Caption for Degree 1-8 Shear Velocity Model Plots

	These maps show degree 1-8 spherical harmonic components of shear
velocity models in the mid-mantle.  S16B30 is from the Scripps Institute of
Oceanography [Masters, et al., 1996], SKS12WM13 is from Harvard University
[Liu and Dziewonski, 1994], SAW12D is from the University of California at
Berkeley [Li and Romanowicz, 1996], the Van der Hilst model is from the
Massachusetts Institute of Technology [Van der Hilst, et al., 1997], and the
Grand model is from the University of Texas [Grand, et al, 1997].  The model
of Van der Hilst has been converted from dln(v_p) to dln(v_s) using
dln(v_p)/dln(v_s) = 0.5 in the lower mantle and dln(v_p)/dln(v_s) = 0.8
in the upper mantle.  These models display considerable variability in both
amplitude and geometry of structures in the mantle.
	Model MM2_L12D8 is the result of inversions of generalized normal
mode splitting functions which have been retrieved from the spectra of 88
multiplets below 3 mHz.  There are no degree 7 constraints in these data,
and the degree 7 component of the model maps is from SKS12WM13.  The normal
mode inversions were damped enough to insure that MM2_L12D8 is less different
from models S16B30, SKS12WM13, and SAW12D than they are from each other, yet
MM2_L12D8 reduces chi-squared misfit to the normal mode structure coefficients
by 58%.  MM2_L12D8 is most notable for low- and high-velocity features in the
mid-mantle (900-1800 km depths), which, more so than other global models, are
consistent with "plumes" rising from the deepest mantle and "slab remnants"
descending from the transition zone and outmost lower mantle.

Model References:

Grand, S. P., R. D. van der Hilst and S. Widiyantoro,
Global seismic tomography: a snapshot of convection in the Earth,
GSA Today, v. 7, n. 4, 1-7, 1997.

Li, X.-D., and B. Romanowicz,
Global mantle shear-velocity model developed using nonlinear asymptotic
coupling theory,
Journal Geophys. Res., 101, 22,245-22,272, 1996.

Liu, X.-F., and A. M. Dziewonski,
Improved resolution of the lower-most mantle shear wave velocity structure
obtained usng SKS-S data,
EOS Trans. Amer. Geophys. Un.,  75, Spring Meet. Suppl., S232-234, 1994.

Masters, G., S. Johnson, G. Laske, and H. Bolton,
A shear-velocity model of the mantle,
Phil. Trans. R. Soc. Lond. A, 354, 1385 - 1411, 1996.

Van der Hilst, R. D., S. Widiyantoro, and E. R. Engdahl, 
Evidence for deep mantle circulation from global tomography,
Nature,386, 578-584, 1997.