Induced Seismicity: Induced Earthquakes in Oklahoma Dropping, But Not Off the Radar
Authors: Jacobs Trent , Rassenfoss Stephen 
Published: August 2017

Induced Seismicity: Induced Earthquakes in Oklahoma Dropping, But Not Off the Radar
Trent Jacobs, JPT Digital Editor
In 2015, Oklahoma recorded just over 900 earthquakes of at least a 3.0 magnitude. In 2016, the total fell to 623 and this year’s figure is on track to be about 300.
Since the vast majority of these earthquakes are linked to produced water injections, the trend line is welcome news to the state’s oil and gas industry. However, for Jeremy Boak, director of the Oklahoma Geological Survey, 300 of these generally small earthquakes is still too many.
“We are seeing seismicity decline,” he said. “But I’m a little uneasy that it’s flattening out at a rate that I have a hard time believing will be acceptable in Oklahoma.”
Boak offered his thoughts on the topic of induced earthquakes while speaking on an expert panel at the Unconventional Resources Technology Conference. Stricter wastewater injection limits and low oil prices are driving the drop in Oklahoma’s earthquake frequency, but Boak said it is not known why that drop is “stalling out” instead of continuing, and for that reason he stressed that the issue continues to demand constant monitoring.
Boak’s agency, which is not a regulator but reports its seismic observations and findings to one, determined in 2015 that swarms of daily earthquakes were being caused by disposal well injections of produced water into Oklahoma’s deepest sedimentary formation (known as the Arbuckle) that sits just above a myriad of pre-Cambrian fault lines.
The panel discussion on which he sat revealed how much regulators, the seismology community, and the oil industry have all learned in the past few years about disposal wells and how they can trigger earthquakes. The talk also served to highlight the unfinished business on the matter, and why Texas may become the next hot spot for induced earthquakes.

Induced Seismicity: Filling in the Blanks To Limit Earthquake Risks
Stephen Rassenfoss, JPT Emerging Technology Senior Editor
It is known that a well injecting a lot of water near a big fault can lead to earthquakes. The problem is, more often than not those faults are not known until after a tremor.
“Only 34% of these earthquakes occur within 2 km of any known fault,” said Jeremy Boak, director of the Oklahoma Geological Survey, which is working on multiple studies to describe and understand how water injection activates critically stressed faults to cause earthquakes.
“We are learning where many faults are,” Boak said at the American Association of Petroleum Geologists annual meeting this spring, where he delivered a paper (2017) along with researchers from Texas, Kansas, and Colorado talking about what they are doing to fill the knowledge gaps.
While the Oklahoma Geological Survey is not a regulator, its work has guided what the state has done to reduce the number of earthquakes by limiting injection in those areas with the most problems.
“The drop is due to decreases in injection,” related to a slowdown in activity since oil prices dropped and the orders to reduce injection in affected areas by the regulator, the Oklahoma Corporation Commission, Boak said.
Speaking at the Unconventional Resources Technology Conference in July, Boak predicted that the number of earthquakes strong enough to feel will total around 300 this year—one-third of the number of the peak that occurred in 2015. Boak said it is far from an acceptable rate of activity in a state where the annual average used to be 1.6 events a year.