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Global and Regional Tomography

Planetary Seismology

Theoretical Studies

This work was done in collaboration with Barbara Romanowicz as part of the Berkeley Global Seismology group.

SAW642AN: a global radially anisotropic mantle shear velocity model


Panning, M.P., and B.A. Romanowicz, "A three dimensional radially anisotropic model of shear velocity in the whole mantle," Geophys. J. Int, 167, 361-379, 2006. pdf

Model files available for download:

gzipped tarfile (~2.9 MB)

The distribution includes all necessary model files, as well as some tools for obtaining model values at specified locations in the mantle. To use these tools, you will need C and Fortran90 compilers. Try the GNU compiler collection if you do not already have these available on your system. Some sample plotting scripts for plotting depth slices and cross sections are also included. These require GMT and the ability to run csh scripts (standard in Unix, linux, and OS X systems).

This model was developed at the Berkeley Seismological Laboratory as part of the Global Seismology group.

Summary (adapted from paper abstract):

We present a 3-D radially anisotropic S velocity model of the whole mantle (SAW642AN), obtained using a large three component surface and body waveform data set and an iterative inversion for structure and source parameters based on Non-linear Asymptotic Coupling Theory (NACT). The model is parameterized in level 4 spherical splines, which have a spacing of approximately 8 degrees. The isotropic portion of the model is shown to the right. The model shows a link between mantle flow and anisotropy in a variety of depth ranges. In the uppermost mantle, we confirm observations of regions with VSH> VSV starting at approximately 80 km depth under oceanic regions and approximately 200 km under stable continental lithosphere, suggesting horizontal flow beneath the lithosphere. We also observe a VSV> VSH signature at 150-300 km depth beneath major ridge systems with amplitude correlated with spreading rate for fast-spreading segments. In the transition zone (400-700 km depth), regions of subducted slab material are associated with VSV>VSH, while the ridge signal decreases. While the mid-mantle has lower amplitude anisotropy (<1%), we also confirm the observation of radially symmetric VSH> VSV in the lowermost 300 km, which appears to be a robust conclusion. The 3-D deviations from this signature are associated with the large-scale low-velocity super plumes under the central Pacific and Africa, suggesting that VSH>VSV is generated in the predominant horizontal flow of a mechanical boundary layer, with a change in signature related to transition to upwelling at the super plumes.