Geospatial analysis shows that Oklahoma earthquakes and wastewater injection volume were spatially correlated beyond 100 km from 2014 to 2017
Injection-induced earthquakes are most prevalent in Oklahoma, where the annual M3+ earthquake rate increased from ~one per year before 2009 to over two per day in 2015. This earthquake rate has fallen in recent years due to a combination of increasing regulation and pricing pressure in the oil and gas markets, but the earthquake rate remains well above the pre-2009 levels.
Our research shows that the geographic centroid (average location) for M3+ earthquakes followed a northwestern migration from 2011 - 2017. This work also shows that the volume-weighted well centroid predicts the M3+ earthquake centroid within a radius gyration defined as one standard deviation from well centroid (Pollyea et al., 2018).
We also found that M3+ earthquake occurrence and wastewater disposal volume are spatially cross-correlated to length scales exceeding 100 km from 2014 to 2017.
This long-range spatial correlation is supported by recent research showing that earthquakes are occurring in southern Kansas at distances up to 90 km from regionally expansive wastewater disposal operations at the Oklahoma-Kansas border (Peterie et al., 2018). These authors state: "…pressure diffusion from cumulative disposal to the south likely induced earthquakes much farther than previously documented from individual injection wells."
A number of physical mechanisms may explain these statistics, and we have found that the hydrogeologic principle of superposition may be the easiest to explain.