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S-Velocity Structure of the Upper Mantle
Sergei Lebedev (Dublin Institute for Advanced Studies), Rob D. van der Hilst (MIT)
Sv-velocity structure of the upper mantle
(crust–660 km) is constrained by the Automated
Multimode Inversion of surface and S-wave forms
[Lebedev et al., 2005], applied to a large global
data set retreived from IRIS facilities [Lebedev
and van der Hilst, 2008]. Structure of the mantle
and crust is constrained by waveform information
from both the fundamental mode Rayleigh waves
(periods from 20 to 400 s) and S and multiple S
waves (higher modes). The reference model used
in the waveform inversions and the tomographic
linear inversion incorporates 3-D crustal structure.
The tomographic model includes isotropic
variations in S- and P-wave velocities and also
S-wave azimuthal anisotropy. The lateral resolution
of the imaging is a few hundred kilometres,
varying with data sampling.
The technique has been benchmarked with a
‘spectral-element’ resolution test: inverting published
global synthetic data sets computed with
the spectral-element method for laterally heterogeneous
mantle models, Lebedev and van der
Hilst [2008] have been able to reconstruct the
synthetic models accurately.
The tomographic model displays low-Sv-velocity
anomalies beneath mid-ocean ridges and backarc
basins that extend down to ~100 km depth
only. In the seismic lithosphere beneath cratons,
strong high velocity anomalies extend to ~200
km. Pronounced low-velocity zones beneath cratonic
lithosphere are rare; where present (South
America; Tanzania) they are often neighboured
by volcanic areas near cratonic boundaries. The
images of these low-velocity zones may indicate
hot material possibly of mantle-plume origin—
trapped or spreading beneath the thick cratonic
lithosphere [Lebedev and van der Hilst, 2008].
Cross-section depths and color-scale limits are specified within each frame. The reference
Sv-wave velocity values are, for increasing depths: 4.38, 4.39, 4.69, 5.27 km/s—all at a reference
period of 50 s.
References
Lebedev, S., G. Nolet, T. Meier, R. D. van der Hilst, Automated multimode inversion of surface and S waveforms, Geophys. J. Int. 162, 951-964,
2005.
Lebedev, S., R. D. van der Hilst, Global upper-mantle tomography with the automated multimode inversion of surface and S-wave forms,
Geophys. J. Int., 173, 505-518, 2008.
2010 IRIS Core Programs Proposal | Volume II | Upper Mantle Structure and Dynamics | II-169