William Ellsworth’s latest study in Science connects Oklahoma’s 5.7 magnitude earthquake in 2011 to fracking operations in the area. These quakes, along with 2 others in Western Texas and Southern Colorado, are known as “trigger induced earthquakes,” or after-shock seismic activity, which occurs sooner and more dramatically near regions saturated with industrial activity. What the study suggests is that an increase in the frequency of tremors in recent years is due – not specifically to fracking treatments – but to the disposal of treated wastewater afterwards. The conclusions mark a stark reversal of previous notions about seismic activity and oil & gas drilling(such as the National Resources Council study in 2012, which found no risks but recommended further research), as well as an unprecedented turn in the fracking debate.
Some seismic activity related to the actual fracking process does transpire occasionally, but these quakes are not often felt at the surface. Puzzled by its origins, seismologists found the 5.7 magnitude earthquake in Oklahoma troubling because the nearby fault was thought to be long dormant. Now, multiple reports published in Geologist and Scientist based on sophisticated seismic monitoring networks have found out why. Wastewater injections from hydraulic fracturing and dewatering operations have placed increased pressure on various faultlines around the country, thus increasing the prospects of potentially dangerous seismic activity. Rock formations vary across states, and flat regions do not typically have the formation variety that better absorbs seismic activity from disastrous, faraway quakes. Wells drilled in lower states can more easily pierce a fault or render it more susceptible to earthquakes occurring miles and miles away that then rupture the faults. So seismologists are looking not where drilling and fracking occurs, but the sites where produced water goes afterwards. And there are 40,000 of these injection wells nationwide.
William Ellsworth, an author of the new study and a seismologist for the USGS, has expressed concern over the major increase in the number of annual earthquakes in the U.S – over 300 with a 3+ magnitude were recorded in the central and eastern regions between 2010-2012. Regions with little history of earthquake activity are now ripe with tremors. But the increased risk isn’t limited to fracking wastewaster disposal; seismic activity has been similarly linked to geothermal plants and dewatering operations that do the same thing – pump water out and back into deep underground reservoirs.
Fracking near faults
Wastewater injections place increased pressure on faults. How? Simply put, the millions of gallons of disposed water weighs heavily on the rock below; consequently, the high pressures generated in disposal wells are sometimes so high as to move the rock. When the water is squeezed into deposits below, it will often find escape routes and leak into faults, fracture the rock near faults, or actually pry faults further open. Wastewater migration of this scale can release enough energy akin to an earthquake – or alter faults in a way where faraway quakes can easily stimulate activity. These faults are everywhere – even the opening of a smaller slip can beget a significantly damaging earthquake. In most cases, however, the effects of injected wastewater deposits merely increase the risk for damage associated with other earthquakes – or a “domino effect” of sorts. Faults collide and spur nearby faults to collide.
List of induced earthquakes linked to fracking wastewater disposal
Clearly, the fears about seismic activity associated with fracking wastewater disposal procedures are not ungrounded. Quake-risks have increased so far in Arkansas, Colorado, Ohio, Texas, and Oklahoma. Worries about fracking in California along or near the San Andreas fault are widespread; The UK placed a yearlong ban on fracking when fracking operations were thought to induce two earthquakes near Blackpool in 2011. Below are major incidences that scientists have linked to with confidence to injection wells:
- Arkansas: The state government declared a ban on underground wastewater disposal activities across a 1,000 square mile area and launched a seismic-risk assessment studies in the Fayetteville Shale play. Seismic activity has prompted residents to sue Chesapeake Energy and BHP Billiton Petroleum, “the first time anyone has sued oil and gas companies for causing an earthquake” (Mother Jones). 1,200 minor earthquakes were recorded, and the number of quakes dropped tw0-thirds after injection activities stopped.
- Prague, Oklahoma: Chronic, abnormal seismic activity has occurred in the region and surrounding area since the 2010 Chilean earthquake. Tremors were triggered again in 2012 after the Sumatra earthquake. Previously, the USGS had registered the Wilzetta fault as “dormant” in its national database, but this is precisely where the quakes have occurred. Before 2008, Oklahoma only experiences a few scattered quakes every year, but in 2010 the state had over 1,000.
- Trinidad, Colorado: In August 2011, a 5.3 magnitude quake struck within 2 kilometers of two major injection wells owned by Pioneer Natural Resources about 15 miles southwest of Trinidad. Over 40 structures were damaged and the Colorado Geological Survey is now involved in long-term seismographic tests in the Ralton Basin to determine the cause – man-made or natural.
- Snyder, Texas: The 9.1 magnitude earthquake in Japan triggered a series of smaller earthquakes in the Cogdell oilfield near Snyder in 2011, the largest of which registered at a magnitude of 4.5.
Our take on frackquakes
Arkansas banned underground wastewaster injections and Ohio’s state governor issued an order that requires operators to conduct seismic studies before they can obtain well permits from the state. Otherwise, no national or state regulatory rule requires the gathering of seismic or geologic data from regions where injection wells will be built and used.
Seismic activity resulting from wastewater disposal via injection arguably poses a greater threat than other mainstream concerns associated with fracking (such as water contamination by fracking fluids, which is fairly rare). Though the induced quakes are usually small and involve minimal damage relative to the behemoth quakes elsewhere, scientists can’t predict with certainty how harmless these “frackquakes” will be in the future. Treating, recycling, and finding alternative ways to dispose of wastewater seems urgent and necessary if fracking is to continue. The heightened frequency of earthquakes strongly correlated with injection wells is pressing and does not yet seem to receive adequate attention beyond media outlets, certainly not in the impact assessments or reports issued by the EPA or state agencies charged with addressing fracking hazards. Because the issue of “frackquakes” at first glance seems so outlandish, the recent publication in Science will hopefully render a more sober analysis and approach to the issue by policymakers.
Three things are predictable whenever earthquakes occur that might be caused by fluid injection: The companies involved deny it, the regulators go into a brain freeze because they don’t know what to do, and the press goes into a feeding frenzy because they get to beat up on the oil and gas industry, whether it is responsible or not. While I’m making a joke here, there is currently no framework for scientifically based regulation. (Mark Zoback, Geophysicist at Stanford University)