Utah State University scientists are part of an international team working on a project to monitor changes in ground stresses deep inside an active earthquake fault.
And it's not just any fault. It's the infamous San Andreas Fault where USU geology professor Jim Evans, graduate student Sarah Draper and soon-to-be senior Kelly Mitchell have been laboring through the hot summer. The fault, a scar in Earth's crust that stretches 800 miles long and reaches down 10 miles, running from San Francisco to the vicinity of San Bernardino, Calif., is one of the most dangerous in the world.
A shift inside the San Andreas Fault caused the earthquake that flattened San Francisco in 1906. The U.S. Geological Survey says the section of the fault near Parkfield in central California generally hosts moderate quakes every 20 to 22 years.
It is near Parkfield, population 18, that scientists are setting up an underground earthquake observatory, two miles beneath the surface and within the fault itself.
The effort is the San Andreas Fault Observatory at Depth, or SAFOD.
Last week, after more than a year of drilling, the project completed the hole, reaching a depth of 13,082 feet. The drilling rig worked at an angle, with the end of the well located about 150 feet northeast of where the fault breaks the ground. Scientists believe that the hole crosses the fault.
In 1966, a magnitude 6 earthquake there broke the ground, says the project's Web site, www.earthscope.org. Parkfield is one of three areas that the parent effort, called EarthScope, is investigating to understand "the structure and evolution of the North American continent and the physical processes controlling earthquakes and volcanic eruptions."
EarthScope is a project of the National Science Foundation and the U.S. Geological Survey. The foundation says SAFOD will be the first instrumented underground observatory to cross an active earthquake fault.
"Drilling officially ended two days ago," Evans said in a telephone interview from a headquarters trailer near the site. "Right now they're doing something called conditioning the hole."
The borehole varies in diameter from about 18 inches at the surface to 8.5 inches at the bottom, he said. It will be cased with steel and concrete, and seismic monitoring instruments will be installed in the hole.
Temperatures at the bottom of the hole reach more than 275 degrees, Evans said. "When the water comes up from the bottom of the hole, it steams."
Also coming up during the drilling were mud and ground-up bits of rock strata. Eventually, besides ground bits of rock, core samples will be taken from the bottom.
"One of the things that I've been funded to do is to study actually the rock and rock materials that have been coming out of the hole," he added.
Fragments of fossil oysters, spotted by a "mud logger" who examines the material pumped from the hole, helped researchers know when the drill was in the fault zone. So did measurements of drilling speed through the rock and measurements of gas samples.
"It's at times exciting, it's sometimes just really tiring," Evans added.
The drill was going around the clock, operated by two crews. "If something important comes up at 2 in the morning, people need to be on top of that," he said. Meanwhile, students may be washing and examining rock samples at any time.
Draper, a volunteer working on her master's degree at USU, said the rock cuttings are about the size of sand, mixed with drilling mud. "Most of my responsibilities include helping to collect and wash and store all of the samples that come up from the borehole," she said.
"The students collect them in buckets at regular intervals. We wash them following a very strict protocol."
She intends to try to discover where the same rock formations break the surface of the ground.
Mitchell worked on site for about five weeks, returning to USU on Tuesday.
"It was really exciting," she said. The area frequently has small earthquakes, Mitchell noted.
Asked to describe some of her work at the site, she said, "I did sample collection, where I would collect samples every hundred feet, wash them, take photos of the cuttings, and dry and separate them."
Also, she worked in separating minerals for identification purposes.
The samples are bits of rock brought up with the mud slurry as the drill progresses. They can tell a great deal about the underground strata.
Mitchell said that when the researchers were in Parkfield, normally with about 18 residents, "we doubled their population."
Students lived in a home at Parkfield, which is five or 10 miles from the drill site. "It was a lot of fun. There were a lot of international students," she said.
Mitchell and Draper usually were the only American students there. "It was a fun experience culturally as well," Mitchell said. Draper agreed: "It's actually quite the multicultural experience."
E-mail: bau@desnews.com