CompuServe Thread

RICHTER SCALE OUTDATED It's what you might call a scandal of the first magnitude: the Richter scale, the venerated measure of earthquake size, has disappeared. "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 zig-zag line generated by a seismograph's needle in 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 have since 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. Since the early 1980s, the most widely used measure has been moment magnitude. It is based on the size of the fault on which an earthquake occurs and the amount the earth slips. The bigger the fault and the larger the slip, the higher the moment magnitude. The Jan. 17 Northridge quake in Los Angeles had a moment magnitude of 6.7. The Loma Prieta quake that rocked the San Francisco Bay area in 1989 had a moment magnitude of 7.0. In the first hours and days after a quake, any measurements are considered preliminary. Figures pour in from a variety of seismographs and are averaged. The numbers are refined as more data is collected. Once aftershocks taper off, most seismologists settle on moment magnitude as the most accurate measure. But not at the U.S. Geological Survey's National Earthquake Information Center in Golden, Colo. Seismologists there prefer surface-wave magnitude, an analysis of seismic waves crackling around the Earth's surface. Confusion arises because the center continues to call the measurement Richter magnitude, resulting in seemingly conflicting numbers. When the Landers earthquake struck the California desert in June 1992, for instance, the Geological Survey's office in Pasadena, using moment magnitude, said the quake had a magnitude of 7.3. The center in Golden, relying on surface waves, said it measured 7.6. The difference meant nothing to the quake's rattled survivors. By either measure, it was huge. Why the concern? Scientists care because they need precise measurements for research and planning. "The problem becomes really serious for bigger quakes," said Seismological Society president Heaton, who is with the Geological Survey in Pasadena. "For instance, the Alaska quake in 1964 has a surface-wave magnitude 8.3 or 8.4 and a moment magnitude of 9.2. "It's really our problem to try to get the National Earthquake Information Center to try to release moment magnitudes instead of surface-wave magnitudes," Heaton added. "And we need to stop them from calling them Richter magnitudes." Nonscientists don't need such precision — but they want it. People want to know if the quake they just survived broke 7.0 or topped out at 6.9. "People get upset, because they want to know the one number," Heaton said. The Geological Survey understands the difficulty. What it lacks is a solution. "I don't think we've quite addressed it, is about the best way I can characterize it," said Gail Wendt, assistant director of public affairs at Survey headquarters in Reston, Va. Across the country in Menlo Park, Calif., another spokeswoman, Pat Jorgenson, is somewhat blunter. "I've been saying we ought to put out a press release on this for five years, and my people in Reston haven't approved it," she said. "The way we skate around it in our news releases is we say 'magnitude.' We don't say 'on the Richter scale,' " Jorgenson explained to a reporter. "And then we hope somebody like you doesn't call." ++++++++++++++++++++++++++++++++++++ REPORT CULLED FROM THE ASSOCIATED PRESS