In the past decade, Oklahoma has turned heads as it has joined the list of places where earthquake insurance is a prudent investment. The sudden uptick in seismic activity is due to injections of foul wastewater into deep disposal wells—triggering what are known as “human-induced earthquakes.”
The Okie state hasn’t been entirely alone in this, though. Because geology doesn’t respect state lines, the oil and gas wells producing all this wastewater—and the deep, salty aquifer it has been pumped down into—extends into Kansas. And a new study led by Justin Rubinstein of the US Geological Survey confirms that they have been causing earthquakes there, too.
While Oklahoma actually experienced some structural damage in several earthquakes, Kansas hasn’t seen anything stronger than a magnitude 4.9 that shook some items off of shelves. But between 2012 and 2016, southern Kansas had six magnitude 4 or larger quakes, which seems far from normal.
To find out, the researchers relied on past records of earthquakes in the state and an array of seismometers that were set out in early 2014 to better measure the recent activity. The simplest analysis is to look for correlations in time and location between the drastic uptick in earthquakes and wastewater injections in the state. These injections have gone on for a long time, but very little wastewater was disposed of this way until 2012. At that point, the amount of injections doubled in a year and more than doubled again by 2014, peaking at over 100 million barrels per year.
Between 1974 and 2012, seismometers recorded just 15 earthquakes of at least magnitude 3, none of which were over magnitude 4. Over the next four years, there were six magnitude 4+ events and a whopping 127 magnitude 3+.
Kansas actually began to limit wastewater injections in reaction to noteworthy earthquakes. This started in early 2015; together with the influence of lower oil prices that slowed production in the area, the injection rate declined nearly as quickly as it rose, falling to less than half the peak rate by the end of 2016. And while the relationship between injections and quakes can be complicated by a time lag between injections and earthquakes, the number of quakes also dropped off rapidly.