Fracking itself is not the primary cause of the earthquake surge in oil- and gas-producing regions of the United States. The real culprit is wastewater disposal, a related but separate process that injects massive volumes of fluid deep underground for months or years at a time. In Oklahoma, where induced earthquakes have been most dramatic, only 1 to 2 percent of those quakes can be linked directly to hydraulic fracturing. The rest are triggered by wastewater injection wells.
Why Wastewater Disposal Matters More
Hydraulic fracturing, or fracking, pumps high-pressure fluid into rock to crack it open and release oil or gas. That process is intense but relatively brief, lasting days to weeks at a single well. Wastewater disposal is different. Oil and gas wells produce enormous quantities of salty, contaminated water as a byproduct, and that water has to go somewhere. Operators pump it into deep underground wells, often running those wells continuously for months or years and injecting far greater total volumes of fluid than fracking ever does.
That sustained, high-volume injection is what destabilizes faults. The distinction matters because public debate often treats “fracking” as shorthand for everything the oil and gas industry does underground, when the earthquake problem is overwhelmingly tied to this one specific waste management practice.
How Underground Fluid Triggers Fault Slip
Deep beneath the surface, rock sits under tremendous pressure, and ancient faults run through it in every direction. Many of these faults are “critically stressed,” meaning they’re already close to their breaking point but held in place by friction. When large volumes of fluid are injected nearby, that fluid seeps into the fault zone and raises the pressure inside the rock’s pore spaces. Higher pore pressure effectively pushes the two sides of a fault apart, reducing the friction that kept them locked together.
Laboratory experiments on granite surfaces show that even a nanometer-thick layer of water between rock faces shifts the point of contact from rock-on-rock to rock-on-water, dramatically cutting the adhesive force holding the surfaces together. Studies have measured friction reductions of 5 to 20 percent, and in some cases basic friction angles drop by as much as 45 percent when rock surfaces go from dry to wet. Once friction falls below a critical threshold on a fault that’s already under tectonic stress, the fault slips and produces an earthquake.
This process can play out far from the injection well itself. Pressurized fluid migrates through permeable rock over time, sometimes reaching faults miles away. That’s one reason earthquakes may appear in locations with no nearby wells and why there can be a lag of months or even years between the start of injection and the onset of seismicity.
Oklahoma’s Earthquake Surge
The numbers tell a striking story. From 1973 through 2008, the central United States averaged 24 earthquakes of magnitude 3.0 or larger per year. Starting in 2009, that rate exploded. Between 2009 and 2014, the average jumped to 193 per year, and 2014 alone saw 688 such earthquakes. From 2014 through 2017, Oklahoma’s rate of magnitude 3.0 and above earthquakes actually exceeded California’s, a state that sits on one of the world’s most active tectonic boundaries.
The timing aligned precisely with a boom in oil and gas production and, more specifically, with the volumes of wastewater being injected underground. When Oklahoma regulators began ordering reductions in injection volumes, earthquake rates dropped significantly, reinforcing the connection.
The Permian Basin Is the New Hot Spot
As Oklahoma’s earthquake rate declined thanks to regulatory action, the Delaware Basin in West Texas and southeast New Mexico saw its own surge. Earthquakes of magnitude 3.0 and above jumped from about 10 per year in 2017 to more than 185 in 2022, tracking closely with rising oil and gas production and wastewater reinjection in the region. The Permian Basin is now one of the most productive oil fields in the world, and its earthquake problem is growing in step with that output.
The USGS has identified this region, along with Oklahoma, southern Kansas, and the Raton Basin straddling Colorado and New Mexico, as areas of high induced earthquake hazard. Since 2016, the agency has published annual one-year hazard forecasts that incorporate induced seismicity alongside natural earthquake risk, a significant shift from decades of treating the central U.S. as seismically quiet.
How Large Can These Earthquakes Get?
Most induced earthquakes are small, magnitude 2.0 or below, and too faint for people to feel. But the tail end of the distribution includes quakes large enough to damage buildings. The largest earthquake directly attributed to hydraulic fracturing in the United States was a magnitude 4.0 event in Texas in 2018. Wastewater disposal has triggered larger ones: Oklahoma experienced a magnitude 5.8 earthquake in 2016, the strongest in the state’s recorded history, which damaged homes and was felt across multiple states.
A magnitude 4.0 quake is roughly 60 times less energetic than a magnitude 5.8, which underscores the gap in risk between the two processes. Fracking-induced quakes tend to be smaller because the volumes of fluid involved are smaller and the injection period is shorter. Wastewater wells, by contrast, can alter pore pressure across a much wider area over time, potentially activating larger and deeper faults.
What Determines Whether an Area Gets Earthquakes
Not every region with oil and gas activity develops an earthquake problem. The key factors are the presence of critically stressed faults, the geology of the rock being injected into, and the volume and rate of injection. Some formations are more permeable, allowing fluid to migrate further and reach faults more easily. Others are better sealed, keeping pressure localized.
Depth matters too. Injecting into formations that sit close to the crystalline basement rock, the ancient, rigid layer beneath sedimentary deposits, carries more risk because that basement rock is where most of the stressed faults reside. In the Delaware Basin, researchers have found that injection into strata both shallower and deeper than producing intervals contributes to seismicity, complicating efforts to find “safe” disposal zones.
The practical upshot is that geology varies dramatically from one oil field to the next, which is why some heavily fracked regions experience almost no induced seismicity while others see hundreds of felt earthquakes per year. The same injection practices that cause no problems in one location can be destabilizing in another.
Reducing the Risk
The most effective tool so far has been limiting wastewater injection volumes and rates, which Oklahoma demonstrated can bring earthquake numbers down within a year or two. Some states now use “traffic light” systems: when seismic monitors detect small earthquakes near injection wells, operators must reduce volumes (yellow) or shut down entirely (red).
The industry is also exploring alternatives to deep well disposal. Recycling produced water for use in new fracking operations reduces the total volume that needs to be injected underground. In some areas, operators are experimenting with treating wastewater to a level where it can be discharged or reused on the surface, though the cost and technical challenges remain significant given the enormous volumes involved. In the Permian Basin alone, operators handle billions of barrels of produced water annually.