SGLOBE-rani: a new global whole-mantle model of isotropic and radially anisotropic shear-wave velocity structure

Abstract:

We present a new global whole-mantle model of isotropic and radially anisotropic S velocity structure (SGLOBE-rani) based on ~43,000,000 surface-wave and ~420,000 bodywave travel time measurements, which is expanded in spherical harmonic basis functions up to degree 35. We incorporate crustal thickness perturbations as model parameters in the inversions to properly consider crustal effects and suppress the leakage of crustal structure into mantle structure. This is possible since we utilize short-period group velocity data with a period range down to 16 s, which are strongly sensitive to the crust. The isotropic S-velocity model shares common features with previous global S-velocity models and shows excellent consistency with several high-resolution upper mantle models. Our anisotropic model also agrees well with previous regional studies. Nevertheless, our new model of 3-D radial anisotropy shows some features not seen in previous whole-mantle models, such as faster SV velocity anomalies along subduction zones at transition zone depths and faster SH velocity beneath slabs in the lower mantle. The derived crustal thickness perturbations also bring potentially important information about the crustal thickness beneath oceanic crusts, which has been difficult to constrain due to poor access compared with continental crusts. We interpret our results in terms of mineralogy and geodynamical processes in the transition zone and uppermost lower mantle.