Observed P wave arrival times for coastal stations in Peru, some 3-6° from epicenters, are up to 4 s early relative to predicted arrival times based on the best fit velocity-depth model used for hypocenter locations. These large negative time residuals appear to be the result of propagation paths which have long segments in the colder, higher-velocity subducting plate. Computed ray paths show that travel times to coastal stations for the eastern Peru events can be satisfactorily modeled with average velocities relative to the surrounding mantle 6% lower within the uppermost slab and 8% higher within the cold uppermost mantle of the slab. Ray tracing for this plate model shows that P wave "shadow zones' can occur if the source-slab-receiver geometry results in seismic rays passing through regions in which the dip angle of the slab changes significantly. -from Authors