Have to agree with Mark Boslough, that such a grazing event would not produce a radial dispersion of trees, etc.
From the article:
"What's more, the pattern of felled trees at the site is radial — emanating from a single point of tremendous energy release, he said. That's something you'd expect to see after an explosion rather than a sonic boom, "even if it had been strong enough to blow trees over." Boslough added that eyewitness accounts at the time of the incident "are consistent with an object that was descending toward the surface before it exploded."
The only logical conclusion is the original, well-conceived postulate that a loose, rocky asteroid detonated due to heating and a vast over-pressure caused by its high speed entry into the atmosphere, and the inability of the asteroid to maintain its structural integrity from the over-pressure. That no sizable debris was found is likely an indication of the force of the detonation, which likely vaporized the asteroid. Fine debris isolated from the site would appear to finish this story (see below).
A quote from wiki*
"Expeditions sent to the area in the 1950s and 1960s found microscopic silicate and magnetite spheres in siftings of the soil. Similar spheres were predicted to exist in the felled trees, although they could not be detected by contemporary means. Later expeditions did identify such spheres in the resin of the trees. Chemical analysis showed that the spheres contained high proportions of nickel relative to iron, which is also found in meteorites, leading to the conclusion they were of extraterrestrial origin. The concentration of the spheres in different regions of the soil was also found to be consistent with the expected distribution of debris from a meteoroid air burst. Later studies of the spheres found unusual ratios of numerous other metals relative to the surrounding environment, which was taken as further evidence of their extraterrestrial origin.
Chemical analysis of peat bogs from the area also revealed numerous anomalies considered consistent with an impact event. The isotopic signatures of carbon, hydrogen, and nitrogen at the layer of the bogs corresponding to 1908 were found to be inconsistent with the isotopic ratios measured in the adjacent layers, and this abnormality was not found in bogs located outside the area. The region of the bogs showing these anomalous signatures also contains an unusually high proportion of iridium, similar to the iridium layer found in the Cretaceous–Paleogene boundary. These unusual proportions are believed to result from debris from the falling body that deposited in the bogs. The nitrogen is believed to have been deposited as acid rain, a suspected fallout from the explosion."
Another quote from wiki*:
"Since the second half of the 20th century, close monitoring of Earth's atmosphere through infrasound and satellite observation has shown that asteroid air bursts with energies comparable to those of nuclear weapons routinely occur, although Tunguska-sized events, on the order of 5–15 megatons, are much rarer. Eugene Shoemaker estimated that 20-kiloton events occur annually and that Tunguska-sized events occur about once every 300 years. More recent estimates place Tunguska-sized events at about once every thousand years, with 5-kiloton air bursts averaging about once per year. Most of these air bursts are thought to be caused by asteroid impactors, as opposed to mechanically weaker cometary materials, based on their typical penetration depths into the Earth's atmosphere. The largest asteroid air burst to be observed with modern instrumentation was the 500-kiloton Chelyabinsk meteor in 2013, 0which shattered windows and produced meteorites."
The Tunguska event almost certainly resulted from the terminal penetration of a large rocky asteroid that exploded due to the heat and vast over-pressure on the body as it raced into the atmosphere. Cannot see how a high altitude shock wave could produce a radial pattern of destruction. Only an air-burst overhead would cause such a pattern. And there is no doubt that isotope ratios (common to asteroids) found in the area of destruction are not going to be deposited by a simple high altitude shock wave.
For an excellent overview on this bolide, and other theories, see: