A map of topography on the 410-km discontinuity from PP precursors

We derive a new map of global topography on the 410-km discontinuity from o bservations of precursors to PP obtained by stacking almost 25,000 long-per iod seismograms. The inferred '410' topography exhibits average peak-to-pea k amplitude of about 30 km, has a strong degree-one component, and is highl y correlated with previous results obtained from SS precursors [Flanagan an d Shearer, 1998]. Spatial variations in '410' topography appear unrelated t o ocean-continent differences, suggesting that continental roots are not a significant factor in observed global temperature variations at 410 km dept h.