More earthquake advisories, such as the one issued for Bishop last week, will be made in the future when deemed appropriate, according to officials of the Geological Survey and the California Office of Emergency Services.
Even though no major seismic or volcanic activity has followed the three USGS advisories issued in the state since 1982, leaders of both agencies still believe the advisories have been useful, both in inducing the public to take basic precautions against injury and encouraging local governments to intensify quake planning.
Clement Shearer, special assistant for natural hazards at USGS national headquarters, said Tuesday, "We've been in discussions with social scientists as to the 'crying wolf' syndrome. We're sensitive to the danger of that. We tend to be cautious about issuing these kinds of statements."
But, Shearer said unequivocally, "USGS anticipates issuing advisories in the future. . . . We think they can be beneficial to both planning agencies--police, fire and city government--and the public itself."
Two key state officials agreed in separate interviews.
William M. Medigovich, director of the California Office of Emergency Services, said, "More warnings will be issued as appropriate. I think it's important to continue that process.
"As these advisories occur, we are sensitizing the public, so they are accustomed to them and won't have an irrational fear of them and, more important, we are causing people to take measures, so that no one will be buried under his books, as was the case with the man in San Diego this month."
This was a reference to an elderly man seriously injured in San Diego on July 13, when the city was shaken by a 5.3 quake centered at sea, 28 miles southwest of Oceanside.
James F. Davis, state geologist and chief of the state Conservation Department's Division of Mines and Geology, said he had concurred in consultations beforehand on issuing the the Bishop advisory.
That July 22 advisory said, in part, "It is our assessment that the region of Chalfant Valley, from Bishop north to the Nevada border, may experience additional earthquakes similar to the (6.1) July 21 event during the next few days." It was allowed to lapse two days later when the USGS said the pattern of aftershock activity alleviated its concern.
Davis said that two weeks before, however, after similar consultations, it was decided not to issue an advisory following the July 8 Palm Springs earthquake, which measured 5.9 on the Richter scale.
"It was decided by both the USGS and us that the prospect of something (more) happening there in the near term was remote enough, so that it wouldn't be useful," he said. "So, there have been contemplated advisories that were not put out, based on our assessment."
Before the Bishop advisory, the USGS had issued one for San Diego on June 17, 1985, following three closely timed 4-magnitude quakes near the city. The USGS warned on that occasion that there was a small chance of a larger quake occurring within five days. No such quake occurred.
Also, on May 25, 1982, the USGS put the Mammoth Lakes area, northwest of Bishop, on notice of a possible volcanic outburst, saying "the outbreak of volcanic activity is a possibility but by no means a certainty." Two years later, in the summer of 1984, it noted that seismic activity in the region was greatly reduced and declared that "a volcanic eruption does not now pose an immediate threat to public safety."
Shearer of the USGS noted Tuesday that in two other instances the agency has been even more explicit than in these three advisories.
"We made a flat prediction last year of a magnitude-6 quake for the Parkfield area (of central California)," he said. "I think we gave a 95% probability for such a quake sometime between 1985 and 1993. Of course, we may not know until '93. That was the most precise statement we've ever issued."
In addition, Shearer recalled, "We made forecasts years ago about the strong likelihood of a great earthquake in Southern California sometime around the beginning of the next century."
Pinpointing a Quake
The bottom line, the USGS official said, is that "we're working on being actually able to predict an earthquake, giving a somewhat specific idea of the magnitude, the location and the time and the probability, whether we are 80% sure or so forth. . . .
"What are the benefits? . . . There are some obvious measures that can be taken. A homeowner can bolt down his foundations, make sure his water heater is well attached, that he has emergency supplies, batteries and water stored, some way of getting along in an emergency. And to the number of steps that individuals can take, there are things schools and municipalities and police can do, pinpointing their procedures and so forth. . . .
"Those are the good things that come out of forecasts. People do take action, even when businessmen are unhappy, as they were last week in Bishop."