State Asking for Locations in Temblor Forecasts

In an attempt to speed up advisories of possibly impending large earthquakes, the state Office of Emergency Services is asking a scientific panel to identify certain areas where quakes of 5.0 or 6.0 magnitude would automatically trigger the warnings.

Deputy Emergency Services Director Richard Andrews said the 10-member California Earthquake Prediction Evaluation Council will be asked to designate such areas, based in part on where there have been sizable foreshocks of major temblors in the past.

A U.S. Geological Survey scientist, Lucile Jones, said three such areas could be the Cajon Pass, Banning and Salton Sea sections of the San Andreas fault. Andrews said another such place could be north of Bishop in the eastern Sierra.

On June 26, the Office of Emergency Services issued a five-day advisory of “a slightly increased likelihood” of a quake of up to 6.5 magnitude in an area south of San Jose after an earthquake there the day before in the 5.0 magnitude range.

No such quake occurred, but Caltech seismologist Kate Hutton later criticized the lateness of the advisory, remarking that by the time it was issued, the period of maximum danger had already passed.

“We want to do everything we can to shorten the period of time before issuing such advisories,” Andrews said in an interview. But, he noted, not all faults experience foreshocks of large earthquakes, and deliberations are required in those cases.

In any event, Andrews said, as such advisories become more routine, he is certain that the process of issuing them will become quicker.

Conflicting Opinions

Scientists from several agencies and universities make up the membership of the Prediction Evaluation Council, and there have been reports of some disagreement in the past as to when an advisory is merited.

But Andrews said it was incorrect to suggest, as Hutton had, that a day had gone by before the state notified local authorities in the San Jose case that there was a possibility of a larger earthquake.

Within four hours of the June 25 earthquake, the scientists had expressed their concerns about an increased risk to the Office of Emergency Services, Andrews said, and within 12 hours the first informal advisories had gone out to the local authorities in a four-county area. It was only the formal advisory that was delayed until the next day, he said.

Public word was further delayed until nearly six hours after the formal advisory, Andrews acknowledged, but he said it was always intended to inform the authorities first, since steps necessary for preparing for a possible emergency affected them more than the public. The odds on a big quake, in any case, were not so great as to mandate a public alarm, he added.

No More Than 2% Chance

The chances assessed of a large magnitude quake in the San Jose episode were never more than about 2%, according to scientists.

But they might be 10% or greater in certain areas along the San Andreas fault when 5.0- to 6.0-magnitude quakes occur in the future, according to Jones, who is presently acting scientist in charge at the U.S. Geological Survey’s Pasadena field office.

Jones noted that the Cajon Pass, Banning and Salton Sea sections of the San Andreas fault are places where scientists have put the chances of a magnitude 8.0 earthquake at up to 60% within the next 30 years. These sensitive locations could well be the sites of automatic advisories in the future if 5.0- or 6.0-magnitude shocks occur, she said.

Jones said that the Office of Emergency Services had specifically requested the scientific panel to advise it when there is even a 2% risk, so that low-level advisories of the kind issued last week could be disseminated.