# Hypocenter

Hypocenter

The hypocenter or hypocentre (literally: 'below the center' from the Greek "υπόκεντρον"), refers to the site of an earthquake or to that of a nuclear explosion. In the former it is a synonym of the focus; in the latter of ground zero.

Earthquakes

The location of an earthquake's hypocenter is the position where the energy stored in the strain in the rock is released, which occurs at the focal depth below the epicentre. The focal depth can be calculated from measurements based on seismic wave phenomena.

As with all wave phenomena in physics, there is an uncertainty in such measurements that grows with the wavelength so the focal depth of the source of these long-wavelength (low frequency) waves is difficult to determine exactly. Very strong earthquakes radiate a large fraction of their released energy in seismic waves with very long wavelengths and therefore a stronger earthquake involves the release of energy from a larger mass of rock.

Air burst explosions

The term hypocenter also refers to the point on the surface of the earth directly below an explosion above the ground, in the atmosphere. In principle, it applies to any such explosion but the term was not found to be necessary until the very large explosions of nuclear bombs became a reality. In this context, the term 'ground zero' was synonymous with hypocenter, though the ground zero term has been rendered less precisely useful, as it has been used by journalists and others ever more loosely.

ee also

* Epicentre
* Ground zero
* Hiroshima Peace Memorial - The closest structure to withstand the 1945 nuclear explosion, it was 150 meters / 490 feet away from the hypocenter.

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### Look at other dictionaries:

• hypocenter — [hī′pō sen΄tər, hī′pəsen΄tər] n. 1. the focus point of an earthquake 2. GROUND ZERO …   English World dictionary

• hypocenter — hipocentras statusas T sritis fizika atitikmenys: angl. hypocenter vok. Hypozentrum, n rus. гипоцентр, m pranc. hypocentre, m …   Fizikos terminų žodynas

• hypocenter — noun Date: 1905 1. the focus of an earthquake compare epicenter 1 2. the point on the earth s surface directly below the center of a nuclear bomb explosion • hypocentral adjective …   New Collegiate Dictionary

• hypocenter — /huy peuh sen teuhr/, n. Geol. focus (def. 5). [1900 05; HYPO + CENTER] * * * …   Universalium

• hypocenter — ALASKA VOLCANO OBSERVATORY GLOSSARY The point within the Earth that is the center of an earthquake. The initial point of rupture during an earthquake …   Glossary of volcanic terms

• hypocenter — hy·po·center …   English syllables

• hypocenter — hy•po•cen•ter [[t]ˈhaɪ pəˌsɛn tər[/t]] n. 1) gel focus 5) 2) ground zero 1) …   From formal English to slang

• hypocenter — …   Useful english dictionary

• Atomic bombings of Hiroshima and Nagasaki — Part of the Pacific War, World War II …   Wikipedia

• Seismic wave — Seismic waves are waves that travel through the Earth, most often as the result of a tectonic earthquake, sometimes from an explosion. Seismic waves are also continually excited by the pounding of ocean waves and the wind. Seismic waves are… …   Wikipedia