Laurie Dingler | Human-caused earthquakes in the Midwest – The Times Standard

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This week, the central time zone was the most seismically active region in the lower 48 states, with 48 recorded earthquakes of magnitude 2.5 or greater. I can usually bet California to take the lead, but this week, states in the central part of the country took the majority, including two M4s in West Texas and one in Kansas.

None of these earthquakes were devastating, but the M4s in Texas and Kansas were very unusual two decades ago. The national network of earthquake stations in the United States is dense enough that no earthquakes of at least a magnitude 4 or greater have been missed since 1980. It is easy for anyone to do a search (click on the recent earthquakes link at https://earthquake.usgs.gov/ In the search catalog selected from the list).

In the 30-year window from 1980 to 2010, 58 M≥4 earthquakes occurred in the central United States between the corresponding longitude ranges of western Wyoming and Oklahoma’s Rattern, with an approximate average of two per year. Most of these earthquakes are located within the mountainous regions of Montana, Wyoming, Colorado, and New Mexico. Only three were in Oklahoma, one in Kansas, and eight in West Texas. This is probably a good picture of the area’s natural background activity.

Research on earthquakes in the 11 years since 2010 shows a different picture. 165 earthquakes of magnitude 4 or greater have been identified in the same area, with an average of 15 earthquakes annually. Activity in mountainous countries is similar; Big increase in the Midwest. The largest contributor is Oklahoma with 94. Prior to 2010, Oklahoma experienced an earthquake of magnitude 4 or greater once every 10 years. In 2015 alone, thirty M4s were registered.

Earthquake activity can be largely from year to year. In the three years between 2016-2019, 31 earthquakes of 4 or greater magnitude occurred in eastern California and Nevada. Since 2019, this number has increased to 228. It is easy to explain what is happening – a series of large earthquakes and their aftershocks. The Ridgecrest sequence began with 6.5 and 7.1 on July 4 and 5, 2019 activity which has continued with the M6.5 Monte Cristo earthquake in western Nevada in May 2020 and earthquakes in the Owens Valley and Antelope Valley.

The recent earthquakes in California and Nevada are classic tectonic earthquakes – caused by regional pressures driven by heat within the Earth. Human activity has nothing to do with the event. These earthquakes occur on faults that may remain quiet for decades or centuries and then be reawakened by one or several large earthquakes followed by years of smaller aftershocks.

Could a similar reason explain the increased seismic activity in the Midwest? Not very similar. These are not typical tectonic sequences with a larger earthquake followed by a smaller earthquake that slowly decreases in frequency over time. Most earthquakes in the Midwest are small and clustered into narrow areas. Volcanic regions and geothermal regions such as the Salton Sea region of Southern California are notable for swarm activity with many earthquakes of roughly equal size occurring over days and weeks. These swarms are associated with the natural movement of hot fluids and magma, which is certainly unlikely in the Midwest.

But fluids are likely to be a large part of the Midwest earthquake story. It’s the fluid source that makes these earthquakes very different from tectonic, volcanic, or geothermal events. The sudden increase in earthquake activity corresponds to a regulatory event. In 2008, the United States banned the disposal of waste fluids from drilling operations in surface reservoirs due to concerns about groundwater contamination and contamination. Oil drilling was required to inject waste fluids into deep wells, often more than 10,000 feet below the surface.

The Environmental Protection Agency designates Class II wells for natural gas disposal and oil drilling fluids, and estimates that 180,000 of these wells are currently operating in the United States. The Environmental Protection Agency estimates that more than 2 billion gallons of brine and other waste are injected into these wells each day.

The vast majority of Class II wells have absorbed this effluent without any noticeable effects. But the exceptions are interesting and a potential seismic threat. The problem first appeared in Oklahoma with a rapid increase in seismic activity. It was difficult to pin down earthquake activity directly to the injectors as the location, rates, and volumes of fluids are proprietary in most states, but the 5.7 damage in 2011 drew national attention.

By 2015, the unusual increase in Oklahoma earthquake activity had become a concern for insurance companies (https://www.reuters.com/article/us-usa-oklahoma-earthquakes/insurers-shun-risk-as-oil-linked-quakes – Fly in Oklahoma (idUSKCN0Y30DC). Oklahoma lawmakers enacted legislation in 2015 to control the volume and rate of fluid injections and the number of earthquakes has fallen rapidly. Only four earthquakes in Oklahoma have reached the 4 magnitude range since 2019.

As activity from Oklahoma decreases, increases occur in other areas. Last week’s seismic activity highlights two new hot spots. The Chihuahua Desert east of El Paso has become one of the most shaken in the country (https://www.eenews.net/articles/earthquakes-linked-to-drilling-are-messing-with-texas/), with thirteen M≥ earthquakes 4 in 2021. The area is remote, earthquakes have not caused damage, and few are felt. But the concern is the potential for stronger earthquakes, and ironically it is the oil and gas industry that will lose the most if the vibration disrupts pipelines and production facilities. This month, state regulators asked operators to develop plans to reduce earthquake activity.

The second hot spot is Kansas. The December 8 M4.3 and 15 4.0 earthquakes were felt near Salina City, Kansas, and hundreds of people were felt as far away as Kansas City, Missouri, and Omaha, Nebraska. Kansas lawmakers have yet to pass regulations on injection activity (https://www.kcur.org/economy/2018-02-15/environmentalists-duel-with-drillers-over-kansas-earthquake-legislation). Keep your eyes peeled – some strong or powerful earthquakes may push them in the same direction as Texas.

Laurie Dingler is Professor Emeritus of Geology at Humboldt State University, and an expert on tsunami and earthquake hazards. Questions or comments about this column, or want a free copy of Preparedness magazine “Living on Shaken Earth”? Leave a message at 707-826-6019 or email [email protected].

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