S U M M A R YWe have developed model S40RTS of shear-velocity variation in Earth's mantle using a new collection of Rayleigh wave phase velocity, teleseismic body-wave traveltime and normalmode splitting function measurements. This data set is an order of magnitude larger than used for S20RTS and includes new data types. The data are related to shear-velocity perturbations from the (anisotropic) PREM model via kernel functions and ray paths that are computed using PREM. Contributions to phase delays and traveltimes from the heterogeneous crust are estimated using model CRUST2.0. We calculate crustal traveltimes from long-period synthetic waveforms rather than using ray theory. Shear-velocity perturbations are parametrized by spherical harmonics up to degree 40 and by 21 vertical spline functions for a total of 35 301 degrees of freedom. S40RTS is characterised by 8000 resolved unknowns. Since we compute the exact inverse, it is straightforward to determine models associated with fewer or more unknowns by adjusting the model damping. S40RTS shares many characteristics with S20RTS because it is based on the same data types and similar modelling procedures. However, S40RTS shows more clearly than S20RTS the abrupt change in the pattern of shear-velocity heterogeneity across the 660-km phase transition and it presents a more complex patern of shear-velocity heterogeneity in the lower mantle. Utilities to visualise S40RTS and software to analyse the resolution of S40RTS (or models for different damping parameters) are made available.

A model of three-dimensional shear wave velocity variations in the mantle reveals a tilted low velocity anomaly extending from the core-mantle boundary (CMB) region beneath the southeastern Atlantic Ocean into the upper mantle beneath eastern Africa. This anomaly suggests that Cenozoic flood basalt volcanism in the Afar region and active rifting beneath the East African Rift is linked to an extensive thermal anomaly at the CMB more than 45 degrees away. In contrast, a low velocity anomaly beneath Iceland is confined to the upper mantle.

[1] Our understanding of large-scale mantle dynamics depends on accurate models of seismic velocity variation in the upper mantle transition zone (400-1000 km depth). With the Mode Branch Stripping technique (MBS) of van Heijst and Woodhouse [1997] it is possible to extract the dispersion characteristics of overtone surface wave signals from single source-receiver overtone waveforms. Such data provide new global transition zone constraints. We combined more than a million measurements of path-average overtone phase velocity with normal-mode splitting functions and body wave travel times to construct model S20RTSb of shear velocity heterogeneity throughout the mantle. We discuss in detail the resolution of structural heterogeneity in the transition zone. The main observations are the following: (1) Large-scale shear velocity variations (15%) in the upper 250 km of the mantle are at least 5 times larger than deeper in the mantle. Highvelocity keels of Archean cratons extend to about 200 km depth. Low velocities related to mid-ocean ridge upwelling are confined to the upper 150 km of the mantle. (2) The 220-km discontinuity in PREM cannot be reconciled with Rayleigh wave dispersion, especially in oceans. (3) The velocity below the oceanic lithosphere (350-400 km depth) is 1-1.5% lower than beneath the continental lithosphere. (4) High-velocity slabs of former oceanic lithosphere are conspicuous structures just above the 670-km discontinuity. They extend to about 1100 km depth in the South American, Indonesian, and Kermadec subduction zones, indicating that slabs penetrate through the 670-km phase transition in several subduction zones. (5) We observe lower-than-average shear velocity below the lithosphere at eight hot spots (including Hawaii, Iceland, Easter, and Afar). It is, however, difficult to accurately estimate their depth extent in the transition zone because of the limited vertical resolution.

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 body wave 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. Anomalous features in our anisotropic model are 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 present the new model SP12RTS of isotropic shear-wave (V S) and compressional-wave (V P) velocity variations in the Earth's mantle. SP12RTS is derived using the same methods as employed in the construction of the shear-wave velocity models S20RTS and S40RTS, and the same data types. SP12RTS includes additional traveltime measurements of P-waves and new splitting measurements: 33 normal modes with sensitivity to the compressional-wave velocity and 9 Stoneley modes with sensitivity primarily to the lowermost mantle. Contrary to S20RTS and S40RTS, variations in V S and V P are determined without invoking scaling relationships. Lateral velocity variations in SP12RTS are parametrised using spherical harmonics up to degree 12, to focus on long-wavelength features of V S and V P and their ratio R. Large-lowvelocity provinces (LLVPs) are observed for both V S and V P. SP12RTS also features an increase of R up to 2500 km depth, followed by a decrease towards the core-mantle boundary. A negative correlation between the shear-wave and bulk-sound velocity variations is observed for both the LLVPs and the surrounding mantle. These characteristics can be explained by the presence of post-perovskite or large-scale chemical heterogeneity in the lower mantle.