Upload
others
View
1
Download
0
Embed Size (px)
Citation preview
SUPPLEMENTARY INFORMATIONdoi: 10.1038/ngeo969
nature geoscience | www.nature.com/naturegeoscience 1
1�
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
2�
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.
nature geoscience | www.nature.com/naturegeoscience 3
SUPPLEMENTARY INFORMATIONdoi: 10.1038/ngeo969
3�
Supplementary Figure S2
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.
4 nature geoscience | www.nature.com/naturegeoscience
SUPPLEMENTARY INFORMATION doi: 10.1038/ngeo969
4�
Supplementary Figure S3
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“.
nature geoscience | www.nature.com/naturegeoscience 5
SUPPLEMENTARY INFORMATIONdoi: 10.1038/ngeo9695�
Supplementary Figure S4
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.
6 nature geoscience | www.nature.com/naturegeoscience
SUPPLEMENTARY INFORMATION doi: 10.1038/ngeo969
6�
Supplementary Figure S5
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“.
nature geoscience | www.nature.com/naturegeoscience 7
SUPPLEMENTARY INFORMATIONdoi: 10.1038/ngeo969
7�
Supplementary Figure S6
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“.
8 nature geoscience | www.nature.com/naturegeoscience
SUPPLEMENTARY INFORMATION doi: 10.1038/ngeo969
8�
Supplementary Figure S7
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
9�
(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.
nature geoscience | www.nature.com/naturegeoscience 9
SUPPLEMENTARY INFORMATIONdoi: 10.1038/ngeo969
10�
Supplementary Figure S8
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.
10 nature geoscience | www.nature.com/naturegeoscience
SUPPLEMENTARY INFORMATION doi: 10.1038/ngeo969
11�
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).
nature geoscience | www.nature.com/naturegeoscience 11
SUPPLEMENTARY INFORMATIONdoi: 10.1038/ngeo969
12�
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).