In Search of Cleaner Fuel

Peter Malin’s Seismology Group Uses Earthquake Technology to Explore Sources of Geothermal Energy p.2

“Basel is very short on non-polluting energy resources,” said Nicholas School seismology professor Peter Malin, who directs the seismology group. “In fact they’ve actually made it illegal to have air conditioning in the city.”

That industrial city—situated in a Los Angeles–like bowl that traps bad air—may be in Switzerland, but it becomes hot and polluted in the summer. “In my hotel room it was close to 90 degrees Fahrenheit all night long, nearly all month long,” Malin said of his July visit.

The entire Rhine River valley, of which Basel is a part, stretches along what geologists call a graben, a length of crust that collapsed like a pile of pipes upon losing their side-supports, said Malin. The collapse happened about 54 million years ago when what is now Europe began splitting apart but then stopped. Heat tapped by that abortive rifting is still stored several miles below the present valley.

Kahn helped build seven quakedetecting seismometers at Duke for use at the Basel site. He then traveled to Switzerland with Malin to install the instruments in drilled shafts at depths ranging from 300 meters to 2.7 kilometers.

In addition, he created a computer program that coordinates data from various seismographs to generate a kind of earthquake-distribution image, providing clues about what is happening underground.

“What we were hoping was that, when they’re pumping water in to crack the rock, these earthquakes would locate where the cracks are forming,” he said. “By mapping the earthquakes, we can measure the propagation of cracks and the growth of the hot rock reservoir.”

Crucial rock-cracking at the Basel site began Dec. 2, delayed from July because of drilling complications. During the five subsequent days before cracking was halted, the seismographs recorded about 15,000 small quakes— all but a few undetected by residents, Kahn said.

Of that larger number, only about 3,500 tremors were locatable using Kahn’s software. Unfortunately, vibrations from Basel’s subway system complicated those measurements, interfering with input from the four seismometers located nearest the surface.

Despite those difficulties, his computer program seemed to provide useful information on the cracks. “It looks promising,” he said. “I have a very good idea from the data what the crack structure in the hot zone is.

“It shows crack growth from the point where the water is being injected. It looks like it’s doing what they want it to. But it’s not large enough yet to make a commercial pool of hot water to actually start creating power.”

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