Assessment of an MASW approach incorporating discrete particle modeling

A Discrete Particle Scheme (DPS) consisting of interacting circular particles is utilized to examine a popular Multichannel Analysis of Surface Waves (MASW) approach. Synthetic earth models of various complexity are generated using the DPS and analyzed by selected MASW dispersion and inversion techniques. For simple two layer and multilayer models where velocity increases with depth, inversion using the dominant fundamental mode results in MASW profiles of shear wave velocity (V-s) that closely match the true synthetic V-s profiles. Inversion using the default parameters produces gradational increases in velocity, rather than true discontinuities. When tested on a multilayer model containing a low velocity layer (LVL), inversion using a fundamental mode assumption results in a moderate increase in error. MASW field tests at a highly Uniform site in Norway (Onsoy) and a site with distinctive layer boundaries in Ireland (Ballinasloe) result in highly repeatable profiles of V-s. Resolution of dispersion curves at low frequencies (< 10 Hz) is a problem at the Ballinasloe test site, which limits the depth of penetration of the technique. MASW inversion results compare excellently with downhole seismic cone tests at the Onsoy test site and reasonably with a seismic refraction survey at the Ballinasloe site.