Earthquakes that shook the Dallas-Fort Worth airport in 2008 marked the start of a man-made quake boom that has made temblors six times more frequent in the Lone Star State.
Since that small series of quakes, Texas has averaged about 12 a year above magnitude 3 in strength, according to a new study looking back nearly a century. The quakes appear to spring from fracking, which creates enormous amounts of wastewater that ends up pumped into deep disposal wells near earthquake fault lines.
These man-made (or “induced”) quakes continue an oil and gas industry trend dating back nine decades, study lead author Cliff Frolich of the University of Texas at Austin told BuzzFeed News. His study applies a five-part test to historical Texas earthquake records to determine if they were natural or man-made, finding a depleted oil field near Houston that sank three feet in 1925 was probably the first recorded man-made quake in Texas. Dozens more have followed, increasing in frequency in the last decade.
“There are lots of places in Texas where you could have earthquakes and no one would notice,” Frolich said. “What has changed is that now we are getting earthquakes near populated cities.”
In March, the U.S. Geological Survey released maps of six states — Oklahoma, Kansas, Texas, Colorado, New Mexico and Arkansas (in order of risk) — where a total of 7 million people live at risk from man-made earthquakes. Oklahoma and Texas have the largest population at risk, largely in Oklahoma City and the Dallas-Fort Worth regions, respectively.
“They have bigger induced earthquakes in Oklahoma, which has Texas riled up,” joked Frolich. “So now we are showing that we have had them for longer.” (Oklahoma topped California as the state with the most felt earthquakes in 2014, and has experienced quakes up to magnitude 5.6.)
With the boom in fracking across the oil and gas belt, industries have dumped more and more water deep underground, triggering the man-made quakes. They represent a third era of induced earthquakes in Texas, Frolich said, based on historical records.
The first, from the 1920s to the 1940s, generally sprang from sinking of the ground after drillers sucked large volumes of oil from shallow oil reservoirs. In the second, the quakes struck after water was pumped into oil fields to increase the reservoir pressure. In the last decade, the fracking boom has triggered larger, moderate quakes, up to magnitude 4.8 and largely within two miles of deep disposal wells.
“As a scientist, we have known about induced earthquakes for some time, so these findings seem quite reasonable,” seismologist John Armbruster of the Lamont-Doherty Earth Observatory at Columbia University told BuzzFeed News. “The fundamental question is, do the people living near these earthquakes know about the risk, and do they accept it?”
There have been protests in Denton, Texas, over earthquakes but not elsewhere. A recent University of Texas poll found that a majority of Texans, 57%, favored allowing towns to halt local fracking, despite a state law forbidding ones such as Reno, Texas from setting limits after nearby quakes.
The historical approach of the University of Texas study leaves out any actual underground pressure data from wells near its earthquakes, said Steve Everley of the Energy In Depth industry advocacy group, in a critique. That means it doesn't offer any insight into Texas geology, he suggested, which might better explain why some towns are more susceptible to earthquakes.
A 2012 report by the U.S. National Academies of Science concluded that fracking itself posed only a small risk of very small earthquakes, but that deep disposal wells needed more monitoring. The risk comes largely from undiscovered faults at the bottom of the deep disposal wells, where cracks in the earth can suddenly give way under the pressure of wastewater injections.
“Just like real estate — what matters with earthquakes is location, location, location,” Frolich said. “A moderate earthquake in a populated area can cause millions of dollars of damage.”
Today, drilling firms have been reluctant to acknowledge that their technologies can set off big earthquakes, he added. But that wasn’t always the case.
In 1925, the state of Texas sued the Humble Oil company to take possession of an oil field that had sunk underwater, making it no longer subject to private ownership. In response, Humble argued that the sinking — as well as the series of small earthquakes it triggered — was entirely its own doing, caused by the roughly 100 million barrels of oil the company had removed from the field over a decade. The court agreed, calling it an “act of man,” and so Humble kept the land.
“Now things are a little different,” Frolich said, “And industry is not always so quick to take credit for earthquakes.”
This post has been updated to include comments from Energy in Depth.