Surface Wave Analysis for the characterization of granular material deposits

Abstract

Knowledge of near-surface seismic-wave velocity of granular materials plays a valuable role in seismic exploration data processing. I will use the surface-wave analysis method for estimation of shear-wave velocity profile and P-wave refraction for estimation of pressure-wave velocity on a data set acquired over a sand dune in The Netherlands, a dune area part of The Holland coast. For surface-wave analysis I exploit the fact that in these materials the velocity profile follows a power-law and I invert for the power-law coefficients using a Monte Carlo inversion. A second power-law is introduced into the Monte Carlo inversion to recover vertically varying structures. The P-wave refraction is applied for estimation of the groundwater depth and P-wave velocity. After the seismic data were acquired, several analyses were made on the extracted dispersion curves from different sources, windowing in space domain indicate the presence of lateral variation. The estimated shear-wave velocity profiles demonstrates the usefulness of imposing a power-law trend to the velocity. Although the inverted power-law coefficients results into small differences with the literature and theoretical values, these can be explained by the varying shapes of the grains. Furthermore, the implementation of the second power-law results into velocities that are lower than the first layer. The depth of the shear-wave velocity profiles is limited by the shallow position of the water-table around 3 m. For the best practice in field work the vibroseis source is advised due to the advantage of the continuous sweep covering the whole frequency band in one signal.