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Scientists hoping to unlock the keys to earthquakes have extracted rocks from two miles beneath the San Andreas Fault, the first rocks obtained from so deep in an earthquake fault.
“Now we can hold the San Andreas Fault in our hands,” said Mark Zoback, Stanford University professor of earth sciences and one of the three principal co-investigators of the San Andreas Fault Observatory at Depth. “We know what it’s made of. We can study how it works.”
The observatory broke ground in 2004 to drill rock samples from deep below the earth’s surface. The project is funded by the National Science Foundation and being carried out in collaboration with Stanford and the United States Geological Survey in Menlo Park. William Ellsworth and Steve Hickman of the USGS are the other principal co-investigators.
“Obtaining cores from the actively slipping San Andreas Fault is truly unprecedented and will allow truly transformative research and discoveries,” said Kaye Shedlock, program manager at the National Science Foundation.
“All earthquakes start small, at a point of rupture,” Ellsworth said. “We don’t understand the physics of a rupture, why earthquakes start, but also why earthquakes stop.”
The rocks extracted from deep underground, where temperatures are 240 degrees, will help scientists understand how earthquakes happen.
“It is a new beginning in earthquake science,” Zoback said.
Geologists extracted 135 feet of rock cores about 4 inches in diameter. The cores weigh about 1 ton.
The observatory has drilled a 2.5-mile borehole into the fault, running from the Pacific plate on the west wide of the fault into the North American plate on the east side. The junction of the two subterranean plates forms the 800-mile-long San Andreas Fault.
The science team will install an array of seismic instruments in the borehole in the next phase of work. The sensors will enable scientists to observe the earthquake generation process as it happens.
The fault observatory is located about 23 miles east of Paso Robles near the small town of Parksfield, which sits on the fault and is famous for the large number of earthquakes there. Most of the Parksfield quakes are modest, triggered by a process called creep in which the two plates slide slowly past each other.
But the San Andreas Fault also produces devastating earthquakes, including the 1906 San Francisco Earthquake. The fault runs through the hills along the Peninsula.
The fault observatory is expected to gather data over the next 10 to 20 years.
Stanford and USGS scientists announced the extraction of the rocks at an 11 a.m. press conference today.
