Richter scale


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Related to Richter scale: Moment magnitude scale, tsunami

Richter scale

(rĭk`tər), measure of the magnitude of seismic waves from an earthquakeearthquake,
trembling or shaking movement of the earth's surface. Most earthquakes are minor tremors. Larger earthquakes usually begin with slight tremors but rapidly take the form of one or more violent shocks, and end in vibrations of gradually diminishing force called
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. Devised in 1935 by the American seismologist Charles F. Richter (1900–1985) and technically known as the local magnitude scale, it has been superseded by the moment magnitude scale, which was developed in the 1970s. The Richter scale is logarithmic; that is, the amplitude of the waves increases by powers of 10 in relation to the Richter magnitude numbers. The energy released in an earthquake can easily be approximated by an equation that includes this magnitude and the distance from the seismograph to the earthquake's epicenter. Numbers for the Richter scale range from 0 to 9, though no real upper limit exists. An earthquake whose magnitude is greater than 4.5 on this scale can cause damage to buildings and other structures; severe earthquakes have magnitudes greater than 7. Like ripples formed when a pebble is dropped into water, earthquake waves travel outward in all directions, gradually losing energy, with the intensity of earth movement and ground damage generally decreasing at greater distances from the earthquake focus. In addition, the nature of the underlying rock or soil affects ground movements. In order to give a rating to the effects of an earthquake in a particular place, the modified Mercalli scale, based on a scale developed by the Italian seismologist Giuseppe Mercalli, is often used. It measures an earthquake's intensity, the severity of an earthquake in terms of its effects on the inhabitants of an area, e.g., how much damage it causes to buildings.
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Richter scale

[′rik·tər ‚skāl]
(geophysics)
A scale of numerical values of earthquake magnitude ranging from 1 to 9.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.

Richter scale

a scale for expressing the magnitude of an earthquake in terms of the logarithm of the amplitude of the ground wave; values range from 0 to over 9
Collins Discovery Encyclopedia, 1st edition © HarperCollins Publishers 2005
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