IS THE RATE OF SEISMICITY IN EASTERN OHIO AND ENVIRONS AFFECTED BY WASTEWATER INJECTION RELATED TO SHALE GAS PRODUCTION?

Shale gas production has increased significantly in Pennsylvania and West Virginia since 2009 and in Ohio since 2012. Wastewater associated with shale gas production is typically disposed of through injection into wells. In some areas of the central United States-for example, Oklahoma- a dramatic increase in seismicity has been spatially and temporally associated with increased injection of wastewater from oil and gas production into disposal wells. It is believed that earthquakes induced by wastewater injection are the cause of the increased seismicity. Because northeastern Ohio has a history of earthquake sequences that are interpreted as induced seismicity related to wastewater injection, we compared seismicity since 2009 with the rate of seismicity prior to 2009 to see if there was any statistically significant increase in the rate of earthquakes correlated with increased shale gas production and resultant wastewater injection. The rate of seismicity in the central and eastern United States was previously represented with a doubly-truncated exponential model relating the number of earthquakes and magnitude with model parameters fit based on an earthquake catalog through 2008. Seismicity since 2008 was compiled for a 450-km radius region centered on eastern Ohio and tested to determine whether the seismicity was consistent with the rate determined from the pre-2009 dataset. Use of a one-sided Poisson’s test showed that the observed seismicity since 2009 is not unexpected given the rate determined for the pre-2009 dataset. Thus, in Ohio, northern West Virginia, and western Pennsylvania, wastewater disposal by injection into wells appears not to have resulted in a general increase in the rate of seismicity for the time period examined. This result does not preclude, however, that individual earthquakes or seismic sequences were caused by wastewater injection.