Oklahoma experienced the largest earthquake in the state’s history in early September. It carried a 5.8 magnitude and could be felt more than 1,000 miles away.
The earthquake was among a number of others that have occurred in a state that isn’t normally associated with them.
Jeremy Boak, the director of the Oklahoma Geological Survey, recently organized a presentation for the Tulsa Geological Society to address some of the questions and concerns of earthquakes in the state.
He explained that Oklahoma experienced an average of two earthquakes per year with a magnitude of 3.0 or greater between the 1980s and 2008. In 2015, that number rose to a staggering 907 in the span of just one year.
What he referred to as the “earthquake pulse” began in 2009 and reached a peak in 2015.
“It peaked at about 4.5 per day and is currently at 2.5 per day this year. The rate has been rapidly decreasing, though we still expect to have some pretty substantial earthquakes,” he told the EXPLORER.
More than 95 percent of the earthquakes have occurred in an area that makes up just 17 percent of the state.
“There are around 14-15 counties that share most of the earthquakes in Oklahoma, they tend to be west of Tulsa and north of Norman. This is the same area where injection sites are located.”
Many feel that the earthquakes are being triggered by wastewater, which is created from oil and gas production and then injected deep into the earth. Boak explained that the pressure that’s attributed to this increases and decreases, which can cause faults to move.
To address the recent pulse of earthquakes, “The Oklahoma Corporation Commission has taken a series of actions beginning in 2014 and 2015 where larger earthquakes have occurred. This includes stepping down the injection in the area. And it has had a measurable affect.”
Following the September earthquake, regulators reduced the volume of wastewater at some of the injection sites and completely shut down others. At the time of publication, this included 67 well sites in more than 1,100 square miles of the state.