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Most likely cause of 2013-14 earthquakes: Combination of gas field fluid injection, removal

SMU-led seismology team reveals Azle findings for an area where the seismology team identified two intersecting faults

Natural and anthropogenic stress changes that may trigger earthquakes in the Azle area. (SMU)
Natural and man-made stress changes that may trigger earthquakes in the Azle area. (SMU)

An SMU-led seismology team finds that high volumes of wastewater injection combined with saltwater (brine) extraction from natural gas wells is the most likely cause of earthquakes occurring near Azle, Texas, from late 2013 through spring 2014.

In an area where the seismology team identified two intersecting faults, they developed a sophisticated 3D model to assess the changing fluid pressure within the rock formation. They used the model to estimate stress changes induced in the area by two wastewater injection wells and the more than 70 production wells that remove both natural gas and significant volumes of salty water known as brine.

Conclusions from the modeling study integrate a broad-range of estimates for uncertain subsurface conditions. Ultimately, better information on fluid volumes, flow parameters, and subsurface pressures in the region will provide more accurate estimates of the fluid pressure along this fault.

“The model shows that a pressure differential develops along one of the faults as a combined result of high fluid injection rates to the west and high water removal rates to the east,” said Matthew Hornbach, SMU associate professor of geophysics. “When we ran the model over a 10-year period through a wide range of parameters, it predicted pressure changes significant enough to trigger earthquakes on faults that are already stressed.”

Modelled pressure changes in the Ellenburger caused by injection and production.
Modelled pressure changes in the Ellenburger caused by injection and production. The images show the system prior to injection (a) through the onset of seismicity (e). Note that the most significant amount of brine removal occurs along the fault trend.

Model-predicted stress changes on the fault were typically tens to thousands of times larger than stress changes associated with water level fluctuations caused by the recent Texas drought.

“What we refer to as induced seismicity – earthquakes caused by something other than strictly natural forces – is often associated with subsurface pressure changes,” said Heather DeShon, SMU associate professor of geophysics. “We can rule out stress changes induced by local water table changes. While some uncertainties remain, it is unlikely that natural increases to tectonic stresses led to these events.”

Surprisingly small changes in stress can reactivate certain faults
DeShon explained that some ancient faults in the region are more susceptible to movement – “near critically stressed” – due to their orientation and direction. “In other words, surprisingly small changes in stress can reactivate certain faults in the region and cause earthquakes,” DeShon said.

The study, “Causal Factors for Seismicity near Azle, Texas,” has been published in the journal Nature Communications. The study was produced by a team of scientists from SMU’s Roy M. Huffington Department of Earth Sciences in Dedman College of Humanities and Sciences, the U.S. Geological Survey, the University of Texas Institute for Geophysics and the University of Texas Department of Petroleum and Geosystems Engineering. SMU scientists Hornbach and DeShon are the lead authors.

Fluid pressure modeling of industry activity and water table fluctuations is first of its kind
SMU seismologists have been studying earthquakes in North Texas since 2008, when the first series of felt tremors hit near DFW International Airport between Oct. 30, 2008, and May 16, 2009. Next came a series of quakes in Cleburne between June 2009 and June 2010, and this third series in the Azle-Reno area northwest of Fort Worth occurred between Nov. 2013 and Jan. 2014. The SMU team also is studying an ongoing series of earthquakes in the Irving-Dallas area that began in April 2014.

In both the DFW sequence and the Cleburne sequence, the operation of injection wells used in the disposal of natural gas production fluids was listed as a possible cause of the seismicity. The introduction of fluid pressure modeling of both industry activity and water table fluctuations in the Azle study represents the first of its kind, and has allowed the SMU team to move beyond assessment of possible causes to the most likely cause identified in this report.

Prior to the DFW Airport earthquakes in 2008, an earthquake large enough to be felt had not been reported in the Fort Worth Basin since 1950. The North Texas earthquakes of the last seven years have all occurred in areas developed for natural gas extraction from a geologic formation known as the Barnett Shale. The Texas Railroad Commission reports that production in the Barnett Shale grew exponentially from 216 million cubic feet a day in 2000, to 4.4 billion cubic feet a day in 2008, to a peak of 5.74 billion cubic feet of gas a day in 2012.

Read the report here.

While the SMU Azle study adds to the growing body of evidence connecting some injection wells and, to a lesser extent, some oil and gas production to induced earthquakes, SMU’s team notes that there are many thousands of injection and/or production wells that are not associated with earthquakes.

The area of study addressed in the report is in the Newark East Gas Field (NEGF), north and east of Azle. In this field, hydraulic fracturing is applied to loosen and extract gas trapped in the Barnett Shale, a sedimentary rock formation formed approximately 350 million years ago. The report explains that along with natural gas, production wells in the Azle area of the NEGF can also bring to the surface significant volumes of water from the highly permeable Ellenburger Formation – both naturally occurring brine as well as fluids that were introduced during the fracking process.

Subsurface fluid pressures are known to play a key role in causing seismicity. A primer produced by the U.S. Department of Energy explains the interplay of fluids and faults:

The fluid pressure in the pores and fractures of the rocks is called the ‘pore pressure.’ The pore pressure acts against the weight of the rock and the forces holding the rock together (stresses due to tectonic forces). If the pore pressures are low (especially compared to the forces holding the rock together), then only the imbalance of natural in situ earth stresses will cause an occasional earthquake. If, however, pore pressures increase, then it would take less of an imbalance of in situ stresses to cause an earthquake, thus accelerating earthquake activity. This type of failure…is called shear failure.

Injecting fluids into the subsurface is one way of increasing the pore pressure and causing faults and fractures to “fail” more easily, thus inducing an earthquake, he said. Thus, induced seismicity can be caused by injecting fluid into the subsurface or by extracting fluids at a rate that causes subsidence and/or slippage along planes of weakness in the earth.

All seismic waveform data used in the compilation of the report are publically available at the IRIS Data Management Center. Wastewater injection, brine production and surface injection pressure data are publicly available at the Texas Railroad Commission (TRC). Craig Pearson at the TRC, Bob Patterson from the Upper Trinity Groundwater Conservation District; scientists at XTO Energy, ExxonMobil, MorningStar Partners and EnerVest provided valuable discussions and, in some instances, data used in the completion of the report.

“This report points to the need for even more study in connection with earthquakes in North Texas,” said Brian Stump, SMU’s Albritton Chair in Earth Sciences. “Industry is an important source for key data, and the scope of the research needed to understand these earthquakes requires government support at multiple levels.” — Kimberly Cobb

Follow SMUResearch.com on twitter at @smuresearch.

SMU is a nationally ranked private university in Dallas founded 100 years ago. Today, SMU enrolls nearly 11,000 students who benefit from the academic opportunities and international reach of seven degree-granting schools. For more information see www.smu.edu.

SMU has an uplink facility located on campus for live TV, radio, or online interviews. To speak with an SMU expert or book an SMU guest in the studio, call SMU News & Communications at 214-768-7650.

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Earth & Climate Energy & Matter Researcher news SMU In The News

Houston Chronicle: New data shows North Texas fault line

It is significant that underground conditions have changed to trigger slips on a fault line that hasn’t moved in human memory.

Houston Chronicle, earthquakes, SMU, DeShon, Stump

Journalist Dylan Baddour covered the recent interim report about the research findings of Southern Methodist University’s seismology team surrounding a recent series of earthquakes in the Irving, Texas area.

His Houston Chronicle report, “New data shows North Texas fault line,” covered the preliminary findings and the progress on the team’s earthquake research.

Initial results reveal that the earthquakes that occurred near the site of the old Texas Stadium were relatively shallow and concentrated along a narrow two mile line that indicates a fault extending from Irving into West Dallas.

SMU and the United States Geological Survey shared the report with the mayors of Dallas and Irving spelling out preliminary information gleaned after SMU’s installation in January of more than 20 portable earthquake monitors around the earthquake sites. SMU seismologists Heather DeShon and Brian Stump, in the Roy M. Huffington Department of Earth Sciences, answered questions during the briefing with reporters.

The article published Feb. 11, 2015.

Read the full story.

EXCERPT:

By Dylan Baddour
Houston Chronicle

North Texas earthquake swarms still baffle geologists, who never expected to study seismic tremors in the Lone Star State. But last month scientists installed equipment to record quakes near Irving, Texas, and last week the first numbers came in.

We still don’t know much about why the region shakes, but here’s what we just learned: the quakes have all been relatively shallow, and have centered along a newly-identified fault line near Irving. The data is thanks 20 seismic monitoring machines, supplied by the U.S. Geological Survey and deployed by scientists from Texas’ Southern Methodist University last month.

“This is a first step, but an important one, in investigating the cause of the earthquakes,” said SMU seismologist Brian Stump. “Now that we know the fault’s location and depth, we can begin studying how this fault moves – both the amount and direction of motion.”

Irving, just north of Dallas, shook first in April 2014, but the area’s strongest quakes struck last month. The so-called “earthquake swarm” follows others since 2008 that have hit North Texas—a region with no history of seismic action. This year, the USGS announced plans to raise the region’s official earthquake risk level. Still, no one knows why the region has started to tremble.

“The two views about them. One: in 150 years there haven’t been natural earthquakes in the Dallas-Fort Worth area, so if these earthquakes were natural, that’s very interesting,” said Cliff Frolich, a geologist at the University of Texas at Austin and a veteran researcher of the North Texas quakes. “On the other hand the earthquakes that occurred in 2008 and subsequently appear to be close to injection wells. The fact that these earthquakes are occurring only a few years later, some people would probably conclude they are related to oil and gas activities.”

Injection wells are where oil and gas drillers dispose of tens of millions of gallons of toxic wastewater left over from hydraulic fracturing, or “fracking,” an extraction technique that’s proliferated in Texas and across the country since 2008. Some scientists have suggested that pressure put on fault lines by high-powered injection into bedrock could trigger the quakes, but nothing is conclusive.

Read the full story.

Follow SMUResearch.com on twitter at @smuresearch.

SMU is a nationally ranked private university in Dallas founded 100 years ago. Today, SMU enrolls nearly 11,000 students who benefit from the academic opportunities and international reach of seven degree-granting schools. For more information see www.smu.edu.

SMU has an uplink facility located on campus for live TV, radio, or online interviews. To speak with an SMU expert or book an SMU guest in the studio, call SMU News & Communications at 214-768-7650.

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Earth & Climate Energy & Matter Researcher news SMU In The News

WFAA Channel 8: SMU study — Quakes shallow, concentrated at fault line

Next step is to investigate what triggered the earthquakes, both natural and man-made.

SMU, earthquakes, Irving, WFAA, Channel 8, Byron Harris, Heather DeShon, Brian Stump

WFAA Channel 8 reporters Byron Harris and Marjorie Owens covered the recent interim report about the research findings of Southern Methodist University’s seismology team surrounding a recent series of earthquakes in the Irving, Texas area.

The Channel 8 report, “SMU study: Quakes shallow, concentrated at fault line,” covered a briefing with the press on Friday, Feb. 6, to explain progress on the team’s earthquake research.

Initial results reveal that the earthquakes that occurred near the site of the old Texas Stadium were relatively shallow and concentrated along a narrow two mile line that indicates a fault extending from Irving into West Dallas.

SMU and the United States Geological Survey shared the report with the mayors of Dallas and Irving spelling out preliminary information gleaned after SMU’s installation in January of more than 20 portable earthquake monitors around the earthquake sites. SMU seismologists Heather DeShon and Brian Stump, in the Roy M. Huffington Department of Earth Sciences, answered questions during the briefing with reporters.

The segment aired Feb. 6, 2015.

Read the full story.

EXCERPT:

By Byron Harris and Marjorie Owens
WFAA

Southern Methodist University has released preliminary results from a study spurred by the recent earthquakes that have rattled North Texas.

The quakes, which have primarily centered near the site of the old Texas Stadium in Irving, “were relatively shallow and concentrated along a narrow two mile line that indicates a fault extending from Irving into West Dallas,” read a statement based on SMU’s findings.

According to the statement, SMU and the United States Geological Survey shared their preliminary findings with the mayors of Dallas and Irving after the university installed 20 portable monitors around the area of the quakes’ epicenters.

“They’re moving a little bit north and they form a linear trend,” said SMU Seismologist Heather DeShon.

Instead of a random pattern of quakes inferred from distant sensors, more-refined data now suggests the January quakes happened in a more focused pattern of major quakes and aftershocks, east and north of the University of Dallas. The scientists estimate the fault that caused the quakes is two miles long and from three-to-five miles deep.

“In order to have an earthquake of 3.6 (as occurred in Irving in January), there has to be a fault there,” Dr. DeShon said.

The study is in its beginning phase, but SMU seismologist said the initial findings are an important start to their investigation.

“We can begin studying how this fault moves – both the amount and direction of motion,” he said.

The seismologists said the reason why the quakes have been felt in far North Texas is because of their relatively close proximity to the surface in the granite “basement.”

Read the full story.

Follow SMUResearch.com on twitter at @smuresearch.

SMU is a nationally ranked private university in Dallas founded 100 years ago. Today, SMU enrolls nearly 11,000 students who benefit from the academic opportunities and international reach of seven degree-granting schools. For more information see www.smu.edu.

SMU has an uplink facility located on campus for live TV, radio, or online interviews. To speak with an SMU expert or book an SMU guest in the studio, call SMU News & Communications at 214-768-7650.

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Earth & Climate Energy & Matter Researcher news SMU In The News

Dallas Morning News: Remap of Dallas-area quakes shows fault closer to fracking wells than thought

Now that SMU’s seismology team has located the fissure, they can begin to study how and why it’s moving.

Dallas Morning News, SMU, earthquakes, Irving, Anna Kuchment, Heather DeShon, Brian Stump

Science journalist Anna Kuchment covered a recent interim report on the research findings of Southern Methodist University’s seismology team surrounding a recent series of earthquakes in the Irving, Texas area.

Kuchment’s Dallas Morning News article, “Remap of Dallas-area quakes shows fault closer to fracking wells than thought,” covered a briefing with the press on Friday, Feb. 6, to explain progress on the team’s earthquake research.

Initial results reveal that the earthquakes that occurred near the site of the old Texas Stadium were relatively shallow and concentrated along a narrow two mile line that indicates a fault extending from Irving into West Dallas.

SMU and the United States Geological Survey shared the report with the mayors of Dallas and Irving spelling out preliminary information gleaned after SMU’s installation in January of more than 20 portable earthquake monitors around the earthquake sites. SMU seismologists Heather DeShon and Brian Stump, in the Roy M. Huffington Department of Earth Sciences, answered questions during the briefing with reporters.

Read the full story.

EXCERPT:

By Anna Kuchment and Avi Selk
Dallas Morning News

Scientists finally have a rough picture of the ancient fault that’s been rattling the Dallas area, and the fissure isn’t where the public thought it was.

Armed with more equipment and better data, SMU scientists have relocated dozens of quakes on the federal government’s imprecise maps. The team released a new map on Friday that shifts the epicenters of nearly all of last month’s temblors, arranging them in a neat line that shadows a fissure miles beneath the earth.

And while the team has just begun to study that fault, they already have some early hints about its nature.

It’s not beneath the old Texas Stadium site, as federal maps suggested.

It’s small (for a fault) and appears to be quieting down after tossing off about four dozen quakes in a year. But it could still produce a tremor much more powerful than any Dallas has yet seen.

And while scientists are skeptical that gas drilling woke it up, they now know the fault runs much closer than previously thought to the only two fracking wells in the area.

If you’ve felt any of the earthquakes to hit the Dallas area since last fall, you may have looked up a map of their epicenters. The rough bull’s eye of quakes around the old Texas Stadium site has sparked wild theories about the stadium’s demolition and jokes about the “Jerry Jones Fault.”

That map is wrong, and scientists have always known it.

The federal government estimated the North Texas epicenters using a small handful of quake detectors, some of which sat miles away and produced inaccurate readings.

The U.S. Geological Survey’s blob of approximate quake locations was of little use to scientists trying to map the underground crack producing them. So in early January, the SMU team began to install nearly two dozen detectors in the Irving area to collect more accurate data.

The earth obliged with more than two dozen quakes since then, including the most powerful yet in Dallas County.

Read the full story.

Follow SMUResearch.com on twitter at @smuresearch.

SMU is a nationally ranked private university in Dallas founded 100 years ago. Today, SMU enrolls nearly 11,000 students who benefit from the academic opportunities and international reach of seven degree-granting schools. For more information see www.smu.edu.

SMU has an uplink facility located on campus for live TV, radio, or online interviews. To speak with an SMU expert or book an SMU guest in the studio, call SMU News & Communications at 214-768-7650.

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Earth & Climate Energy & Matter

SMU analysis of recent North Texas earthquake sequence reveals geologic fault, epicenters in Irving and West Dallas

Shallow depths explain why so many felt relatively small quakes; not unusual for earthquakes to occur at different fault levels.

Locations of seismic instruments as of Jan. 30, 2015, with revised earthquake locations in dark red. (USGS)
Locations of seismic instruments as of Jan. 30, 2015, with revised earthquake locations in dark red. (USGS)

Initial results from the seismology team at Southern Methodist University reveal that a recent series of North Texas earthquakes occurring near the site of the old Texas Stadium in the Dallas-Fort Worth area were relatively shallow and concentrated along a narrow two mile line that indicates a fault extending from Irving into West Dallas.

SMU and the United States Geological Survey on Friday, Feb. 6, 2015 shared an interim report with the mayors of Dallas and Irving spelling out preliminary information gleaned after SMU’s installation in January of more than 20 portable earthquake monitors around the earthquake sites.

“This is a first step, but an important one, in investigating the cause of the earthquakes,” said SMU seismologist Brian Stump. “Now that we know the fault’s location and depth, we can begin studying how this fault moves — both the amount and direction of motion.”

“Then we can move on to what might have triggered it – examining factors both natural and manmade,” said SMU seismologist Heather DeShon. “Sometimes what triggers an earthquake can be very small, so all of these factors have to be considered when looking for that trigger.”

The earthquakes have occurred in the granite “basement,” below the layers of sedimentary rock that make up the large geological formation known as the Fort Worth Basin, at depths between 4.5 and 7 kilometers, according to the report. It is not unusual for earthquakes to occur at different levels on a fault. Those depths are considered relatively close to the surface in earthquake terms, however, which helps explain why people as far away as the northern suburb of Plano feel even smaller magnitude 2 earthquakes in the area.

January 2015 earthquakes actually have occurred along a line from Irving to West Dallas
The USGS initially mapped the earthquake locations as being spread out in a roughly circular area centered on the old Texas Stadium site, developing those locations from data collected by distant seismic monitors ranging from the closest at about 40 miles away to as far as 900 miles away. But once SMU installed more than 20 monitors in the immediate area – supplied by the USGS and the academic consortium IRIS – the enhanced data they were able to retrieve shows the January 2015 earthquakes actually have occurred along a line from Irving to West Dallas, running north-by-northeast from TX Highway 114 to Walnut Hill Road along the Trinity River.

That line indicates the approximate location of a subsurface fault.

This initial mapping of the fault provides important information for municipal hazard assessment in Irving and Dallas, Stump said, allowing city officials to know which parts of their cities might experience the worst shaking if the fault remains active. As has been the case with other earthquake sequences in North Texas since 2008, this latest bout of seismic activity appears to be diminishing over time. But SMU scientists stress that there is no way to predict when the series will end, or what the largest magnitude will be.

The earthquakes in the Irving area began in April 2014. SMU scientists had just installed the first of its local monitors in the city of Irving on Jan. 5, 2015 when the area recorded its two largest earthquakes – 3.5 and 3.6 magnitude events – on Jan. 6.

SMU seismology team installed more than 20 seismographs in the affected area
During January, members of the SMU seismology team installed more than 20 seismographs in the affected area, including 12 short-term units that had to be removed from the field to collect their data. There will be 11 temporary seismographs running as part of the Irving network moving forward.

The report notes the presence of two wells drilled for shale gas (only one was put into production, last producing in 2012) near the earthquake epicenters and the location of a wastewater injection well approximately eight miles to the northwest. Production and disposal activities in this region are generally confined to the sedimentary layers above the “basement” layers where regional earthquakes have occurred.

“Scientific questions about the nature of events in North Texas have heightened local and national concerns about the impact of activities related to shale gas production on geological infrastructure and subsurface infrastructure,” the report reads. “SMU scientists continue to explore all possible natural and anthropogenic (due to human activity) causes for the Irving earthquakes and do not have a conclusion at this time.”

The next steps of the Irving study already are underway.

Signing the report were Heather DeShon, SMU associate professor of geophysics; Brian Stump, SMU Albritton Chair of Geological Sciences; Chris Hayward, senior scientist and director of SMU’s Geophysics Research Program; Beatrice Magnani, SMU associate professor of geophysics; Matthew Hornbach, SMU associate professor of geophysics; and Robert Williams and Michael Blanpied of the USGS Earthquake Hazards Program. — Kimberly Cobb

Follow SMUResearch.com on twitter at @smuresearch.

SMU is a nationally ranked private university in Dallas founded 100 years ago. Today, SMU enrolls nearly 11,000 students who benefit from the academic opportunities and international reach of seven degree-granting schools. For more information see www.smu.edu.

SMU has an uplink facility located on campus for live TV, radio, or online interviews. To speak with an SMU expert or book an SMU guest in the studio, call SMU News & Communications at 214-768-7650.