Speed of blast from supernova How fast does the blast front of a supernova expand at? Is it close to the speed of light or is it less than a quarter of the speed of light?
The speed of the blast front depends on the initial energy release and the density of the medium into which it is expanding, see here.

Theory suggests and measurements confirm expansion rates of the order of thousands of km/s or a few $\times 10^6\ \mbox{m/s}$ or  $\sim 1\% \mbox{c}$.