The number of earthquakes in the central and eastern United States has increased dramatically over the past few years, and scientists think the reason could be due to the disposal of wastewater associated with oil and gas production.
According to a report by the U.S. Geological Survey
, there were more than 300 earthquakes above magnitude 3.0 from 2010 to 2012. That’s a five-fold increase from earthquakes observed from 1967 to 2000, when the average number was 21 per year.
In 2011, a 5.6 magnitude quake struck central Oklahoma, injuring several people and damaging over a dozen homes. According to the report, wastewater disposal appears to have been the cause of the temblor. Had an earthquake that size hit a more populated area, there would be the potential for severe damage and possible deaths.
“There is a hazard, and I think it’s greater than people thought before,” said William Ellsworth, a geophysicist with the U.S. Geological Survey. “If small earthquakes start occurring near injection sites, that’s something to pay attention to. With that in mind one can ask how this can be managed. Clearly there’s a lot of research to be done.”
Wastewater earthquakes occur because water that is salty or mixed with chemicals needs to be disposed of so as not to contaminate freshwater sources such as aquifers. The most common way of doing that is to inject the water deep underground.
Ellsworth’s research showed that when wastewater is deposited near faults and underground conditions are right, earthquakes can be more likely. If water pressure inside a fault gets high enough it can cause the release of tectonic stress in the form of an earthquake. Even faults that have not moved for millions of years can be made to slip if the conditions are right.
Wastewater is often a byproduct of certain types of energy production, extracting oil and gas from shale rock formations, for example. Wastewater can also be produced through hydraulic fracturing, also known as “fracking,” when water is injected into rock formations to extract oil and gas.
Ellsworth said no fracking sites have been implicated with earthquakes.
The time between the injection of wastewater and an earthquake is variable, Ellsworth said.
“It can be very soon, or it can be years,” he said. “It’s very complicated and very dependent on the conditions under ground.”
Despite the dramatic increase in the number of quakes, Ellsworth points out that very few of the more than 30,000 wastewater wells appear to have caused earthquakes.
Still, the research raises red flags, and according to Ellsworth, shale rock suited for this kind of drilling can be found all over the world, and how the wastewater will be dealt with remains a question.
In the U.S. the regulations about wastewater disposal center on the protection of drinking water and do not address the potential for man-made earthquakes.
Because of that, Ellsworth notes, the timeliness of reporting injection volumes and pressures is lacking. More reporting of injection data would “be a step in the right direction,” in addition to measuring pre-injection water pressure and tectonic stress.