Shockwave: A strong compression wave where there is a sudden change in gas velocity, density, pressure and temperature.

Acoustic waves are prduced when the atoms/ molecules are displaced from there EQUITIBRIUM rest position by a CYCLIC OSCILLATING FORCE.

You cannot have a SHOCKWAVE in empty space, it's possible for the effects of an explosion to be felt away from the source.

When the gas and debris collide with an atmosphere, they could produce a SHOCKWAVE but only if they arrive in sufficient concentration to force the air molecules they hit to move together.

If an explosion occured far away,the gas molecules would be very spread out by the time they hit the atmosphere and because more as a bunch of sepreate,rapidly moving particles than as a gas.