Emergency Officials Attempt to Squelch Rumors of Big One : Seismology: State office concedes the risk of a major quake is higher, but it has not ordered an increased state of alert.

Responding to heightened fears of an impending major earthquake, the director of the state Office of Emergency Services said Wednesday that “there are no assessments we are aware of that indicate a major earthquake is imminent” in Southern California, and he sought to squelch rumors that state authorities had ordered an increased state of alert.

While conceding that “the risk is higher” and that “public preparedness efforts should continue,” Director Richard Andrews said, “there is nothing more definitive in terms of public policy steps that should be taken right now. We are not putting out any message of heightened immediate alert.”

The spate of rumors, which also came to news media outlets, occurred on a day when the National Earthquake Information Center in Golden, Colo., revised upward the magnitudes of the June 28 Landers and Big Bear earthquakes to 7.5 and 6.6, based on new data from 20 widely scattered seismological stations.

Preliminary magnitudes of the two earthquakes were set on the day they happened at 7.4 and 6.5. Revisions are common in the weeks after major quakes, and there may be further revisions in the months ahead, said geophysicist Willis Jacobs of the national center. Nonetheless, if it stands, the new 7.5 magnitude for the Landers earthquake moves it into a tie for third position among the strongest temblors in California this century.

Meanwhile on Wednesday, representatives of both Caltech and the U.S. Geological Survey reported that in the last 24 hours they had received frequent telephone calls suggesting that water tables were falling or there was new turbidity in water--possible signs of earthquakes--or saying callers had heard that Caltech had shut its campus and sent employees home.

“All of this is absolutely untrue,” said Robert O’Rourke, assistant vice president for public relations at Caltech.

“We’ve heard rumors that we’ve suspended operations for three weeks and that a group of our seismologists have left town. There is no credence at all to any of this. These are strictly rumors, and I underline rumors.”

Andrews said: “There have been persistent rumors since the 28th of June that unnamed scientists have indicated a big quake is imminent.”

But he said there is a wide spectrum of thought in the scientific community on the possibility of a major quake.

“We (at emergency services) have continued to say there is a significant chance of aftershocks in the 5 to 6 magnitude range and that that will continue to be the case for weeks,” the emergency director said.

Andrews said that two weeks ago his office briefed law enforcement and fire officials in Southern California, “including San Bernardino and Riverside counties, and we discussed possible risks along the San Andreas Fault.

“There are uncertainties,” he said. “But in terms of what the (exact) risk is . . . there is no certainty.” In a 1988 statement, a task force of scientists said there was a 60% chance of a major earthquake on the southern San Andreas within the next 30 years. Some scientists now suggest the quake might happen sooner than later.

Among the most common of the rumors Wednesday were reports that water tables had fallen dramatically in Southern California, possibly presaging a big earthquake.

Spokesmen for both the Metropolitan Water District and, close to the scene of the Landers earthquake, the High Desert Water District, said they have detected no change in water tables.

Aftershocks of the Landers and Big Bear quakes continued Wednesday. One, at 5:45 a.m., registered a magnitude 3.6. A 3.0 aftershock occurred near Yucaipa on the San Andreas Fault at 1:34 p.m.