FIRST-HAND ACCOUNT
Paul Riggs lives a quiet life in eastern Atascosa County. Minus the sound of cattle, there’s not much noise. Which is why the cloud-free night of July 19, 2023 was so startling.
“We were totally asleep. I mean, me and my wife and the dog, and all of a sudden, we heard a big boom,” Riggs said. “I thought somebody hit our metal gate. I grabbed the flashlight, grabbed my gun, and went out to investigate.”
Just down the road, Paul’s father, Weldon, had a similar reaction.
“I went out and looked around, and thought maybe our butane tank had exploded. I thought some plane crashed or something like that,” he said.
There was enough concern that Weldon Riggs called the sheriff’s office.
”They said, ‘No, y’all had an earthquake’ and this was about 11:30 p.m.,” Riggs recalled. “And I said, ‘No, earthquakes don’t explode like that.’ I mean, it was a big boom, just a great big explosion.”
Turns out, it was a shallow, relatively weak earthquake, measuring 3.8 in magnitude, but the epicenter was nearby the Riggs’ homes. Neighbors along Black Hill Road reported similar experiences.
It may have been jarring, but it was not the first time. Riggs recalled another tremor around 2011.
“I was feeding cows. I didn’t feel it because I was on the tractor. But when I came back in the house, my wife and daughter said something about it,” Riggs said.
INCREASING IN FREQUENCY
The Riggs live just southwest of Floresville. Last year’s earthquake was one of hundreds reported within the last decade within a 50-mile radius of their home. Most of them are weak and many are not even felt. Almost all of them, however, happened atop the Eagle Ford Shale, a busy oil and gas region south of San Antonio.
Several drilling sites could be seen from Black Hill Road.
”Starting about 10 years ago, we have seen a pretty dramatic increase in the number of earthquakes that have been happening in Texas,” said Dr. Elizabeth Cochran, a seismologist with the U.S. Geological Survey (USGS).
”They absolutely are becoming more common,” added Dr. Matt Cannon, assistant professor of instruction, earth, and planetary sciences at UTSA. “If you go back 30 years, we had, on average, one earthquake per decade. And now, as anyone living south of San Antonio knows, we have hundreds.”
By now, you’ve probably heard that there is a connection to oil and gas. This is, in fact, undeniably true. But how exactly? And does the future bring concerns for damaging earthquakes in the future, as the Eagle Ford play stays active? To understand these questions, we must first understand fracking.
HYDRAULIC FRACTURING
Hydraulic fracturing, or fracking, has revolutionized the oil and gas industry. It’s allowed oil and gas reserves to be tapped that weren’t accessible before. The process is done by drilling a well and inserting sand, water, and proprietary chemicals to break up rock formations.
”You’re going to inject fluids, sand, and a cocktail of chemicals, which every company has their own proprietary going-to chemicals, at very high pressures,” Cannon said. “High enough pressures that it will crack the rock.”
In some cases, millions of gallons of water are injected into the well at a rapid pace. Sand is then forced into the fractures to keep them open and the oil or gas is extracted.
”When you’re finishing that process, you have to pump all that fluid back out,” Cannon said. “That ends up being a pretty nasty slurry of stuff.”
The preferred method to get rid of that slurry is to inject it deep back into the ground, which, of course, raises concerns.
”It is very tightly regulated. And if everything is done by the book, there should be no danger to the aquifers,” Cannon said.
WHAT IS IT ABOUT FRACKING THAT CAUSES EARTHQUAKES?
The process of fracking and the injection of the fluids are connected, but separate processes and when it comes to earthquakes, had led to a division among geologists. Which step was causing the earthquakes?
“If you had asked me these questions five years ago, I would have said that it was almost entirely the injection of wastewater from fracking that was causing earthquakes,” Cannon said.
But, new research has changed his opinion. That research is revealing that it’s the fracking process, itself, that is the biggest catalyst. The other issue to keep in mind is that fracking is not organically causing the shaking, nor is solely responsible. There are pre-existing faults, which are behind all the earthquakes in the world, all across Texas. It’s just that those faults would never be active in our lifetime if not for the pressures that fracking creates.
HOW STRONG?
”I mean, the vast majority of these are not felt,” Cannon said. “You know, and even the ones that are felt, they are typically in the magnitude three range.”
A Magnitude 3 earthquake might shake your dishes. It’s not often until Magnitude 4 and higher that you begin to see minor damage. But, as fracking continues, is there a concern that the intensities of the earthquakes will increase for those who live over the Eagle Ford play?
”No, I don’t think they have any immediate need to be worried. Certainly not for loss of life or major damage to infrastructure,” Cannon said.
And according to Cannon, out of the thousands of wells, only around 10% of those drilled ever cause an earthquake.
RESIDENTS DON’T SEE EARTHQUAKES AS A PROBLEM
While earthquakes are becoming more frequent, there’s a philosophical question to be asked: If there’s little damage and the oil and gas is benefitting, are those who live on the Eagle Ford comfortable with taking the good with the bad? Other than a nuisance, is the seismic activity a problem? Those we talked to said “no”.
”I don’t mind it,” said Paul Riggs. “You just know not to put certain things up on shelves and stuff. I had one small little picture frame fall down off the shelf and that’s it.”
”It’s good for the economy,” added Weldon Riggs. “Not just Texas, not just Pleasanton, Atascosa, Wilson, and Karnes County, but for the state.”
You need only look at the Eagle Ford cities to see the money it has injected into the economy. Many cities have benefitted over the last decade.
The Riggs have not directly benefitted from oil companies drilling on their property, but some of their neighbors have.
”Maybe it’ll come this way. sure, sure, that that’d be alright,” joked Weldon Riggs.
”You know, we do live in an interconnected world where if we’re not producing our own oil, we are relying on regimes in other parts of the world, some of which don’t particularly like us,” Cannon said. “Having our own local sources of oil, even with things like induced seismicity that come along with them, is geopolitically advantageous.”
COULD SAN ANTONIO EVER SEE AN EARTHQUAKE?
San Antonio has, for the most part, avoided earthquakes, even with the mighty Balcones Fault Zone running right through the city. Geologists will tell you that it’s a fault that hasn’t moved in millions of years and shows no signs of doing so in the future.
”These are really old faults that maybe we wouldn’t, without the oil and gas production, we wouldn’t have considered active,” Cochran said. “The evidence is that they were last active was millions of years ago, but these are faults that are sitting there. There wasn’t stress accumulating on them until we started changing where the fluids are distributed under the ground.”
In this case though, the Balcones Fault also created the Edwards Aquifer, which comes with stringent regulation and protection by proxy.
”Because the Balconies Fault system is so intimately tied to our local aquifer, there’s no way that any regulator is ever going to allow any of this stuff anywhere near the bulk of this fault system,” Cannon said.
In other words, San Antonio won’t be shaking anytime soon, at least not in a big way. Still, those who work downtown might remember November 16, 2022, when a 5.3-magnitude earthquake occurred hundreds of miles away in West Texas. In San Antonio that day we received numerous reports from those working in high-rise buildings downtown, saying they were swaying. Those on the ground didn’t feel a thing.
”If you imagine my finger being the building as I move the base, a minor move in the base results in a much larger amplitude of motion of the top,” Cannon said.
It’s possible that shockwaves from earthquakes over the fracking zones in Texas, often far away, could cause some minor shaking in high-rise buildings in the future.