Reconciling the hemispherical structure of Earth/'s inner core with its super-rotation

Waszek, Lauren and Irving, Jessica C. E. and Deuss, Arwen (2011) Reconciling the hemispherical structure of Earth/'s inner core with its super-rotation. Nature Geoscience, 4 (4). pp. 264-267. ISSN 1752-0894 EISSN:1752-0908 DOI 10.1038/ngeo1083

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Official URL: http://dx.doi.org/10.1038/ngeo1083

Abstract

Earth’s solid inner core grows through solidification of material from the fluid outer core onto its surface at rates of about 1 mm per year1, freezing in core properties over time and generating an age–depth relation for the inner core. A hemispherical structure of the inner core is well-documented: an isotropic eastern hemisphere with fast seismic velocities contrasts with a slower, anisotropic western hemisphere2, 3, 4. Independently, the inner core is reported to super-rotate at rates of up to 1° per year5, 6, 7. Considering the slow growth, steady rotation rates of this magnitude would erase ’frozen-in’ regional variation and cannot coexist with hemispherical structure. Here, we exploit the age–depth relation, using the largest available PKIKP–PKiKP seismic travel time data set, to confirm hemispherical structure in the uppermost inner core, and to constrain the locations of the hemisphere boundaries. We find consistent eastward displacement of these boundaries with depth, from which we infer extremely slow steady inner core super-rotation of 0.1°–1° per million years. Our estimate of long-term super-rotation reconciles inner core rotation with hemispherical structure, two properties previously thought incompatible. It is in excellent agreement with geodynamo simulations8, 9, while not excluding the possibility that the much larger rotation rates inferred earlier5, 6, 7 correspond to fluctuations in inner core rotation on shorter timescales10.

Item Type: Article
Uncontrolled Keywords: 2011AREP; IA62;
Subjects: 02 - Geodynamics, Geophysics and Tectonics
Divisions: 02 - Geodynamics, Geophysics and Tectonics
Journal or Publication Title: Nature Geoscience
Volume: 4
Page Range: pp. 264-267
Identification Number: 10.1038/ngeo1083
Depositing User: Sarah Humbert
Date Deposited: 29 Apr 2011 16:45
Last Modified: 23 Jul 2013 10:02
URI: http://eprints.esc.cam.ac.uk/id/eprint/2054

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