Seismic tomography of the Earth
Mercredi 10 février 2010
Mercredi 10 février, à 11h en salle C. Brot
To understand the processes that lead to cooling of planet Earth and the associated plate motions at its surface, imaging of the seismic velocity variations caused by temperature anomalies inside the Earth is very important. In the past thirty years, 3D global seismological models have been deduced mostly from two sets of data : normal mode frequencies and body wave travel times. For the latter, ray theory- as in optics - was assumed to be adequate. With the growth of both the quality and the quantity of seismic data, it has become clear that body waves are able to diffract around heterogeneities in the Earth, rendering the arrival times - observed using cross-correlation techniques - dependent on the wavelength. First-order scattering theory can be used to linearize such dispersion effects and use it in tomographic imaging. The first applications of such ’finite-frequency’ interpretations resulted in the first images of rising thermal plumes in the lower mantle.
Géosciences Azur, Sophia Antipolis
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