Phase transition Clapeyron slopes and transition zone seismic discontinuity topography

The depths, widths, and magnitudes of the 410-km and 660-km seismic discontinuities are largely consitent with an isochemical phase change origin. Recent seismic studies suggest greater topography on the 660. The relevant Clapeyron slopes are reexamined in light of experimental studies as well as the requirements of internal thermodynamic consistency. The bulk of the evidence indicates a greater Clapeyron slope magnitude for the 410 than for the 660. Thus the recent seismic results are unexpected. -from Authors