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Workshops

Computational Mineral Physics: Applications to Geophysics

October 11, 2010 to October 14, 2010
Location : CECAM-ETHZ, Zurich, Switzerland
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The Seismic Signature of Strong Thermal Heterogeneity in the Lowermost Mantle

Bernhard Schuberth
University of Nice, France

Coauthor(s) : Hans-Peter Bunge and Guust Nolet


Abstract

One major challenge in the study of Earth's deep interior is to improve existing conceptual models of mantle flow. Understanding the dynamic behavior of the mantle is important as it drives plate tectonics and controls the way the Earth looses its heat. Thus, it is a crucial factor in tectonic modeling or in simulations of the geodynamo or the thermal history of the Earth. In the last decade, the classical viewpoint has been put into question that only a small part of the heat leaving the mantle at the top is coming from the underlying core (2-3 TW or ~5% of the total surface heat flux). A number of studies from various fields have recently promoted the idea of a much larger core contribution to the mantle energy budget of as much as 10 TW (~30% of the surface heat flow). For example, finite frequency tomography has produced images of large plumes in the lower mantle, which potentially carry a significant amount of heat to the surface (Nolet et al. [2006]). This strengthens the notion that the dynamic role of these plumes is larger than inferred classically from observation of dynamic topography. Here, we demonstrate that plume structures predicted for such a high core heat flux by high-performance computations of 3-D mantle flow are compatible with seismic tomography and small rates of polar wander.
An important aspect in such comparisons is that the resolving power of seismic tomography is limited due to uneven data coverage. One possibility to account for this effect is to apply the resolution operator of the tomographic inversions to our synthetic structures. However, this operator can only be constructed for tomographic models with a small number of free parameters, thus limiting its use. Therefore, we will explore new ways to test dynamic flow calculations for Earth's mantle against seismic data and tomographic models. One possible approach is to perform large-scale simulations of 3-D seismic wave propagation through both tomographic models as well as our predicted elastic structures of the mantle. This bears the potential to directly test the resulting synthetic seismograms against real data.