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5.7.2: Earthquake Forecasting by Scientists

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    5999
  • Overview

    Most of the so-called predictors, including those who have been interviewed on national television, will claim that an earthquake prediction is successful if an earthquake of any magnitude occurs in the region. Let’s say that I predict that an earthquake will occur in the Puget Sound region within a two-week period of June of this year. An earthquake occurs, but it is of M 2, not “large” by anyone’s definition. Enough M 2 earthquakes occur randomly in western Washington that a person predicting an earthquake of unspecified magnitude in this area is likely to be correct. Or say that a person predicts that an earthquake of M 6 or larger will occur somewhere in the world in June of this year. It is quite likely that some places will experience an earthquake of that size around that time. Unless the damage is done, this earthquake might not make the newspapers or the evening news, except that the predictor would point to it as a successful prediction ignored by the scientific establishment.

     

    To issue a legitimate prediction, a scientist, or anyone else, for that matter, must provide an approximate location, time, and magnitude. The prediction must be made in such a way that its legitimacy can be checked. The prediction could be placed in a sealed envelope entrusted to a respected individual or group, which would avoid frightening the public in case the prediction was wrong. But for a prediction to be of value to society, it must be made public, but until prediction becomes routine (if it ever does), one must consider the negative impact on the public of a prediction that fails.

     

    Prediction was one of the major goals of the federal earthquake program when it was established in 1977, and at one time it looked as if that goal might be achieved sooner than expected. In the early 1970s, a team of seismologists at Columbia University suggested that the speed of earthquake waves passing through the Earth’s crust beneath the site of a future earthquake would become slower, then return to normal just before the event. The changes in the speed of earthquake waves had been noted before small earthquakes in the Adirondacks of New York State and in Soviet Central Asia.

     

    In 1973, Jim Whitcomb, a seismologist at Caltech, reported that seismic waves had slowed down, then speeded up, just before a M 6.7 earthquake in 1971 in the northern San Fernando Valley suburb of Los Angeles. Two years later, he observed the same thing happening near the aftershock zone of that earthquake: a slowdown of earthquake waves, presumably to be followed by a return to normal speed and another earthquake. Other seismologists disagreed. Nonetheless, Whitcomb issued a “forecast”—not his term, for he characterized it as “a test of a hypothesis.” If the changes in the speed of earthquake waves were significant, then there should be another earthquake of magnitude 5.5 to 6.5 in an area adjacent to the 1971 shock in the next twelve months.

     

    My students and I happened to be doing fieldwork on an active fault just west of the San Fernando Valley during this twelve-month period. Each night the coyotes started to howl, we would bolt upright from our sleeping bags at our campsite along the fault and wonder if we were about to have an earthquake.

     

    Whitcomb became an overnight celebrity and was written up in People magazine. An irate Los Angeles city councilman threatened to sue both Whitcomb and Caltech. In the meantime, the predicted time span for the earthquake ran out, with no earthquake. Meanwhile, other scientists tested the Columbia University theory and found a relatively poor correlation between the variation in speed of earthquake waves in the crust and future earthquakes. (Maybe Whitcomb was right in location but off on the time and magnitude. The Northridge Earthquake struck the San Fernando Valley 23 years after the earlier earthquake; its magnitude was 6.7, larger than expected.)

     

    At about the same time as the San Fernando “test of a hypothesis,” a prediction was made by Brian Brady, a geophysicist with the U.S. Bureau of Mines, who worked in the field of mine safety (Olson, 1989). Between 1974 and 1976, Brady published a series of papers in an international peer-reviewed scientific journal, Pure and Applied Geophysics, in which he argued that characteristics of rock failure leading to wall collapse in underground mines are also applicable to earthquakes. Brady’s papers combined rock physics and mathematical models to provide what he claimed to be an earthquake “clock” that would provide the precise time, place, and magnitude of a forthcoming earthquake. Brady observed that earthquakes in 1974 and 1975 near Lima, Peru, had occurred in a region where there had been no earthquakes for a long time, and he forecast a much larger earthquake off the coast of central Peru. Brady’s work received support from William Spence, a respected geophysicist with the USGS.

     

    His prediction received little attention at first, but gradually it became public, first in Peru, where the impact to Lima, a city of more than seven million people, would be enormous, later in the United States, where various federal agencies grappled with the responsibility of endorsing or denying a prediction that had very little support among mainstream earthquake scientists. The prediction received major media attention when Brady announced that the expected magnitude would be greater than 9, and the preferred date for the event was June 28, 1981. The Peruvian government asked the U.S. government to evaluate the prediction that had been made by one of its own government scientists. In response to Peru’s request, a NEPEC meeting was convened in January 1981, to evaluate Brady’s prediction and to make a recommendation to the director of the USGS on how to advise the Peruvians. The panel of experts considered the Brady and Spence prediction and rejected it.

     

    Did the NEPEC report make the controversy go away? Not at all, and Brady himself was not convinced that his prediction had no scientific merit. An interview of Brady by Charles Osgood of CBS News shortly after the January NEPEC meeting was not broadcast until June 1981, close to the predicted arrival time of the earthquake. Officials of the Office of Foreign Disaster Assistance took up Brady’s cause, and the NEPEC meeting was described as a “trial and execution.” The NEPEC panel of experts was labeled a partisan group ready to destroy the career of a dedicated scientist rather than endorse his earthquake prediction.

     

    John Filson, an official with the USGS, made a point of being in Lima on the predicted date of the earthquake to reassure the Peruvian public. The earthquake did not keep Brady’s appointment with Lima, Peru. It has not arrived to this day.