For 300 million years faults showed no activity, and then wastewater injections from oil and gas wells came along. Study authors took a different approach in the new work — they hunted for deformed faults below Texas.
Science journalist Anna Kuchment covered the landmark earthquake research of a team of SMU geophysicists led by SMU Associate Professor Beatrice Magnani in the SMU Department of Earth Sciences. Kuchment wrote Drilling Reawakens Sleeping Faults in Texas, Leads to Earthquakes for Scientific American.
The SMU researchers tapped seismic data to analyze earthquakes in Texas over the past decade.
The results of the analysis showed that human activity is causing the earthquakes as a result of movement in faults that have been silent for at least 300 million years, until recent injection of oil and gas wastewater.
By Anna Kuchment
Scientific American
Since 2008, Texas, Oklahoma, Kansas and a handful of other states have experienced unprecedented surges of earthquakes. Oklahoma’s rate increased from one or two per year to more than 800. Texas has seen a sixfold spike. Most have been small, but Oklahoma has seen several damaging quakes stronger than magnitude 5. While most scientists agree that the surge has been triggered by the injection of wastewater from oil and gas production into deep wells, some have suggested these quakes are natural, arising from faults in the crust that move on their own every so often. Now researchers have traced 450 million years of fault history in the Dallas-Fort Worth area and learned these faults almost never move. “There hasn’t been activity along these faults for 300 million years,” says Beatrice Magnani, a seismologist at Southern Methodist University in Dallas and lead author of a paper describing the research, published today in Science Advances. “Geologically, we usually define these faults as dead.”
Magnani and her colleagues argue that these faults would not have produced the recent earthquakes if not for wastewater injection. Pressure from these injections propagates underground and can disturb weak faults. The work is another piece of evidence implicating drilling in the quakes, yet the Texas government has not officially accepted the link to one of its most lucrative industries.
Magnani and her colleagues studied the Texas faults using images of the subsurface similar to ultrasound scans. Known as seismic reflection data, the images are created by equipment that generates sound waves and records the speeds at which the waves bounce off faults and different rock layers deep within the ground. Faults that have produced earthquakes look like vertical cracks in a brick wall, where one side of the wall has sunk down a few inches so the rows of bricks no longer line up. Scientists know the age of each rock layer—each row of bricks–based on previous studies that have used a variety of dating techniques.
The study authors took a different approach in the new work — they hunted for deformed faults below Texas.
The Washington Post covered the landmark earthquake research of a team of SMU geophysicists led by SMU Associate Professor Beatrice Magnani in the SMU Department of Earth Sciences.
The researchers tapped seismic data to analyze earthquakes in Texas over the past decade.
The results of the analysis showed that human activity is causing the earthquakes as a result of movement in faults that have been silent for at least 300 million years, until recent injection of oil and gas wastewater.
By Ben Guarino
The Washington Post
An unnatural number of earthquakes hit Texas in the past decade, and the region’s seismic activity is increasing. In 2008, two earthquakes stronger than magnitude 3 struck the state. Eight years later, 12 did.
Natural forces trigger most earthquakes. But humans are causing earthquakes, too, with mining and dam construction the most frequent suspects. There has been a recent increase in natural gas extraction — including fracking, or hydraulic fracturing, but other techniques as well — which produces a lot of wastewater. To get rid of it, the water is injected deep into the ground. When wastewater works its way into dormant faults, the thinking goes, the water’s pressure nudges the ancient cracks. Pent-up tectonic stress releases and the ground shakes.
But for any given earthquake, it is virtually impossible to tell whether humans or nature triggered the quake. There are no known characteristics of a quake, not in magnitude nor in the shape of its seismic waves, that provide hints to its origins.
“It’s been a head-scratching period for scientists,” said Maria Beatrice Magnani, who studies earthquakes at Southern Methodist University in Dallas. Along with a team of researchers at the U.S. Geological Survey, Magnani, an author of a new report published Friday in the journal Science Advances, attempted to better identify what has been causing the rash of Texas quakes.
A cluster of earthquakes around a drilling project can, at best, suggest a relationship. “The main approach has been to correlate the location to where there has been human activity,” said Michael Blanpied, a USGS geophysicist and co-author of the new study.
Study by Beatrice Magnani, USGS and other SMU scientists shows recent seismicity in Fort Worth Basin occurred on faults not active for 300 million years
Recent earthquakes in the Fort Worth Basin — in the rural community of Venus and the Dallas suburb of Irving – occurred on faults that had not been active for at least 300 million years, according to research led by SMU seismologist Beatrice Magnani.
The research supports the assertion that recent North Texas earthquakes were induced, rather than natural – a conclusion entirely independent of previous analyses correlating seismicity to the timing of wastewater injection practices, but that corroborates those earlier findings.
“To our knowledge this is the first study to discriminate natural and induced seismicity using classical structural geology analysis techniques,” said Magnani, associate professor of geophysics in SMU’s Huffington Department of Earth Sciences. Co-authors for the study include Michael L. Blanpied, associate coordinator of the USGS Earthquake Hazard program, and SMU seismologists Heather DeShon and Matthew Hornbach.
The results were drawn from analyzing the history of fault slip (displacement) over the lifetime of the faults. The authors analyzed seismic reflection data, which allow “mapping” of the Earth’s subsurface from reflected, artificially generated seismic waves. Magnani’s team compared data from the North Texas area, where several swarms of felt earthquakes have been occurring since 2008, to data from the Midwestern U.S. region that experienced major earthquakes in 1811 and 1812 in the New Madrid seismic zone.
Frequent small earthquakes are still recorded in the New Madrid seismic zone, which is believed to hold the potential for larger earthquakes in the future.
“These North Texas faults are nothing like the ones in the New Madrid Zone – the faults in the Fort Worth Basin are dead,” Magnani said. “The most likely explanation for them to be active today is because they are being anthropogenically induced to move.”
In the New Madrid seismic zone, the team found that motion along the faults that are currently active has been occurring over many millions of years. This has resulted in fault displacements that grow with increasing age of sedimentary formations.
In the Fort Worth Basin, along faults that are currently seismically active, there is no evidence of prior motion over the past 300 million years.
“The study’s findings suggest that the recent Fort Worth Basin earthquakes, which involve swarms of activity on several faults in the region, have been induced by human activity,” said USGS scientist Blanpied.
The findings further suggest that these North Texas earthquakes are not simply happening somewhat sooner than they would have otherwise on faults continually active over long time periods. Instead, Blanpied said, the study indicates reactivation of long-dormant faults as a consequence of waste fluid injection.
Seismic reflection profiles in the Venus region used for this study were provided by the U.S. Geological Survey Earthquake Hazards Program.
Seismic reflection profiles for the Irving area are proprietary. Magnani and another team of scientists collected seismic reflection data used for this research during a 2008-2011 project in the northern Mississippi embayment, home to the New Madrid seismic zone. — Kim Cobb, SMU
Long-awaited study puts forth explanation for exponential increase in North Texas earthquakes, citing unprecedented wastewater injection into a geological formation above seismically active zones.
In an article contributed to The Dallas Morning News, science journalist Anna Kuchment covered the research of SMU seismologists on a possible explanation for the spate of earthquakes in North Texas in recent years.
Co-authors are SMU students and faculty Madeline Jones, Monique Scales, Heather DeShon, Beatrice Magnani, Brian Stump, Chris Hayward and Mary Layton, and University of Texas at Austin seismologist Cliff Frohlich.
By Anna Kuchment
Dallas Morning News
In a long-awaited study, researchers have offered a possible explanation for how oil and gas activity may have triggered earthquakes in Dallas and Irving last year.
The disposal of wastewater from oil and gas production and hydraulic fracturing “plausibly” set off the tremors, which shook Dallas, Irving, Highland Park and other cities from April 2014 through January 2016, said Matthew Hornbach, the study’s lead author and professor of geophysics at Southern Methodist University.
While the quakes were too small to cause much damage to buildings, they spread alarm through a metro area unaccustomed to feeling the ground shift.
The quakes contributed to a tenfold increase in North Texas’ earthquake hazard level, prompted the Federal Emergency Management Agency to warn of stronger quakes that could cause billions of dollars of damage, and moved local emergency managers to begin preparing for worst-case scenarios.
The study, posted online this week in the peer-reviewed journal Physics of the Earth and Planetary Interiors, is the first scientific work to offer an explanation for the Dallas and Irving quakes. It also provides new evidence that other recent quakes in North Texas’ were likely induced by humans.
Such findings in recent years have prompted pushback from oil and gas companies. This week, through a trade group, they again came out swinging. Steve Everley, a spokesman for an arm of the Independent Petroleum Association of America, questioned the scientists’ work. “Were they looking for media attention?” Everley said in an email. “The authors’ willingness to shift assumptions to fit a particular narrative is concerning, to say the least.”
The state agency that regulates oil and gas, the Railroad Commission, said in a statement that it was reviewing the report “to fully understand its methodology and conclusions.”
Independent experts contacted by The Dallas Morning News praised the study, while cautioning that more work remains before the cause of the Dallas and Irving earthquakes can be firmly established.
“It’s the single best explanation for the increase in earthquakes within the Dallas-Fort Worth basin,” said Rall Walsh, a Ph.D. candidate in geophysics at Stanford University who studies human-triggered earthquakes.
Southern Methodist University preliminary earthquake catalog for the Irving-Dallas earthquake swarm. The SMU North Texas seismic network has recorded over 600 earthquakes ranging from magnitude 0.0-3.6 in the Dallas-Irving region. Earthquakes recorded prior to Jan. 17, 2015 have a higher location uncertainty than events recorded after the complete seismic network was installed. Current seismic sensors recording the sequence are shown as gray symbols; note that some sensors are outside of the map boundaries. US Geological Survey NetQuakes data (squares) can be viewed online. Earthquake symbol size is scaled by magnitude and color coded by date of occurrence. The map is provided as part of the ongoing collaboration between SMU, the USGS, Irving, Dallas, and neighboring cities. The SMU preliminary earthquake locations and magnitudes have not been published in the peer-reviewed scientific literature and are subject to change. Prepared March 22, 2016.
The United States Geological Survey (USGS) today released maps showing potential ground shaking from induced and natural earthquakes, including forecasts for the DFW metropolitan area. The North Texas Earthquake Study at Southern Methodist University provided data, and SMU scientists co-authored peer-reviewed publications cited in the report. The new earthquake ground shaking forecasts are a reminder to the cities and residents in the region that the occurrence of earthquakes increases the earthquake hazard in the area, regardless of cause. Residents should be prepared to experience ground shaking, just as we are prepared to experience tornadoes, hail storms and other events.
FAQs
1. How did SMU research contribute to the USGS report?
SMU and partners currently operate a 30-station seismic network across North Texas, and stations are denser around the ongoing earthquake sequences (Azle-Reno, Irving-Dallas, and Venus-Johnson County). We focus on cataloging the ongoing seismicity over a wider range of magnitudes than the national USGS catalog documents, conducting detailed source studies to understand the physics of faulting, and identifying and mapping faults currently or potentially generating seismicity. We also study cause with the aim of potentially mitigating the increased seismicity rates experienced in North Texas since 2008. Finally, in order to provide improved local estimates of both the size of the earthquakes as well as their source characteristics, we are analyzing the locally recorded waveforms to produce empirical estimates of how ground shaking decays with range for each of the instrumented source regions. These empirical decay rates may provide data for refining the ground shaking forecasts.
The SMU research in its entirety helps inform appropriate parameter ranges for earthquake hazard mapping, and we therefore collaborate and cooperate with the USGS, as was done in preparation for the 2016 report being released Monday, and with city, state and federal agencies.
Peer-reviewed publications by SMU scientists and collaborators were used to classify most North Texas earthquakes as induced. These publications include those on the 2008-2009 DFW sequence (Frohlich et al., 2011), the 2009 Cleburne earthquakes (Justinic et al., 2012), and the 2013-2014 Azle-Reno earthquakes (Hornbach et al., 2015). Dr. Cliff Frohlich (UT-Austin) has published on induced earthquakes in Johnson County near the eventual 2015 Venus earthquake (Frohlich, 2012). Peer-reviewed publications regarding cause for the Irving-Dallas sequence had not been accepted for publication and the earthquakes were left classified as “undetermined cause” in the 2016 Induced Earthquake Hazard Mapping Project and treated as natural earthquakes in the probabilistic calculations for ground motion.
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2. What can and should DFW Metroplex residents do with this information?
The new earthquake ground shaking forecasts are a reminder to the cities and residents in the region that the occurrence of earthquakes increases the earthquake hazard in the area, regardless of cause. Residents should be prepared to experience ground shaking, just as we are prepared to experience tornadoes, hail storms and other events. People should remember to Drop, Cover and Hold On during an earthquake and not to evacuate a building until after shaking has stopped. Brick façade damage is possible under low to mid-intensity shaking, and you are most likely to be injured by falling objects and broken windows than by building collapse at the levels of ground shaking outlined in the USGS report.
We encourage residents to explore online resources on preparedness, such as the resources made available through FEMA and the USGS. Following the seven steps to earthquake safety is always a good idea: http://earthquakecountry.org/sevensteps/.
3. Have you been recording earthquakes in the Dallas-Irving area or has that sequence stopped?
The Irving-Dallas earthquakes began in April 2014 with the largest events occurring in January 2015. Earthquake rates in the Dallas-Irving area have been highly variable. While the rate has decreased over the last few months, we have seen similar short-term decreases in the past, and therefore the rate change should not be over-interpreted.
4. What is the earthquake magnitude equivalent of the USGS ground shaking forecast?
Earthquake magnitude is not the same as ground shaking intensity. Hazard maps are used to forecast ground shaking intensities, regardless of the magnitude of the earthquake that creates the motion. Ground motion, and hence hazard, depends on the earthquake size, distance from the epicenter, local geology, etc. Online resources equating intensity to magnitude are “rule of thumb” and should not be interpreted as directly relating the ground shaking forecasts to earthquake magnitude in the DFW area. Risk calculations use the known properties of building and infrastructure to estimate the probability of damage based on the underlying hazard assessment from ground shaking intensities.
Magnitude tells you the overall size of the earthquake. A single earthquake has one magnitude.
Intensity tells you what the earthquake shaking was like at a particular location. A single earthquake produces a range of intensities that depend on the location. The USGS “Did you feel it?” for the 2015 Irving-Dallas M3.6 illustrates this point. The Modified Mercalli Scale is described further here: http://earthquake.usgs.gov/learn/topics/mercalli.php. — Kim Cobb
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