Drilling Into Earthquakes

Utah State University geologists are involved in a breakthrough drilling project that lays the groundwork for the first subterranean earthquake observatory established directly within a seismically active fault.

Geology professor Jim Evans, grad student Sarah Draper, undergrad Kelly Mitchell and Aggie alum John Solum, now with the U.S. Geological Survey, are among researchers working on-site with the San Andreas Fault Observatory at Depth (SAFOD) project. Launched in 2003, SAFOD is one of three major components of EarthScope, a National Science Foundation-funded initiative being carried out in collaboration with the USGS to investigate powerful geological forces that shape the North American continent.

Drilling personnel completed the project's 13,082 foot-long curved borehole, which penetrates an active area of the San Andreas Fault and reaches a vertical depth of about 2 miles, Aug. 9. Located on a private ranch near Parkfield, Calif., about halfway between Los Angeles and San Francisco, the borehole will be lined with steel and concrete in preparation for installation of a variety of instruments and sensors to provide round-the-clock measurement of temperature, fluid pressure, strain accumulation and other processes.

"We've drilled into earthquakes," said Evans. "For one of the first times we can look at rocks in a zone where we know earthquakes occur."

Drilling into the precise location was easier said than done. Rather than an obvious gash in the ground apparent with up and down thrust faults, much of the 800-mile long strike-slip San Andreas is barely visible to the lay observer. It consists of two roughly parallel, underground plates that move back and forth like cross-country skis. While drilling into the carefully selected site, researchers discovered different rock types than their models suggested.

"We took samples at every 100 feet of drilling depth to anticipate when we'd cross the fault and hit the active zone," said Mitchell, the lone undergraduate in the multi-university 10-member student contingent of the research team.

Mitchell and Draper spent days in 100-plus degree heat scooping expelled drilling mud into buckets, washing and separating rock cuttings, and carefully analyzing the cuttings’ composition.

Mitchell said it took longer than expected to hit the tell-tale heavy silicates indicative of the target zone. She recounted a false alarm in late July when she and fellow students were roused in the wee hours of the morning from their drilling rig-side double-wide trailer to witness breaking developments.

"We all rushed to the drilling platform," she said. "The drilling break — meaning the rate that you're penetrating the rock — suddenly increased and we thought we'd crossed the fault."

The team's efforts were rewarded Aug. 2, when the drill sped up again, hit bursts of radon, carbon dioxide and hydrocarbon gases and breached the active zone.

William Ellsworth, chief of the Earthquake Hazards Team at the USGS in Menlo Park, Calif., and a principle investigator on the project, told national media the successful borehole marks a major milestone in understanding how quakes start, how they grow into deadly tremblors and whether scientists can learn to accurately predict them.

Until now, said Evans, geologists have been limited to study of exhumed faults — that is, faults that were once at depth and have subsequently risen to the surface due to mountain building processes.

"In those cases, we are never sure that the faults we look at were truly earthquake-producing," he said. "Now we're able to observe the actual earthquake machine in real-time."

Evans, Mitchell and Draper said they are grateful for the unprecedented opportunity to participate in a project that provides a literal window into previously unseen geophysical phenomena.

"This is a very cool project," said Evans.

For more information about SAFOD, visit its Web site. For more information about Earthscope, visit its Web site.

Writer: Mary-Ann Muffoletto, 797-1429, maryann.muffoletto@usu.edu

Contact: Jim Evans, 797-1267, jpevans@cc.usu.edu