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.
Scientists have long sought to understand the triggering mechanism that causes the Earth to suddenly release the tension built up in fault zones by the gradual movement of the giant masses of the planet's crust--called tectonic plates--that migrate over its molten core.
Triggering Device Unknown
The stresses that develop along the lines where those plates crunch together are the primary causes of earthquakes, but scientists have never been sure of the triggering mechanism that causes the Earth to suddenly release that stress in the form of a major quake.
Kilston set out to find that mechanism in the aftermath of the San Fernando Valley earthquake of 1971.
Moments after the quake, Kilston said, "I looked out the window and I saw a full moon."
At that point most astronomers might have headed for intellectual cover. But Kilston knew that the moon was full because it was aligned with the Earth and the sun, and he wondered if that alignment had anything to do with the earthquake.
Clues in 'Moonquakes'
The effect on quakes of the alignment of the sun, Earth and moon has been demonstrated on the moon itself.
During the Apollo space program, seismological instruments placed on the moon revealed that the moon has far more "moonquakes" when it is aligned with the Earth and the sun than at any other time. Like Earth, the moon "flexes" because of the influence of gravity from other bodies, and the gravitational pull is strongest when the three are aligned.
In checking the records, Kilston found that major earthquakes in this region seemed to occur in cycles of 18 to 19 years. As an astronomer, he knew that the moon wobbles in its orbit around the Earth by about five degrees, and that it takes 18.6 years for the moon to complete one "wobble." Thus, every 18.6 years the moon reaches the northernmost point in its orbit around the Earth.
He also found that most major earthquakes had occurred near either sunrise or sunset, a time when the sun's gravitational pull would be the greatest on the tectonic plates that form the San Andreas Fault system.
Haunted by the unlikelihood that all of this could be coincidental, Kilston discussed his findings with Knopoff. The two had met through Knopoff's daughter, who was in a high school science class taught by Kilston.
Debunked Theory Earlier
Several years earlier, Knopoff had written a paper for the Bulletin of the Seismological Society of America, in which he debunked the idea that solar and lunar tides could play a significant role in triggering earthquakes. Knopoff had studied the issue on a global scale, and, like several other geophysicists, he concluded then that the global record did not support such a theory.
But he decided to join Kilston in taking another look, this time at one specific region where a major fault system is configured so as to maximize any effects of tidal forces.
After months of research, Knopoff became a convert.
The sun and the moon, Kilston said, could be the "last-straw push" needed to break the fault loose. "The big ones need everything they can get," he said. "To get them to go takes a little more of a kick."
Tug of War
Kilston reasoned that, during a full moon, the moon and the sun are aligned on opposite sides of the San Andreas, and they would tug on the tectonic plates in opposing directions, possibly breaking the friction that keeps the fault from slipping.
In the case of a new moon, the moon and the sun are aligned on the same side of the fault, and they would pull more on the closer plate than the other, thus achieving a similar result, Kilston said.
The pull would be strongest during the full moon, because the sun and moon are on opposite sides of the fault, pulling the plates directly apart.
The scientists limited their study to one section of California, roughly the area from San Diego north to San Simeon.
In studying all earthquakes in the region, they found that smaller quakes did not conform to any particular pattern. But that was not surprising because the trigger for most smaller quakes is known to be other earthquakes, not tidal forces.
"We know that from aftershocks," Knopoff said.
They then discovered that, by excluding earthquakes of less than 6 on the Richter scale, 10 out of 13 struck around sunrise or sunset, and most occurred near the 18.6-year interval--coinciding with the northernmost position of the moon. Most also occurred during an either full or new moon.
'An Annoying Problem'
Still, they are somewhat troubled by the fact that the "triggering" corresponded with the rising and setting of the sun rather than the moon, which has a stronger tidal influence on the Earth because it is so much closer.
"That's been an annoying problem," Knopoff said.
It could be that the moon's influence is harder to pinpoint, he speculated. Like the tides of the oceans, the land masses of the Earth also have tides--though far less pronounced--as the ground flexes in accordance with the pull of the moon and the sun. But the most notable effect of lunar gravity is on the oceans, where tidal fluctuations are well known.
Not a Prediction
Kilston and Knopoff emphasized during interviews that, while their studies do show a correlation between major earthquakes and lunar and solar cycles, they are not making a prediction.
Still, their paper in the journal Nature nearly three years ago made it clear that Southern California may have entered a very interesting period, especially as the "maximum lunar declination" approaches in November, 1987.
The paper stated:
"A literal extrapolation of our observations implies that during a window of a few years width astride this date, at times near full or new moon, and near sunrise or sunset, one might be more likely than otherwise to observe one or more large earthquakes in Southern California."
DO THE SUN AND MOON TRIGGER EARTHQUAKES?
Studies suggest the gravitational pull of the moon and sun may trigger major earthquakes in Southern California along faults that run in a north-south direction. The two bodies, when aligned, may pull faults apart, thus relieving friction and setting off quakes. If so, Southern California should expect a major quake some time over the next three or four years.
During a full moon, the sun and moon are aligned on opposite sides of faults, such as the San Andreas, that run north to south. Studies suggest they may pull the fault apart slightly, triggering major earthquakes.
During a new moon, the sun and moon are aligned on the same side of the fault, and their gravitational pull could tend to lift the land on that side of the fault, thus reducing the friction that keeps the fault from slipping.