More than 2,500 small earthquakes have hit Oklahoma in the past five years, and nearly all of them can be linked to the process of drilling for oil and gas, according to a recent study published in the journal Science.

The study, led by Cornell University geophysics professor Katie Keranen, is the latest of many scientific studies showing a probable connection between earthquakes and drilling-related activity across the country. Specifically, the quakes are linked not to the fuel extraction itself, but to a process called “wastewater injection,” in which companies take the leftover water used to frack wells and inject it deep into the ground.

Scientists increasingly believe that the large amount of water that is injected into the ground after a well is fracked can change the state of stress on existing fault lines to the point of failure, causing earthquakes. Keranen’s study analyzed four prolific wastewater disposal wells in southeast Oklahoma City, which collectively inject approximately four million barrels of wastewater into the ground each month.

The research showed that fluid from those wells were migrating along fault lines for miles, and Keranen’s team determined the migration was likely responsible for earthquakes occurring as far as 22 miles away.

The link between earthquakes and wastewater injection from fracking is not definitive. As Jennifer Dlouhy in Fuel Fix notes, the research lacks necessary data on sub-surface pressure, which is rarely accessible.

However, Oklahoma is not the only place in America that has seen an unprecedented increase in small- to medium-sized earthquakes at the same time that fracking has increased in the area. A sharp increase in earthquakes corresponding with increased fracking activity has been seen in Ohio, Arkansas, Texas, and Kansas.

The quakes have been relatively small for now, but some scientists have warned that seismic activity stands to get stronger and more dangerous as fracking increases.

“I think ultimately, as fluids propagate and cover a larger space, the likelihood that it could find a larger fault and generate larger seismic events goes up,” Western University earth sciences professor Gail Atkinson said at a Seismological Society of America conference in May.

Because of this and other warnings, the U.S. government is beginning to track the risks that these so-called “frackquakes” pose, and start including them on official maps that help influence building codes. Though the U.S. Geological Survey is known for mapping regular earthquakes and alerting local governments about their risks, it has never taken man-made quakes into account. It made the decision to do so, however, after finding that two strong earthquakes in heavily-drilled areas of Colorado and Oklahoma in 2011 were likely the result of wastewater injection from fracking.

Keranen’s research adds to a list of scientific papers warning of fracking-induced quakes. Researchers at Southern Methodist University, for example, have linked a string of 2009 and 2010 earthquakes in Texas to the injection of fracking wastewater into the ground. In early 2013, fracking wastewater disposal was also linked to the 109 earthquakes that shook Youngstown, Ohio in 2011 — an area that hadn’t ever experienced an earthquake before an injection well came online in December 2010.