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Scientists Plan Journey Toward Center of Earth : Earthquakes: California team seeks funding to drill a six-mile hole near the San Andreas Fault. They hope to determine what causes temblors.

April 12, 1993|KENNETH REICH | TIMES STAFF WRITER

California scientists are proposing a $50-million project to drill more than six miles deep into the San Andreas Fault zone in an attempt to learn more about the cause of major earthquakes.

The scientists from Stanford University, the Lawrence Livermore National Laboratory and the U.S. Geological Survey seek to begin drilling in 1996 after extensive study to determine which of 18 possible sites along the fault would be best for the project. The drilling would take about six years to complete.

It would be one of the two deepest and most extensive efforts ever made to try to determine how earthquakes occur. And it comes at a time when the views held by most scientists for the last century--mainly ascribing quakes to stress buildups--have been undergoing sharp alteration.

A growing number of earthquake experts now believe that highly heated liquids, perhaps rising from the Earth's mantle, may permeate fault zones and do more to trigger quakes than the accumulation of stress. They see fault zones as weak strands in the Earth's crust, with the quakes resulting from possibly minor changes in liquid pressure.

Only in Germany, where a six-mile-deep drilling project in mountains near the Czech border is under way, have scientists tried to send instruments into areas more than five miles beneath the surface, where most major temblors are generated.

"We don't know what the fault system is made of at those depths," said Bill Ellsworth of the Geological Survey. "We want to find out to what extent fluids are present, and if there are fluids, how they are tied to what happens."

Although the bore hole will be only about eight inches in diameter at the lower depths of the fault zone, the scientists hope that small instruments will be able to determine over time how earthquakes start, spread and stop, and what factors influence how often they recur.

The proposal, which researchers will submit for funding to the U.S. and German governments, has been a subject of intense discussion among more than 100 scientists participating in the project.

Stanford geophysicist Mark D. Zoback said that even the preliminary work of choosing a site for the drilling would give researchers a lot of new information about the nature of the San Andreas and other major California faults.

They are soliciting the Germans for funding because the Germans have committed resources to such a project and might be inclined to fund another to give themselves a comparison elsewhere in the world, Zoback said. They also speculate that they might be able to use the same drilling rig the Germans have been using.

As some scientists have noted in their assessment of a possible drilling site at Cajon Pass, a potential danger of such a project is the "risk of triggering (the) Big One," the giant quake widely expected to eventually hit Southern California.

But Zoback said that such risk is believed to be remote.

Geothermal drilling that has been done at lesser depths in the Imperial Valley and near Clear Lake in Northern California has not been linked to any damaging quakes.

The number of drilling sites being considered may soon be narrowed to four, the scientists said. As part of the process to select a final site, shallow exploratory core holes about three-fifths of a mile deep would be drilled at each of the four sites.

Once the best location is settled upon and full funding is obtained, the main hole would be dug at about a quarter-mile from the surface trace of the fault. Side shafts would be dug directly across the fault at three depths, with at least two going in at shallower levels where many small quakes occur.

At present, the sites range from Point Arena in Northern California to the Coachella Valley in Southern California and include four sites that are on other faults--San Jacinto, Calaveras, Hayward and Rodgers Creek.

Deep Drilling Plan

Scientists want to drill deep into the San Andreas fault zone to study new theories that the cause of major earthquakes may be less the buildup of stress, as has been commonly believed, than the injection of liquids, perhaps from the Earth's mantle.

Schedule: The drilling of a 6-mile-deep hole would get start in 1996 and take up to six years.

Funding: $50 million is being sought from the U.S. and German governments.

Location: 18 sites across the state are being considered.

Scientists hope to learn:

* What factors determine the start of quakes, their spread along rupture zones and their recurrence?

* What determines the maximum depth of seismic activity?

* What is the origin and composition of fault zone fluids?

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