It is changing as individual mantle models evolve. These are provided by Masters et al. Dziewonski et al.
All models are available either through Web pages, anonymous ftp or by email to the author.
A click on the name of the model will show a plot of maps of shear velocity perturbation at 12 depths throughout the mantle. The perturbations are in percent with respect to the mean for that particular depth which was taken out. HRV SIO Berk Grand Calt HRV . This page is solely my responsibility. It is not my intention to recommend one model over another.