Variability of the topographic core-mantle torque calculated from core surface flow models

Asari, Seiki; Shimizu, Hisayoshi; Utada, Hisashi

doi:10.1016/j.pepi.2005.09.002

Cited by 7 publications

(7 citation statements)

References 51 publications

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“…The pressure torque induced by topography has been thought to give rise to length-of-day variations (e.g. Jault and Le Mouël, 1990;Hide et al, 1993;Kuang and Bloxham, 1993;Asari et al, 2006;Dehant et al, 2017) by transferring angular momentum between the mantle and core (see Buffett, 2015, for a review of possible core-mantle interactions). In addition, estimates of CMB topography aid in constraining mantle viscosity (e.g.…”

Section: Introductionmentioning

confidence: 99%

Toward Consistent Seismological Models of the Core–Mantle Boundary Landscape

Koelemeijer

2021

Mantle Convection and Surface Expressions

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The dynamic topography of the core-mantle boundary (CMB) provides important constraints on dynamic processes in the mantle and core. However, inferences on CMB topography are complicated by the uneven coverage of data with sensitivity to different length scales and strong heterogeneity in the lower mantle. Particularly, a trade-off exists with density variations, which ultimately drive mantle flow and are vital for determining the origin of mantle structures. Here, I review existing models of CMB topography and lower mantle density, focusing on seismological constraints. I develop average models and vote maps with the aim to find model consistencies and discuss what these may teach us about lower mantle structure and dynamics. While most density models image two areas of dense anomalies beneath Africa and the Pacific, their exact location and relationship to seismic velocity structure differs between studies. CMB topography strongly influences the retrieved density structure, which helps to resolve differences between recent studies based on Stoneley modes and tidal measurements. Current CMB topography models vary both in pattern and amplitude and a discrepancy exists between models based on body-wave and normal-mode data. As existing models feature elevated topography below the Large-Low-Velocity Provinces (LLVPs), very dense compositional anomalies may currently be ruled out as possibility. To achieve a similar consistency as observed in lower mantle models of S-wave and P-wave velocity, future studies should combine multiple data sets to break existing trade-offs between CMB topography and density. Important considerations in these studies should be the choice of theoretical approximation and parameterisation. Efforts to develop models of CMB topography consistent with body-wave, normal-mode and geodetic data should be intensified, which will aid in narrowing down possible explanations for the LLVPs and provide additional insights into mantle dynamics.

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Section: Introductionmentioning

confidence: 99%

Toward Consistent Seismological Models of the Core–Mantle Boundary Landscape

Koelemeijer

2021

Mantle Convection and Surface Expressions

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“…The irregular shape of the CMB may influence the flow in the outer core; a representative example is the formation of Taylor columns [ Anufriyev and Braginski , 1975, 1977a, 1977b]. In addition, the Earth's rotation may fluctuate in terms of the length of day and the polar position through topographic core‐mantle coupling [ Hide , 1969; Jault and Le Mouël , 1990; Kuang and Chao , 2003; Asari et al , 2006]. On the other hand, as mantle convection may deform the CMB topography, it may constrain the mantle properties such as viscosity and density variations [ Steinberger and Holme , 2008; Yoshida , 2008].…”

Section: Introductionmentioning

confidence: 99%

Constraints on the core‐mantle boundary topography from P4KP‐PcP differential travel times

Tanaka¹

2010

J. Geophys. Res.

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[1] P4KP-PcP differential travel times are examined to infer the core-mantle boundary (CMB) topography. A total of 362 P4KP-PcP times are measured with a measurement error of 0.5 s. The travel times are corrected for the Earth's hydrostatic ellipticity and mantle heterogeneity using a P-wave tomographic model. Spherical harmonic expansion up to degree 4 is adopted for model parameterization. The P-wave velocity heterogeneity is then estimated in the lowermost 150 km of the mantle to overcome the problem of underestimation of the velocity perturbation at the base of the mantle in the global 3-D P-wave mantle model. Subsequently, the CMB topography is inferred using the residues of the above processes. Since the odd-degree components of the CMB topography are insensitive to the P4KP-PcP times, only the components of degrees 2 and 4 are solved for. The resultant features indicate that the maximum amplitude of the CMB topography does not exceed ±2 km, with an uncertainty of less than 0.5 km. A numerical test confirms that the pattern of degree 4 is more reliable with less amplitude recovery. The obtained degree 4 pattern shows an amplitude of less than ±1 km and indicates the presence of depressions under the circum-Pacific, the central Pacific, and South Africa.Citation: Tanaka, S. (2010), Constraints on the core-mantle boundary topography from P4KP-PcP differential travel times,

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“…Core‐mantle boundary (CMB) topography is an important geophysical quantity for studies of core‐mantle coupling [ Hide , 1969; Asari et al , 2006] and for the dynamics of flow at the top of the core and magnetic secular variation [ Kuang and Chao , 2001]. Models of this topography can be obtained by seismology and by geodynamic modeling.…”

Section: Introductionmentioning

confidence: 99%

Mantle flow models with core‐mantle boundary constraints and chemical heterogeneities in the lowermost mantle

Steinberger¹,

Holme²

2008

J. Geophys. Res.

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[1] Decorrelation between s-wave and bulk sound velocities in the lowermost mantle and explicit density models based on seismic tomography give evidence for non-thermal lateral density variations in the lowermost mantle. Here we implement such variations in a numerical model of mantle flow driven by density anomalies which are derived from seismic tomography. In the lowermost %300 km, we either use both s-wave and bulk sound velocities to infer both thermal mantle density anomalies and non-thermal heterogeneities, or we assume that regions with s-wave speed anomalies below À1% have an additional non-thermal density anomaly. We predefine the shape of the viscosity profile in the upper mantle, transition zone and lower mantle, but absolute values of viscosity in the lithosphere, upper mantle, transition zone and lower mantle are free parameters. We use geoid, radial heat flux profile, viscosity ''Haskell'' average, core-mantle boundary (CMB) excess ellipticity, as well as (optionally) long-wavelength root mean square (RMS) CMB topography and reliable point estimates of CMB topography as constraints to optimize the model in parameter space in a least squares sense. We are able to obtain a reasonable fit to all data constraints. Computed RMS CMB topography is predominantly long-wavelength and with 1-1.5 km RMS amplitude somewhat larger than the long-wavelength component inferred from seismology. Geoid variance reduction is 75 to 83% in our preferred parameter range. Best fit models have a viscosity maximum close to 10 23 Pas about 600 km above the CMB, and a viscosity drop near the base of the mantle, corresponding to a thermal boundary layer about 300 km thick with temperature increase from %2500 to 3500-4000 K.Citation: Steinberger, B., and R. Holme (2008), Mantle flow models with core-mantle boundary constraints and chemical heterogeneities in the lowermost mantle,

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Variability of the topographic core-mantle torque calculated from core surface flow models

Cited by 7 publications

References 51 publications

Toward Consistent Seismological Models of the Core–Mantle Boundary Landscape

Toward Consistent Seismological Models of the Core–Mantle Boundary Landscape

Constraints on the core‐mantle boundary topography from P4KP‐PcP differential travel times

Mantle flow models with core‐mantle boundary constraints and chemical heterogeneities in the lowermost mantle

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