Assessing the Importance of Crustal Corrections for Global Upper Mantle Radial Anisotropy Models With a Bayesian Approach

Abstract:

Crustal correction plays an important step in modeling global upper mantle radial anisotropy with surface waves. It has been shown that the choice of the prior crustal model to correct the data can strongly influence the anisotropy model and potentially lead to different geodynamic interpretations. In comparing tomographic models of radial anisotropy obtained from different crustal corrections, previous studies did not, however, determine quantitative model uncertainties. Mantle models resulting from different prior crustal corrections are statistically different only if the posterior model errors stemming from the non-uniqueness of the inverse problem are smaller than the effect of the crustal correction itself. Here, we applied a model space search approach to surface wave phase velocity maps to determine quantitative model uncertainties on seismic velocities and radial anisotropy. We then assessed the significance of the choice of the crustal model by comparing model errors to the differences in mantle structure resulting from different crustal corrections. We tested prior crustal models CRUST2.0, CRUST1.0, and 3SMAC. Our study shows that the use of prior crustal corrections from different crustal models yields significant discrepancies in mantle velocities around 50km depth and in radial anisotropy down to 100km. The effect of the crustal model is most significant in continental regions, which has important consequences for determining the depth of continental roots and understanding continent formation. Our work also demonstrates that the prior crustal model does not significantly affect radial anisotropy and velocities at depths greater than 100km. This implies that if geodynamic interpretations of radial anisotropy below 100km depth were to account for tomographic model uncertainties, they would not depend on the choice of the prior crustal model.