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A conventional 1-D representation of the soil profile employed in Multi-channel Analysis of Surface Waves (MASW) consists of a fixed grid of layers. Each layer is assumed elastic with material properties of S-wave velocity, P-wave velocity, and mass density. Of these three, the S-wave velocity dominates. Phase velocity dispersion of the Rayleigh wave fundamental mode is often inverted with the S-wave velocity in each fixed layer being the primary object of investigation.

This paper presents an alternative representation of the soil profile. In this alternative, control points are the target of investigation. These control points are free to move both in the S-velocity and depth directions. Between the control points, the elastic moduli are interpolated into fine layers which are able to represent gradational variation. In this way, the number of unknowns is kept small compared to the large number of layers. Gradational trends in phase velocity dispersion have been represented well with this approach. The method is illustrated with synthetic data.  references to field data papers are also provided. The inversion method employed is Singular Value Decomposition (SVD).