Assessing the effects of model parameter assumptions on surface-wave inversion results

Surface-wave inversion is a powerful tool for revealing the Earth’s internal structure. However, aside from shear-wave velocity (v_S), other parameters can influence the inversion outcomes, yet these have not been systematically discussed. This study investigates the influence of various parameter assumptions on the results of surface-wave inversion, including the compressional and shear velocity ratio (v_P/v_S), shear-wave attenuation (Q_S), density (ρ), Moho interface, and sedimentary layer. We constructed synthetic models to generate dispersion data and compared the obtained results with different parameter assumptions with those of the true model. The results indicate that the v_P/v_S ratio, Q_S, and density (ρ) have minimal effects on absolute velocity values and perturbation patterns in the inversion. Conversely, assumptions about the Moho interface and sedimentary layer significantly influenced absolute velocity values and perturbation patterns. Introducing an erroneous Moho-interface depth in the initial model of the inversion significantly affected the v_S model near that depth, while using a smooth initial model results in relatively minor deviations. The assumption on the sedimentary layer not only affects shallow structure results but also impacts the result at greater depths. Non-linear inversion methods outperform linear inversion methods, particularly for the assumptions of the Moho interface and sedimentary layer. Joint inversion with other data types, such as receiver functions or Rayleigh wave ellipticity, and using data from a broader period range or higher-mode surface waves, can mitigate these deviations. Furthermore, incorporating more accurate prior information can improve inversion results.