epicenter: Definition from Answers.com
- ️Sun Apr 20 2008
n.
- The point of the earth's surface directly above the focus of an earthquake.
- A focal point: stood at the epicenter of the international crisis.
epicentral ep'i·cen'tral adj.
USAGE NOTE Epicenter is properly a geological term identifying the point of the earth's surface directly above the focus of an earthquake. No doubt this is why the Usage Panel approves of figurative extensions of its use in dangerous, destructive, or negative contexts. Eighty-two percent of the Panel accepts the sentence If Rushdie were not at the terrifying epicenter of this furor, it is the sort of event he might write about. The Panel is less fond but still accepting of epicenter when it is used to refer to the focal point of neutral or positive events. Sixty-two percent approve of the sentence The indisputable epicenter of Cortina's social life is the Hotel de la Poste, located squarely in the village center.
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The noun has one meaning:
Meaning #1:
the point on the Earth's surface directly above the focus of an earthquake
Synonym: epicentre
The epicenter is directly above the earthquake's focus.
The epicenter or epicentre is the point on the Earth's surface that is directly above the hypocenter or focus, the point where an earthquake or underground explosion originates. The word derives from the Greek ἐπίκεντρον (epikentron), "occupying a cardinal point", from ἐπί (epi), "on, upon, at" + κέντρον (kentron), "centre"[1].
The epicenter is usually the location of greatest damage. However, in some cases the epicenter is above the start of a much larger event. In these cases, damage may be spread across a larger area with the greatest damage possibly occurring some distance from the epicenter. For example, in the magnitude 7.9, 2002 Denali earthquake in Alaska, the epicenter was at the western end of the rupture, but the greatest damage occurred about 330 km away at the eastern end of the rupture zone.[2]
Epicentral distance
During an earthquake, Seismic waves propagate spherically out from the hypocenter. Seismic shadowing occurs on the opposite side of the Earth from the earthquake epicenter because the liquid outer core refracts the longitudinal or compressional (P-waves) while it absorbs the transverse or shear waves (S-waves). Outside of the seismic shadow zone both types of wave can be detected, but due to their different paths through the Earth, they arrive at different times. By measuring the time difference on any seismograph as well as the distance on a travel-time graph at which the P-wave and S-wave have the same separation, geologists can calculate the distance to the earthquake's epicenter. This distance is called the epicentral distance, commonly measured in ° (degrees) and denoted as Δ (delta) in seismology.
Once epicentral distances have been calculated from at least three seismographic measuring stations, it is a simple matter to find out where the epicenter was located using trilateration.
Epicentral distance is also used in calculating seismic magnitudes developed by Richter and Gutenberg.[3]
References
- ^ Epikentron, Henry George Liddell, Robert Scott, A Greek-English Lexicon, at Perseus
- ^ Fuis, Gary; Wald, Lisa. "Rupture in South-Central Alaska—The Denali Fault Earthquake of 2002". USGS. Retrieved on 2008-04-20.
- ^ Tyler M. Schau (1991). "The Richter Scale (ML)". USGS. Retrieved on 2008-09-14.
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