Heterogeneity and anisotropy of seismic attenuation in the inner core

Oreshin, Sergey; Vinnik, Lev

doi:10.1029/2003gl018591

Cited by 62 publications

(40 citation statements)

References 23 publications

(39 reference statements)

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“…Observations tell us that the inner core is seismically anisotropic, with P wave velocities ∼3% faster along the polar axis than in the equatorial plane (Creager, 1992;Song and Helmberger, 1993;Song, 1997;Song and Xu, 2002;Sun and Song, 2002;Beghein and Trampert, 2003;Oreshin and Vinnik, 2004). This would suggest that some of the crystals that make up the inner core have aligned in such a way that, overall, the seismically fast direction through the crystal aggregate is oriented along the polar axis of the Earth.…”

Section: Summary Statementsmentioning

confidence: 99%

New Frontiers in Integrated Solid Earth Sciences

Cloetingh¹,

Negendank²

2010

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The book series is dedicated to the United Nations International Year of Planet Earth. The aim of the Year is to raise worldwide public and political awareness of the vast (but often under-used) potential of Earth sciences for improving the quality of life and safeguarding the planet. Geoscientific knowledge can save lives and protect property if threatened by natural disasters. Such knowledge is also needed to sustainably satisfy the growing need for Earth's resources by more people. Earths scientists are ready to contribute to a safer, healthier and more prosperous society. IYPE aims to develop a new generation of such experts to find new resources and to develop land more sustainably.

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Section: Summary Statementsmentioning

confidence: 99%

New Frontiers in Integrated Solid Earth Sciences

Cloetingh¹,

Negendank²

2010

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“…Studies have shown evidence of anisotropy, oriented with the fast direction aligned to Earth's rotation axis (Poupinet et al, 1983;Morelli et al, 1986;Woodhouse et al, 1986;Creager, 1992;Vinnik et al, 1994;Irving and Deuss, 2011). A distinct east-west asymmetry has also been observed in the inner core, whereby the west hemisphere has lower velocity, weaker attenuation and stronger anisotropy than the east (Tanaka and Hamaguchi, 1997;Niu and Wen, 2001;Cao and Romanowicz, 2004;Oreshin and Vinnik, 2004;Deuss et al, 2010;. The difference in isotropic velocity between the hemispheres has been found to be between 0.5% (Sun and Song, 2008) and 1.5% (Garcia, 2002), with most studies finding a value of 0.8%-1% (Tanaka and Hamaguchi, 1997;Niu and Wen, 2001;Cao and Romanowicz, 2004).…”

Section: Introductionmentioning

confidence: 99%

Measuring the seismic velocity in the top 15 km of Earth’s inner core

Godwin

Waszek

Deuss

2018

Physics of the Earth and Planetary Interiors

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A B S T R A C TWe present seismic observations of the uppermost layer of the inner core. This was formed most recently, thus its seismic features are related to current solidification processes. Previous studies have only constrained the eastwest hemispherical seismic velocity structure in the Earth's inner core at depths greater than 15 km below the inner core boundary. The properties of shallower structure have not yet been determined, because the seismic waves PKIKP and PKiKP used for differential travel time analysis arrive close together and start to interfere. Here, we present a method to make differential travel time measurements for waves that turn in the top 15 km of the inner core, and measure the corresponding seismic velocity anomalies. We achieve this by generating synthetic seismograms to model the overlapping signals of the inner core phase PKIKP and the inner core boundary phase PKiKP. We then use a waveform comparison to attribute different parts of the signal to each phase. By measuring the same parts of the signal in both observed and synthetic data, we are able to calculate differential travel time residuals. We apply our method to data with ray paths which traverse the Pacific hemisphere boundary. We generate a velocity model for this region, finding lower velocity for deeper, more easterly ray paths. Forward modelling suggests that this region contains either a high velocity upper layer, or variation in the location of the hemisphere boundary with depth and/or latitude. Our study presents the first direct seismic observation of the uppermost 15 km of the inner core, opening new possibilities for further investigating the inner core boundary region.

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“…Early studies using either of these techniques (Morelli et al, 1986;Woodhouse et al, 1986;Creager, 1992) proposed that the seismic velocity anisotropy in the inner core was both laterally invariant and depth-independent and that the axis of cylindrical anisotropy is aligned with Earth's rotation axis. More recent body wave studies have built up a picture of an inner core with a degree one 'hemispherical' structure (Tanaka & Hamaguchi, 1997;Creager, 1999;Oreshin & Vinnik, 2004) and a distinct innermost inner core where the anisotropy axis is at an angle of 45 • to the anisotropy axis in the rest of the inner core (Ishii & Dziewonski, 2002;Cormier & Stroujkova, 2005;Cao & Romanowicz, 2007;Sun & Song, 2008).…”

Section: Introductionmentioning

confidence: 99%

Stratified anisotropic structure at the top of Earth's inner core: A normal mode study

Irving

Deuss

2011

Physics of the Earth and Planetary Interiors

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Please cite this article as: Irving, J.C.E., Deuss, A., Stratified anisotropic structure at the top of Earth's inner core:a normal mode study, Physics of the Earth and Planetary Interiors (2010), doi:10.1016/j.pepi.2011 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. Page 1 of 40A c c e p t e d M a n u s c r i p tWe probe the isotropic layer at the top of Earth's inner core using normal modes. Normal mode data are compatible with an isotropic layer of up to 250km thick. Normal modes can therefore be reconciled with previous body wave studies. We further show seismic data support the presence an S-wave isotropic layer. *HighlightsPage 2 of 40 A c c e p t e d M a n u s c r i p t AbstractBody wave studies support the presence of an isotropic layer at the top of the inner core. Recent normal mode models of inner core anisotropy do not contain such a layer, but instead have anisotropic structure extending to the inner core boundary. Here, we use full-coupling of normal mode oscillations sensitive to inner core structure in order to investigate the discrepancy between models of the inner core developed using these two different types of data. We impose an isotropic layer onto existing normal mode models of inner core anisotropy, and calculate frequencies, quality factors and synthetic seismograms for radial modes, PKIKP modes and PKJKP modes. Using full-coupling allows us to make the first simulations of the effect of an isotropic layer on radial modes.The presence of an uppermost isotropic layer has an effect on the frequencies and attenuation of normal modes. By calculating the misfit between data from four large earthquakes and synthetic seismograms created for models of the inner core with isotropic layers of varying thickness, we find that normal mode data are compatible with the presence of an isotropic layer of up to 250km thickness at the top of the inner core. Thus, normal modes can be reconciled with previous body wave studies. The influence of such a layer on PKJKP modes is the only way that S-wave isotropy at the top of the inner core can currently be studied;we show, for the first time, that seismological data support the presence an S-wave isotropic layer.

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Heterogeneity and anisotropy of seismic attenuation in the inner core

Cited by 62 publications

References 23 publications

New Frontiers in Integrated Solid Earth Sciences

New Frontiers in Integrated Solid Earth Sciences

Measuring the seismic velocity in the top 15 km of Earth’s inner core

Stratified anisotropic structure at the top of Earth's inner core: A normal mode study

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Heterogeneity and anisotropy of seismic attenuation in the inner core

Cited by 62 publications

References 23 publications

New Frontiers in Integrated Solid Earth Sciences

New Frontiers in Integrated Solid Earth Sciences

Measuring the seismic velocity in the top 15 km of Earth’s inner core

Stratified anisotropic structure at the top of Earth's inner core: A normal mode study

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Measuring the seismic velocity in the top 15 km of Earth’s inner core