Rangely, a small town near the western border of Colorado, sits about 30 km southeast of the town of Dinosaur via the Stegosaurus Freeway. It also happens to be the site of the first, and probably only, attempt to trigger earthquakes intentionally. I recently became acquainted with Rangely during a presentation on the seismic consequences of fracking and wastewater disposal at the American Physical Society’s April meeting last week in Salt Lake City, Utah.
The story of the Rangely experiment is especially relevant today. In 1969, when the experiment was performed, scientists envisioned inducing minor earthquakes to reduce the probability of a big one. Nowadays quakes are induced frequently, but not for the application Rangely scientists had in mind. According to a March report by the US Geological Survey (USGS), parts of the central US are just as prone to damaging earthquakes, most of them induced, as infamous hot spots in California.
Inspiration for the research at Rangely came from the curious ordeal of the Rocky Mountain Arsenal, a chemical-weapons manufacturing facility run by the US Army and located outside Denver. The historically seismically inactive area abruptly started experiencing minor earthquakes in 1962, when Arsenal engineers began pumping hundreds of thousands of gallons of wastewater deep underground. Geophysicists suspected that the pressurized fluid was lubricating a buried fault, which made it easier for slabs of earth along the fault to slip.
Seeking to test the concept far from a metropolitan area, USGS geophysicists Barry Raleigh and Jack Healy and hydrologist John Bredehoeft converged on Rangely. In September 1969 the three scientists, funded by the US Department of Defense’s Advanced Research Projects Agency, began trying to control seismic activity in part of an oil field owned by Chevron.
Jack Healy (left) and Barry Raleigh at the Rangely site. Image credit: US Geological Survey.
Within the area of the experiment, four injection wells were used to change the fluid pressure at depth. During the first 13 months, when fluid was pumped into the wells, the scientists detected more than 900 earthquakes. Then, from November 1970 through May 1971, fluid was removed to relieve the pressure. The earthquake rate quickly fell to about one a month. In late 1972 and early 1973, the pressure was raised again, and the quake rate shot up to 26 per month.
The ability to stimulate or silence seismic activity gave the three USGS researchers big ideas. They raised the prospect of drilling multiple 7-km-deep holes along critical sections of the San Andreas Fault to explore the possibility of inducing quakes to relieve pressure from the country’s most notorious seismic zone. “Given the encouraging results of the research reported in this article,” they wrote in Science in March 1976, “we feel that control of the San Andreas fault could ultimately prove to be feasible.”
That research never came to pass. “There was a lot of hubris in the 70s,” says Arthur McGarr, an author of the recent USGS report, who gave the APS presentation. And as it turned out, the research by Raleigh, Healy, and Bredehoeft was only the tip of the iceberg in exploring humans’ ability to induce earthquakes. The recent boom in oil and gas production in the central and eastern US has resulted in a staggering increase in earthquake incidence due to wastewater injection.
Although most of today’s injection sites don’t trigger earthquakes large enough to be felt at the surface, the ones that do can cause considerable damage. The greater the rate of injection, the more frequent the induced quakes, researchers have found. The maximum magnitude of an induced quake, which so far has peaked at 5.6, rises along with the total volume of injected fluid.
In retrospect, the Rangely experiment served as an unheeded lesson in how easy it is to trigger earthquakes. Fluid injection, rather than being used to quiet down the most treacherous faults, is now awakening previously harmless ones.
Extra Dimensions is a new blog written by Andrew Grant, the online editor at Physics Today. The blog provides a forum for exploring the physics behind events in the news and offering fresh perspectives on recent developments in physics and the related sciences.