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The challenges inherent to earthquake research do not daunt Rensselaer researchers. “The fact that the Earth is complicated, well, that’s what you have to deal with,” says Steve Roecker, professor of earth and environmental sciences. Roecker is undertaking multiple projects designed to help reveal, case by case, what substances lie underneath faults, and how these materials relate to their motion.
Roecker spent the summer of 2005 in Kyrgyzstan, studying the Tien Shan mountains considered a geologic puzzle because they exist not at the edge of a tectonic plate but in the middle of one, the Eurasia Plate. “The real mystery is why there are mountains there at all,” Roecker says. It’s possible that there could be a large fault covered up by the mountains, or a series of smaller fractures near the Earth’s surface that act like miniature plate boundaries.
To study the Earth’s insides, Roecker sets up networks of seismometers sensitive measuring devices and records the speed of the waves generated by earthquakes. For a geophysicist, this data reveals much about the materials lying underground. High-temperature rocks, for instance, slow down earthquake waves. Recent technological advances now allow small seismometers to pick up waves originating far away. “We’re able to make some nice pictures just by setting up instruments and waiting for an earthquake to happen anywhere in the world,” says Roecker.
"As engineers, to be able to understand a certain phenomenon and design for it, you need to know what is happening. With a centrifuge, you have instrumentation, you can recreate the event, and now you can improve the design and foundation of buildings."
For the Tien Shan project, those pictures may involve the Earth’s mantle, the viscous layer underneath the crust that ranges roughly 20 to 2,000 miles below the Earth’s surface a distance almost impossible to reach with today’s technology. By contrast, in California, Roecker is part of a project called the “San Andreas Fault Observatory at Depth,” an attempt to drill just a couple of miles into the Earth’s surface. Scheduled for completion in 2006, it aims to reveal what substances enable plates to slip and slide past one another (underground water is a prime suspect).
Roecker’s efforts to turn the data into maps of the Earth’s interior, at any depth, are often conducted with colleagues at Rensselaer’s Inverse Problems Center, including mathematicians Margaret Cheney and Joyce McLaughlin, who have years of relevant experience from analogous areas like medical imaging. “They have a very fundamental understanding of these techniques,” says Roecker. Ultimately, he says, “the idea is to try to connect the stuff at the surface, like mountain-building, with the forces driving it beneath the surface.”
Thus, when engineers in the centrifuge center conduct tests, they both expose a structure to a powerful force and examine how that structure will react in certain ground conditions.
Consider pilings under a building, or pipes running through the ground. Near the surface, the Earth creates little stress. But further down, the stress increases. The centrifuge can mimic those stresses either as a catastrophic event or an accumulation of stress over time and tell engineers if their structures will pass muster.
A typical test in the Rensselaer centrifuge might have a length of pipe embedded in a mix of soil, on a tray fixed to the whirling arm of the machine. The pipe will be heavily wired with sensors transmitting information for analysis. “The interaction between the soil resisting and the building pushing in, that’s what creates the actual response,” says Abdoun.
Indeed, the roots of the center go back to soil studies Dobry and Thomas Zimmie, professor of civil engineering, started pursuing in the 1970s. In the late 1980s, Rensselaer acquired the centrifuge. A decade later, spurred on by the National Science Foundation (NSF), a new idea in earthquake research took hold: Forming NEES as a network of linked labs. “The information revolution was in full swing, and the emphasis changed,” says Dobry. “Instead of upgrading a bunch of separate earth engineering centers around the country, the idea became to build an integrated national laboratory.”
Backed by NSF funding for refurbishment including $5 million over the next five years the upgraded center, along with the rest of NEES, opened in the fall of 2004. The center is replete with intriguing-looking equipment, in addition to the centrifuge, including a “shake table,” a rectangular metal frame with segmented walls that can replicate seismic effects; a related octagonal tool the staff call “the slinky;” a robot on the centrifuge that alters models while swinging around in mid-experiment; and a videoconferencing center. The staff includes computer specialists and a variety of engineers.
“As we build things in the center, we’re interacting with mechanical engineers, electrical engineers, robotic engineers, and information technologists,” says Dobry. “It’s the definition of interdisciplinary research.”
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