USU team studying stresses inside San Andreas

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."