Nonlinear Least-Squares Estimation of Shear Wave Speeds in Viscoelastic Media

Rapid simulations of three-dimensional (3D) shear wave propagation in viscoelastic media with a Kelvin-Voigt model are enabled by Green's functions accelerated with graphics processing unit (GPU) parallelization using high performance computing (HPC) resources. From
$\mathbf{3D}$
waveforms, shear wave speed estimates are obtained through cross-correlations, where previous efforts have demonstrated that errors in the estimated shear wave speed increase with rising viscosity. To reduce the error in the shear wave speed estimate, a nonlinear least-squares approach accounting for propagation, attenuation, and waveform spreading is proposed for viscoelastic materials. The nonlinear least-squares approach yields an estimate of shear elasticity and shear viscosity.