EarthScope: Looking into North America

Following in the footsteps of Lewis and Clark's expedition two centuries ago, a large group of U.S. scientists that includes U-M's Ben van der Pluijm has embarked upon an unprecedented exploration of the North American continent.

One of several hundred USArray stations that will be used to image the subsurface of North America. (Photo by http://www.earthscope.org)

But instead of mapping mountains and rivers visible above ground, the modern-day explorers will use state-of-the-art instruments to document the continent's underlying structure "from crust to core" and probe the physical processes that control earthquakes, volcanic eruptions and plate movements.

In contrast to the Lewis and Clark expedition, "this is not a project where you just go out and see what you run into," van der Pluijm says. "We're not going into the complete unknown. We have well-defined goals and expected outcomes, or at least multiple hypotheses that we can test with well-honed experiments. Still, it's a new chance at major discoveries, no doubt about it."

In van der Pluijm's part of the EarthScope project, a borehole is being drilled into the San Andreas Fault, about halfway between Los Angeles and San Francisco. Rock and fluid samples will be taken, and instruments will be installed in the borehole to create a kind of underground observatory for monitoring how the fault zone changes before, during and after earthquakes.

The researchers hope that studying the rocks and fluids along faults will help them understand why some faults are "weaker"—more easily moved and more earthquake-prone—than others, van der Pluijm says. "It's possible, and not unlikely, that material in the narrow band of rock where the fault occurs acts as a lubricant or somehow changes the coupling between the two blocks that slide past each other."

It's already known from earthquakes that tremendous amounts of energy are released in fault zones, actually melting the rock in some places. That probably isn't happening at the depth of San Andreas Fault drilling, van der Pluijm says, but similar rock transformations might be at work.

The San Andreas Fault Observatory at Depth drill rig near Parkfield, Calif., in summer 2004. (Photo by http://www.earthscope.org)

Drilling for the underground observatory, overseen by Stanford University and the U.S. Geological Survey (USGS), began this summer. The curved borehole is expected to pass through the fault zone next summer. The observatory will provide the first opportunity to determine directly the conditions under which shallow earthquakes occur, to collect fault rocks and fluids for laboratory study and to monitor continuously an active, potentially devastating fault zone at depth.

Van der Plujm says it will not aid in earthquake prediction immediately.

"It won't likely help us make predictions with enough accuracy to say that an earthquake will happen tomorrow morning or next week or two weeks from now, but we expect it will help us better understand the earthquake process," he says. "And what we learn will not only apply to the San Andreas Fault. Other faults that are in the news all the time—in Turkey and New Zealand, for example—are the same type of fault, so the fundamental information we gather here will help us understand what may happen at all of these faults."

The EarthScope project is funded by the National Science Foundation, with an initial equipment investment of $220 million, and is conducted in partnership with USGS.