Peaks are observed in a depth dependent power spectrum of P-wave velocity fluctuations determined from an inversion of P wave coherences observed by the USArray. These peaks correlate with the depths of the majority of silicate mineral phase changes predicted by a thermodynamic model of the upper 1000 km of a pyrolitic mantle. To within ± 25 km we identify the phase change of orthopyroxene to HP-clinopyroxene at 275 km, the olivine to wadsleyite phase change at 425 km, the wadlsleyite to ringwoodite phase change at 505 km, and the initiation of an akimotoite phase at 600 km and a signature of a phase change at 775 km, both associated with the existence of fragments of subducted oceanic crust. Non-detection of a phase change at or near 660 is consistent with the phase change of ringwoodite to Mg-perovskite and magnesiowusite occurring over a depth interval much smaller than 25 km.