Influence of variable uncertainties in seismic tomography models on constraining mantle viscosity from geoid observations

Abstract

. (2011) AbstractThe radial viscosity structure of the Earth is explored on the basis of the geoid observations. The variations of uncertainty in seismic tomography models are accounted for when finding the radial viscosity structure. The new methodology we propose attempts to fit more closely those features of the geoid that are better constrained by tomography models and avoids to fit those features that are poorly constrained. This approach is particularly important because the error of geoid predictions caused by uncertainties in seismic tomography models is overwhelmingly larger than the noise in the geoid measurements. The synthetic tests indicate that the viscosity structures obtained by disregarding the uncertainty variations in seismic tomography models can be biased depending on the geoid spectral band and on the 'input' seismic tomography model.When the uncertainty variations in seismic models are considered in the inversion process, results do not indicate a viscosity in the transition zone lower than in the upper mantle. A robust feature found with the new method is a viscosity in the upper mantle two orders of magnitude smaller than in the lower mantle. The error covariance of seismic tomography models is critical for the method we suggest. A covariance matrix rigorously derived by seismologists should help to even more reliably infer the viscosity structure and relation between anomalies in density and seismic velocities from surface observations such as the geoid, and thus lead to a better knowledge of the Earth interior.

Seismically observable features of mature stagnant-lid convection at the base of the lithosphere: Some scaling relationships

“…Their downwellings widened with depth and then ponded ∼300 km beneath the top of the asthenosphere. Their viscosity increased by a factor of 37 over that interval to approximately 10 20 Pa s, consistent with the results of Lee et al [2011] and Harig et al [2010]. From the model heat flow in equilibrium with thin lithosphere in the model of van Wijk et al [2010] is about 2.5 times that in my models, so the anomaly from is 2.5 times mine, 1750 K km.…”

“…I use joint inversions of tomography and geoid data. Global inversion yields ∼10 20 Pa s at mid‐depths in the upper mantle [e.g., Lee et al , 2011]. Analysis of geoid anomalies on the leading and trialing continental margins of Australia yields this viscosity for the asthenosphere and 10 to 100 times this viscosity for the transition zone [ Harig et al , 2010].…”

“…Viscosity may well increase with depth in the asthensosphere. I proceed using the results of geoid models that constraint the overall viscosity in the asthenosphere to ∼10 20 Pa s [ Harig et al 2010; Lee et al , 2011]. However, a thin region of low viscosity near the top of the asthenosphere is permitted.…”

Dynamic topography, gravity and the role of lateral viscosity variations from inversion of global mantle flow

“…Uncertainties of the seismic tomographic models would be expected to influence the parameters recovered in inversions (Lee et al, 2011). However, all the seismic tomography models tested by Lee et al (2011) yield a low viscosity transition zone compared to the upper mantle. The five layer viscosity inversions yield a low viscosity asthenosphere (Fig.…”

Density structure of the mantle transition zone and the dynamic geoid

“…For example, Panasyuk and Hager (2000a) have found this feature employing a whole-mantle convection model. On the other hand, Lee et al (2011) have demonstrated that it disappears if one considers the variable uncertainties of tomography models. Therefore, (Gu et al, 2003) including the TZ boundaries; (dashed) for the previous S20a model (Ekström and Dziewonski, 1998).…”