Radial Anisotropy: Flow in the mantle

What is the nature of flow in the mantle?
How fast do waves travel anywhere on Earth?
Where can radial anisotropy be robustly detected?
Can we reconcile a broad spectrum of seismic data? What are the benefits?

We use normal-mode splitting functions in addition to surface-wave phase anomalies, body-wave travel times and long-period waveforms to construct a three-dimensional model of anisotropic shear-wave velocity in the Earth's mantle. This is the first tomographic study to exploit the sensitivity of mode-splitting data to constrain radial anisotropy in the Earth's mantle jointly with several other types of data. Our modeling approach inverts for mantle velocity and anisotropy as well as transition-zone discontinuity topographies, and incorporates new crustal corrections for the splitting functions that are consistent with the nonlinear corrections we employ for the waveforms. Our preferred anisotropic model, S362ANI+M, is an update to the earlier model S362ANI, which did not include normal-mode splitting functions in its derivation.

[I] We develop a new method to invert jointly four distinct types of seismic data for anisotropic shear velocities and discontinuity topographies in the Earth's mantle while accounting accurately for the crustal structure.
[II] We show that the mode-splitting data require strong isotropic v_S heterogeneity in the transition zone and changes to the southern hemisphere in the mid to lower mantle.
[III] We report the improved consistency between recent studies on the long-wavelength isotropic structure, especially in the transition zone and the lower mantle.
[IV] We show that the datasets used in this study, especially the mode-splitting data, do not require radial anisotropy in the deep mantle.
[V] We demonstrate that the mode-splitting data suppress spurious anisotropic anomalies in the mid mantle and reduce even-degree tradeoffs between anisotropic and isotropic variations in the lowermost mantle.

Please cite the following work if you use this data or software.

[A] Moulik, P. & Ekström, G., 2014. An anisotropic shear velocity model of the Earth's mantle using normal modes, body waves, surface waves and long-period waveforms, Geophys. J. Int., 199(3), 1713-1738, doi: 10.1093/gji/ggu356. pdf

You can also cite the dataset and software from this Zenodo page (Optional).

[B] Moulik, P. & Ekström, G., 2014. Dataset and Software for An anisotropic shear velocity model of the Earth's mantle using normal modes, body waves, surface waves and long-period waveforms. In Geophys. J. Int. (v1.0, Vol. 199, pp. 1713–1738). Zenodo. doi: 10.5281/zenodo.8357379