Relative teleseismic P wave residuals between Alaskan-Aleutian stations from deep focus (>500 km) Fiji-Tonga earthquakes are examined in detail. At large station separations the effects of hypocenter mislocation become important. When both sources and stations are widely separated, we observe effects produced by differences between travel time tables, by plate structure beneath the stations, by deep expression of the descending plate at the source, and/or by lateral variations in lower mantle structure. When either source or station separations are small, these effects are considerably reduced, so that relative residuals between stations can be resolved to within ¿0.1 s. Average levels of relative residuals between Alaskan stations can be explained to first order by a plate structure beneath Alaska.