New York Skyline

A 150 kiloton bomb constructed by terrorists is detonated in the heart of Manhattan, at the foot of the Empire State Building. The bomb goes off without warning at noon time. It's a clear spring day with a breeze to the east.

Assumptions

There is no warning. The population has not been evacuated nor sought shelter. Both measures could reduce casualties.

There is clear weather, with visibility of 9 miles (16 km).

This is an isolated attack, leaving the rest of the country free to respond.

A large percentage of the day time population is outside - 25%.

The daytime population density is roughly uniform and about 125,000 per square mile.

The shock wave will spread out uniformly in all directions, being minimally affected by structures.