Is high-rate injection causing the increase in U.S. mid-continent seismicity?

An unprecedented increase in earthquakes in the central and eastern US (CEUS) began in 2009. Many of these earthquakes have been documented as likely induced by wastewater injection. To better understand the likelihood of an induced seismic event from a given injection well, we compare the location and timing of earthquakes and injection operational parameters across the CEUS. We compiled a database of more than 187,000 injection wells in the CEUS, both active and inactive. In combination with the Advanced National Seismic System's (ANSS) comprehensive earthquake catalog from 1973 to mid-2014, we use spatial and temporal filtering methods to discriminate injection wells that may be associated with earthquakes from those that are not. Our goal was to understand whether or not well operational parameters such as injection rate, cumulative injected volume, injection pressure and injection depth affect the likelihood that a well is spatiotemporally associated with an earthquake.

We found more than 14,000 injection wells (~8% of all wells) that may be associated with earthquakes in the CEUS. Our spatiotemporal filter succeeded in capturing every suspected case of induced seismicity that we are aware of. We also found that the likelihood of an injection well being associated with an earthquake increased with increasing injection rate and cumulative injected volume. This phenomenon was observed over a wide range of geologic and hydrogeologic provinces in states such as Oklahoma, Colorado, New Mexico and Arkansas. Operational parameters such as injection pressure and injection depth do not show a clear trend towards an increased likelihood of spatiotemporal association with an earthquake.

In all, the cumulative number of CEUS earthquakes potentially associated with injection has risen sharply from 112 out of 545 in year 2000 (~19%) to more than 732 out of 1325 by May 2014 (~55%). This increase in earthquakes spatiotemporally associated with wells accounts for the vast majority of increased seismicity in the CEUS since 2009. Given that injection rate and total injected volume appear to affect the likelihood of wells being associated with earthquakes, industry or regulators can use injection parameters to lower the likelihood of earthquakes associated with injection wells.