Parkfield, Calif., is not what most folks would call a happening town. Isolated in a valley about 45 miles northeast of San Simeon, Parkfield (population 37) is a small collection of log and clapboard buildings -- fire station, school, inn -- nestled in a landscape of vineyards and amber hayfields. Stands of live oak and gray pine dot the crumpled hillsides, shading the cattle from the midday heat as they doze and flick their tails at flies. Wild turkeys scratch the dust, alert for the occasional sound of approaching pickup trucks.
Hunting those turkeys is a favorite pastime of the locals. But when Stanford geophysicist Mark Zoback goes to Parkfield, he doesn't track what's on top of the ground; he's interested in what's beneath. That's because the Parkfield valley sits on a particularly intriguing part of the San Andreas fault: here -- in contrast to the wrenching major earthquakes characteristic of its northern and southern reaches -- the fault creeps, producing numerous shallow "microquakes." (The area used to be known for stronger, deeper quakes that happened, uncannily, every 22 years, until the one due around 1988 failed to occur.) Over the last 15 years, geophysicists planted several million dollars' worth of seismometers and other monitoring equipment on private ranches in the valley, making it one of the most closely watched spots on earth. But Zoback, MS '73, PhD '75, wants to dig deeper -- about 2 1/2 miles down -- into that part of the fault (see box).
Working with scientists from the U.S. Geological Survey, the geophysics professor is in charge of a drilling experiment at Parkfield to study the composition of the San Andreas, a ragged, 650-mile-long seam between the North American and Pacific tectonic plates. The $26 million project involves scientists from dozens of universities and research institutions in the United States and abroad. If current funding negotiations are successful, Zoback says with an optimistic grin, drilling could begin as early as the fall of 2000.
Zoback's ambitious project comes at the end of a fertile decade of quake-related research by Stanford scientists and engineers. Much of it was sparked by an infusion of grant money after Loma Prieta. At the John A. Blume Earthquake Engineering Center on campus, for example, assistant professor Laura Lowes has been trying to figure out why '50s-era bridge connections made of reinforced concrete beam-columns -- similar to those that collapsed beneath Oakland's Cypress Freeway in 1989 -- are so vulnerable in major earthquakes. Some of her civil engineering department colleagues, including associate professor Gregory Deierlein and research assistant Wei-Ming Chi, are analyzing welded-steel-framed structures to find out why so many of their beam-column connections fractured following the 1994 Northridge earthquake.
Stanford scientists have published some 20 papers based on Loma Prieta so far. "Ten years after the fact," says geophysics associate professor Greg Beroza, "there's still something to be gained by analyzing the records of that earthquake, as well as the smaller earthquakes that have followed." For example, scientists still puzzle over why Loma Prieta originated so deep within the earth's crust (about 11 miles down), compared with typically shallow California quakes, or why the fault moved in such complex ways during the aftershocks, compared to its slippage during the main shock.
By drilling into the fault at Parkfield, Zoback hopes to get closer to where the seismic action is. "We have little direct knowledge of the San Andreas fault zone at depth," he explains. "What are the properties of the rocks down there? How strong are they? What forces are acting on them, and what is the pressure of the groundwater in the cracks and pores?" Without direct observation, Zoback says, scientists can't verify or disprove their hypotheses. "Drilling would provide us the opportunity to address a fundamental question about the San Andreas that has haunted scientists for 30 years: why are these plate boundaries so much weaker than the surrounding crust?"To visit Zoback's proposed drilling site, you have to hitch a ride with Rich Liechti, a sun-scorched man with a reddish beard and a cowboy hat who serves as Parkfield's resident technician for the usgs. Liechti first came to Parkfield in 1985 to set up ground-level monitoring equipment in preparation for the "characteristic" quake expected between 1988 and 1993. It still hasn't hit, and Liechti's back is starting to ache; it's his solitary job to maintain the hundreds of aging seismometers, creep meters, strain meters and magnetometers that dot the valley -- not to mention maintaining relations with the local ranchers whose lands he must traverse. "It's been pretty stagnant here for a number of years," he says wearily, pulling his white Ford Bronco up close to the proposed drilling site. The new project, he says, "will be a real shot in the arm."
The proposed site is on a patch of tinder-dry grazing land, about 8 miles northwest of Parkfield proper. When finished, the borehole, ranging from about 17 inches in diameter at the surface to about 6 inches at the bottom, will be lined with steel pipe and fitted with scientific instruments. Later, the researchers plan to retrieve sample core sections of the surrounding rock, to get a better idea of its composition.
No, Zoback says patiently (and clearly not for the first time), they're not worried about triggering another Loma Prieta, because big earthquakes never occur at the depths they're drilling. Moreover, routine microquakes already disturb that section of the fault. "It's not as if nothing is going on there and then we're coming along and messing up the natural system," Zoback points out. Nevertheless, the project will have its nailbiting moments. Although oil rigs commonly go deeper, few have attempted to drill such a deep hole in such an active geological environment, and the equipment might get twisted and stuck.
On the other hand, the rewards could be tremendous. In addition to advancing scientists' understanding of earthquake physics, Zoback says, the drilling project may someday lead to that most elusive goal: successful earthquake prediction. "Some scientists claim that earthquakes are unpredictable, period, but I think that's an irresponsible position at this time," he says flatly. "We do know earthquake prediction is not easy, but the simple fact is that we don't understand the physics of faulting well enough to know whether or not we can predict earthquakes. If we better understood how faults worked, we'd be able to make better laboratory and computer simulations, and then we'd be able to make better forecasts."
By directly monitoring what is going on deep inside the fault zone, Zoback says, scientists will more easily be able to detect strange, telltale things that may happen before an earthquake. Is the fault creeping a little before it breaks? Is the fluid pressure building? "It will be like watching an earthquake with a microscope," he says excitedly. "We'll be placing instruments as close to these shallow earthquakes as my desk is to the opposite wall, and we've never done that before."
It could be the biggest thing to happen around Parkfield in a very long time.
