building collapsed to ground level.

The limiting radius for severe displacement of roof tiles in Nagasaki was
about 10,000 feet although isolated cases were found up to 16,000 feet.
In Hiroshima the general limiting radius was about 8,000 feet; however,
even at a distance of 26,000 feet from X in Hiroshima, some tiles were
displaced.

At Mogi, 7 miles from X in Nagasaki, over steep hills over 600 feet high,
about 10% of the glass came out. In nearer, sequestered localities only 4
miles from X, no damage of any kind was caused. An interesting effect was
noted at Mogi; eyewitnesses said that they thought a raid was being made on
the place; one big flash was seen, then a loud roar, followed at several
second intervals by half a dozen other loud reports, from all directions.
These successive reports were obviously reflections from the hills
surrounding Mogi.



GROUND SHOCK


The ground shock in most cities was very light. Water pipes still carried
water and where leaks were visible they were mainly above ground.
Virtually all of the damage to underground utilities was caused by the
collapse of buildings rather than by any direct exertion of the blast
pressure. This fact of course resulted from the bombs' having been
exploded high in the air.