Pn wave velocities beneath the Tanzania Craton and adjacent rifted mobile belts, East Africa

P wave travel times from regional earthquakes recorded by the Tanzania Broa dband Seismic Experiment have been inverted for long wavelength (>100 km) P n velocity variations beneath Tanzania using a generalized inverse algorith m. Pn velocities, on average, are 8.40 to 8.45 km/s beneath the center of t he Tanzania Craton, 8.30-8.35 km/s beneath the terminus of the Eastern Bran ch of the rift system, and 8.35-8.40 km/s beneath the Western Branch. These velocities indicate that there are no broad (>100 km wide) thermal anomali es in the uppermost mantle beneath areas of rifting in Tanzania, and sugges t that thermal anomalies present deeper in the mantle have not yet reached the base of the crust.