Lately, life has become a little more unpredictable in the central United States. The region has seen a significant increase in earthquakes over the past six years — some of them capable of causing some real damage — when before there was very little seismic activity in the area.
Scientists pretty much agree that the earthquakes are being caused by human activity in the area. But there’s some confusion among the public about exactly what activities are causing the rumbles, with the major misconception being that hydraulic fracturing, or “fracking,” is the main culprit. Now a new paper, published Tuesday in the journal Seismological Research Letters, sets the record straight on what’s actually causing the ground to shake out there and what we can do about it going forward.
Between 1973 and 2008, the central United States saw an average of 24 earthquakes with a magnitude of 3.0 or higher each year — a number that rose to an annual average of 193 between 2009 and 2014, claims the new paper. According to authors Justin Rubinstein of the U.S. Geological Survey (USGS) and Alireza Babaie Mahani of the Geological Survey of Canada, injecting fluids into the earth — a technique used in several industrial processes — is causing all the earthquakes by increasing fluid pressure in the ground and causing faults to slip. But while fracking is one activity that involves fluid injection, it’s not the main cause of the quakes. It turns out that wastewater disposal, which injects unusable water into the ground to get rid of it, is the major culprit.
Wastewater injection is a process often used to get rid of the contaminated water that comes up as a byproduct of oil and gas extraction. And there’s some confusion about how exactly it’s produced, according to the authors. A second major misconception they address is the idea that all wastewater is produced from the fracking process — but this isn’t the case at all. In fact, any type of oil or gas extraction is likely to produce wastewater. That’s because the ground is full of briny water that is often already trapped in the same pores that contain oil and gas. It tends to come up during the extraction process, whether fracking is used to get it or not. In some parts of the central United States, fracking does produce a large amount of the wastewater being disposed of. But in other areas, such as Oklahoma, fracking accounts for hardly any of the wastewater produced.
Of course, fracking and certain other processes, such as enhanced oil recovery, also inject fluids into the earth, but they cause significantly fewer quakes. That’s because wastewater disposal injects much larger volumes of fluid into the ground for much longer periods of time. In fact, wastewater disposal wells can operate for years, while fracking typically goes on for just a few days.
So why the sudden increase in human-induced earthquakes now? Simply put, there’s just more wastewater injection going on, the authors write. This is at least partly thanks to some new production techniques being used in the area, says William Ellsworth, a geophysicist at the USGS Earthquake Science Center. (Ellsworth has also co-authored several papers on the topic of induced seismicity in the central United States, including a paper published this month in the journal The Leading Edge.)
The primary method that’s been introduced in recent years is known as dewatering, he says, a process that involves drilling into rock formations not previously identified as oil reservoirs and pumping out the oil inside. Huge amounts of saltwater usually come out with the oil — anywhere from 15 to 50 barrels of water per barrel of oil, according to Ellsworth.
Figuring out how much of a threat these induced earthquakes pose, or “hazard modeling,” is one obvious concern. “One of the big challenges is understanding how strong the earthquakes might be and where they are likely to occur,” says Ellsworth. The USGS already produces a long-term hazard model for natural earthquakes, which includes risks over a 50-year period. But the next step will be to produce a hazard model for induced earthquakes, which Ellsworth says will include be a much shorter forecast, perhaps of a year. He says the USGS hopes to put out such a report by the end of the year.
While it may not help in long-term decision making, like writing building codes, the model could help local citizens prepare for the amount of seismic activity they’re likely to experience and may aid policymakers in making decisions about repairs or updates to older buildings and transportation systems, Ellsworth says.
Scientists are also hopeful that strategies can be developed to diminish the earthquakes themselves. “Fortunately, some authors have suggested that there is hope for mitigating the likelihood of damaging earthquakes through detailed seismic monitoring, variations of injection rates and pressures in response to ongoing seismicity, and a clear management plan,” write authors Rubinstein and Mahani.
The authors suggest that more information is needed regarding three different types of data in order to be able to mitigate induced earthquakes. The first is more seismic data, which requires sensitive instruments. In some cases, fault lines (which cause earthquakes) are completely unknown to scientists until an earthquake occurs. Additionally, better resources are needed to collect high-quality data on earthquakes in real time, says Ellsworth.
“Over much of the area where these earthquakes are currently occurring, we are really suffering from inadequate scientific resources,” Ellsworth says. “In particular, many of these areas do not have seismic stations located anywhere or too few to provide accurate information.”
The other types of data needed, according to the paper’s authors, are more geologic data about faults and the stresses that are placed on them, as well as more industrial data on injection rates and pressures. A better understanding of this kind of information could help industrial workers alter injection rates and pressures as needed and potentially stop earthquakes before they become damaging.
Bringing these issues to the public’s attention is obviously in the best interest of public safety. But according to Ellsworth, it’s also relevant to anyone with an interest in the way the energy industry is conducted in the United States.
“I think that the public has a big stake in what’s being done in terms of new ways of developing oil and gas reserves in the country. I think people want to see it done safely and responsibly,” Ellsworth says. “It’s in everyone’s interest to understand the scientific basis of earthquakes.”