. Red stars are data from S-to-P conversions (Sp) at

individual stations3. Observations from ScS reverberations4-6 are indicated in

green. Observations from a joint study of Ps and S-wave triplications7 are

indicated in blue. Ps and Sp array observations8-11 are indicated in red.



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Observed (left) and synthetic (right) receiver functions computed for the 89

stations of Fig. 1a in four period ranges: 10-75 s (panels A, E), 7-75 s (panels

B, F), 5-75 s (panels C, G) and 3-75 s (panels D, H). The left and right columns

of this figure are equivalent to Fig. 2c and 2d except that the different period

ranges are shown separately. The facts that (i) there is no symmetric side lobe

underneath the "410" and (ii) using different filters does not change the position

of the negative signal, suggest that the negative signal near 350 km depth is not

a side lobe of the P410s.



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Receiver functions filtered in the 7-75 s period range and recorded in North

America (NA), Europe (EU), Asia (AS), South America and Africa (SA+AF),

Australia and Antarctica (AU+AN) and in oceanic regions (OC). (A) Stations

with a negative signal atop the “410”. (B) Stations with no significant signal atop

the “410“.


SUPPLEMENTARY INFORMATIONdoi: 10.1038/ngeo9695�


Global map of the LVL atop the “410“ discontinuity. Stations where the LVL is

detected are shown with red stars. Our strongest observations (see Method

section) are outlined with red circles. Black triangles indicate stations where the

LVL is not observed. Blue patches show the approximate locations of

subduction zones in the transition zone, as indicated by the +0.5% shear wave

velocity anomaly at 600 km depth in global S-wave tomography12. Large

igneous provinces13 are shown in orange and red dots indicate hotspot

locations14.



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Receiver functions filtered in the 7-75 s period range and sorted according to

three a priori geodynamical provinces: "subduction"12, "hotspots and large

igneous provinces (LIPS)"13,14 and "normal mantle" (i.e regions located away

from hotspots, LIPs and subduction zones). (A) Stations with a negative signal

atop the “410“. (B) Stations with no significant signal atop the “410“.



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Receiver functions filtered in the 7-75 s period range for different continental

provinces15: Archean, Proterozoic and Phanerozoic. (A) Stations with a

negative signal atop the “410“. (B) Stations with no significant signal atop the

“410“.



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Stacked waveforms obtained in four period ranges (3-75 s; 5-75 s; 7-75 s; 10-

75 s) for synthetic16 receiver functions computed in the IASP9117 velocity model

and for data recorded at BOSA (South Africa), ARU (Russia) and MAJO

(Japan). "Robust" negative amplitudes (beyond the -2σ(t) level given by

bootstrap resampling18) recorded at BOSA, ARU and MAJO are emphasized

with grey amplitudes. The reference time at 0 s corresponds to the arrival of the

P-wave. The strongest positive impulse around 5 s is associated with the P-to-S

conversion at the Moho (Pms). Multiple reverberations PpPms (positive) and

PpSms+PsPms (negative) between the Moho and the surface are seen near 15

and 25 s respectively. Conversions at the 410 and 660-km discontinuities

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(P410s and P660s) show up clearly on synthetics, at BOSA and ARU stations,

but not at MAJO. The MAJO station is rejected by our selection procedure.



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Slant-stack diagrams for Wushi in China (WUS) and Palmer Station in

Antarctica (PMSA) in two period ranges (10-75 s; 5-75 s). Times and

slownesses are relative to the P-wave arrival. Negative waveforms are filled in

black. Red crosses indicate travel-time and slowness predictions for the P410s

and P660s conversions in IASP9117. Red dots indicate travel-time and slowness

predictions for a conversion at 350 km depth. Cyan and red contours give the -1

and-1.5% amplitude levels relative to the P-component.



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References

1. Chevrot, S., Vinnik, L. & Montagner, J. P. Global-scale analysis of the mantles Pds

phases. J. Geophys. Res. 101, 20,203-20,219 (1999).

2. Bostock, M. Mantle stratigraphy and evolution of the Slave province. J. Geophys.

Res. 103, 21,183-21,200 (1998).

3. Vinnik, L. & Farra, V. Low velocity atop the 410-km discontinuity and mantle

plumes. Earth Planet. Sc. Lett. 262, 398-412 (2007).

4. Revenaugh, J. & Sipkin, S. Seismic evidence for silicate melt atop the 410-km

discontinuity. Nature 369, 474–476 (1994).

5. Courtier, A. & Revenaugh, J. Deep upper mantle melting beneath the Tasman and the

Coral seas detected with multiple ScS reverberations. Earth Planet. Sc. Lett. 259, 66-76

(2007).

6. Bagley, B., Courtier, A. & Revenaugh, J. Melting in the deep upper mantle

oceanward of the Honshu slab. Phys. Earth Planet. Inter. 175, 137-144 (2009).

7. 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).

8. Wittlinger, G. & Farra, V. Converted waves reveal a thick and layered tectosphere

beneath the Kalahari super-craton. Earth Planet. Sc. Lett. 254, 404-415 (2007).

9. Jasbinsek, J. & Dueker, K. Ubiquitous low-velocity layer atop the 410-km

discontinuity in the northern Rocky Mountains. Geochem. Geophys. Geosys. 8,

doi:10.1029/2007GC001661 (2007).



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10. Vinnik, L., Ren, Y., Stutzmann, E., Farra, V. & Kiselev, S. Observations of S410p

and S350p at seismograph stations in California. J. Geophys. Res. 115, B05303 (2010).

11. Schaeffer, A. J. & Bostock, M. G. A low-velocity zone atop the transition zone in

Northwestern Canada. J. Geophys. Res. 115, B06302 (2010).

12. Grand, S. Mantle shear-wave tomography and the fate of subducted slabs,

Philosophical Transactions: Mathematical, Physical and Engineering Sciences 360,

2475-2491 (2002).

13. Coffin, M. F. & Eldholm, O. Large Igneous Provinces: Crustal structure,

dimensions, and external consequences, Reviews of Geophysics 32, 1-36 (1994).

14. Anderson, D. & Schramm, K. in Plates, Plumes, Paradigms (eds Foulger, G. R.,

Natland, J. H., Presnall, D. C., and Anderson, D. L.) 19-29 (Special Paper 388,

Geological Society of America, Boulder, 2005).

15. Nataf, H. & Ricard, Y. 3SMAC: An a priori tomographic model of the upper mantle

based on geophysical modeling. Phys. Earth Planet. Int. 95, 101-122 (1996).

16. Fuchs, K. & Müller, G. Computation of synthetic seismograms with the reflectivity

method and comparison with observations Geophys J. R. astr. Soc. 23, 417-433 (1971).

17. Kennett, B. L. N. & Engdahl, E. R. Travel times for global earthquake location and

phase identification. Geophys J. Int. 105, 429-465 (1991).

18. Efron, B. & Tibshirani, R. Statistical data analysis in the computer age. Science 253,

390-395 (1991).

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