Whether by gas production, mining, or the impoundment of reservoirs: When it comes to extracting raw materials, and energy or sometimes just restoring the natural condition, human activity can trigger earthquakes. If these so-called induced earthquakes become too strong or too frequent, critical situations for nearby settlements can evolve. To avoid this, there are often restrictions or terminations of mining or production operations, for example at gas fields. Texas chooses another method. The US state with its large oil reserves has learned from the mistakes of its neighbors and is going on its own way: it simply pushes the earthquakes to places where they are less disruptive. However, it is questionable whether and for how long this way will go well.

Western Texas has an earthquake history. Unlike the plains around Dallas and Houston, the hilly to a mountainous area between El Paso and Odessa lies in the foothills of the Rocky Mountains, a mountain range with ongoing geological processes, active faults, and also volcanism. According to the USGS database, eleven earthquakes above magnitude 4 occurred between 1900 and 2000, including two damaging events with magnitudes 5.7 and 5.8 in 1995 and 1931. No comparison with the seismic states of California and Nevada, but roughly at the level of the most seismically active areas of Central Europe for example.

Texas earthquake activity increased by 16,000%

It is 2022 now and the USGS has just registered the ninth M4 of the year in Western Texas. Quake number three in June alone. The most earthquake-prone year in history, 2021, with eleven M4s, is about to lose this status at an early stage. Looking at the distribution of these and minor earthquakes, a huge, elongated cluster about 35 kilometers south of the New Mexico border becomes visible. Almost all of the earthquakes of the last two years, the majority of all Texas earthquakes, are concentrated here. In an area that was almost earthquake-free before 2019.

To understand why there are so many earthquakes in Texas at the moment, one has to go back a few years.
Since the beginning of the 21st century, some US states have had a problem with induced earthquakes. Due to the increased use of hydraulic fracturing to develop gas and oil reservoirs, the production rate has increased massively. But in addition to millions of barrels of oil, the wells also produced another substance for which there is no further use: water.
Partly contaminated with chemicals or salts, this water became a common byproduct of oil extraction. Instead of cleaning it up in special facilities, many fields use the former reservoirs as final storage. In the rock layers that hosted the black gold for millions of years, wastewater should find its resting place.

Earthquakes in Texas
Distribution of earthquake epicenters in Texas since 2017 (Data: Texas Seismological Network). Smaller clusters of shallow (less than 10 km depth) seismicity are observed across the state. Recently, the large earthquake cluster in the Permian Basin south of the New Mexican border became active and is now the area with the highest seismicity in whole Texas. The largest quakes of this cluster happen in the westernmost part close to known active faults.

Waste water disposal trigger earthquakes

However, the physical properties of oil and water are different. In addition, the reservoir was geologically altered as a result of previous exploration and extraction. Both together allow the water, once enough of it has been pumped into the rock, to induce pressure on previously inactive geological fault zones. Like a lubricant, it releases natural stresses in the rock that have survived the past geological ages. As a result, earthquakes occur. More water means more hydrostatic pressure, smaller earthquakes, and in the end a higher probability of higher magnitudes.

Oklahoma was the first US-State to suffer from these earthquakes. In 2011, a magnitude 5.7 quake caused extensive damage in the nearby town of Prague. In 2016, the town of Pawnee was also hit with a magnitude of 5.8. Two more magnitudes 5 earthquakes and dozens of magnitude 4 earthquakes within a few years made Oklahoma the Earthquake State number one in the United States. Only the Chinese province of Sichuan, where earthquakes were significantly more devastating, suffered from induced earthquakes of comparable proportions. Only through massive reduction of water volume and closing of wells, earthquake numbers in Oklahoma drop again in recent years.

Also, Texas was not spared from the earthquakes. Unlike in sparsely populated Oklahoma, many oil fields are located near larger towns and cities. Earthquakes such as 2011 near Snyder (magnitude 4.3), 2015 in downtown Dallas (magnitude 3.5), or 2018 near Amarillo (magnitude 3.8) led to great concern. What if there were earthquakes of magnitude 5.7 or higher like in Oklahoma or Sichuan? Possible damage and loss of life as in China would be an unacceptable risk for oil companies and especially state regulators. So it was decided in recent years to largely stop injecting water in these places. Minor earthquakes, which were often part of everyday life between 2010 and 2018, mostly disappeared since 2021.

Decrease in earthquake activity in Eastern Texas

But the oil production and thus the production of waste water continued. Sewage treatment plants are built to increase cleaning capacity. Some water is now also being reused for Fracking. In the end, however, the path of most water leads into the earth. Instead of being disposed of directly on-site or near urban centers, it is sometimes first transported hundreds of kilometers through pipelines. Into the Wild West of Texas, where only pumas live. Into the Permian Basin, where the oil industry was on the upswing anyway, also related to the war in Ukraine, and where the water is used again and finally finds its repository.

The massive increase in earthquake activity in Western Texas since 2020 is the expected result. Expected side effects of a powerful and increasingly important industry are shifted to where they cause fewer problems. On the one hand, a balancing interim solution that also reduces fresh water consumption. On the other hand, nothing more than a Texas roulette game. Towns like Pecos, Van Horn or the large city Juarez in Mexico are far away and not immediately endangered. With the number and strength of the earthquakes that have been reached in recent months, however, there are still frequent weak shakes observed by residents. Weak shakes that are not guaranteed to keep their low intensity.

The size (magnitude) of induced earthquakes, whether induced by pumping water, as is the case here or by gas extraction, fracking (which is by the way not responsible for any earthquake in Texas), or mining, depends primarily on the natural conditions of that region. If it is an area with naturally low earthquake activity, such as the Groningen region in the Netherlands, seismicity remains below magnitude 4 despite intensive gas production. If, as in Sichuan, severe earthquakes are happening even without anthropogenic intervention, induced earthquakes easily reach magnitude 6.

More water = more earthquakes

Western Texas has an earthquake history. Magnitude 5.8 in the last century. Magnitude 7 in prehistoric times. The further west you go, the higher the risk of damaging earthquakes. The probability of hitting the loaded gun rises with the number of injection wells. From today’s epicenter to the active West Delaware Mountains fault it is still about 25 kilometers.
Magnitude 4 is harmless, magnitude 5 is acceptable. But M6-7 would be a disaster for smaller towns like Dell City. Depending on the exact epicenter, problems even for Pecos and Juarez are possible.

Targeted injection at non-critical locations means that severe earthquakes can be almost completely ruled out. Scientific studies recently opened the door to possibly control induced earthquakes and show where and how the hydrocarbon industry can produce with low seismic risk. A residual risk remains, however. The ongoing earthquake storm in Western Texas, away from cities, away from damage claims, is a temporary solution and at the same time a kind of experiment under semi-controlled conditions. If all goes well, induced earthquakes in the USA could no longer be of great importance in the future. If things go wrong, they will have to face justified criticism.

In the coming years, even more, water is expected to be pumped into the depths of the earth. Accordingly, new injection wells are already planned. But local authorities in Texas and New Mexico are already seeing the massive increase in activity as a warning sign. They urge reducing injection at the densest points of the earthquake cluster to avoid large events. More water should be recycled and cleaned, instead of expanding the wells. A solution with less risk, but more immediate costs.