Abstract

We present stacked record sections of Global Seismic Network data that image the average amplitude and polarization of the high-frequency Pdiff coda and investigate their implications on the depth extent of fine-scale (∼10 km) mantle heterogeneity. The extended 1-Hz coda lasts for at least 150 sec and is observed to a distance of 130°. The coda's polarization angle is about the same as the main Pdiff arrival (4.4 sec/deg) and is nearly constant with time. Previous studies show that multiple scattering from heterogeneity restricted to the lowermost mantle generates an extended Pdiff coda with a constant polarization. Here we present an alternative model that satisfies our Pdiff observations. The model consists of single scattering from weak (∼1%) fine-scale (∼2 km) structures distributed throughout the mantle. Although this model is nonunique, it demonstrates that Pdiff coda observations do not preclude the existence of scattering contributions from the entire mantle.

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