Wastewater injection may be cause of Oklahoma 'earthquake swarm,' USGS study suggests

Between 1975 and 2008, Central Oklahoma experienced about one to three manginute 3.0 earthquakes per year. Since 2009, that figure has jumped to around 40 per year.

In an effort to explain these tremors, the US Geological Survey (USGS) and the Oklahoma Geological Survey have been researching the changes and trying to figure out whether they may be linked to wasterwater disposal from oil and gas producers in the region.

According to a recent news release by the USGS, the changes don't seem to be the result of "typical, random fluctuation in natural seismicity rates." In fact, results suggest that a contributing factor may be injection-induced seismicity caused by waste-water disposal methods of oil and gas companies.

While hydraulic fracturing routinely produces harmless micro-earthquakes – those with magnitudes below 2.0 – wastewater disposal by injection into deep wells "poses a higher risk" because it can result in larger quakes, according to an article in Science.

The USGS refers to a "swarm" of earthquakes over the past two years, which includes the largest earthquake ever recorded in Oklahoma – a magnitude 5.6 quake from 2011 that destroyed 14 homes and injured two.