The existence of radial anisotropy in Earth's upper inner core revealed from seismic normal mode observations

TitleThe existence of radial anisotropy in Earth's upper inner core revealed from seismic normal mode observations
Publication TypeJournal Article
Year of Publication2015
AuthorsLythgoe KH, Deuss A
JournalGeophysical Research Letters
Volume42
Issue12
Pagination4841-4848
Date Published06/2015
Abstract

As we strive to understand the most remote region of our planet, one critical area of investigation is the uppermost inner core since its structure is related to solidification of outer core material at the inner core boundary (ICB). Previous seismic studies have used body waves to show that the top ∼100 km of the inner core is isotropic. However, radial anisotropy cannot be uniquely determined by body wave observations. Alternatively, normal mode center frequencies are sensitive to spherically symmetric Earth structure, therefore may provide a constraint on the existence of radial anisotropy in the inner core. Here we show that normal mode center frequency measurements are compatible with 2–5% radial anisotropy in the top ∼100 km of the inner core with a fast direction radially outward and a slow direction along the ICB. Given the uncertainties in the mineral physics and processes that produce anisotropy, the observed radial anisotropy may be reconciled with predictions based on either solidification processes or from texturing due to anisotropic growth.

DOI10.1002/2015GL064326