Scholte wave dispersion by rippled liquid/solid interface topography

Abstract

The effect of sand ripples on seismoacoustic waves is not yet understood. Quantitative results are presented characterizing the dispersion of Scholte waves propagating along a rippled surface of an immersed ‘‘soft’’ solid half-space. One model has a sinusoidal profile with a ratio of corrugation amplitude to wavelength of 0.25. The observed Bragg frequency components of broadband transient received waveforms are shifted by 180° as the receiver is displaced one cycle along the corrugation, however, the other frequency components are delayed by a smaller amount following the dispersion characteristics. Scholte and Rayleigh wave experimental dispersion graphs obtained from ‘‘soft’’ solid models are compared with replotted scaled numerical results on Rayleigh wave dispersion along a ‘‘hard’’ corrugated solid half-space [Glass et al., ‘‘Propagation of Rayleigh surface waves across a large-amplitude grating,’’ Phys. Rev. B 24, 6843–6861 (1981)]. The findings reveal that a rippled ‘‘soft’’ liquid/solid interface can decrease the velocity by more than 70% of high-frequency Scholte wave components propagating normal to the ripples. The accuracy of acoustic inversion and detection of buried objects depends on predicting the effect of seafloor topography. [Work supported by ONR.]