DEVELOPING CRITERIA TO CHARACTERIZE AND CLASSIFY DISCRETE CLUSTERS OF EARTHQUAKES FROM 2012-2016 IN NORTH-CENTRAL ARKANSAS AS NATURAL OR INDUCED

North-central Arkansas has seen a significant increase in both unconventional resource development and seismicity within the Fayetteville Shale Play since 2009. The study area is historically seismically active, but it has seen a significant increase in seismic activity since 2009 that is likely a combination of both natural and human-induced clusters and even swarms of earthquakes (including the Guy-Greenbrier earthquake swarm of 2010-2011). We reviewed earthquake catalogs from the Center of Earthquake Research and Information (CERI), the Arkansas Geological Survey (AGS), and Advanced National Seismic System (ANSS) to obtain key characteristics including location, magnitude, and depth of the earthquakes within each discrete cluster. We then determined if a spatial and temporal correlation existed between discrete individual clusters of regionally-detected earthquakes that had occurred within 5-km of active Class II saltwater disposal wells, or within 5-km of production wells undergoing hydraulic fracturing (using the hydraulic fracturing notifications - HFNs) during the time of the seismic activity. We used template matching to produce a catalog of potentially induced earthquakes for each cluster of earthquakes. We are developing criteria to rate and assign a probabilistic classification to these clusters of earthquakes as to their likelihood of being natural or induced. The information from this technique of discriminating natural from induced earthquakes can be used to help determine which earthquakes should be included in future Short-term Induced Seismicity Models and the National Seismic Hazard Maps.