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Elastic full-waveform inversion (EFWI) is a state-of-the-art seismic tomographic method. Recent advances in technology and instrumentation, combining crosstalk-free source-encoded FWI (SE-FWI) with multicomponent marine data acquisition using ocean-bottom nodes (OBNs), enable full-physics wave propagation and parameter inversion without the computational burden of traditional FWI. With OBN acquisition, P waves, S waves, and P-to-S conversions are recorded. It is not well understood to what extent adding horizontal components to SE-FWI improves the resolution of subsurface modeling. We assess their potential for the reconstruction of shear and compressional wave speeds (V_Pand V_S) by using a synthetic data set modeled after a recently acquired OBN survey in the North Sea. We perform synthetic inversion tests to design suitable strategies that leverage the information recorded in the horizontal components of the data to improve the reconstructed model resolution laterally and in depth. We advocate for a hierarchical inversion approach to recover the elastic parameters. We exploit the P and P-to-S converted waves recorded on the horizontal components to robustly reconstruct both V_Pand V_S. Adding horizontal components to the SE-FWI modeling workflow results in improved spatial resolution, enhanced depth coverage, and more accurate elastic wave speed estimates. 

SUMMARY Improving the resolution of seismic anelastic models is critical for a better understanding of the Earth’s subsurface structure and dynamics. Seismic attenuation plays a crucial role in estimating water content, partial melting and temperature variations in the Earth’s crust and mantle. However, compared to seismic wave-speed models, seismic attenuation tomography models tend to be less resolved. This is due to the complexity of amplitude measurements and the challenge of isolating the effect of attenuation in the data from other parameters. Physical dispersion caused by attenuation also affects seismic wave speeds, and neglecting scattering/defocusing effects in classical anelastic models can lead to biased results. To overcome these challenges, it is essential to account for the full 3-D complexity of seismic wave propagation. Although various synthetic tests have been conducted to validate anelastic full-waveform inversion (FWI), there is still a lack of understanding regarding the trade-off between elastic and anelastic parameters, as well as the variable influence of different parameter classes on the data. In this context, we present a synthetic study to explore different strategies for global anelastic inversions. To assess the resolution and sensitivity for different misfit functions, we first perform mono-parameter inversions by inverting only for attenuation. Then, to study trade-offs between parameters and resolution, we test two different inversion strategies (simultaneous and sequential) to jointly constrain the elastic and anelastic parameters. We found that a sequential inversion strategy performs better for imaging attenuation than a simultaneous inversion. We also demonstrate the dominance of seismic wave speeds over attenuation, underscoring the importance of determining a good approximation of the Hessian matrix and suitable damping factors for each parameter class.