Ground zero

In terms of nuclear explosions and other large bombs, the term "ground zero" (sometimes also known as "surface zero") describes the point on the Earth's surface closest to a detonation. In the case of an explosion above the ground, ground zero refers to the point on the ground directly below the nuclear detonation and is sometimes called the hypocenter (from Greek ὑπο- "under-" and ).

Generally, the term is also used in relation to earthquakes, epidemics, and other disasters to mark the point of the most severe damage or destruction. The term is distinguished from the term zero point in that the latter can also be located in the air, underground, or underwater.

The origins of the term "ground zero" began with the Trinity test in Jornada del Muerto desert near Socorro, New Mexico, and the atomic bombings of Hiroshima and Nagasaki in Japan. The Strategic Bombing Survey of the atomic attacks, released in June 1946, used the term liberally, defining it as: "For convenience, the term 'ground zero' will be used to designate the point on the ground directly beneath the point of detonation, or 'air zero.'"William Laurence, an embedded reporter with the Manhattan Project, reported that "Zero" was "the code name given to the spot chosen for the [Trinity] test" in 1945.

The Oxford English Dictionary, citing the use of the term in a 1946 New York Times report on the destroyed city of Hiroshima, defines ground zero as "that part of the ground situated immediately under an exploding bomb, especially an atomic one." The term was military slang, used at the Trinity site where the weapon tower for the first nuclear weapon was at "point zero", and moved into general use very shortly after the end of World War II. At Hiroshima, the hypocenter of the attack was Shima Hospital, approximately 800 ft (240 m) away from the intended aiming point at Aioi Bridge.

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