We have recently investigated the elastic properties of five compounds gene
rally considered as potential consituents of the Earth's lower mantle. Full
elastic constant tensors of MgSiO3 and CaSiO3 perovskites, MgO, CaO, and S
iO2 have been determined as a function of pressure up to 140 GPa and at zer
o temperature using the first principles plane wave pseudopotential method
within the local density approximation. We report comprehensive comparisons
of the calculated high-pressure elastic wave velocities of these phases wi
th seismically derived lower mantle properties. The effects of iron and tem
perature are estimated in the case of Mg-silicate perovskite based on avail
able experimental data. Comparison of the P and S wave velocity profiles of
perovskite along a series of high-temperature isotherms to the lower mantl
e supports the view that this region is primarily composed of Mg-rich silic
ate perovskite. Our study also suggests that among the candidate phases usu
ally considered, none are invisible. Minor phases which may be present, inc
luding magnesiowustite, CaSiO3 perovskite, and the high-pressure polymorphs
of SiO2 and CaO, have elastic wave velocities that differ significantly fr
om those of Mg-rich silicate perovskite and may be detectable seismically.