I don't know much about MASW.
To determine the elastic constants (R.E. Sheriff "Encyclopedic Dictionary of Exploration Geophysics") you need an estimate of the density. This can be obtained with empirical formulas e.g. Gardner's Equation estimating density rho from P-wave velocity Vp :
rho = 0.31 * pow(Vp, 0.25)
with Vp in m/s and rho in g/cm3 . See
https://en.wikipedia.org/wiki/Gardner%27s_relation
and
http://www.crewes.org/ForOurSponsors/ResearchReports/1991/1991-17.pdfNext you can obtain Shear Modulus G from shear wave velocity Vs and density rho according to Sheriff :
Vs = pow(G/rho, 0.5) gives
G = pow(Vs, 2.0) * rho
Now you can obtain other elastic constants (Young's modulus E, Bulk modulus k,
Lame's Landa constant) from Poisson's Ratio and Shear Modulus. See formulas in
R.E. Sheriff "Encyclopedic Dictionary of Exploration Geophysics", SEG Tulsa OK ISBN 0-931830-31-3 and
http://li.mit.edu/Archive/Links/iso_elast_const/index.html and
http://www.efunda.com/formulae/solid_mechanics/mat_mechanics/calc_elastic_constants.cfm. You can use Surfer Grid Math to transform P-wave velocity 2D grid to density grid, S-wave velocity grid to Shear Modulus grid etc. as in above Poisson.pdf tutorial.
Finally you can image obtained 2D .GRD grids for above elastic constants with Surfer Map|Image Map command.