Geospatial analysis of Oklahoma (USA) earthquakes (2011-2016); quantifying the limits of regional-scale earthquake mitigation measures

The annual earthquake rate in Oklahoma (United States) has increased dramatically in recent years, owing in large part to the rapid proliferation of salt-water disposal (SWD) wells associated with unconventional oil and gas recovery. This study presents a geospatial analysis of earthquake occurrence and SWD volume within a 68,420 km (super 2) area in north-central Oklahoma between 2011 and 2016. Results indicate that (1) the annual geographic centroid of Arbuckle Group SWD well locations predicts the geographic centroid for M3.0+ earthquake occurrence within an approximately 1sigma radius of gyration when the well centroid is geometrically weighted by SWD volume; (2) between 2014 and 2016 Arbuckle SWD volume and earthquake occurrence are spatially cross-correlated to a length scale of 125 km; and (3) earthquake mitigation strategies implemented in late 2015 and 2016 are preferentially affecting the joint variability of SWD volume and small-magnitude earthquakes. These results suggest that current earthquake mitigation may require further volume reductions and/or greater areal extent to increase effectiveness.