Occam's inversion of high-frequency Rayleigh wave dispersion curves for shallow engineering applications

摘要

The shear-wave (S-wave) velocity in the shallow subsurface (soil, rock, roadbed) is an important parameter in environmental and engineering studies and applications. A 2-D S-wave velocity profile with a low velocity layer (LVL) is estimated from dispersion analysis of surface waves data, whose maximum depth of investigation is around 16 m. The measured field dispersion curves are automatically inverted using an iterative weighted solution technique named Occam's algorithm that proved very effective in high-frequency range for S-wave velocity profiles and uncertainty of inversion results are estimated. Convergence of inverse procedure is guaranteed through appropriate selection of the smoothing parameter in the Lagrange multipliers method. We compare Occam's inversion algorithm with the Levenberg-Marquardt (L-M) and singular value decomposition (SVD) technique. Results demonstrate that S-velocity profiles inverted by Occam's algorithm agree well with practical geological structure and SVD inversion results. Maximum uncertainty of Occam's inversion is 7.4%, and maximum difference with SVD inversion is 8.2% in our case study.