Radial earth models revisited

The current set of reference models for the radial variation of Earth structure have been in use for several decades, and provide a good representation of many aspects of the seismic wavefield. Nevertheless, strong constraints from the differential times between pairs of SmKS phases indicate the need to modify the P wave speed profile in the upper part of the outer core. In order to incorporate such a change and maintain the representation of the full suite of seismic phases compensatory adjustments have to be made, dominantly in the mantle. Using multi-objective optimization, a new preferred radial model ek137 has been generated that provides a good representation of the traveltimes of all core phases. An adiabatic profile can be maintained through most of the outer core, but departures are needed at the base, as in the ak135 model. The latest estimates for inner core shear wave speed are included in ek137.