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Radial Reference Models: Core Structure and Spin Transition Effects

Description: 

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 wavespeed profile in the upper part of the outer core. To incorporate such a change and maintain the representation of the full suite of seismic phases compensatory adjustments must be made, dominantly in the mantle. Using multi-objective optimisation, a new preferred radial model ek137 has been generated that provides a good representation of the travel times of all core phases, whilst retaining a good representation of mantle phases.

In the iron bearing minerals of the lower mantle, there is the potential for a transition from the high-spin state to the low-spin state, though there is, as yet, no definite consensus on behaviour. The relative behaviour of the shear and bulk modulus as a function of pressure for the ak135 and ek137 models is suggestive of a residual effect of a 3-D averaged spin transition in the ferropericlase component of the lower mantle. The character of the spin transition is commonly compared against reference models (particularly PREM) but needs to be compared with the defining data.

Session: Earth’s Structure From the Crust to the Core

Type: Oral

Date: 4/18/2023

Presentation Time: 10:30 AM (local time)

Presenting Author: Brian L. N. Kennett

Student Presenter: No

Invited Presentation: 

Authors