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.

Measuring the melting curve of iron at super-Earth core conditions

Science ◽  
2022 ◽  
Vol 375 (6577) ◽  
pp. 202-205
Author(s):  
Richard G. Kraus ◽  
Russell J. Hemley ◽  
Suzanne J. Ali ◽  
Jonathan L. Belof ◽  
Lorin X. Benedict ◽  
...  
Keyword(s):  
Liquid Metal ◽  
Inner Core ◽  
Melting Curve ◽  
Radiation Shielding ◽  
Metal Core ◽  
Earth Core ◽  
Core Boundary ◽  
Earth Like Planets ◽  
Earth’S Inner Core ◽  
Core Conditions

Terapascal iron-melting temperature The pressure and temperature conditions at which iron melts are important for terrestrial planets because they determine the size of the liquid metal core, an important factor for understanding the potential for generating a radiation-shielding magnetic field. Kraus et al . used laser-driven shock to determine the iron-melt curve up to a pressure of 1000 gigapascals (see the Perspective by Zhang and Lin). This value is about three times that of the Earth’s inner core boundary. The authors found that the liquid metal core lasted the longest for Earth-like planets four to six times larger in mass than the Earth. —BG

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.

scholarly journals Fe Alloy Slurry and a Compacting Cumulate Pile Across Earth's Inner‐Core Boundary

2019 ◽  
Vol 124 (11) ◽  
pp. 10954-10967 ◽  
Author(s):  
Youjun Zhang ◽  
Peter Nelson ◽  
Nick Dygert ◽  
Jung‐Fu Lin
Keyword(s):  
Inner Core ◽  
Core Boundary ◽  
Earth’S Inner Core

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.

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