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Core structure re-examined using new teleseismic data recorded in Antarctica: evidence for, at most, weak cylindrical seismic anisotropy in the inner core

journal contribution
posted on 2023-05-17, 03:00 authored by Leykam, D, Tkalcic, H, Anya ReadingAnya Reading
We present a significant addition to the data set of traveltimes of seismic PKP waves that sample the Earth's lowermost mantle and core along the Earth's rotation axis. Recorded at permanent Global Seismic Network (GSN) and temporary SSCUA deployment broad-band seismographic stations in Antarctica, the new data improve the previously poor and biased coverage that underlies the seismic constraints on recent models of inner core structure and anisotropy. On the one hand, new differential PKP traveltime measurements improve the sampling of predominantly the eastern inner core hemisphere. PKPab-df and PKPbc-df differential traveltime residuals, with respect to the spherically symmetric model ak135, are consistently smaller than two seconds along the north–south paths sampled. Axially symmetric models of inner core seismic anisotropy with fast axis parallel to the Earth's rotation axis require a weak anisotropy of (0.7 ± 0.1) per cent to be consistent with our PKPbc-df observations. PKPbc-df residuals from the quasi-eastern hemisphere indicate (0.4 ± 0.1) per cent anisotropy. If only PKPbc-df observations from the top 200 km of this hemisphere are considered, this is reduced to (0.1 ± 0.2) per cent, consistent with an isotropic layer. On the other hand, new absolute PKP traveltime measurements add to the sampling of both hemispheres of the inner core, but it is difficult to use them with more confidence to assess structure of the core since they are affected by crustal and mantle structure and source uncertainties. The newly collected data set also increases constraints on D" structure beneath the South Pole. In contrast to previous inferences based on data from northern stations, we find no evidence of a velocity heterogeneity in the outer core near the inner core boundary associated with the cylinder tangent to the inner core in the southern hemisphere.

History

Publication title

Geophysical Journal International

Volume

180

Pagination

1329-1343

ISSN

0956-540X

Department/School

School of Natural Sciences

Publisher

Blackwell Publishing Ltd

Place of publication

9600 Garsington Rd, Oxford, England, Oxon, Ox4 2Dg

Rights statement

The definitive published version is available online at: http://interscience.wiley.com

Repository Status

  • Restricted

Socio-economic Objectives

Expanding knowledge in the earth sciences

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