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'Moonquake' : Theory Advanced by 2 Scientists Says Sun, Lunar Forces Could Trigger Huge Temblor Here Any Time

April 06, 1986|LEE DYE | Times Science Writer

Southern Californians should expect a major earthquake any time now, if two scientists who believe that the sun and moon may trigger large quakes in this region are right.

The scientists, who published their findings in a 1983 article in Nature, the prestigious British science journal, have not won the full backing of their colleagues, but their theory has not been dismissed either. Their article led to several studies that are still under way to test the controversial theory.

Astronomer Steven Kilston and geophysicist Leon Knopoff believe their study shows that Southern California has entered the time when a major earthquake is most likely to strike, probably at around sunrise or sunset. Their statistical analysis, they said, indicates that the sun and moon may have triggered the major earthquakes of 1857, 1933, 1952 and 1971.

According to the two, who based their conclusions on admittedly meager historical data, tidal forces from the moon and sun may be the "last straw" needed for an earthquake that is just waiting to happen.

Their conclusions are based partly on the fact that the overwhelming majority of earthquakes in this region in the last five decades have occurred near sunrise or sunset, suggesting the strong influence of solar gravity on major earthquakes.

According to their theory, Southern California has entered a period when the odds will be greater than normal for a major earthquake on the San Andreas Fault, or any of the many other faults in this area that run in a north-south direction. The San Andreas system, one of the most active earthquake regions in the world, runs in a northwesterly direction and may be unusually susceptible to the pull of gravity from the sun and moon because of the east-west orientation of solar-lunar influences.

Such a possibility comes at a time of growing concern that Southern California is due for a catastrophic earthquake because of prolonged inactivity on the central and southern sections of the giant fault system.

History indicates that such earthquakes occur at fairly regular intervals. And there has been no major earthquake in Southern California since 1971--the longest quiet spell since scientists began keeping comprehensive records.

The study by Kilston and Knopoff suggests that the window of vulnerability will peak in November, 1987, when the moon will be at the northernmost point of its orbit around the Earth--something that occurs once every 18.6 years--and thus be in a position to exert its strongest pull on the west flank of the San Andreas.

Major earthquakes that fit this cycle, give or take a few years, include those killer quakes of 1857, 1933, 1952 and 1971. The giant earthquake of 1857, believed to have been greater than 8 on the Richter scale, was the last catastrophic quake on the southern half of the main fault. It rumbled across a Southern California that was so sparsely populated that there are few reports of damage. In 1971, an earthquake of only 6.4 on the San Fernando Fault--which is part of the San Andreas system--caused hundreds of millions of dollars in damage and killed 65 people.

Knopoff works at UCLA's Institute of Geophysics and Planetary Physics. Kilston is a systems engineer at Hughes Aircraft Co. in El Segundo.

Scientists have long sought a link between solar and lunar cycles, which have the strongest influence of all natural phenomena on the Earth's crust, but earthquakes have seemed to occur so randomly that no link could be established.

Yet, when Kilston and Knopoff limited their study to Southern California, disregarded all the minor earthquakes and then studied the major ones individually, they found that 10 out of 13 had struck near sunrise or sunset. In addition, most of them had occurred near the 18.6-year intervals that coincide with the northernmost position of the moon.

"While not every recurrence of the cycle has produced large quakes here, there is about a 50% chance for one during the next four years," Kilston said.

"But we're not predicting an earthquake in November of 1987," Knopoff added.

The correlation between past major quakes and the solar-lunar cycles "is definitely there," Knopoff said, although conceding that the theory "is relatively fragile in that it rests on observations of a small number of earthquakes."

"Knopoff is certainly an eminent scientist," said Caltech's Clarence Allen, an international leader in seismology who knows well his cross-town colleague. "I know of no one who thinks he's all wet." But, he added, "It doesn't seem to me that the correlation is a very strong one."

The weakness in the "correlation" that concerns Allen, as well as Kilston and Knopoff, is the fact that some major earthquakes just do not seem to fit the pattern.

All earthquake research is hampered somewhat by a paucity of accurate records. In geological terms, the recorded history of earthquakes is but a blip on a scale that stretches for eons, thereby rendering any conclusions tentative at best.

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