Combination of Compressional and Shear Wave Velocities to Investigate Heterogeneous, Unconsolidated Shallow Sediments

Abstract

Propagation of seismic waves through porous media is primarily governed by compressibility in the case of compressional waves, and rigidity in the case of shear waves, as well as by density and porosity in both cases. The compressional and shear wave velocities vary considerably with variations of elastic and petrophysical parameters, lithological constituents and their mineralogical composition, degree of saturation and kind of saturant filling pore spaces, and depth. In this study, the compressional wave velocity (υ p ) and the shear wave velocity (υ s ) were obtained for heterogeneous, unconsolidated shallow sediments (northern Germany), using seismic refraction measurements. The υ p shows a general range of between 134 and 2,060 m/s, with an overall average value of 1,153 m/s, and υ s shows a general range of between 81 and 863 m/s, with an overall average value of 471 m/s, corresponding to the top surface soil, and the underlying partially and totally saturated sediments. A clear distinction was observed for υ p and υ s when the waves propagate along the surface or through the surface soil, and when they change their propagation from the partially saturated sediments to the totally saturated sediments. A direct relationship between υ p and υ s , with a coefficient of correlation of 0.94, was obtained for the whole column of the soils and sediments investigated.