Joint estimation of modal attenuation and velocity from multichannel surface wave data

Abstract

We evaluated a method for the simultaneous analysis of velocity and attenuation of multichannel surface wave data. It allowed us to estimate the phase velocity and attenuation curves using an array of receivers, possibly unevenly spaced, and a set of multiple shots at different locations. After reviewing the properties of surface waves in dissipative media, the estimation algorithm was evaluated. It was based on the estimation of the complex wavenumber of multiple normal modes. It can be considered as a high-resolution subspace-based method able to deal with irregularly sampled multichannel-multishot data. The interference between multiple modes was considered without the need of a prior specific multimode Rayleigh spreading function, so that multiple modal attenuation curves can be extracted. The validity of the approach was tested using synthetic data, with small and large mode interference, as well as with multimode real data. The benefits and the robustness of the proposed method were particularly relevant with data with multiple modes. The possibility of considering multiple shot points into a receiver array allowed the increase of the modal resolution without increasing the receiver aperture, thus without compromising the lateral resolution. The estimation of the modal attenuation coefficient enabled the estimation of the subsurface material damping ratio, and the definition of a dissipative propagation model.