GyPSuM: Simmons, Forte, Boschi and Grand (2010) -- JGR
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*22 depth layers for Vs and Vp perturbations are included.

*Perturbations are constant within given depth ranges (block parameterization). 

*Density will included in a future package.

*Each model file contains a vector with percent perturbations.

*A file with lat/lon definitions is provided (Grid.LatsLons.1deg.txt).

*The reference shear wave velocity model is an average of the TNA/SNA models in Grand and Helmberger (1984). (file included)

*The reference P-wave model is the 1-second, isotropic equivalent PREM (Table II of Dziewonski and Anderson, 1981) (file included).

*File name format: Grid.GyPSuM.(field).(layernumber).(depth range).txt
Where:
	 	field=S is S velocity, 
		field=P is P velocity 	
