Dallas Morning News
By ANNA KUCHMENT, RANDY LEE LOFTIS, JAMES OSBORNE and AVI SELK
Staff Writers
Published: 10 January 2015 11:23 PM
Updated: 11 January 2015 07:25 PM
The earth under North Texas barely stirred for at least a century, until something down there snapped in 2008.
Swarms of small quakes rippled up from unknown faults beneath the soil. They rustled Cleburne, Azle and Irving. Last week’s 15 temblors around the old Texas Stadium site included the strongest yet in Dallas County, and their waves shook downtown office towers.
But after six years and more than 130 quakes, scientists are just beginning to map the fissures beneath us, figure out why they woke up, and predict what they might do next.
No one knows for sure whether the quakes are signs of a geological realignment, the aftermath of gas drilling or something else entirely.
What lies under Irving? That may be the biggest mystery facing the team of scientists investigating the latest earthquake swarm to hit North Texas.
“There are no known faults near the earthquake site,” said Beatrice Magnani, one of nine Southern Methodist University researchers studying the temblors.
That means about three dozen quakes that have rocked Irving since April are coming from a previously undiscovered fissure, deep underground.
“In this area of the world, researchers don’t know a lot about these faults, because the faults don’t come to the surface,” said Heather DeShon, a seismologist with the university.
Science can only tell us so much. Geological earthquake records are spotty before 1970, though they show no evidence of anything like the current spate in North Texas history.
And it may be impossible to predict how long the current rash of quakes will last. The Azle area got 27 quakes over three months. Cleburne was hit by two clusters, in 2009 and 2012.
But without knowing the size of the fault under Irving, scientists have no way to tell whether it might one day produce a devastating quake — something thousands of times more powerful than the 3.6-magnitude temblor that struck this week. (Scientists say the majority of earthquake swarms do not culminate in large, damaging events.)
To that end, the SMU team is trying to pinpoint each new quake and use the earthquakes’ locations to map the Irving fault’s size and depth.
The team is also trying to figure out which of several nearby fault systems Irving’s fissure belongs to. To the west, a system of small, deep faults has been linked to previous quakes in Azle, Cleburne and Dallas/Fort Worth International Airport. In the east, the large Balcones and Ouachita fault systems wind south to the Gulf of Mexico and beyond.
The U.S. Geological Survey, which locates earthquakes across the world, places most of Irving’s temblors near the former Texas Stadium site. With sparse equipment near the quakes, the agency’s estimates can be off by miles. So last week, the SMU team added nearly two dozen seismometers — quake detectors — in and around Irving.
The team has also asked the Texas Railroad Commission and energy companies to help them gather information.
“Since the oil and gas industry are actively drilling into those rocks, they tend to know more than we do about subsurface fault structure,” said DeShon.
But the team has another purpose in investigating nearby gas wells and wastewater wells: To see whether underground pressure changes related to those wells are significant enough to cause quakes. READ MORE