In Oklahoma, the largest-ever recorded earthquake was caused in part by operations related to oil and gas production. Now, the United States Geological Survey and the Oklahoma Geological Survey say that ongoing oil and gas operations have raised the risk of a large earthquake hitting again.
On November 11, 2011, a magnitude 5.6 earthquake struck outside Prague, Oklahoma. It was the largest ever seen in the state, and the shaking caused damage to a number of structures. But that tremblor was just the largest in a recent surge in earthquake activity in the region, says the USGS:
A new U.S. Geological Survey and Oklahoma Geological Survey analysis found that 145 earthquakes of magnitude 3.0 or greater occurred in Oklahoma from January 2014 (through May 2; see accompanying graphic). The previous annual record, set in 2013, was 109 earthquakes, while the long-term average earthquake rate, from 1978 to 2008, was just two magnitude 3.0 or larger earthquakes per year.
The uptick in earthquake activity, they say, is due in part to companies injecting waste water from oil and gas operations into underground wells. Pumping high pressure water into the wells puts pressure in the surrounding rock, and this pressure can cause preexisting (but largely inactive) faults to slip. The USGS suggests that the elevated earthquake activity also raises the probability of future large earthquakes.