A theoretical expression showing the radial dependence of permeability in geologic media as a function of the distance from the point of detonation has been derived. This relationship shows that created permeability decreases as a function of radius (1/r^5 around a spherical blast and 1/r^4 around a cylindrical shot). Excellent correlation was found when this prediction was compared with permeability measurements made around the site of the Hardhat Nuclear Event fired in granodiorite and a chemical explosive detonated in coal.