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SUMMARY:From Mantle Convection to Seismic Observations – and Back?: The 
 Impact of Tomographic Resolution and Mineralogical Uncertainty on Reconstr
 ucted Mantle Evolution - Bernhard Schuberth (LMU Munich) 
DTSTART:20260304T140000Z
DTEND:20260304T150000Z
UID:TALK243157@talks.cam.ac.uk
CONTACT:Alice Turner
DESCRIPTION:Understanding the structure and evolution of Earth's mantle is
  fundamental for constraining plate-driving forces\, lithospheric stresses
 \, and the long-term behaviour of the geodynamo. While the present-day the
 rmodynamic state of the mantle can be estimated from seismic tomography an
 d high-pressure mineral physics\, putting tight constraints on temperature
  and chemical heterogeneity based on seismic observations still remains a 
 major challenge. Geodynamic simulations\, by contrast\, provide theoretica
 l predictions for mantle evolution. However\, their quality depends on how
  well input parameters are known\, and they are only meaningful when rigor
 ously tested through geodynamic–tomographic comparisons or\, ideally\, b
 y comparing secondary predictions to a broad range of Earth observations.\
 nIn this talk\, I will discuss recent developments and potential future di
 rections aimed at providing a quantitative\, physically consistent link be
 tween temperatures predicted by mantle circulation models (MCMs) and the w
 ealth of information contained in seismic recordings. For example\, using 
 global 3-D seismic wavefield simulations and full-coupling free-oscillatio
 n calculations for the MCM-derived structures\, synthetic traveltime resid
 uals and seismic spectra can be computed that accurately capture the vario
 us non-linearities in the relation to the underlying temperatures. A criti
 cal component in this context is the effect of mineral anelasticity\, and 
 it is particularly important to account for the associated uncertainties w
 hen comparing synthetic and real data.\nIn addition to this forward approa
 ch\, geodynamic adjoint inverse modelling can be used to retrodict mantle 
 flow back in geologic time starting from the present-day state derived fro
 m tomographic images. Key challenges therein include determining the resol
 ution and uncertainty of the tomography used and how they affect adjoint-s
 tate reconstructions\, as well as assessing how accurately temperatures ca
 n be recovered using uncertain mineralogical information. Addressing the s
 cale discrepancy between fluid dynamic predictions and seismically imaged 
 structures is crucial\, as validating reconstructed mantle flow involves s
 urface topography calculations that are highly sensitive to the tomographi
 c input. To improve future retrodictions\, we conducted synthetic experime
 nts illustrating the challenges of integrating tomographic and geodynamic 
 models. Using a reference MCM as the "true" structure\, we employed the li
 near SOLA Backus–Gilbert framework to explore spatially optimised averag
 ing kernels and noise-related uncertainties\, proposing a workflow to iden
 tify ideal SOLA parameters for next-generation adjoint models. Furthermore
 \, synthetic closed-loop experiments demonstrate that tomographic damping\
 , spatial blurring\, and simplified mineralogies cause substantial deviati
 ons from "true" temperatures\, especially near phase transitions. When suc
 h temperatures are used to prescribe buoyancy in geodynamic simulations\, 
 the errors will amplify non-linearly\, potentially activating incorrect ph
 ase transitions and significantly altering reconstructed flow trajectories
 .
LOCATION:Wolfson Lecture Theatre
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