I was reading this article here, which includes an interesting photo of Hiroshima:

The caption on the photo indicates that it was taken three weeks after the atomic bomb was dropped.
The photo seems to show a 'scattershot' pattern of relatively small (I'm guessing maybe 50-100 feet in diameter, based upon the size relative to buildings and vehicles) and strikingly uniform blast/impact craters, spread across a wide area. My question is, what caused these?
I know the simple answer is almost certainly "the atomic bomb", but what specific aspects of an atomic blast and/or the design of the bomb used to produce it would lead to this sort of result? Intuitively I would expect a single large crater/blast area, and what the photo shows looks more like it would have been caused by some sort of cluster-munition than an atomic weapon.
How does a single atomic bomb produce this kind of pattern?