Two relatively large earthquakes struck northwest of Oklahoma City midday on Monday within a span of about 20 minutes. The 4.0 magnitude and 4.5 magnitude quakes were accompanied by another 4.1 quake about seven hours later around 8:20 p.m. Two more smaller earthquakes also rattled the region throughout the day. The largest ever earthquake in Oklahoma was a 5.6-magnitude jolt in 2011.
While there were no reports of damage due to Monday’s quakes, they could be felt as far across five states — Oklahoma, Kansas, Texas, Missouri, and Arkansas — according to the Weather Channel.
The high level of seismic activity, especially in these closely linked swarms, follows a recent trend in fossil fuel-rich Oklahoma in which a dramatic spike in quakes has been tied to wastewater injection wells accompanying proliferating oil and gas drilling operations. In April, the New Yorker published an article on the recent surge in Oklahoma quakes that found that nearly two-dozen peer-reviewed papers have concluded disposal wells and quakes are likely connected.
In recent months, Oklahoma’s government has embraced the research showing such links and has begun to try to address the problem. Earlier in July, state oil and gas officials put more than 200 new wastewater disposal wells under extra review as “Areas of Interest” for the possibility that they are contributing to the recent earthquake swarms. This was in addition to 300 wells originally placed under the directive in March. According to E&E News, the 4.5 magnitude quake on Monday centered less than three miles away from an oil and gas wastewater disposal well recently added to the list.
As of mid-July, of the 300 wells originally on the Area of Interest list, 124 had reduced their depth, 54 were limiting the volume of wastewater injected into wells to less than 1,000 barrels a day, 25 had cut their injection rate in half, and 37 had stopped injecting.
As of April 2015, there were about 3,200 active disposal wells in Oklahoma.
The Oklahoma Corporation Commission (OCC) is in charge of permits for these wastewater disposal wells, otherwise known as Class II disposal wells, in which produced water associated with the production of oil and natural gas is injected deep beneath the surface of the earth.
According to the OCC, Oklahoma experienced 585 magnitude 3-plus earthquakes in 2014 compared to 109 in 2013. A recent report from the U.S. Geological Survey found that prior to 2012 there were virtually no earthquakes in southern Kansas and northern Oklahoma. In the last two years, several hundred have been recorded. Oklahoma was the most seismically active state in the Lower 48 in 2014, recording three times as many earthquakes as California.
The OCC recently wrote that there is “broad agreement among seismologists” that disposal of wastewater in wells that go below an Oklahoma geologic formation called the Arbuckle pose “a potential risk of causing earthquakes,” as this puts the wells in contact with so-called “basement” rock. The top of the Arbuckle formation sits around 4,000 feet to 10,000 feet below the surface and can be more than 6,000 feet thick. It is made up primarily of dolomites and limestones, but also contains sands, silts, and shales.
According to a 2012 article by Amerex Resources Corp., a private oil and gas company, the Arbuckle formation makes a “very attractive disposal zone” for wastewater in many places due to its “porosity and permeability” and its separation from “underground sources of drinking water” which makes permits easily obtainable.
Earlier in July, Michael Teague, Oklahoma Secretary of Energy and Environment, said expanding the Area of Interest for wastewater wells is the right thing to do.
“Though it’s too soon to know the results of the first directive, seismologists agree that injection into or in communication with the basement poses a high risk for seismicity, so this expansion makes sense,” he said.
While the OCC is attempting to confront the problematic proliferation of quakes, the Oklahoma legislature is not on quite the same page. In June, Republican Gov. Mary Fallin signed a bill that prohibits localities from choosing whether or not to have oil and gas operations within their jurisdictions — a law that amounts to a ban on local fracking bans.
Oklahoma was the second state to pass a law banning local fracking bans. Texas became the first when Gov. Greg Abbott signed legislation that prohibits cites and towns from banning the process.