Project to drill into Earth fault

By Maggie Shiels
in California

UNDERGROUND OBSERVATORY Project will drill directly into San Andreas quake zone Measure changes in rock before, during, after tremors Data compared with other surface measurements

An ambitious project by scientists in the US to try to predict earthquakes will go ahead thanks to a $20m grant from the National Science Foundation.

Researchers from the United States Geological Survey and Stanford University are working to put instruments directly inside the San Andreas fault.

The crack in the Earth's surface, which runs through California, is one of the most studied faults on the planet.

The new data will come from sensors lowered down a 4-km-deep drill hole.

Scientists on the Safod (San Andreas Fault Observatory at Depth) project hope to observe directly what goes on underground, to help them figure out when and where an earthquake will strike.

Such a quest has become something of a Holy Grail for geophysicists.

The new money will bankroll the project through to 2008 and give the research team a unique view of how earthquakes work.

Underground lab

Stanford University's Mark Zoback, who is one of the project leaders, said: "Our current knowledge of fault zone processes is so poor that not only are we unable to make reliable short-term earthquake predictions, we don't know whether such predictions are even possible.

"By making continuous observations directly within the San Andreas fault zone at depths where earthquakes start, we will be able to test and extend current theories about phenomena that might precede an impending earthquake."

To really understand earthquakes, we need to see up close the processes that cannot be observed from Earth's surface Bill Ellsworth, USGS

Work to insert the world's first continuous monitoring probe will start in June 2004.

The underground observatory will be built on a private ranch near Parkfield in California.

The tiny rural town is located halfway between Los Angeles and San Francisco.

The ranch straddles the fault, a 1,300-kilometre-long (800 miles) rift that runs from the Mexican border to the northern part of the state.

The fault marks the boundary between two great land masses that are slowly moving in opposite directions - the Pacific tectonic plate on the west and the North American plate on the east.

As the plates grind against one another, earthquakes are triggered along the fault.

Inside view

Last year a 2.2-km-deep (1.4 miles) vertical pilot hole was drilled on the Parkfield ranch, just to the west of the fault.

Seismic monitors and others sensors were placed in the pilot hole to give researchers valuable information about drilling techniques that will be used in the Safod experiment.

"Safod will be deeper and more challenging than the pilot hole," explains Steve Hickman, of the USGS Earthquake Hazards Team, in California's Menlo Park.

"Using advanced directional drilling technologies developed for the oil and gas industry, we will steer Safod as close as possible to a cluster of small earthquakes, known as microearthquakes, that occur repeatedly within the centre of the fault zone.

SAN ANDREAS FAULT Part of Pacific and North American plate boundary Parkfield dubbed 'world's earthquake capital' Town experiences regular magnitude six quakes

"These earthquakes are rarely felt, but they can end up rupturing a football-sized piece of the fault."

Drilling is expected to last until September 2005 when the entire borehole will be encased in cement. For the next two years after that, the focus will be on finding the exact location of the microearthquake clusters inside the fault zone.

"Earthquakes start miles below ground," noted Bill Ellsworth, chief scientist for the USGS Earthquake Hazards Team.

"Faults may rupture at the surface in large earthquakes, but the place where the forces are stored and released are deep within the fault.

"The Safod hole will go deep enough to get into the heart of the fault zone, where earthquakes really begin."

The key to the Safod experiment is placing an array of monitoring devices and other sensitive instruments right inside the fault zone where it is producing earthquakes to allow scientists detect exactly how the tremors work.

"So far, we have been forced to look through miles of rock which obscure and distort signals. To really understand earthquakes, we need to see up close the processes that cannot be observed from Earth's surface," says Ellsworth.

Earth 'machine'

Funding for Safod has been provided as part of a far-reaching new initiative launched by the National Science Foundation called EarthScope.

This five-year project is a scientific exploration of the structure, evolution, and dynamics of the North American Continent, as well as the physical processes controlling its earthquakes and volcanic eruptions.

Directional drilling techniques will be employed

Other EarthScope projects include the installation of an array of 400 seismometers to form a moving net of geologic sensors across the contiguous 48 states and Alaska.

The seismometers will occupy 2,000 locations over 10 years, and will construct an image of the internal structure of the continent from crust to core.

EarthScope will also work with the US space agency (Nasa) to develop a Synthetic Aperture Radar Satellite to map changes in Earth's surface before, during and after major earthquakes and volcanic eruptions.

"EarthScope will revolutionize Earth sciences," claimed Jim Whitcomb, a section head in Earth Sciences at NSF.

"It is like constructing a telescope that looks into the Earth. It will tell us how Earth's engine works."