² Figure (a) showing a map of earthquake epicenters represented by small circles, reported by the U.S. Geological Survey. Figure (b) showing a map of the Permian Basin in West Texas.

In the city of Pecos, Texas in Reeves County, there’s more going on beneath the surface than most people would expect. Since 2007, there has been an unprecedented amount of seismic activity going on in the area. Pecos has experienced the single largest increase in seismic activity in the known history of Texas. 

 

Experts were puzzled by the ramp in earthquake activity and tried to pinpoint the cause. Some believed a correlation to exist between the increasing number of earthquakes and increased oil production and saltwater disposal activities in the surrounding areas. However, correlation does not equal causation. Sourcewater’s Director of Geoscience, Casee Lemons, coauthored a publication that dives into the “why” behind the unusual seismic activity in Pecos and uncovers the answer as to what is causing these events. In this post, we will be breaking down the results of the aforementioned study titled Onset and Cause of Increased Seismic Activity Near Pecos, West Texas, United States, From Observations at the Lajitas TXAR Seismic Array.

 

Earthquake Causes

Seismicity can be human induced or natural. Human-induced earthquakes are believed to be caused by surface mining (including potash and rock quarries)³, oil and gas production,^{4 5} water and gas injection, including saltwater disposal,^{6 7 8 9} and hydraulic fracturing.^{10 11}

 

Importance

In some parts of Texas, such as the Dallas-Fort Worth metroplex, human-induced seismicity caused by oil and gas activity results in large disruption to the economy by negative backlash from townspeople who believe the earthquakes affect them. In metroplexes such as Dallas-Fort Worth, citizens are not largely reliant on the oil and gas industry as the primary career sector. In contrast, citizens in West Texas cities, like Pecos, rely on the oil and gas industry as the primary source of economic stimulus. Given that most people rely on this industry to feed their families, citizens are more accommodating of hazards that are potentially caused by the industry they depend on to survive. However, understanding what has caused these earthquakes is the primary step to mitigating the problem and preventing more from happening.

This study analyzed a combination of modern and historic earthquake events in the region to identify the time of onset in earthquake surges and correlate those with known human activity. For example, earthquakes caused by quarry blasts can be correlated back to the time of day, 10:00 am and 2:00 pm, Monday through Friday. Additionally, modern onset can be differentiated from background historical earthquakes that are natural and not induced.  This study found that earthquakes in the City of Pecos did experience an onset of seismicity, around the clock (not dictated by work hours) in 2010, beginning with the onset of hydraulic fracturing into the unconventional Wolfcamp Formation. No known correlations can be found to quarries, oil and gas production, or injection. This confirms the conclusion by the TexNet Seismic Monitoring Network that the earthquakes in the City of Pecos, and only Pecos, are caused by hydraulic fracturing¹² into the Wolfcamp.

 

Conclusion

It is important to emphasize that only this set of earthquakes in the city of Pecos is associated with hydraulic fracturing. This region is in stark contrast to the metroplex area of Dallas-Fort Worth, where fear of hydraulic fracturing, but not an association of hydraulic fracturing with earthquakes, caused hydraulic fracturing to be banned in the metroplex. We are all very lucky that Pecos relies heavily on the oil and gas industry, where fear mongering will not cut off the livelihoods of the citizens. The City of Pecos Town Council recognizes the earthquake activity and strives to put its citizens first. The Town Council regularly consults with the State of Texas, the TexNet Seismic Monitoring Program, and the Center for Integrated Seismicity Research to reach a full understanding of the cause and future prevention of these earthquakes in Pecos, Texas.

 

You can access the full study here.

1. Frohlich, C., Hayward, C., Rosenblit, J., Aiken, C., Hennings, P., Savvaidis, A., et al. (2020). Onset and Cause of Increased Seismic Activity Near Pecos, West Texas, United States, From Observations at the Lajitas TXAR Seismic Array. Journal of Geophysical Research: Solid Earth, 125. e2019JB017737 https://doi.org/10.1029/2019JB017737.
2. Frohlich, C., Hayward, C., Rosenblit, J., Aiken, C., Hennings, P., Savvaidis, A., et al. (2020). Onset and Cause of Increased Seismic Activity Near Pecos, West Texas, United States, From Observations at the Lajitas TXAR Seismic Array. Journal of Geophysical Research: Solid Earth, 125. e2019JB017737 https://doi.org/10.1029/2019JB017737.
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