Group Velocity Maps
-------------------

The group velocity files each end with a ".1". Contents
are defined by the name; for example,

RG_100.1 -- is the 100 sec Rayleigh wave group velocity file,
LG_20.1  -- is the 20 sec Love wave group velocity file.

Each line if formatted: lon   lat   value (gr vel in km/sec)

Grid is 1x1 degree minus the poles.



Tomography was performed with the Diffraction Tomographic method
described by:

Ritzwoller, M.H., N.M. Shapiro, M.P. Barmin, and A.L. Levshin, 
Global surface wave diffraction tomography, J. Geophys. Res., 
107(B12), 2335, 2002. 

Data processing method was described by:

Ritzwoller, M.H. and A.L. Levshin, 
Eurasian surface wave tomography: Group velocities, 
J. Geophys. Res., 103, 4839 - 4878 1998.