I report strong seismic PKP precursors recorded in the seismic stations in Tanzania for earthquakes occurred in the Fiji subduction zone. The observed PKP precursors show clear onsets and rapid variations of amplitude for different events and stations. I develop a technique to use the precursor onset times to determine the location of seismic scatterers and apply forward modeling of precursor amplitudes to place constraints on the magnitude of seismic anomalies. The travel time analysis indicates that these recorded PKP precursors are caused by the seismic scattering in the lowermost 360 km of the mantle beneath the Comoros hotspot. The amplitudes of the observed PKP precursors suggest a rather complex seismic structure with a P velocity variation of at least 8%, likely associated with partial melt. ¿ 2000 American Geophysical Union