Figure 8b: Metamorphic facies for wet basalt, showing seismic P-wave velocities (km/s), from Peacock (1993) and Helffrich (1996). Black lines show P-T trajectories of subducting material for upper (UC) and lower (LC) crust. For comparison, mantle peridotite should have velocities of 8.0-8.2 km/s under similar conditions, and unaltered crust near 6.5 - 7.0 km/s. The seismic wave distortion measurements shown in Figure 8a are consistent with lawsonite blueschist (LB) or with mixtures of eclogite and basalt (EB).