SUPPLEMENTARY INFORMATION

Transcription

1 SUPPLEMENTARY INFORMATION Seismic evidence for a global low velocity layer within the Earth s upper mantle SUPPLEMENTARY MATERIAL Benoît Tauzin 1, Eric Debayle 2 & Gérard Wittlinger 3 1 Department of Earth Sciences, Utrecht University, P.O. Box , 3508 TA Utrecht, The Netherlands 2 Laboratoire de Sciences de la Terre, Université de Lyon I, CNRS and Ecole Normale Supérieure de Lyon, UMR5570, F Villeurbanne, France 3 Ecole et Observatoire des Sciences de la Terre, UMR-CNRS 7516, 5 rue René Descartes, Strasbourg Cedex, France nature geoscience 1

2 supplementary information 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 stations 1,2. Red stars are data from S-to-P conversions (Sp) at individual stations 3. Observations from ScS reverberations 4-6 are indicated in green. Observations from a joint study of Ps and S-wave triplications 7 are indicated in blue. Ps and Sp array observations 8-11 are indicated in red. 2 nature geoscience

3 supplementary information Supplementary Figure S2 Observed (left) and synthetic (right) receiver functions computed for the 89 stations of Fig. 1a in four period ranges: 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. nature geoscience 3

4 supplementary information 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 nature geoscience

5 supplementary information 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 tomography 12. Large igneous provinces 13 are shown in orange and red dots indicate hotspot locations 14. nature geoscience 5

6 supplementary information 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 nature geoscience

7 supplementary information Supplementary Figure S6 Receiver functions filtered in the 7-75 s period range for different continental provinces 15 : Archean, Proterozoic and Phanerozoic. (A) Stations with a negative signal atop the 410. (B) Stations with no significant signal atop the 410. nature geoscience 7

8 supplementary information Supplementary Figure S7 Stacked waveforms obtained in four period ranges (3-75 s; 5-75 s; 7-75 s; s) for synthetic 16 receiver functions computed in the IASP91 17 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 resampling 18 ) 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 (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. 8 nature geoscience

9 supplementary information 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 IASP 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. nature geoscience 9

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