Distant Quakes Trigger Tremors at U.S. Waste-Injection Sites
This double repost excerpts the releases for two new important articles in the journal Science. The first is “Enhanced Remote Earthquake Triggering at Fluid-Injection Sites in the Midwestern United States” (subs. req’d). The second is a review article, “Injection-Induced Earthquakes” (subs. req’d) by U.S. Geological Survey geophysicist William Ellsworth. The first release, from Columbia University’s Lamont-Doherty Earth Observatory, explains:
A surge in U.S. energy production in the last decade or so has sparked what appears to be a rise in small to mid-sized earthquakes in the United States. Large amounts of water are used both to crack open rocks to release natural gas through hydrofracking, and to coax oil and gas from underground wells using conventional techniques. After the gas and oil have been extracted, the brine and chemical-laced water must be disposed of, and is often pumped back underground elsewhere, sometimes causing earthquakes.
Earthquakes induced by fracking wastewater reinjection are a major concern because those wells are already prone to fail and leak (see “Natural Gas, Once A Bridge, Now A Gangplank“). The Propublica exposé in Scientific American, “Are Fracking Wastewater Wells Poisoning the Ground beneath Our Feet?” quoted engineer Mario Salazar, who worked for a quarter century as a technical expert with the EPA’s underground injection program: “In 10 to 100 years we are going to find out that most of our groundwater is polluted. A lot of people are going to get sick, and a lot of people may die.”
Here is an extended excerpt from the Columbia release:
Large earthquakes from distant parts of the globe are setting off tremors around waste-fluid injection wells in the central United States, says a new study. Furthermore, such triggering of minor quakes by distant events could be precursors to larger events at sites where pressure from waste injection has pushed faults close to failure, say researchers.
Among the sites covered: a set of injection wells near Prague, Okla., where the study says a huge earthquake in Chile on Feb. 27, 2010 triggered a mid-size quake less than a day later, followed by months of smaller tremors. This culminated in probably the largest quake yet associated with waste injection, a magnitude 5.7 event which shook Prague on Nov. 6, 2011. Earthquakes off Japan in 2011, and Sumatra in 2012, similarly set off mid-size tremors around injection wells in western Texas and southern Colorado, says the study….
“The fluids are driving the faults to their tipping point,” said lead author Nicholas van der Elst, a postdoctoral researcher at Columba University’s Lamont-Doherty Earth Observatory. “The remote triggering by big earthquakes is an indication the area is critically stressed.”
… “We’ve known for at least 20 years that shaking from large, distant earthquakes can trigger seismicity in places with naturally high fluid pressure, like hydrothermal fields,” said study coauthor Geoffrey Abers, a seismologist at Lamont-Doherty. “We’re now seeing earthquakes in places where humans are raising pore pressure.”
The new study may be the first to find evidence of triggered earthquakes on faults critically stressed by waste injection. If it can be replicated and extended to other sites at risk of manmade earthquakes it could “help us understand where the stresses are,” said William Ellsworth, an expert on human-induced earthquakes with the USGS who was not involved in the study.
What follow is an extended excerpt of the other release, by William Ellsworth, Jessica Robertson, and Christopher Hook via USGS blog. It is an excellent overview of this important subject. For ease of reading, I’m not indenting the text.
The number of earthquakes has increased dramatically over the past few years within the central and eastern United States. More than 300 earthquakes above a magnitude 3.0 occurred in the three years from 2010-2012, compared with an average rate of 21 events per year observed from 1967-2000.
This increase in earthquakes prompts two important questions: Are they natural, or man-made? And what should be done in the future as we address the causes and consequences of these events to reduce associated risks? USGS scientists have been analyzing the changes in the rate of earthquakes as well as the likely causes, and they have some answers.
USGS scientists have found that at some locations the increase in seismicity coincides with the injection of wastewater in deep disposal wells. Much of this wastewater is a byproduct of oil and gas production and is routinely disposed of by injection into wells specifically designed and approved for this purpose.
Review Article on Injection-Induced Earthquakes
U.S. Geological Survey geophysicist William Ellsworth reviewed the issue of injection-induced earthquakes in a recent study published in the journal Science. The article focused on the injection of fluids into deep wells as a common practice for disposal of wastewater, and discusses recent events and key scientific challenges for assessing this hazard and moving forward to reduce associated risks.
What is Induced Seismicity?
Although it may seem like science fiction, man-made earthquakes have been a reality for decades. It has long been understood that earthquakes can be induced by impoundment of water in reservoirs, surface and underground mining, withdrawal of fluids and gas from the subsurface, and injection of fluids into underground formations.
What is Wastewater Disposal?
Water that is salty or polluted by chemicals needs to be disposed of in a manner that prevents it from contaminating freshwater sources. Often, it is most economical to geologically sequester such wastewaters by injecting them underground, deep below any aquifers that provide drinking water.
Wastewater can result from a variety of processes related to energy production. For example, water is usually present in rock formations containing oil and gas and therefore will be co-produced during oil and gas production. Wastewater can also occur as flow back from hydraulic fracturing operations that involve injecting water under high pressure into a rock formation to stimulate the movement of oil and gas to a well for production.
When wastewater disposal takes place near faults, and underground conditions are right, earthquakes may be more likely to occur, Ellsworth’s research showed. Specifically, an earthquake can be triggered by the well-understood mechanism of raising the water pressure inside a fault. If the pressure increases enough, the fault may fail, releasing stored tectonic stress in the form of an earthquake. Even faults that have not moved in millions of years can be made to slip and cause an earthquake if conditions underground are right.
While the disposal process has the potential to trigger earthquakes, not every wastewater disposal well produces earthquakes. In fact, very few of the more than 30,000 wells designed for this purpose appear to cause earthquakes.
Many questions have been raised about whether hydraulic fracturing — commonly known as “fracking”— is responsible for the recent increase of earthquakes. USGS’s studies suggest that the actual hydraulic fracturing process is only very rarely the direct cause of felt earthquakes. While hydraulic fracturing works by making thousands of extremely small “microearthquakes,” they are rarely felt and are too small to cause structural damage. As noted previously, wastewater associated with hydraulic fracturing has been linked to some, but not all, of the induced earthquakes.
Unknowns and Questions Moving Forward
USGS scientists are dedicated to gaining a better understanding of the geological conditions and industrial practices associated with induced earthquakes, and to determining how seismic risk can be managed.
One risk-management approach highlighted in Ellsworth’s article involves the setting of seismic activity thresholds for safe operation. Under this “traffic-light” system, if seismic activity exceeds preset thresholds, reductions in injection would be made. If seismicity continued or escalated, operations could be suspended.
The current regulatory framework for wastewater disposal wells was designed to protect drinking water sources from contamination and does not address earthquake safety. Ellsworth noted that one consequence is that both the quantity and timeliness of information on injection volumes and pressures reported to the regulatory agencies is far from ideal for managing earthquake risk from injection activities….
There is a growing interest in understanding the risks associated with injection-induced earthquakes, especially in the areas of the country where damaging earthquakes are rare.
For example, wastewater disposal appears to have induced the magnitude-5.6 earthquake that struck rural central Oklahoma in 2011, leading to a few injuries and damage to more than a dozen homes. Damage from an earthquake of this magnitude would be even worse if it were to happen in a more densely populated area….
Reposted from USGS blog.