A Multi-Component Approach to the Seismic Characterization of Real Multi-Layered Media

The dispersion behaviour of ground roll has been exploited in recent decades for the imaging and acoustic characterization of the shallow subsurface, often using the Multichannel Analysis of Surface Waves (MASW) method. The effectiveness of the method in providing an accurate shear wave profile of a soil deposit and the identification of seismic event largely depends on the degree of interference from other noise sources, unrelated to the primary signal of interest. In MASW a wavefield transformation in the frequency-wavenumber (f-k) domain is usually performed exploiting vertical components of a seismic event, picked up at different positions, theoretically allowing the identification of different wave-types and higher Rayleigh wave (R-wave) modes. In this work a multi-component approach to seismic characterization of the shallow subsurface is proposed. The body wave content is lowered and the Rayleigh wave content is enhanced by simultaneously exploiting the vertical and horizontal components of the seismic event in the direction of propagation of the ground roll (i.e. the direction of the receivers array), in the time domain. The effects of this multi-component approach are investigated in detail by finite element modelling and with respect to an in-situ experimental study. In general, the approach was found to be beneficial in enhancing the Rayleigh wave content of the seismic signal, hence improving mode separation in the f-k domain. It augments the range of detectable frequencies actually excited by ground roll and improves the resolution of the f-k transformation by a factor of two.