Dr. Daniel A. Frost: Constraining the history of the inner core with seismic anisotropy

Abstract:

Progressive crystallisation of Earth's inner core is the present-day source of energy for convection in the outer core and thus magnetic field generation. Therefore, determining the rate and pattern of inner core growth is crucial to understanding the evolution of the geodynamo and our magnetic field. The growth history of the inner core is likely recorded in the distribution and strength of its seismic anisotropy, the directional dependence of seismic velocity, which arises from deformation texturing constrained by conditions at the inner-core solid-fluid boundary. Since the inner core grows from the centre out, the deeper we look into the inner core the further back in time we see.

I will present an analysis of seismic body waves which sample the inner core (called PKP) showing that the strength of seismic anisotropy increases with depth within the inner core, and that the strongest anisotropy is offset from Earth's rotation axis into the western hemisphere. Then, using geodynamic growth models and mineral physics calculations, I simulate the development of inner core anisotropy in a self-consistent manner. I test several phases of iron and compositions and find that an inner core composed of hexagonally close-packed iron-nickel alloy, deformed by a combination of preferential equatorial growth and slow translation, can match our enigmatic seismic observations. With this model I can make inferences on how old the inner core is, how hot it is, and how it powers the life of our planet, contributing to our understanding of the evolution of the whole Earth.

Host: Dr. Andy Darling

This is a hybrid event, if you are unable to join us in person please join via zoom. 

Meeting ID: 997 2477 2096

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