New developments in analysis of high-frequency Rayleigh waves

The shear (S)-wave velocity of near-surface materials (such as soil, rocks, and pavement) and its effect on seismic-wave propagation are of fundamental interest in many ground-water, engineering, and environmental studies. The multichannel analysis of surface waves has been applied to various near-surface problems. Tens near-surface Rayleigh wave application papers have appeared in the literature over last eight years. Surface-wave techniques show their capability of providing accurate S-wave velocities of shallow materials and high potential of providing attenuation properties of near-surface rocks. New developments in surface-wave techniques have been made over the last two years. We developed a scheme using the finite-difference method to model high-frequency Rayleigh-waves in near-surface mediums. This stable and efficient scheme provides a valuable tool in understanding of characteristics of Rayleigh waves in various near-surface geological settings. We have developed an algorithm of estimating S-wave velocities of a compressible Gibson half-space (a non-layered earth model) from Rayleigh waves. This algorithm allows us to estimate S-wave velocities of the non-layered earth model with minimum of three Rayleigh-wave phase velocities. We have also developed an algorithm of generating image of dispersive energy by slant stacking. The real power of the algorithm is its capability to generate an image of dispersive energy from data acquired in an arbitrary acquisition geometry (for example fan configuration), which lays down a foundation for true 3D surface-wave analysis. We have studied feasibility of detecting voids with Rayleigh-wave diffraction. The results of this study are encouraging.