A study intended to detect time-dependent velocity decreases beneath the Aleutians and/or Alaska has resulted in the discovery of some remarkable plate effects on relative teleseismic P-wave residuals. The data are relative residuals between an Aleutian station (ADK) and two Alaskan stations (PMR, GIL) from deep focus (>300 km) earthquakes in the Fiji-Tonga source region. These stations have maximum differences of only 17¿ in distance and 12¿ in azimuth from this source. Differences of up to 2 sec in the relative residuals correlate very well with the geographic location of events at the source. The persistence of these differences in the residuals at 600--700 km depth indicates most likely the presence of velocity anomalies of large magnitude below 700 km beneath the slab. Observed changes in relative residuals with depth of focus appear bounded by 10% velocity differences at the source between station ray paths. A subset of these data shows no well defined velocity change near ADK before the magnitude 6.8 Adak Canyon earthquake of May 2, 1971.