By Laura Fattaruso, M.S., Ph.D. Candidate, UMass Amherst (@labtalk_laura)
A recent study finds that ground motions from earthquakes induced by oil and gas operations are similar to those produced by tectonic earthquakes.
Citation: Fattaruso, L. (2020), Induced earthquakes can cause as much damage as tectonic quakes, Temblor, http://doi.org/10.32858/temblor.083
On March 26, residents in West Texas and Southeast New Mexico felt a series of earthquakes, ranging from magnitude 3.0 up to magnitude 5. More than 1,000 reports of shaking were logged in the USGS ‘Did you feel it?’ database. While it’s too early to conclude with certainty if these earthquakes were triggered by human activity, the USGS reports that the region in Texas where the earthquakes originated contains gas-producing shale and has previously hosted earthquakes induced by oil and gas operations.
Human activities that trigger earthquakes include hydraulic fracturing of shale to extract natural gas, deep injection of wastewater used during hydraulic fracturing, and deep water injection to extract geothermal energy. These are all processes that inject fluids deep–up to several kilometers–into the ground. Other human activity like dam construction and moving earth can also trigger quakes.
The mechanisms that cause these earthquakes differ from those that cause tectonic quakes. Seismologists wonder if that difference means that induced earthquakes are more likely to cause damage.
Seismologist Gail Atkinson of Western University in Ontario, Canada, addresses this uncertainty in a recent study published in the Bulletin of the Seismological Society of America. To determine whether induced shaking triggered by human activities might pose a different degree of hazard than tectonically triggered quakes, Atkinson compared the ground motions from induced earthquakes to those produced by natural tectonic processes.
Determining the hazard
To make this comparison, Atkinson used data from three different regions— earthquakes produced by tectonic plate motion in California, Oklahoma earthquakes induced by deep water injection, and earthquakes in Western Canada triggered by hydraulic fracturing. By comparing temblors of similar sizes from these three datasets, Atkinson found that despite differences in triggering mechanisms and landscape, the ground motions produced within 50 km of the hypocenter are similar for quakes of similar sizes throughout the three regions.
Understanding the ground motions produced during an earthquake is critical to assessing the potential for damage to nearby buildings and infrastructure.
“It’s good for practical applications” says Yihe Huang, a seismologist at University of Michigan who also studies induced earthquakes but was not involved with this study. She argues that this study gives researchers a basis for evaluating how much damage to expect for buildings close to an induced quake.
The largest earthquake known to be induced by fluid injection was the 2016 magnitude 5.8 Pawnee, Oklahoma earthquake that left six buildings uninhabitable, and was felt across the Central United States from Denver, Colorado, to Chicago, Illinois (Yeck et al., 2017).
In the recent study, Atkinson advises that induced earthquakes within 5 km of infrastructure need to be kept below magnitude 3.5 to prevent damage to buildings. But limiting the magnitude of those induced quakes is challenging.
Previous studies of induced earthquakes found that they can be triggered by fluid injection at sites as far 40 km away (Goebel et al., 2017). While changes to pore pressure due to fluid injection directly on a fault can trigger an earthquake over shorter distances, injection of large volumes of fluids can also change the stress conditions in the crust—yielding triggered quakes over much greater distances. This makes controlling the geographic location of induced temblors hard.
Another challenge is knowing where the faults that can produce earthquakes are located. Many faults in the central US had not been identified until fluid injection started to trigger earthquakes on them. “These earthquakes have shown a lot of fault structures we hadn’t seen before.” explains Huang.
Reducing the hazard
One approach to limiting the size of induced quakes is the “traffic light system.” Under such a system, induced earthquakes are monitored, and as certain magnitude thresholds are crossed, actions are shifted accordingly—reducing or stopping the injection of fluids into the ground. But a study published in 2019 looking at induced seismicity around geothermal fields and gas production wells found that the largest magnitude earthquakes often occurred after injections had already stopped (Baisch et al., 2019). This suggests that the traffic light system may not be especially effective for controlling the magnitude of induced quakes. Some researchers are working on alternative methods to forecast induced quakes.
“You can avoid having earthquakes in a region with vulnerable buildings, but controlling the magnitude to stop at precisely 3.5 would be really hard.” says Huang.
In the study, Atkinson notes that we can’t rely solely on the history of damage caused by induced quakes to fully understand them. She explains, “Statements such as ‘the earthquake caused no damage’ are not meaningful unless accompanied by an understanding of the structures nearby that might potentially have been damaged. For this reason, I focus on damage potential, recognizing that such potential will not always be realized.”
Curious about your earthquake risk? Check it at Temblor.
Further Reading
Atkinson, G. M. (2020). The Intensity of Ground Motions from Induced Earthquakes with Implications for Damage Potential. Bulletin of the Seismological Society of America.
Baisch, S., Koch, C., & Muntendam‐Bos, A. (2019). Traffic light systems: to what extent can induced seismicity be controlled?. Seismological Research Letters, 90(3), 1145-1154.
Goebel, T. H. W., Weingarten, M., Chen, X., Haffener, J., & Brodsky, E. E. (2017). The 2016 Mw5. 1 Fairview, Oklahoma earthquakes: Evidence for long-range poroelastic triggering at> 40 km from fluid disposal wells. Earth and Planetary Science Letters, 472, 50-61.
Yeck, W. L., Hayes, G. P., McNamara, D. E., Rubinstein, J. L., Barnhart, W. D., Earle, P. S., & Benz, H. M. (2017). Oklahoma experiences largest earthquake during ongoing regional wastewater injection hazard mitigation efforts. Geophysical Research Letters, 44(2), 711-717.
