The magnitude of the blast effect is related to the height of the burst above ground level. In general, large buildings are destroyed by the change in air pressure, while people and objects such as trees and utility poles are destroyed by the wind.
The shock wave of air radiates outward, producing sudden changes in air pressure that can crush objects, and high winds that can knock objects down. Most damage comes from the explosive blast. In some publications, ground (or surface) zero is called the 'hypocenter' of the explosion. The term 'surface zero' or 'surface ground zero' is also commonly used for ground surface and underground explosions.
For a burst over (or under) water, the corresponding point is generally called 'surface zero'. The term 'ground zero' refers to the point on the earth's surface immediately below (or above) the point of detonation. Each of these effects are calculated from the point of detonation. The delayed effects, such as radioactive fallout and other possible environmental effects, inflict damage over an extended period ranging from hours to years. Blast, thermal radiation, and prompt ionizing radiation cause significant destruction within seconds or minutes of a nuclear detonation. Nuclear explosions produce both immediate and delayed destructive effects.
