A glassy lowermost outer core

Cormier, Vernon F.

doi:10.1111/j.1365-246x.2009.04283.x

Cited by 29 publications

(22 citation statements)

References 32 publications

(34 reference statements)

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“…Their interpretations included the possibility of strong gradients in shear modulus on either the outer or inner core side of the ICB. Possibly consistent with observed lateral variations in P-velocity gradient in the lowermost outer core (Yu et al 2005) is a region of laterally varying viscosity associated with a frequency dependent shear modulus in the lowermost outer core (Cormier 2009). Lateral variations in this region above the ICB may be coupled to lateral variation in the solidification process of the inner core (Cormier 2007) and lateral variations of flow in the outer core (Aubert et al 2008).…”

supporting

confidence: 76%

On the inner-outer core density contrast from PKiKP/PcP amplitude ratios and uncertainties caused by seismic noise

Tkalčić

Kennett

Cormier

2009

Geophysical Journal International

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S U M M A R YThe inner core boundary (ICB) of the earth is characterized by a discontinuous change in elastic properties between the liquid outer and solid inner core. In the ray theory approximation, a measure of the density contrast at the ICB is given by the amplitude ratio of P waves reflected from the core-mantle boundary (CMB; PcP waves) and the ICB (PKiKP waves), since that ratio conveniently appears in an explicit form in the transmission/reflection coefficient equations. The results for inner-outer core density contrast derived from direct amplitude picks of these waves in the time domain have varied significantly among different authors.The transmission/reflection coefficients on the liquid-solid and solid-liquid boundaries derived from ground displacements enable a direct comparison between the amplitude measurements on displacement seismograms in the time domain and theoretical values. A new approach is proposed and applied to integrate effects of microseismic and signal-generated noise with the amplitude measurements, thus providing a direct maximal uncertainty measure. To suppress the effects of varying radiation pattern and distinctively different ray paths at longer epicentral distances, this new method was applied to high-quality arrivals of PcP and PKiKP waves from a nuclear explosion observed at epicentral distances 10 • -20 • from recording stations. The resulting uncertainties are high precluding precise estimates of the ICB density contrast, but provide a robust estimate of an upper bound from body waves of about 1100 kg m −3 . Median values of two amplitude ratios observed around 17 • epicentral distance indicate a small density contrast of 200-300 kg m −3 and suggest the existence of zones of suppressed density contrast between the inner and the outer core, a density contrast stronger than 5000 kg m −3 at the CMB, or a combination of both.

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supporting

confidence: 76%

On the inner-outer core density contrast from PKiKP/PcP amplitude ratios and uncertainties caused by seismic noise

Tkalčić

Kennett

Cormier

2009

Geophysical Journal International

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“…Nutations also favor a viscosity increase at ICB (see details in Souriau and Calvet, 2015). A viscosity increase is consistent with the possibility of a non-zero shear velocity Vs, as proposed by Mochizuki and Ohminato (1989) from normal mode analysis (Vs = 0.1-0.5 km/s), and by Cormier (2009) from the amplitudes of waves reflected at ICB (Vs ∼ 0.5 km/s, viscosity of about 10 9 Pa s at ICB). The viscosity is crucial to support lateral heterogeneities inside the layer.…”

Section: The Dense Basal Layer In the Outer Core And The Uppermost Isupporting

confidence: 85%

Presumption of large-scale heterogeneity at the top of the outer core basal layer

Souriau

2015

Earth and Planetary Science Letters

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“…Such a heterogeneity could not be sustained by the liquid unless its viscosity is very high (Cormier et al, 2011). This is not completely excluded: This layer could be a zone of small, nonzero rigidity (v S ¼ 0.1-0.5 km s À1 ), as revealed by both normal modes (Mochizuki and Ohminato, 1989) and PKiKP waves reflected at the ICB (Cormier, 2009); thus, it could also be a zone of increased viscosity. The free inner core nutations suggest a viscosity of $10 5 Pa s (Koot et al, 2010).…”

Section: The Stratification At the Base Of The Liquid Corementioning

confidence: 99%