Shear Properties of Earth's Inner Core

2021 ◽  
Vol 50 (1) ◽  
Author(s):  
Hrvoje Tkalčić ◽  
Sheng Wang ◽  
Thanh-Son Phạm
Keyword(s):  
Shear Wave ◽  
Inner Core ◽  
Normal Modes ◽  
Outer Core ◽  
Annual Review ◽  
Publication Date ◽  
Shear Properties ◽  
Shear Wave Speed ◽  
Earth’S Inner Core ◽  
Shear Structure

Understanding how Earth's inner core (IC) develops and evolves, including fine details of its structure and energy exchange across the boundary with the liquid outer core, helps us constrain its age, relationship with the planetary differentiation, and other significant global events throughout Earth's history, as well as the changing magnetic field. Since its discovery in 1936 and the solidity hypothesis in 1940, Earth's IC has never ceased to inspire geoscientists. However, while there are many seismological observations of compressional waves and normal modes sensitive to the IC's compressional and shear structure, the shear waves that provide direct evidence for the IC's solidity have remained elusive and have been reported in only a few publications. Further advances in the emerging correlation-wavefield paradigm, which explores waveform similarities, may hold the keys to refined measurements of all inner-core shear properties, informing dynamical models and strengthening interpretations of the IC's anisotropic structure and viscosity. ▪ What are the shear properties of the inner core, such as the shear-wave speed, shear modulus, shear attenuation, and shear-wave anisotropy? Can the shear properties be measured seismologically and confirmed experimentally? Expected final online publication date for the Annual Review of Earth and Planetary Sciences, Volume 50 is May 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

scholarly journals On shear wave velocity in the top of the Earth’s inner core

2019 ◽  
Vol 488 (4) ◽  
pp. 434-438
Author(s):  
D. N. Krasnoshchekov ◽  
V. M. Ovtchinnikov ◽  
O. A. Usoltseva
Keyword(s):  
Shear Wave ◽  
Wave Velocity ◽  
Shear Wave Velocity ◽  
Inner Core ◽  
Solid Core ◽  
The Earth ◽  
Inner Surface ◽  
Core Boundary ◽  
Standard Models ◽  
Earth’S Inner Core

Analysis of PKIIKP waves reflected off the inner surface of the solid core boundary and recorded close to the antipode indicates the shear wave velocity in its top can be by 10-60% below 3.5 km/s envisaged by standard models of the Earth.

Shear wave anisotropy of textured hcp-Fe in the Earth's inner core

2010 ◽  
Vol 298 (3-4) ◽  
pp. 361-366 ◽  
Author(s):  
Jung-Fu Lin ◽  
Zhu Mao ◽  
Hasan Yavaş ◽  
Jiyong Zhao ◽  
Leonid Dubrovinsky
Keyword(s):  
Shear Wave ◽  
Inner Core ◽  
Earth’S Inner Core

scholarly journals Superrotation of Earth’s Inner Core, Extraterrestrial Impacts, and the Effective Viscosity of Outer Core

2015 ◽  
Vol 2015 ◽  
pp. 1-8 ◽  
Author(s):  
Pirooz Mohazzabi ◽  
John D. Skalbeck
Keyword(s):  
Steady State ◽  
Effective Viscosity ◽  
Eddy Viscosity ◽  
Inner Core ◽  
Outer Core ◽  
Gravitational Coupling ◽  
Geological Time ◽  
New Model ◽  
Earth’S Inner Core

The recently verified superrotation of Earth’s inner core is examined and a new model is presented which is based on the tidal despinning of the mantle and the viscosity of the outer core. The model also takes into account other damping mechanisms arising from the inner core superrotation such as magnetic and gravitational coupling as well as contribution from eddy viscosity in the outer core. The effective viscosity obtained in this model confirms a previously well constrained value of about 103 Pa s. In addition, the model shows that the currently measured superrotation of the inner core must be almost exactly equal to its asymptotic or steady-state value. The effect of extraterrestrial impacts is also investigated, and it is shown that perturbations due to such impacts can only persist over a short geological time.

Viscous drag and the differential rotation of the Earth's core

1997 ◽  
Vol 57 (1) ◽  
pp. 231-233
Author(s):  
DAVID L. BOOK ◽  
J. A. VALDIVIA
Keyword(s):  
Simple Model ◽  
Differential Rotation ◽  
Dynamic Viscosity ◽  
Inner Core ◽  
Outer Core ◽  
Viscous Drag ◽  
Earth’S Rotation ◽  
The Core ◽  
The Earth ◽  
Earth’S Inner Core

It is proposed that the differential rotation of the Earth's inner core deduced by Song and Richards is due to a combination of the deceleration of the Earth's rotation and the viscous drag between the Earth's inner and outer cores. If this model is correct then the dynamic viscosity in the outer core of the Earth can be estimated to be μ≈104 poise. Besides providing a novel way of determining the viscosity of the core, this simple model suggests some new tests and shows how astronomical effects can influence geological phenomena.

Core–mantle topographic coupling: a parametric approach and implications for the formulation of a triaxial three-layered Earth rotation

2021 ◽  
Vol 225 (3) ◽  
pp. 2060-2074
Author(s):  
Huifeng Zhang ◽  
Wenbin Shen
Keyword(s):  
Earth Rotation ◽  
Inner Core ◽  
Normal Modes ◽  
Outer Core ◽  
Chandler Wobble ◽  
Parametric Approach ◽  
Layered Earth ◽  
Fluid Core ◽  
Adopted Model ◽  
Topography Model

SUMMARY We propose a parametric approach to the topographic (TOP) coupling between the mantle and outer core for refinement of the latest triaxial three-layered Earth rotation theory. Based on three models of the core–mantle boundary (CMB) topography, we obtain the axial components of the TOP torque as −2.08 × 1019, −2.72 × 1018 and −1.97 × 1017 N m, respectively. Under the frame of the triaxial three-layered Earth rotation theory, we solve the corresponding periods of free core nutation as −(329.83 ± 28.12), −(457.54 ± ∼) and −(428.23 ± 1.09) mean solar days (d), respectively. The other three normal modes, namely, Chandler wobble, inner core wobble and free inner core nutation, are almost not affected by the TOP coupling of the CMB, their period values being 433.24, 2718.69 and 934.02 d, respectively. Calculations show that the TOP torque is highly sensitive to the adopted model of the topography, which is known to be robust. Taking into account the normal modes of the triaxial three-layered Earth rotation, the results of the CMB topography obtained by seismic tomography can be constrained in the future to a certain extent. In this study, considering the TOP coupling with the appropriate topography model, the estimates for the dynamic ellipticity ef of the fluid core lie between 0.0026340 and 0.0026430, values that are 3.56 % higher than the hydrostatic equilibrium value.

scholarly journals A simple 3-D numerical model of thermal convection in Earth's growing inner core: on the possibility of the formation of the degree-one structure with lateral viscosity variations

2015 ◽  
Vol 7 (4) ◽  
pp. 3817-3841
Author(s):  
M. Yoshida
Keyword(s):  
Thermal Convection ◽  
Inner Core ◽  
Outer Core ◽  
Limited Range ◽  
Asymmetric Structure ◽  
Planetary Scale ◽  
Core Boundary ◽  
Earth’S Inner Core ◽  
East West ◽  
Rheological Heterogeneity

Abstract. An east-west hemispherically asymmetric structure for Earth's inner core has been suggested by various seismological evidence, but its origin is not clearly understood. Here, to investigate the possibility of an "endogenic origin" for the degree-one thermal/mechanical structure of the inner core, I performed new numerical simulations of thermal convection in the growing inner core. A setup value that controls the viscosity contrast between the inner core boundary and the interior of the inner core, ΔηT, was taken as a free parameter. Results show that the degree-one structure only appeared for a limited range of ΔηT; such a scenario may be possible but is not considered probable for the real Earth. The degree-one structure may have been realized by an "exogenous factor" due to the planetary-scale thermal coupling among the lower mantle, the outer core, and the inner core, not by an endogenic factor due to the internal rheological heterogeneity.

Vibronic and Environmental Effects in Simulations of Optical Spectroscopy

2021 ◽  
Vol 72 (1) ◽  
Author(s):  
Tim J. Zuehlsdorff ◽  
Sapana V. Shedge ◽  
Shao-Yu Lu ◽  
Hanbo Hong ◽  
Vincent P. Aguirre ◽  
...  
Keyword(s):  
Optical Spectroscopy ◽  
Normal Modes ◽  
Nonlinear Spectroscopy ◽  
Annual Review ◽  
Publication Date ◽  
Cumulant Expansion ◽  
Dynamic Approach ◽  
Excitation Energies ◽  
Static Approach ◽  
Phase Systems

Including both environmental and vibronic effects is important for accurate simulation of optical spectra, but combining these effects remains computationally challenging. We outline two approaches that consider both the explicit atomistic environment and the vibronic transitions. Both phenomena are responsible for spectral shapes in linear spectroscopy and the electronic evolution measured in nonlinear spectroscopy. The first approach utilizes snapshots of chromophore-environment configurations for which chromophore normal modes are determined. We outline various approximations for this static approach that assumes harmonic potentials and ignores dynamic system-environment coupling. The second approach obtains excitation energies for a series of time-correlated snapshots. This dynamic approach relies on the accurate truncation of the cumulant expansion but treats the dynamics of the chromophore and the environment on equal footing. Both approaches show significant potential for making strides toward more accurate optical spectroscopy simulations of complex condensed phase systems. Expected final online publication date for the Annual Review of Physical Chemistry, Volume 72 is April 2021. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Shear properties of Earth’s inner core constrained by a detection ofJwaves in global correlation wavefield

Science ◽  
2018 ◽  
Vol 362 (6412) ◽  
pp. 329-332 ◽  
Author(s):  
Hrvoje Tkalčić ◽  
Thanh-Son Phạm
Keyword(s):  
Inner Core ◽  
Reference Model ◽  
Shear Properties ◽  
Shear Moduli ◽  
Wave Speeds ◽  
Global Correlation ◽  
Core Boundary ◽  
Earth’S Inner Core ◽  
Seismic Wavefield ◽  
Dynamical Interpretation

SeismicJwaves, shear waves that traverse Earth’s inner core, provide direct constraints on the inner core’s solidity and shear properties. However, these waves have been elusive in the direct seismic wavefield because of their small amplitudes. We devised a new method to detectJwaves in the earthquake coda correlation wavefield. They manifest through the similarity with other compressional core-sensitive signals. The inner core is solid, but relatively soft, with shear-wave speeds and shear moduli of 3.42 ± 0.02 kilometers per second and 149.0 ± 1.6 gigapascals (GPa) near the inner core boundary and 3.58 ± 0.02 kilometers per second and 167.4 ± 1.6 GPa in Earth’s center. The values are 2.5% lower than the widely used Preliminary Earth Reference Model. This provides new constraints on the dynamical interpretation of Earth’s inner core.

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