Halfway between Los Angeles and San Francisco, tiny Parkfield (population 36) sits atop one of the most seismically active regions in the world, right where the San Andreas fault starts to shift. Every couple of years, a football field-sized segment of the fault experiences magnitude-2.1 temblors. For scientists, this makes it the ideal place to study earthquakes. The problem: The sweet spot, the center of all those tremors, is 2 miles below the earth's surface, directly under 3,000-foot-tall Middle Mountain.
Until recently, that meant the area was out of reach. But now, buoyed by advances in sideways drilling and sensor technologies, a team of more than 100 US, French, German, and Japanese scientists is embarking on a $21 million project to bore a hole straight through the Pacific plate into the North American plate. In early June, researchers at the San Andreas Fault Observatory at Depth began drilling into the tenuous granite under Parkfield. The path: a 1-mile vertical descent, then after swerving 50 degrees to the east, another 1.6-mile drop dug diagonally at 250 feet per day. Once the drill hits the target, scientists will line the 2.6-mile-long hole with sensors to measure the activity that happens before, during, and after a quake: fluctuations in fluid pressure, temperature, and rock shape. It'll be the first-ever earthquake lab situated at the source of a temblor. Monitoring will continue for two decades in the hopes of gathering enough data to create computer simulations of fault-zone activity.
The goal is to create a model that predicts not only the timing of earthquakes, but also the severity. Though they can't knock over buildings, microquakes have a lot in common with the more lethal variety – all 7.0s start out small. Identifying the warning signs of a microquake could help researchers develop a way to anticipate the Big One. "We want to know how patches of the fault that sit next to each other interact, how they feed into the basics of earthquake mechanics," says Bill Ellsworth, a seismologist at the US Geological Survey and one of the observatory's principal investigators. "If we solve that, it would greatly improve our ability to forecast the behavior of much larger pieces of the fault."
The project isn't designed for quick results: The last of the sensors won't be in place until the summer of 2007. Until then, paranoid Californians are just going to have to live with the angst of floating off toward Hawaii.
1. Breaking Ground In June, scientists from Stanford University and the US Geological Survey began drilling under the 5-acre San Andreas Fault Observatory site outside Parkfield, California, boring through layers of granite, sandstone, shale, and greenstone. Operations will run around the clock through October, then break for eight months while seismologists monitor the fault.
2. Vertical Drilling A 2,000-horsepower rotary drill tears into the Parkfield rock. A muddy slurry is pumped in (blue arrow) to push rock samples to the surface for testing (red arrows). A 700,000-pound steel pipe is fed into the hole, followed by a layer of concrete around it, to prevent the hole from collapsing under 12,000 pounds-per-square-inch of pressure.
3. Sideways Drilling When the drill turns diagonally at the 1-mile mark, gravity no longer helps keep it on target. As a result, scientists expect fault-zone obstacles, such as high fluid pressure and fractured rock, to cause the drill to veer from its trajectory. Using downhole gyroscopes that provide data on the drill's position, the team points the drill toward the target area.
4. Installing Sensors Scientists will line the interior of the steel pipe with two dozen ruggedized sensors that can endure extreme pressure and temperatures as high as 275 degrees Fahrenheit. Strapped to inflatable tubes, the sensors are pushed against the inner wall of the pipe, allowing them to perceive rock movement through the steel and concrete. Fiber optic cables relay the data from the sensors to the surface.
5. Hitting the Sweet Spot After monitoring data from the bottom section of the hole for two years, scientists will core four 250-meter "sidetracks" to reach the target area. It's in these that they expect to discover the origins of the microquakes – and perhaps the warning signs of a 6.0. Newly placed sensors will monitor hydrological changes in these ancillary shafts as some seismologists believe rising fluid pressure tips off an incoming temblor.
Six Types of Sensors Fluid pressure sensor: Detects fluid buildup around rocks, which may precede an earthquake. Seismometer: Measures velocity of ground movement (in nanometers per second). Temperature sensor: Measures temperature changes (to 1/1,000th of a degree) as rocks rub together to create friction. Accelerometer: Logs fault vibration and acceleration (in meters per second squared) of the earth during seismic events. Ultrasonic imager: Uses sound to record ultrasonic images of rock fractures. Strainmeter: Quantifies rock deformation by measuring changes in shape and size of the hole (in parts per billion).
Brendan I. Koerner (brendan@wiredmag.com) is a Wired contributing editor.
