Radial earth models revisited

2020 ◽  
Vol 222 (3) ◽  
pp. 2189-2204
Author(s):  
B L N Kennett
Keyword(s):  
Wave Speed ◽  
Inner Core ◽  
Outer Core ◽  
P Wave ◽  
Good Representation ◽  
Multi Objective Optimization ◽  
Shear Wave Speed ◽  
Reference Models ◽  
Radial Model ◽  
Seismic Wavefield

SUMMARY The current set of reference models for the radial variation of Earth structure have been in use for several decades, and provide a good representation of many aspects of the seismic wavefield. Nevertheless, strong constraints from the differential times between pairs of SmKS phases indicate the need to modify the P wave speed profile in the upper part of the outer core. In order to incorporate such a change and maintain the representation of the full suite of seismic phases compensatory adjustments have to be made, dominantly in the mantle. Using multi-objective optimization, a new preferred radial model ek137 has been generated that provides a good representation of the traveltimes of all core phases. An adiabatic profile can be maintained through most of the outer core, but departures are needed at the base, as in the ak135 model. The latest estimates for inner core shear wave speed are included in ek137.

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.

The constitution of the core: seismological evidence

1982 ◽  
Vol 306 (1492) ◽  
pp. 11-20 ◽  
Keyword(s):  
Inner Core ◽  
Outer Core ◽  
Body Waves ◽  
P Wave ◽  
Necessary Condition ◽  
Strong Increase ◽  
Linear Perturbation ◽  
The Core ◽  
Rate Of Increase ◽  
Seismic Quality Factor

The present best estimates of seismic velocities in the core are compared with the 1939 solution of Jeffreys, with emphasis on the remaining uncertainties and present resolution capability. The relative contributions of measurements of seismic body waves and terrestrial eigenspectra to the inverse problem of the determination of elastic parameters, density and damping in the core are compared. Linear perturbation algorithms and smoothing functions used with the spectral data reduce their capacity for fine structural definition. Between radii of 1400 and 3300 km (shell E), the outer core appears to be substantially homogeneous and non-stratified, with small or zero rigidity and a dimensionless seismic quality factor, Q ,of order 10 4 . It is a sufficient but still not a necessary condition that density p follows precisely the Adams-Williamson equation in E; for an averaging interval of 400 km, estimates of have a standard error there of about 0.2 g cm -3 . There is as yet no unequivocal seismological evidence for or against a boundary shell (thickness less than about 200 km) at the top of the liquid outer core. At the bottom of the outer core, the evidence is becoming stronger that any reduction in the rate of increase with depth of P wave velocity is confined to a minor transition layer little more than 100 km thick. The inner core has a sharp outer boundary at about 1216 km radius, but below it only average physical properties are estimated with any confidence. The average seismic compressions and shear velocities are about — 11.2 and /? — 3.5 km s -1 and 12.5 < p < 13.6 g cm-3, yielding a peculiar mean Poisson ratio of 0.44 or greater. At the inner core boundary, jumps in parameters are: A « 0.65, A/? — 2.0- 3.0 km s-1 and A p» 1.0 g cm -3 . Recent travel-time and waveform synthetics suggest a strong increase of P (and perhaps S) velocity in the upper 300 km of the inner core, which could be interpreted as a mixing or melting effect. Damping properties in the inner core may have an unusual dependence on wave frequency with an order of magnitude increase in Q from 1 Hz to 4 mHz vibrations.

Reconciling elasticity tensor constraints from mineral physics and seismological observations: applications to the Earth’s inner core

2020 ◽  
Vol 222 (2) ◽  
pp. 1135-1145
Author(s):  
Brent G Delbridge ◽  
Miaki Ishii
Keyword(s):  
Shear Wave ◽  
Elastic Constants ◽  
Wave Speed ◽  
Inner Core ◽  
Body Wave ◽  
Elasticity Tensor ◽  
The Body ◽  
Wave Speeds ◽  
Mineral Physics ◽  
Shear Wave Speed

SUMMARY This study establishes the proper framework in which to compare seismic observations with mineral physics constraints for studies of the inner core by determining how the elements of the elasticity tensor are sampled by the normal modes of the Earth. The obtained mapping between the elements of the elasticity tensor and the seismic wave speeds shows that the choice of averaging scheme used to calculate isotropic properties is crucial to understand the composition of the inner core, especially for comparison with the shear wave speed such as that provided in PREM. For example, the appropriate shear wave speed calculated for an Fe-Ni-Si hcp alloy at inner-core conditions differs from the shear wave speed obtained by taking a Reuss average by as much as $27\, {\rm per\, cent}$. It is also shown for the first time that by combining the isotropic observations based upon normal-mode characteristic frequencies and anisotropic parameters from their splitting, the five independent elastic parameters (A, C, F, L and N) that fully describe a transversely isotropic inner core can be uniquely constrained. The elastic values based upon a variety of mode-splitting studies are reported, and the differences between models from various research groups are shown to be relatively small ($\lt 10\, {\rm per\, cent}$). Additionally, an analogous body-wave methodology is developed to approximately estimate the five independent elastic constants from observations of compressional wave traveltime anomalies. The body-wave observations are utilized to consider the depth dependence of inner-core anisotropy, in particular, the structure of the innermost inner core. Finally, we demonstrate that substantial errors may result when attempting to relate seismically observed P and S wave speeds from Debye velocities obtained through nuclear resonant inelastic X-ray scattering. The results of these experiments should be compared directly with the Debye velocity calculated from seismically constrained elastic constants. This manuscript provides a new set of formulae and values of seismic observations of the inner core that can be easily compared against mineral physics constraints for better understanding of the inner-core composition.

The origin of precursors to core waves

1970 ◽  
Vol 60 (3) ◽  
pp. 939-952 ◽  
Author(s):  
Eystein Husebye ◽  
Raúl Madariaga
Keyword(s):  
Inner Core ◽  
Outer Core ◽  
P Wave ◽  
Long Tail ◽  
The Core ◽  
Short Period ◽  
Diffracted Waves ◽  
Multiple Paths ◽  
Core Boundary ◽  
The Waves

Abstract The origin of the precursors of the core waves in the range 105°-142° is studied. Between 105° and 125° a long tail is observed after the P wave diffracted by the core. In the range 130° ≦ Δ ≦ 142° we usually observe short-period onsets a few seconds before PKIKP; these are the waves called P(GH). Reflection at a discontinuity in the outer core, near the inner-core boundary, is shown to produce the P(GH) branch. Reflections in the outer core are rejected as a mechanism for the tail of the P diffracted wave. A theoretical study of diffraction of P by the core shows that higher modes of diffracted waves cannot explain the observations of the tail of P diffracted. We conclude, by elimination, that it is due to reflections or multiple paths in the upper mantle.

scholarly journals Osmotic stress and vesiculation as key mechanisms controlling bacterial sensitivity and resistance to TiO2 nanoparticles

2021 ◽  
Vol 4 (1) ◽  
Author(s):  
Christophe Pagnout ◽  
Angelina Razafitianamaharavo ◽  
Bénédicte Sohm ◽  
Céline Caillet ◽  
Audrey Beaussart ◽  
...  
Keyword(s):  
Lipid Peroxidation ◽  
Osmotic Stress ◽  
Inner Core ◽  
Metal Oxide Nanoparticles ◽  
Membrane Vesicles ◽  
Outer Core ◽  
Membrane Composition ◽  
Cell Turgor ◽  
Bacterial Sensitivity ◽  
Membrane Components

AbstractToxicity mechanisms of metal oxide nanoparticles towards bacteria and underlying roles of membrane composition are still debated. Herein, the response of lipopolysaccharide-truncated Escherichia coli K12 mutants to TiO2 nanoparticles (TiO2NPs, exposure in dark) is addressed at the molecular, single cell, and population levels by transcriptomics, fluorescence assays, cell nanomechanics and electrohydrodynamics. We show that outer core-free lipopolysaccharides featuring intact inner core increase cell sensitivity to TiO2NPs. TiO2NPs operate as membrane strippers, which induce osmotic stress, inactivate cell osmoregulation and initiate lipid peroxidation, which ultimately leads to genesis of membrane vesicles. In itself, truncation of lipopolysaccharide inner core triggers membrane permeabilization/depolarization, lipid peroxidation and hypervesiculation. In turn, it favors the regulation of TiO2NP-mediated changes in cell Turgor stress and leads to efficient vesicle-facilitated release of damaged membrane components. Remarkably, vesicles further act as electrostatic baits for TiO2NPs, thereby mitigating TiO2NPs toxicity. Altogether, we highlight antagonistic lipopolysaccharide-dependent bacterial responses to nanoparticles and we show that the destabilized membrane can generate unexpected resistance phenotype.

scholarly journals Spatial variations in Achilles tendon shear wave speed

2014 ◽  
Vol 47 (11) ◽  
pp. 2685-2692 ◽  
Author(s):  
Ryan J. DeWall ◽  
Laura C. Slane ◽  
Kenneth S. Lee ◽  
Darryl G. Thelen
Keyword(s):  
Achilles Tendon ◽  
Shear Wave ◽  
Wave Speed ◽  
Spatial Variations ◽  
Shear Wave Speed

Measured temperature and pressure dependence of Vp and Vs in compacted, polycrystalline sI methane and sII methane–ethane hydrate

2003 ◽  
Vol 81 (1-2) ◽  
pp. 47-53 ◽  
Author(s):  
M B Helgerud ◽  
W F Waite ◽  
S H Kirby ◽  
A Nur
Keyword(s):  
High Pressure ◽  
Shear Wave ◽  
Pressure Dependence ◽  
Gas Hydrate ◽  
Pressure Vessel ◽  
Wave Speed ◽  
Measured Temperature ◽  
Shear Wave Speed ◽  
Temperature And Pressure ◽  
Fixed End

We report on compressional- and shear-wave-speed measurements made on compacted polycrystalline sI methane and sII methane–ethane hydrate. The gas hydrate samples are synthesized directly in the measurement apparatus by warming granulated ice to 17°C in the presence of a clathrate-forming gas at high pressure (methane for sI, 90.2% methane, 9.8% ethane for sII). Porosity is eliminated after hydrate synthesis by compacting the sample in the synthesis pressure vessel between a hydraulic ram and a fixed end-plug, both containing shear-wave transducers. Wave-speed measurements are made between –20 and 15°C and 0 to 105 MPa applied piston pressure. PACS No.: 61.60Lj

scholarly journals A novel semi-implicit scheme for elastodynamics and wave propagation in nearly and truly incompressible solids

2021 ◽  
Author(s):  
Chennakesava Kadapa
Keyword(s):  
Wave Propagation ◽  
Wave Speed ◽  
Critical Time ◽  
Incompressible Material ◽  
Implicit Scheme ◽  
Bulk Wave ◽  
Lumped Mass ◽  
Time Step ◽  
Material Models ◽  
Shear Wave Speed

AbstractThis paper presents a novel semi-implicit scheme for elastodynamics and wave propagation problems in nearly and truly incompressible material models. The proposed methodology is based on the efficient computation of the Schur complement for the mixed displacement-pressure formulation using a lumped mass matrix for the displacement field. By treating the deviatoric stress explicitly and the pressure field implicitly, the critical time step is made to be limited by shear wave speed rather than the bulk wave speed. The convergence of the proposed scheme is demonstrated by computing error norms for the recently proposed LBB-stable BT2/BT1 element. Using the numerical examples modelled with nearly and truly incompressible Neo-Hookean and Ogden material models, it is demonstrated that the proposed semi-implicit scheme yields significant computational benefits over the fully explicit and the fully implicit schemes for finite strain elastodynamics simulations involving incompressible materials. Finally, the applicability of the proposed scheme for wave propagation problems in nearly and truly incompressible material models is illustrated.

On the reliability of PKIIKP phase identification at a single station

2021 ◽  
Author(s):  
Olga Usoltseva ◽  
Vladimir Ovtchinnikov
Keyword(s):  
Inner Core ◽  
Seismic Velocity ◽  
Seismic Station ◽  
Shear Velocity ◽  
Outer Core ◽  
Joint Analysis ◽  
Time Range ◽  
Model Parameters ◽  
Phase Identification ◽  
Single Station

&lt;p&gt;&lt;span&gt;Study of the contact zone between the inner and outer core represents considerable interest for understanding of properties, structures and dynamic of the Earth's core. One of &lt;/span&gt;&lt;span&gt;the &lt;/span&gt;&lt;span&gt;sources of &lt;/span&gt;&lt;span&gt;the &lt;/span&gt;&lt;span&gt;data about the processes proceeding in the top part of the inner core is the seismic wave PKIIKP once reflected from an undersize inner core boundary. Amplitudes of these waves are sensitive to the shear velocity in the top part of the inner core and are small. Therefore their identification at a single seismic station is not reliable without application of additional methods of analysis. &lt;/span&gt;&lt;span&gt;Significant in this regard is the discussion about the source (in inner core or in mantle) of anomalous arrivals&lt;!-- &amp;#1069;&amp;#1090;&amp;#1086; &amp;#1084;&amp;#1086;&amp;#1078;&amp;#1085;&amp;#1086; &amp;#1091;&amp;#1076;&amp;#1072;&amp;#1083;&amp;#1080;&amp;#1090;&amp;#1100; --&gt; detected at the TAM station in North Africa [1,2] in the time range of PKIIKP phase.&lt;/span&gt;&lt;/p&gt;&lt;p&gt;&lt;span&gt;To estimate influence of model parameters (S and P seismic velocity) on the characteristics of PKIIKP wave (amplitude and travel time) we calculated sensitivity kernels for upper mantle and inner core for dominant period 1.2 s, azimuth step 0.2 degrees and radius step 20 km by using DSM Kernel Suite algorithm. It was revealed that PKIIKP amplitude is more sensitivities to mantle heterogeneities than to inner core ones. &lt;/span&gt;&lt;span&gt;For reducing the effects of the overlying structures we suppose to use &lt;/span&gt;&amp;#1072; &lt;span&gt;joint analysis PKIIKP and pPKIIKP waves. &lt;/span&gt;&lt;span&gt;With this approach, an incorrect i&lt;/span&gt;&lt;span&gt;dentification&lt;/span&gt;&lt;span&gt; of the PKIIKP wave is most likely excluded. &lt;/span&gt;&lt;span&gt;We&lt;!-- &amp;#1041;&amp;#1099;&amp;#1083;&amp;#1086; &amp;#1073;&amp;#1099; &amp;#1093;&amp;#1086;&amp;#1088;&amp;#1086;&amp;#1096;&amp;#1086; &amp;#1087;&amp;#1088;&amp;#1080;&amp;#1074;&amp;#1077;&amp;#1089;&amp;#1090;&amp;#1080; &amp;#1087;&amp;#1088;&amp;#1080;&amp;#1084;&amp;#1077;&amp;#1088; --&gt; demonstrate the effectiveness of the approach on the example of processing the seismogram of the 11.02.2015 earthquake re&lt;/span&gt;&amp;#1089;&lt;span&gt;o&lt;/span&gt;&lt;span&gt;rded at the GZH station in China at a distance of 179.4 degrees.&lt;/span&gt;&lt;/p&gt;&lt;p&gt;&lt;span&gt;1. Wang W., Song X. Analyses of anomalous amplitudes of antipodal PKIIKP waves&lt;/span&gt;&lt;span&gt;,&lt;/span&gt;&lt;span&gt; E&lt;!-- &amp;#1059;&amp;#1076;&amp;#1072;&amp;#1083;&amp;#1103;&amp;#1077;&amp;#1090;&amp;#1089;&amp;#1103; &amp;#1074;&amp;#1084;&amp;#1077;&amp;#1089;&amp;#1090;&amp;#1077; &amp;#1089; &amp;#1090;&amp;#1077;&amp;#1082;&amp;#1089;&amp;#1090;&amp;#1086;&amp;#1084;, &amp;#1074;&amp;#1099;&amp;#1076;&amp;#1077;&amp;#1083;&amp;#1077;&amp;#1085;&amp;#1085;&amp;#1099;&amp;#1084; &amp;#1074;&amp;#1099;&amp;#1096;&amp;#1077; &amp;#1047;&amp;#1077;&amp;#1083;&amp;#1077;&amp;#1085;&amp;#1099;&amp;#1084; &amp;#1094;&amp;#1074;&amp;#1077;&amp;#1090;&amp;#1086;&amp;#1084;. --&gt;aPP. 2019. V. 3. P. 212-217. doi: 10.26464/epp2019023&lt;/span&gt;&lt;/p&gt;&lt;p&gt;&lt;span&gt;2. Tsuboi S., Butler R. Inner core differential rotation inferred from antipodal seismic observations&lt;/span&gt;&lt;span&gt;,&lt;/span&gt;&lt;span&gt; PEPI&lt;/span&gt;&lt;span&gt;,&lt;/span&gt;&lt;span&gt; 2020. V.301. 106451. &lt;/span&gt;&lt;/p&gt;

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