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Deep Earth Probe Starts Drilling Along Quake Fault

December 8, 1986

DEVORE, Calif. (AP) _ Drilling began Monday on the deepest research hole ever attempted in the continental United States, a 16,000-foot borehole more than halfway into the Earth’s crust to study the San Andreas Fault.

″The knowledge we get on how this fault works will be fundamental in developing earthquake prevention strategy. This model should be the basis of any rational earthquake prediction strategy,″ said the project chief scientist, Mark Zoback of Stanford University.

″This is going to test the magnitude of the stresses dividing the fault,″ Zoback said. ″We’re also trying to measure the amount of heat generated by the fault and ultimately determine exactly how the fault works.″

Scientists from seven universities will place instruments inside the 17 1/2 -inch diameter hole that they hope will allow them to resolve discrepancies among differing theories of earthquake causes, which Zoback said are based on different types of data.

″Lab measurements of (San Andreas) faultal sample have shown stresses to be quite high,″ he said. ″But temperature measurements have shown stresses to be quite low.

The San Andreas Fault, which crosses Interstate 15 about two miles south of the drilling site, forms the boundary between the Pacific and North American continental plates, which move alongside each other at a rate of several inches annually. Sections of the fault which stick must eventually break, producing the shock felt at the surface as an earthquake.

At 16,000 feet, the hole will be more than halfway through the Earth’s crust, the planet’s outermost layer, he said. That makes it the deepest scientific research hole in the United States, although at least one producing gas well in southwestern Wyoming was drilled to 16,780 feet. A scientific test well in northern Russia was drilled to more than 30,000 feet.

The drilling site is on federal land in the upper reaches of the Cajon Pass, 55 miles northeast of Los Angeles.

The project is being conducted by a non-profit corporation formed by a consortium of about 30 universities, called Deep Observation and Sampling of the Earth’s Continental Crust.

The $7 million, two-year project is being funded mainly by the National Science Foundation, consortium spokeswoman Ruth Barritt said.

The 20-story drilling rig will be stopped for about a day when it reaches 825 feet so engineers can install a protective casing, but then drilling will continue practically non-stop for about three months, Zoback said.

Drilling then will be halted again for tests until October, when drilling will resume for five or six more months, he said.

″We’ll stop for testing periodically, but it’s basically going to be a 24- hour operation,″ Zoback said. ″We get opportunities like this very rarely, so we’re trying to maximize the scientific return.″

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