Importance of crustal corrections in the development of a new global model of radial anisotropy

Abstract

Accurately inferring the radially anisotropic structure of the mantle using seismic waveforms requires correcting for the effects of crustal structure on waveforms. Recent studies have quantified the importance of accurate crustal corrections when mapping upper mantle structure using surface waves and overtones. Here, we explore the effects of crustal corrections on the retrieval of deep mantle velocity and radial anisotropy structure. We apply a new method of nonlinear crustal corrections to a three‐component surface and body waveform data set and invert for a suite of models of radially anisotropic shear velocity. We then compare the retrieved models against each other and a model derived from an identical data set but using a different nonlinear crustal correction scheme. While retrieval of isotropic structure in the deep mantle appears to be robust with respect to changes in crustal corrections, we find large differences in anisotropic structure that result from the use of different crustal corrections, particularly at transition zone and greater depths. Furthermore, anisotropic structure in the lower mantle, including the depth‐averaged signature in the core‐mantle boundary region, appears to be quite sensitive to choices of crustal correction. Our new preferred model, SAW642ANb, shows improvement in data fit and reduction in apparent crustal artifacts. We argue that the accuracy of crustal corrections may currently be a limiting factor for improved resolution and agreement between models of mantle anisotropy.