Quake Team Helps Shed Light On North Texas Tremors

By Kimberly Cobb
With earthquakes continuing to rattle North Texas – and the nerves of its residents – the search is on for the source of the activity. That’s been the focus since 2008 for a team of SMU earth scientists who have become the go-to experts on North Texas earthquakes. Even though the largest quake in the Dallas-Fort Worth area (Jan. 6, 2015) measured only 3.7, and was a relatively small-magnitude quake that caused no major damage, the tremors do provoke concern.

“Most people in North Texas have never felt an earthquake in their lives,” says seismologist Brian Stump, Albritton Professor of Earth Sciences in the Roy M. Huffington Department of Earth Sciences, Dedman College. “People don’t understand what the earthquakes are, so it can be scarier [to experience] than it should be.”
The scientists have deployed seismic monitors, gathered and distributed data and explained the earthquake activity to national and local news media, community groups, government officials, oil and gas industry researchers and other scientists. SMU is funding the research, using monitoring equipment loaned by the United States Geological Survey (USGS) and Incorporated Research Institutions for Seismology (IRIS).
Texas lies within a geologic region where earthquakes large enough to be felt were once infrequent. But starting Halloween night of 2008, the earth below North Texas shook hard enough to be felt for the first time in more than 100 years.
Since then, the USGS reports that there have been almost 150 earthquakes large enough to be felt within 100 kilometers of Dallas-Fort Worth (thousands, if including quakes too small to be felt). They have occurred in or near areas developed for natural gas extraction from a basin-like geologic formation known as the Barnett Shale.
In April this year, SMU scientists published a study of earthquakes occurring near Azle from November 2013 through April 2014. Their findings suggest that the most likely cause of the quakes are subsurface pressure changes created by high volumes of wastewater known as “brine,” extracted from producing gas wells, combined with the nearby injection of gas field waste fluids. The study used numerical computer modeling to simulate the changing fluid pressure within a rock formation in the affected area near the intersection of two fault lines. Conclusions from the modeling were drawn from a broad range of estimates for subsurface conditions.
Data used in the Azle study came from locally installed seismic monitors, oil and gas companies, the Texas Railroad Commission and the Upper Trinity Groundwater Conservation District.
More recently, when small earthquakes began rumbling near the site of the old Texas Stadium, including two widely felt earthquakes (magnitude 3.5 and 3.6) on Jan. 6, the SMU scientists located as the source of the seismicity a previously unidentified shallow fault extending about two miles from Irving into Dallas. That study continues.
The SMU team has a broad range of expertise, says Heather DeShon ’99, associate professor of geophysics, an expert in earthquake location and a former President’s Scholar. Other team members are geophysicist Matthew Hornbach, associate professor of geophysics, whose focus is dynamic earth processes, including fluid movement; seismologist Beatrice Magnani, associate professor of geophysics, who does seismic imaging of subsurface geology; and senior scientist Chris Hayward, who handles instrumentation and processing, modeling and interpretation of data.
The team shares a sense of serendipity in doing research in a region that has unexpectedly become a hotbed of seismic activity. “In many instances, it takes very little for fault systems to fail,” Hornbach says. “All that’s really happening [with these earthquakes] is lubricating and stressing a system that’s ready to fail.”
More research is needed, say the scientists, in part due to the lack of public data about North Texas’ subsurface faults. A larger monitoring network is necessary to measure smaller magnitude quakes and better pinpoint their locations.
Read more:
SMU Seismology Team To Cooperate With State, Federal Scientists
North Texas Earthquakes news site