In 2015 alone, residents of Oklahoma felt the earth move beneath them a total of 907 times, as an unprecedented number of magnitude three or higher earthquakes racked the state.
While Oklahoma has historically experienced its share of seismicity, in the last eight years the rate of earthquake occurrence in the state has increased by a factor of 43—approximately 4,000%.
According to earthquake researchers, including civil and environmental engineering (CEE) Ph.D. student Pengyun Wang, wastewater injection and other fluid injection technologies have something to do with it.
Along with his advisors CEE Professor Mitchell Small and Assistant Professor Matteo Pozzi, and collaborator William Harbert, professor of Geology and Environmental Science at the University of Pittsburgh, Wang has spent the last two years investigating the dramatic increase in seismic activity in Oklahoma. And while it is difficult to draw causal relationships in earthquake research, the glut of seismic data in Oklahoma provides researchers a unique opportunity to study the link between seismic activity and fluid injection.
“Because the earthquake activity there has seen such a significant increase, the state has an impressive network of monitoring infrastructure,” Wang says. “They have installed a huge number of sensors across the state, and the database of the readings they collect is well-organized and open to the public.”
Fluid injection is the process by which wastewater, brine, or other fluids are shot through man-made openings in the earth deep into underground wells or reservoirs. Often, this is used as a disposal method for water used in hydraulic fracturing and other industrial processes that introduce chemicals into the water, which makes this water unsafe to reintroduce into the environment.
Based on the data gathered in Oklahoma, the researchers have come up with several mechanisms explaining how fluid injection might be causing an increase in seismic activity.