Distribution of Fine-Scale Mantle Heterogeneity from Observations of Pdiff Coda

by Paul S. Earle and Peter M. Shearer

Abstract

We present stacked record sections of Global Seismic Network data that image the average amplitude and polarization of the high-frequency P_diff 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 P_diff 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 P_diff coda with a constant polarization. Here we present an alternative model that satisfies our P_diff 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 P_diff coda observations do not preclude the existence of scattering contributions from the entire mantle.

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