Velocity evolution of the Si II feature. Same sample criteria and graphs as in Fig. 7. Left: Plot of all SNe in the sample for which Si II velocities were measured. Many ordinary type Ic-BL SNe and GRB-SNe evolve rapidly at early times (< 20 days). Following this, they then begin to plateau. A continuum of velocities exists for ordinary type Ic-BL SNe and GRB-SNe. GRB100316D-SN2010bh has a much higher velocity at all epochs studied than the rest of the sample. Right: Selection of SNe for which the velocity evolution has been fitted. The velocities have been scaled to highlight the overall trend. The scaling factor is computed from the fitted velocity at 15 days divided by the fitted velocity of GRB980425-SN1998bw at 15 days. Several ordinary type Ic-BL SNe and GRB-SNe can be fitted by power law decays. Supernovae that evolve more rapidly tend to have a higher initial velocity and vice-versa. Some type Ic-BL SNe and GRB-SNe show broken power law decays, with the breaks all occurring around 15 days.