Low seismic resolution cannot explain S/P decorrelation in the lower mantle

Abstract

Inverted models of the deep mantle show a decorrelation between maps of shear V<inf>S</inf> and compressional V<inf>P</inf> wave velocities, an anti-correlation between the bulk sound velocity V <inf>$\phi$</inf> and V<inf>S</inf> and a much larger variability of V<inf>S</inf> with respect to V<inf>P</inf>, expressed by large values of the ratio of their relative lateral variations. We carried out synthetic tests to verify if these features could be artifacts, explained by limits in tomographic resolution: synthetic data are calculated for an "input" model, and linearly inverted, as in tomography, to find an "output" model. Comparing the values of the aforementioned parameters for two different chemically homogeneous input models with the associated reconstructed output ones, we found that artifacts caused by realistic data noise and the nonuniform distribution of seismic sources and stations over the globe are not sufficient to introduce the features previously described. We confirm that compositional effects are required to explain them. Copyright 2011 by the American Geophysical Union.