Richter scale - what it is and what it measures

SINGAPORE, JAN. 26. Most people have heard of the Richter scale - the measure of the strength of an earthquake - but what does it really measure and what does it mean?

The U.S. Geological Survey estimated that today's quake which killed hundreds in India measured 7.9 on the scale. The quake which killed 2,400 people in Taiwan in September 1999 measured 7.6 - so does that mean the Indian quake was just slightly stronger than the one in Taiwan?

The answer is no. As the strength of earthquakes rises in steps up the Richter scale, earthquake releases 31 times more energy than one registered at the previous notch.

Introduced in 1935, the scale is named after the American Physicist, Charles F. Richter, of the California Institute of Technology, who evolved it from patterns he discovered by studying more than 200 earthquakes a year. The scale is a more objective, quantitative basis of measuring earthquakes than the other widely-used standard, the 12-point Mercalli scale, the U.S. Geological Survey says.

The Richter scale does not measure an earthquake's effects, but gives its strength in terms of the energy released, as measured by seismographs.

The scale starts at one end and has no upper limit; each unit is 10 times greater than the one before. Mathematicians refer to this method of arranging numbers on a scale as logarithmic.

For instance, the survey says, a magnitude of 5.3 might be calculated for a moderate earthquake, and a strong earthquake might be classed as magnitude 6.3.

- Reuters

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