Compressional sound velocity as a function of pressure. Violet crossed diamonds (Crowhurst et al., 2004); blue open diamonds (Decremps et al., 2014); red open circles (Antonangeli et al., 2004b; 2012); green lined circles (Ohtani et al., 2013). The star is the ultrasonic determination reported in Mao et al., (1998). PREM is shown as crosses. The solid line is the extrapolation to higher pressure after the Birch’s fit in Figure 6.