Roanoke Times
Copyright (c) 1995, Landmark Communications, Inc.
DATE: THURSDAY, April 28, 1994 TAG: 9404280222
SECTION: NATIONAL/INTERNATIONAL PAGE: A6 EDITION: METRO
SOURCE: Associated Press
DATELINE: NEW YORK LENGTH: Medium
``There is no such thing as the Richter scale,'' Thomas Heaton, president of the Seismological Society of America, says flatly.
Seismologists acknowledge there's still something warm and fuzzy about the 63-year-old Richter scale, a familiarity that gives earthquake survivors something to cling to, a bloodless measure of the troubles they've seen.
The professionals, who largely abandoned Richter's specifics years ago, view it differently.
``It's my impression that the Richter scale is something invented by the press to mean the largest number available,'' said Kate Hutton, staff seismologist at the California Institute of Technology.
By far the best-known measure of earthquake size, the Richter ``served its purpose very well for its original intended use,'' said Paul Richards, a seismologist at Columbia University in New York City. ``But it turns out it is not based on well-defined physical principles.''
The late Charles Richter, a seismologist at Cal Tech, devised his scale in 1931, basing it on the widest swing in the zigzag line generated by a seismograph's needle during a quake.
It worked well for years, assigning to small quakes magnitudes in the range of 2 to 3 and to large quakes magnitudes up to 7 or 8, or higher.
After strong quakes, the public became accustomed to announcements of definite numbers, followed by the solemn intonation ``on the Richter scale.'' Over the years, however, seismologists realized the scale had problems.
For one, it isn't very accurate for the biggest quakes, those in the range of 8 or 9.
Secondly, it's based on readings taken close to quakes, within 100 miles or so. That's fine in Southern California, where seismographs are as common as sushi bars. But the scale is less precise in other parts of the world, where the nearest seismograph may be nations away from the rumbling.
The Richter scale was calibrated on a now-obsolete model of seismograph. Researchers since have devised new ways to rate the shaking.
``You can rank people by height, by intelligence, by beauty, by weight,'' Richards said. ``And you can do the same thing with earthquakes.''
Although the newer measures calculate magnitude in different ways, each is adjusted to produce numbers similar to Richter's because those are so familiar.
by CNB