scholarly journals Synthetic seismic anisotropy models within a slab impinging on the core–mantle boundary

2014 ◽  
Vol 199 (1) ◽  
pp. 164-177 ◽  
Author(s):  
Sanne Cottaar ◽  
Mingming Li ◽  
Allen K. McNamara ◽  
Barbara Romanowicz ◽  
Hans-Rudolf Wenk
Keyword(s):  
Seismic Anisotropy ◽  
Mantle Boundary ◽  
Core Mantle Boundary ◽  
The Core

scholarly journals Anisotropic diffusion creep in postperovskite provides a new model for deformation at the core−mantle boundary

2019 ◽  
Vol 116 (52) ◽  
pp. 26389-26393
Author(s):  
David P. Dobson ◽  
Alexander Lindsay-Scott ◽  
Simon A. Hunt ◽  
Edward Bailey ◽  
Ian G. Wood ◽  
...  
Keyword(s):  
Anisotropic Diffusion ◽  
Seismic Anisotropy ◽  
Shear Zones ◽  
Dislocation Creep ◽  
Diffusion Creep ◽  
Chemical Diffusivity ◽  
Crystallographic Preferred Orientation ◽  
Mantle Boundary ◽  
Core Mantle Boundary ◽  
The Core

The lowermost portion of Earth’s mantle (D″) above the core−mantle boundary shows anomalous seismic features, such as strong seismic anisotropy, related to the properties of the main mineral MgSiO3postperovskite. But, after over a decade of investigations, the seismic observations still cannot be explained simply by flow models which assume dislocation creep in postperovskite. We have investigated the chemical diffusivity of perovskite and postperovskite phases by experiment and ab initio simulation, and derive equations for the observed anisotropic diffusion creep. There is excellent agreement between experiments and simulations for both phases in all of the chemical systems studied. Single-crystal diffusivity in postperovskite displays at least 3 orders of magnitude of anisotropy by experiment and simulation (Da= 1,000Db;Db≈Dc) in zinc fluoride, and an even more extreme anisotropy is predicted (Da= 10,000Dc;Dc= 10,000Db) in the natural MgSiO3system. Anisotropic chemical diffusivity results in anisotropic diffusion creep, texture generation, and a strain-weakening rheology. The results for MgSiO3postperovskite strongly imply that regions within the D″ region of Earth dominated by postperovskite will 1) be substantially weaker than regions dominated by perovskite and 2) develop a strain-induced crystallographic-preferred orientation with strain-weakening rheology. This leads to strain localization and the possibility to bring regions with significantly varying textures into close proximity by strain on narrow shear zones. Anisotropic diffusion creep therefore provides an attractive alternative explanation for the complexity in observed seismic anisotropy and the rapid lateral changes in seismic velocities in D″.

Application of spherical Slepian functions to the inversion of virtual observatory satellite magnetic data into localised regions of flow on the core-mantle boundary

2021 ◽  
Author(s):  
Hannah Rogers ◽  
Ciaran Beggan ◽  
Kathryn Whaler
Keyword(s):  
Spherical Surface ◽  
Surface Flow ◽  
Magnetic Data ◽  
Virtual Observatory ◽  
Core Surface ◽  
Flow Models ◽  
Mantle Boundary ◽  
Core Mantle Boundary ◽  
The Core ◽  
Slepian Functions

<p>Spherical Slepian functions (or ‘Slepian functions’) are mathematical functions which can be used to decompose potential fields, as represented by spherical harmonics, into smaller regions covering part of a spherical surface. This allows a spatio-spectral trade-off between aliasing of the signal at the boundary edges while constraining it within a region of interest. While Slepian functions have previously been applied to geodetic and crustal magnetic data, this work further applies Slepian functions to flows on the core-mantle boundary. There are two main reasons for restricting flow models to certain parts of the core surface. Firstly, we have reason to believe that different dynamics operate in different parts of the core (such as under LLSVPs) while, secondly, the modelled flow is ambiguous over certain parts of the surface (when applying flow assumptions). Spherical Slepian functions retain many of the advantages of our usual flow description, concerning for example the boundary conditions it must satisfy, and allowing easy calculation of the power spectrum, although greater initial computational effort is required.</p><p><br>In this work, we apply Slepian functions to core flow models by directly inverting from satellite virtual observatory magnetic data into regions of interest. We successfully demonstrate the technique and current short comings by showing whole core surface flow models, flow within a chosen region, and its corresponding complement. Unwanted spatial leakage is generated at the region edges in the separated flows but to less of an extent than when using spherical Slepian functions on existing flow models. The limited spectral content we can infer for core flows is responsible for most, if not all, of this leakage. Therefore, we present ongoing investigations into the cause of this leakage, and to highlight considerations when applying Slepian functions to core surface flow modelling.</p>

Multiple inner core reflections from a Novaya Zemlya explosion

1972 ◽  
Vol 62 (4) ◽  
pp. 1063-1071 ◽  
Author(s):  
R. D. Adams
Keyword(s):  
Lower Bound ◽  
Inner Core ◽  
Nuclear Explosion ◽  
Outer Core ◽  
Low Velocity ◽  
Mantle Boundary ◽  
Core Mantle Boundary ◽  
Novaya Zemlya ◽  
The Core ◽  
Velocity Channel

Abstract The phases P2KP, P3KP, and P4KP are well recorded from the Novaya Zemlya nuclear explosion of October 14, 1970, with the branch AB at distances of up to 20° beyond the theoretical end point A. This extension is attributed to diffraction around the core-mantle boundary. A slowness dT/dΔ = 4.56±0.02 sec/deg is determined for the AB branch of P4KP, in excellent agreement with recent determinations of the slowness of diffracted P. This slowness implies a velocity of 13.29±0.06 km/sec at the base of the mantle, and confirms recent suggestions of a low-velocity channel above the core-mantle boundary. There is evidence that arrivals recorded before the AB branch of P2KP may lie on two branches, with different slownesses. The ratio of amplitudes of successive orders of multiple inner core reflections gives a lower bound of about 2200 for Q in the outer core.

The thermal signature of subducted lithospheric slabs at the core–mantle boundary

1998 ◽  
Vol 160 (3-4) ◽  
pp. 551-562 ◽  
Author(s):  
Catherine Mériaux ◽  
Amotz Agnon ◽  
John R. Lister
Keyword(s):  
Mantle Boundary ◽  
Core Mantle Boundary ◽  
The Core ◽  
Thermal Signature

scholarly journals PandPcPtravel time tomography for the core-mantle boundary

1997 ◽  
Vol 102 (B8) ◽  
pp. 17825-17841 ◽  
Author(s):  
Masayuki Obayashi ◽  
Yoshio Fukao
Keyword(s):  
Mantle Boundary ◽  
Core Mantle Boundary ◽  
The Core

scholarly journals Synthesis of heavy hydrocarbons at the core-mantle boundary

2015 ◽  
Vol 5 (1) ◽  
Author(s):  
Anatoly B. Belonoshko ◽  
Timofiy Lukinov ◽  
Anders Rosengren ◽  
Taras Bryk ◽  
Konstantin D. Litasov
Keyword(s):  
Heavy Hydrocarbons ◽  
Mantle Boundary ◽  
Core Mantle Boundary ◽  
The Core

The excess temperature of plumes rising from the core-mantle boundary

1996 ◽  
Vol 23 (24) ◽  
pp. 3567-3570 ◽  
Author(s):  
Michael Albers ◽  
Ulrich R. Christensen
Keyword(s):  
Excess Temperature ◽  
Mantle Boundary ◽  
Core Mantle Boundary ◽  
The Core
Sign in / Sign up

Export Citation Format

Share Document