Underwater MASW to ewaiuate stiffness ef mater-hott&m sediments

摘要

Stiffness measurements are often necessary for geotechni-cal characterization of an underwater site. Seismically, these measurements can be made through the dispersion analysis of the Rayleigh-type surface waves. Successful terrestrial application of this method has been reported by many investigators using spectral analysis of surface waves (SASW) and more recently using multichannel analysis of surface waves (MASW). The MASW method was originally developed as a land survey method to investigate the near-surface materials for their elastic properties: for example, the shear-wave velocity (Vs), by recording and analyzing Rayleigh-type surface waves using a vertical (impulsive) seismic source and receivers. The acquired data are first analyzed for dispersion characteristics and, from these the shear-wave velocity is estimated using an inversion technique. In land applications, the MASW method has been successfully applied to map 2D bedrock surface, zones of low strength, Poisson's ratio, voids, as well as to generate Vs profiles for various other geotechnical problems. Recently, several underwater applications of the MASW method were made to characterize stiffness distribution of water-bottom sediments; one survey was under shallow-water (1-6 m) and the other under deeper-water (70-130 m) environments.