Abstract:

We present stacked record sections of Global Seismic Network data that image the average amplitude and polarization of the high-frequency P diffracted coda and show that these observations are consistent with a model containing weak ~1% fine-scale (2 km) structure distributed throughout the mantle. The extended 1 Hz coda remains above the noise to a distance of 130 degrees and has a nearly constant polarization. Our modeling demonstrates that single scattering from evenly distributed mantle heterogeneities can produce an extended P diffracted coda, but we can not preclude alternate interpretations that invoke multiple scattering with heterogeneity restricted to the lowermost mantle.