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GEYSER ERUPTION PATTERN MAY PRESAGE QUAKES

A study published Friday suggests that the eruption pattern of an "Old Faithful"-type of geyser in California could give warning of impending large earthquakes.

Two Carnegie Institution researchers said the Old Faithful Geyser of California, located near Calistoga, experienced a sudden variation in its eruption pattern within one to three days before three major earthquakes in northern California.Paul G. Silver and Nathalie J. Valette-Silver, a husband and wife team at Carnegie's Department of Terrestrial Magnetism in Washington, said a 20-year record of eruptions shows clear evidence that large quakes within 155 miles of the site affect the spouting pattern of the geyser.

"Either this is all a coincidence and nature is playing a practical joke" or the geyser is exhibiting changes that are precursors to large earth movements, Silver said in a statement released by Carnegie. The researchers are out of the country and not reachable by telephone.

In the report in the journal Science, the Silvers said they entered into a computer records of the geyser eruptions since 1971 and then compared the eruption pattern for months around major earthquake events.

They found that three major earthquakes within 155 miles of the geyser occurred within one day to three days after the geyser's eruption pattern underwent abrupt and dramatic changes.

On the day before the Oroville, Calif., earthquake of Aug. 1, 1975, the Silvers said the interval between geyser eruptions suddenly changed from 50 minutes to 120 minutes. The geyser returned to a 50-minute pattern 40 days after the earthquake.

In 1984, the geyser was erupting every 40 minutes. But the day before the April 24 Morgan Hill, Calif., quake, the pattern switched to an interval sequence with eruptions every 25, 40 and 50 minutes. This new pattern persisted for six months after the quake.

A change was also noted before the Loma Prieta, Calif., earthquake of Oct. 17, 1989. The Silvers said that 21/2 days before the quake, eruption intervals at the geyser suddenly shifted from 90 minutes to 150 minutes. Eruptions returned to the 90-minute interval 70 days after the earthquake, they said.

All three of the seismic events were considered significant earthquakes. Oroville was 6.1 magnitude on the Richter scale, Morgan Hill was 5.9 and Loma Prieta was 7.1.

The researchers said that a number of things, including rainfall, can affect the regularity of eruptions in "Old Faithful"-type geysers. These geysers, including the famed Old Faithful of Yellowstone National Park, also tend to vary slightly when measured over months and years.

A mathematical examination of the Calistoga record, however, eliminates both chance and the effects of rainfall as an explanation for the abrupt pattern changes preceding the earthquakes, the Silvers said.

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(Additional information)

Temblor-related changes

Here is a summary of the apparently earthquake-related changes observed in the Calistoga, Calif., geyser:

- Interval between eruptions increased from 50 minutes to 120 minutes the day before the Oroville, Calif., earthquake of Aug. 1, 1975.

- Interval abruptly changed from every 40 minutes to an interval sequence of 25, 40 and 50 minutes. Change started a day before the Morgan Hill, Calif., earthquake of April 24, 1984 and continued for six months.

- Interval increased from 90 to 150 minutes 21/2 days before the Loma Prieta, Calif., earthquake of Oct. 17, 1989.