Determination of near-surface variability using Rayleigh waves.

摘要

Rayleigh wave dispersion was used to examine seasonal variability of the near-surface (up to approximately 15 m depth) elastic properties. Seismic surface waves were generated using a sledgehammer source and collected using an array of three-component geophones at 0.5 m spacing with offsets ranging from 7 to 38 m. Multiple data sets were obtained at the Edmonton Research Station over the course of the summer and early fall of 1999 at 2 to 3 week intervals. Dispersion analysis of the vertical component data indicates that there are three strong Rayleigh modes present, the phase velocities of which change very little between survey dates. There are, however, indications that the attenuation properties of the top 1 to 2 m do change over the study period. Inversion of the three Rayleigh mode dispersion curves using a fast simulated annealing algorithm (Sen and Stoffa, 1995) coupled with a matrix propagator forward modelling technique (Menke, 1979) yields S-wave velocity profiles that agree well with geological information and vertical seismic profile results. Resolution of the inverted velocity profiles is excellent down to a depth of about 8 m after which the uncertainty increases.