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(US), epicenter
the point on the earth's surface directly above the focus of an earthquake or underground nuclear explosion



(1) The projection of the hypocenter of an earthquake onto the earth’s surface (seeHYPOCENTER). The location of the epicenter is determined from recordings by seismic stations, and the epicentral region is determined by the degree of destruction on the surface. Epicenter maps showing the magnitudes of earthquakes are used in seismic zoning. (See alsoEARTHQUAKES.)

(2) The projection onto the earth’s surface of the center of an atmospheric (underwater or underground) nuclear explosion.


A point on the surface of the earth which is directly above the seismic focus of an earthquake and where the earthquake vibrations reach first.
The center of a circle that generates an epicycloid or hypocycloid.
References in periodicals archive ?
There were about 2,000 bridges in the epicentral region of the Northridge quake.
As in the 1989 Loma Prieta earthquake, the implementation of hinge and joint restrainers is credited with preventing the collapse of many of the bridges in the epicentral region.
The literature provides a number of empirical relationships that model the intensity decay in varied regions of the world as a function of epicentral or hypocentral distance.
Mathematically, the attenuation of intensity is written as the difference between epicentral and site intensity.
The most simple energy attenuation model for spherically expanding waves is an inverse relationship based on the square of the epicentral distance.
In the epicentral region, team geoscientists mapped portions of the 80 kilometer surface rupture of the earthquake-generating reverse fault, and investigated sites experiencing vertical uplifts of up to 8 meters, numerous landslides (several with displacements of up to 100 meters), and other spectacular ground failures.
Geological Survey (USGS) installed a simple warning system that detected aftershocks in the epicentral region and radioed a warning to Oakland, providing 12 to 20 seconds of warning for people working on the collapsed 1-880 highway overpass.
In the epicentral region, the earthquake generated a fault rupture of 110 kilometers and ground shaking intensities of VIII to X on the Modified Mercalli Intensity (MMI) scale.
These measures may have an impact provided they are implemented immediately," Episkopou, the CEO of Epicentral Consultancy Ltd.
The local magnitude of some shallow earthquakes was calculated using shocks with epicentral distances ranging between 10km and 300km as well as the magnitudes of some deep earthquakes with hypocentral distances ranging between 100km and 600km.
Comparing the two epicentral regions, Ellsworth says, "instead of 125,000 living in the immediate area where the ground shaking was hardest, there will be 1.
It took a full 25 seconds for the strongest seismic waves from the Loma Prieta earthquake last October to reach San Francisco and Oakland, roughly 90 kilometers from the epicentral region.