The extraordinary earthquake in Japan last month and the terrifying tsunami that followed left the country's electricity infrastructure crippled. But for some green technologies, the worry is not that they will be damaged by earthquakes but that they can cause earthquakes. Measured or anticipated seismic shocks associated with geothermal energy, hydropower, and carbon sequestration are raising questions about the wisdom of energy projects and in some cases stopping them in their tracks.
"We're observing earthquakes. People are feeling them. The people running projects are denying responsibility, and I don't think most people are buying it," says seismologist David Oppenheimer, project chief for the U.S. Geological Survey's Northern California Seismic Network. "It's foolish to go in with eyes closed."
Tectonic pressures cause the vast majority of earthquakes, but geophysicists also recognize the existence of human-induced seismicity. Hydropower reservoirs, for example, frequently cause small, shallow quakes as shifting water levels change the strains on the rock layers below. Such microseismicity—up to magnitude 4 on the Richter scale—is also caused by wells that inject hazardous waste and wastewater into deep rock formations at high pressure.
Microseismicity is merely an irritant, but human-induced seismicity can be deadly if it triggers the release of accumulated tectonic strain on a large fault. The textbook case occurred in 1967 when the filling of a reservoir behind India's hydroelectric Koyna Dam—completed six years earlier—unleashed a magnitude 6.3 quake, killing 180 people and leaving thousands homeless. Geophysicists continue to debate whether the Zipingpu Dam, completed in 2004, triggered the 7.9-magnitude earthquake that devastated China's Sichuan province three years ago, killing over 70 000.
In the United States and Europe, it's geothermal energy that's front and center as a source of induced seismic shocks. Draining hot-water reservoirs to generate power can induce shocks, as can reinjecting cool water to recharge the aquifer. The link to shocks is tighter still with enhanced geothermal systems, or EGS, whereby developers deliberately fracture hot rock formations with high-pressure water blasts to access geothermal heat.
Community backlash over microseismicity has stalled or killed leading EGS efforts in Europe. Officials in Basel, for example, canceled a promising EGS project after it set off a magnitude 3.4 quake in 2006, which revived awareness of a 14th-century temblor that leveled the Swiss city.
A similar story is playing out in the United States. EGS projects have multiplied there since a seminal 2007 report predicting that EGS could provide 10 percent of U.S. power demand by 2050—25 times as much as what geothermal now delivers. But getting EGS projects going has proved tough. AltaRock Energy, based in Sausalito, Calif., scrubbed exploratory EGS drilling at the Geysers, a geothermal hot spot north of San Francisco, after facing protests from residents and technical challenges with its wells. Northern California towns were already unsettled by continual microseismicity caused by conventional geothermal power plants built in the region since the 1960s.
Oppenheimer says geophysicists are in a poor position to reassure the public on the safety of geothermal production at the Geysers. He notes that the region is contracting as it cools—a rejiggering of geophysical strains that could trigger a quake of magnitude 6 to 7 on one of Northern California's large faults. The probability? "Unknown," says Oppenheimer, because "nobody has done the formal study."
EGS firms are beginning to assess risks. AltaRock, for example, released a seismic report in November for existing wells it hopes to start fracturing this summer on the flank of Oregon's dormant Newberry Volcano. The report asserts that the resulting shocks should be lower than magnitude 4, posing "more of a nuisance than a hazard" to the closest community, 14 kilometers away.
AltaRock needs to do still more, according to Ernest Majer, a geophysicist at the U.S. Department of Energy's Lawrence Berkeley National Laboratory. He is lead author on a protocol for managing risks that could become mandatory by June for federally funded EGS projects (including the work at Newberry). AltaRock's contractor, for example, based its estimate on shocks induced at the Geysers and other EGS sites—an assumption that AltaRock project manager Will Osborn defends as a "conservative approach," given the minimal seismic activity observed at Newberry. But ground movement is highly site specific, and Majer says that AltaRock should model induced shocks based on the subsurface conditions at Newberry before it moves forward.
Geothermal's teething troubles may foreshadow an even bigger problem for carbon sequestration, which governments worldwide see as a key strategy to control atmospheric levels of carbon dioxide. In recent months geoscientists have begun speaking out on the increased strain that millions of tons of CO2 will place on subsurface rock formations. At the American Geophysical Union's annual meeting this past December, Stanford geophysicist Mark Zoback warned that even small earthquakes could crack the cap rocks overlying carbon sequestration sites, enabling the buoyant CO2 to escape.
Modeling reported last fall by a U.S.-based consortium showed that concern was well founded for sections of the Mount Simon Formation, a rock layer spanning the U.S. Midwest that is a key target for CO2 sequestration. According to lead researcher Mark Person, a hydrologist at the New Mexico Institute of Mining and Technology, fluid pressures from CO2 injection in the formation's southern sections approach levels associated with earthquakes thought to have been caused by injecting hazardous waste into a well near Ashtabula, Ohio. Person says there is added reason for concern because the region has a history of massive earthquakes: The nearby New Madrid Seismic Zone delivered quakes with a magnitude of 7 to 8 in the early 19th century.
Person says carbon sequestration proponents need to anticipate and manage the risk of induced earthquakes, for example by injecting CO2 at lower pressure. Failure to do so, warns Person, could be fatal to the whole endeavor. As Person puts it, "One big temblor, say a magnitude 6 earthquake, could shut the U.S. sequestration program down."