These spline interpolation knots can be found in lib/libS20/splhsetup.f from http://www.earth.lsa.umich.edu/~jritsema/research.html
The first number corresponds to the CMB, the last to the Moho depth.
-1.00000 
-0.78631 
-0.59207 
-0.41550 
-0.25499 
-0.10909 
0.02353
0.14409 
0.25367 
0.35329 
0.44384 
0.52615 
0.60097 
0.66899
0.73081 
0.78701 
0.83810 
0.88454 
0.92675 
0.96512 
1.00000
