[Robert A Cook PE]

The blast wave, depending on the size of the blast, can travel much faster then the speed of sound. And this was one big blast. I’d said about the size of a tactical nuke, 1 or 2 kilotons, so I think it is a safe bet that the blast wave exceeded the speed of sound.

Well, no. Technically, the speed of sound (in any given material) IS the maximum (and minimum also) speed of a blast wave in that substance.
Now, a bigger (faster or “sharper”) blast will create a larger pressure differential across that blast wave, but the speed of its arrival is the same in the same air conditions everywhere. A slowly expanding blast - like from a fire or burning of gasoline - will more slowly “ramp up” the pressure wave than a rapid explosion. But both travel at the same speed through air.

The shock wave going through rock is faster than that through dirt, faster in dirt than water, and all dense materials are much faster than air. So you would have seen the light waves - arriving at the speed of light - then felt the ground move, then feel the air blast.

[jpsb]

A blast wave in fluid dynamics is the pressure and flow resulting from the deposition of a large amount of energy in a small very localised volume. The flow field can be approximated as a lead shock wave, followed by a 'self-similar' subsonic flow field. In simpler terms, a blast wave is an area of pressure expanding SUPERSONICALLY outward from an explosive core. It has a leading shock front of compressed gases. The blast wave is followed by a blast wind of negative pressure, which sucks items back in towards the center. The blast wave is harmful especially when one is very close to the center or at a location of constructive interference. High explosives, which detonate, generate blast waves.

[jpsb]

"Unlike ordinary sound waves, the speed of a shock (blast) wave varies with its amplitude. The speed of a shock (blast) wave is always greater than the speed of sound in the fluid and decreases as the amplitude of the wave decreases. When the shock wave speed equals the normal speed, the shock wave dies and is reduced to an ordinary sound wave.

[rlmorel]

Yeah. When I was in the USN, they used to drop bombs on targets in the water, and you would feel and hear the explosion through the hull long before you heard it in the air...

[Rocky]

So, the following from Wikipedia is wrong? (I’m not saying Wikipedia is infallible. Far from it. Just wondering what your take on this is.)

“When a shockwave is created by high explosives such as TNT (which has a detonation velocity of 6,900 m/s), it will always travel at high, supersonic velocity from its point of origin.”

http://en.wikipedia.org/wiki/Shock_wave

[TalonDJ]

IS the maximum (and minimum also) speed of a blast wave in that substance.

This is only true for incompressible substances.