The rigidity of the Earth’s inner core

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Keith Edward Bullen


The evidence for the existence of significant rigidity in the Earth's inner core is summarised and discussed in the light of recent work. Quantum-mechanical calculations, based on a Thomas-Fermi-Dirac model, suggest that an earlier estimate of 3.6 × 10¹² dyn/cm² for this rigidity may need to be reduced by 0.5 × 10¹² dyn/cm². The theoretical travel-times of the phase PKJKP would then need to be increased by amounts ranging from zero to 40 seconds. It is shown that the use of Gutenberg's seismic data in place of that of Jeffreys would reduce the estimated rigidity of the inner core by a further 1.6 × 10¹² dyn/cm², approximately. It is suggested that Gutenberg's data lead to the lowest likely value for the rigidity of the inner core, namely 1.5 × 10¹² dyn/cm², so that, on all present evidence, it is improbable that the inner core is less than about twice as rigid as steel is at zero pressure.

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Bullen KE. The rigidity of the Earth’s inner core. Ann. Geophys. [Internet]. 2010Feb.23 [cited 2021Dec.4];53(1):1-5. Available from: