So many earthquakes have struck the west Texas county of Scurry in the past week – more than 100 at last count – local officials have declared a state of emergency.
Scurry County Judge Dan Hicks wrote in his Friday declaration of disaster that since the first earthquake, registering magnitude 4.9, was felt the night of July 22, "damage has been found throughout Scurry County in businesses and residences."
The county’s buildings can handle a few quakes here and there, but the cumulative effects of so many small ones, punctuated by larger shaking, have become cause for concern.
From his second-floor office in the Scurry County Courthouse, Hicks told the Abilene Reporter-News, part of the USA TODAY Network, workers in the building became alarmed during a 5.0 quake Friday, which hit at 9:28 a.m. local time. Trophies rattled inside display cabinets, and pictures bounced against the walls.
“The building was shaking pretty good,” Hicks said.
From the first large quake of magnitude 4.9, the county has experienced a total of 103 earthquakes, including 12 of magnitude three or more, said Justin Rubinstein, a geophysicist with the U.S. Geological Survey in Menlo Park, California.
The rash of earthquakes is not naturally occurring, as Texas, in general, is not a very seismically active part of the country. Instead, it is"almost 99% likely" to be linked to local oil fields, Rubinstein said.
“We can say with confidence that these are related to oil and gas extractions," he said.
The temblors are very likely linked to new forms of oil and natural gas drilling technology that allow companies to drill not just down into the earth but horizontally along an oil formation.
They are reaching deeply buried oil and natural gas deposits that are the decomposed remnants of plants and animals in ancient oceans. When the oil comes up, the salt water, which can be millions of years old, also comes up.
This is called "produced water" and there's a lot of it.
"The ratio of oil to saltwater is low. It can be five or 10 or even 20 barrels of saltwater for every barrel of oil," said Rubinstein.
This prehistoric water is much saltier than ocean water and can't be disposed of in rivers or even the ocean, in part, because it can contain contaminants such as hydrocarbons.
Instead, it must be pumped back deep underground where it cannot leech into groundwater, a process called saltwater disposal.
The large amounts of water being pumped underground in turn can cause earthquakes. "We've found evidence that saltwater disposal is the most likely cause of the earthquakes in Scurry County. This specific area has seen seismic activity going back to 2020," Rubinstein said.