| Description: |
Bernhard Schuberth, Ludwig-Maximilians-Universität München (LMU)
A profound understanding of the interaction between surface geological processes and the deep Earth requires knowledge of mantle properties in space and time. Accurate estimates of the buoyancy forces that drive plate tectonics, for example, are of fundamental importance for modelling lithospheric stresses and earthquake ruptures. The evolution of lower mantle temperatures and the associated core heat flow, on the other hand, are crucial components in geodynamo simulations that aim at modelling the reversal frequency pattern of Earth's magnetic field on geologic time scales. However, a data-driven
quantitative understanding of the evolution of buoyancy forces and temperature variations in the mantle is still lacking. Despite the great success of tomographic studies and the progress in mineral physics in the last decades, it remains a major challenge to constrain the present-day thermodynamic state of the mantle based on seismic observations. Predictions of mantle structures with realistic length-scales and magnitudes of temperature variations are nevertheless available through geodynamic forward modelling. High-resolution mantle circulation models (MCMs), which assimilate plate reconstructions as surface boundary condition, can nowadays be produced on a routine basis using the available sophisticated numerical tools and modern high-performance computing infrastructures. The robustness of these MCMs then needs to be assessed through either geodynamic-tomographic model comparisons, or by direct comparison of secondary predictions to Earth observations.
Here, I will present one possible approach to link hypothetical temperature fields to seismic recordings in a quantitative way. By combining mantle circulation models with mineralogical thermodynamics and global 3-D seismic wavefield simulations, synthetic traveltime residuals can be computed that correctly capture the various non-linearities in the relation to the underlying temperatures. A major contribution in this respect comes from the effects of mineral anelasticity. It is thus particularly important to take the associated uncertainties related to poorly constrained parameters into account when comparing to real data. I will further illustrate how analyzing 3-D wavefield effects in hypothetical Earth models opens up a way to constrain the spectrum of seismic structures in the mantle. Finally, I will touch upon recent developments and potential future directions in this emerging field of 'virtual seismology' that aims at providing a physically consistent link between geophysical hypotheses and the wealth of information contained in seismic recordings. |
