Quake Prediction: Is Farm Town the Key? : Scientists Look for Forecasting Clues in Parkfield on San Andreas Fault

Most evenings, when the atmospheric conditions are just right, Duane Hamann drives the winding, dusty road to the top of a hill on the edge of this Central California farming community, unlocks the door of a brown shed and fires up a powerful laser.

From his hilltop perch, Hamann can scan the peaceful hills in every direction, from the carefully cultivated Circle C Ranch to the south, to the one-room school where he is the only teacher in the tiny town below, to the oak-studded hills on the distant horizon. A riverbed cuts through the valley below, passing beneath the slightly twisted bridge that leads to the community of Parkfield.

It is the riverbed that concerns Hamann and the scientists at the U.S. Geological Survey, for whom he works part time.

The riverbed marks the course of the San Andreas Fault, the great demon of California that scientists say could cause a catastrophe of far greater dimensions than this country has ever known.

Sophisticated Laser Used

Hamann is here most nights, playing his role in a scientific drama that will put Parkfield on the map once and for all. He uses a sophisticated laser to measure even the slightest movement along the fault as part of a major effort to unlock the secrets of the San Andreas. The work is under way here because Parkfield, while it may look like scores of other farming communities scattered across California, is a unique place as far as seismologists are concerned.

For more than a century, the San Andreas Fault has ruptured in Parkfield with an earthquake of 5.5 to 6 magnitude on the Richter scale once about every 22 years. The most recent quake was in 1966, so one is due around 1988, although it could occur at any time now. The only exception to the pattern came in 1934, when the quake arrived 10 years early.

So if the past has anything to do with the future, in the next couple of years or so the earth here will shudder, sending a strong but probably not catastrophic earthquake rumbling down the Cholame Valley.

That much is clear, say the scientists who plan to spend a lot of evenings on the hillsides here during the months ahead. What is less clear, they say, is whether the temblor at Parkfield will unlock a larger section of the San Andreas, possibly causing extensive damage to cities from Paso Robles to Bakersfield.

The certainty of the Parkfield quake and the uncertainty of how far it will extend illustrate the state of the fledgling field of earthquake prediction. In some rare cases, earthquakes may be extremely predictable. But in most cases in the foreseeable future--especially those in which the consequences could be the most grave--the quakes will probably continue to surprise even those who have dedicated their lives to studying them.

Do scientists working in the field expect to see the day when earthquakes can be predicted routinely?

“Am I going to see it?” asked Caltech’s Clarence Allen, one of the leaders in the field of quake prediction and past chairman of the National Earthquake Prediction Evaluation Council. “I’m 60 years old. I would be surprised if I see it in my lifetime. But within the next generation, I wouldn’t be surprised.”

Bruce Bolt--director of the seismological lab at the University of California, Berkeley, and president of the California Academy of Sciences--is less optimistic.

“There will be certain lines of evidence that will prove to be helpful in some cases,” Bolt said. “But in other cases these lines will be absent. We have to be prepared to accept the fact that earthquakes may occur with no warning.”

He said the reasons that the ground ruptures in some places “may always be beyond our grasp.”

The frustration is not limited to scientists in this country, he added.

“The Japanese have had a very well-financed program with first-rate people, and they have not been successful,” Bolt said. He said the accurate prediction of one Chinese earthquake a few years ago was actually misleading because the quake was preceded by tremors in an area with no known history of temblors. The Chinese have not been successful in predicting less obvious earthquakes, Bolt said.

Funding a Problem

Allen, while he remains a true believer in the future of earthquake prediction, said: “We have not been as successful as we had hoped. It has proved to be more difficult than we had thought it would be.”

That is one of the reasons Allen and his colleagues will most likely be making another pilgrimage to Washington soon. Each year the U.S. Geological Survey’s budget for research in earthquake prediction is cut severely, and each year the practitioners of the art are called upon to testify before Congress, which in the past has reinstated the funds.

“Every year we have to fight (for the funding),” Allen said. “Every year we’re in there testifying.”

He said the budget for next year also calls for drastic reductions.

The effort to gain funding has been hindered by the fact that there have been no dramatic breakthroughs, and many scientists who support the effort believe it is unrealistic to expect any in the immediate future.

“To me, there is no question that it’s an important part of seismology,” said UC’s Bolt. “From the beginning, people have wanted to know when earthquakes are coming. But it’s a very difficult thing to do seismologically. I’ve never been confident that in the short run we could make uniform, reliable predictions.

“It seems to me one should approach this very realistically, although that’s not good for raising funds.”

Bolt said the field of earthquake prediction began with “great expectations that you would find certain flags” that would point to an impending quake.

“God might have made this world so that you are lucky,” Bolt said. “But if they (flags) are there, nobody has found them.”

Enthusiasm Still High

None of that, however, has dampened the enthusiasm for research that is now under way at Parkfield, which Bolt termed “an extraordinary case.”

What sets Parkfield apart is its apparent predictability.

Robert G. Wallace, senior scientist at the U.S. Geological Survey’s Menlo Park office and a member of the quake prediction council, said that the precise pattern of temblors at Parkfield is “unique.”

That is fortunate in the sense that it provides scientists with an extraordinary opportunity to set up a laboratory at one point on the San Andreas where they hope to learn precisely what happens before, during and after an earthquake.

It is unfortunate, however, in that what is learned at Parkfield may not be applicable to other areas where the earthquake dynamics could be quite different, an important factor in terms of developing a reliable system for predicting earthquakes.

No Other Examples

Bolt, who is also chairman of the California Seismic Safety Commission, said he has repeatedly asked other experts to point out other areas like Parkfield, but none have been suggested.

“I can see nothing else like it,” he said.

Caltech’s Allen, who is searching for a similar target area in Southern California, said he also has had a problem finding an area to match Parkfield. He said that he has at least one candidate in the San Jacinto Mountains near the town of Anza. But it may well be that Parkfield is the only place in the state where essentially the same magnitude of earthquake has occurred at essentially the same interval over a period of many years.

Thus Parkfield would seem to be an ideal seismological field laboratory. But one piece of its history could make the art of predicting earthquakes here very sticky indeed. Scientists may be able to predict the time, but not the potential danger, of a quake at Parkfield.

“We’re not sure yet how we’re going to handle that,” said Wallace.

Gradual Slippage

The San Andreas is slipping gradually--and thus releasing some of its tension--to the north of Parkfield, but the fault appears to be locked to the south. There is considerable speculation among reputable seismologists that Parkfield serves as the trigger for the area to the south, which ruptures an average of once every 140 years and is expected to do so again within 30 years.

In 1857, the San Andreas ruptured from Parkfield south to the Cajon Pass in a massive earthquake. Only hours before, there had been a smaller quake at Parkfield.

A repetition of the 1857 event could result in a massive earthquake of at least 8 on the Richter scale, causing widespread damage and thousands of deaths throughout much of Southern California. However, the prevailing thought among seismologists who have studied the geological history of the San Andreas seems to be that if Parkfield triggers a quake to the south, it would not rupture all the way to Cajon Pass and would probably be no stronger than a 7 magnitude.

That would still be strong enough, however, to cause substantial damage in communities throughout Central California.

A number of scientists are digging in at Parkfield in an effort to learn exactly what is taking place beneath the grassy plains and the gentle slopes of the Cholame Valley. They have established an array of instruments, including creep meters to measure any movement along the fault, strain meters to detect strain in the Earth’s crust and a two-color laser to detect any crustal deformation, regarded by some seismologists as among the most promising indication of an impending earthquake.

Glistening Ruby

During one recent evening, Hamann demonstrated the laser by focusing on a reflector more than three miles away. The red light from the laser lit up the reflector like a glistening ruby on a distant horizon. At that distance, the laser should detect if the reflector has moved even 1-50th of an inch, according to Robert O. Burford of the U.S. Geological Survey and one of the principal scientists on the laser experiment.

Atmospheric conditions can throw off the measurement, Burford said, so the system uses both red and blue beams of light that are affected differently by the atmosphere. The difference in the measurement by the two beams reflects the atmospheric conditions, and that can be fed into a computer to ensure that the measurements remain accurate.

In the past, when only the red laser was used, instruments had to be taken up in an airplane and flown back and forth between the laser and the reflector to measure the atmospheric conditions.

“It was a real zoo,” Burford said.

Ten reflectors are scattered around the Parkfield hilltop, some on one side of the San Andreas and the others on the other side. A map of the area, with lines drawn from the laser to the reflectors, looks like a wheel with spokes.

Hamann began taking measurements for the Geological Survey last June. So far, Burford said, the results show slight movement of some of the reflectors, but the pattern is too vague to draw any conclusions.

The theory behind the experiment is that shortly before an earthquake, geological tension deep below the surface will cause the ground to deform. Rapid deformation may mean an earthquake is imminent.

Background Information

Burford hopes that he has at least a year or two to collect data before the quake hits. That will provide background information that could help scientists learn far more about the events preceding the quake.

Whether what they learn there will be applicable elsewhere is debatable, however.

No matter how it turns out, many scientists are eagerly watching the Parkfield experiment because it constitutes a long-term, carefully instrumented commitment to analyzing one earthquake.

The result “will be a quantum leap ahead in terms of understanding the process,” Wallace said.