Model Computations for Low-Velocity Surface Waves on Marine Sediments

Abstract

In seismology Rayleigh waves, which propagate along the free surface, are of great importance for determining the elastic parameters of the upper mantle. With regard to shear-wave velocities in the upper layers of ocean sediments the same may apply to Scholte waves, which propagate along the interface between ocean and sea floor. In the case of homogeneous halfspaces both, Rayleigh and Scholte waves are nondispersive, however the dependences of propagation velocities on the elastic parameters are different. But in presence of layers the Rayleigh as well as the Scholte wave splits up into a finite number of dispersive modes. As for Rayleigh waves this effect seems to be of importance for Scholte waves, too. Measurements of Schirmer et al. from the shore belt of the North Sea show two different dispersive modes. In this paper simple theoretical models are presented in order to investigate the dispersion of “Rayleigh” — and “Scholte”-modes on ocean sea-floors. Compared to the earth mantle the sea floor propagates Rayleigh (and Scholte) waves of much smaller wavelength, and moreover the ratio of shear to compressional wave-velocity is lower by a factor of about 10.