Seismic Swarm S20210617.1 Near Carney, Oklahoma

SeismoSight recorded seismic swarm S20210617.1 approximately 3 km southeast of Carney in Lincoln County, Oklahoma. The sequence began at 21:07 on 16 June 2021 and concluded at 07:08 on 18 June 2021, spanning 34 hours and producing 34 earthquakes.

The largest event reached magnitude 3.7 at a depth of 7 km shortly after initiation. Subsequent events ranged between magnitudes 0.6 and 2.5, with the majority occurring at depths of 5–7 km. Activity clustered densely in the first 12 hours, then tapered gradually, consistent with swarm behavior driven by fluid migration rather than a single mainshock-aftershock pattern.

Geologically, the Carney area lies within the stable cratonic interior of North America, underlain by Precambrian basement rocks of the Southern Oklahoma Aulacogen province. Regional fault systems, including segments of the Wilzetta and Nemaha faults, provide pre-existing planes of weakness. Although natural seismicity remains low, fluid injection associated with oil and gas operations has reactivated these structures since the mid-2000s, elevating earthquake rates across central Oklahoma.

Historical records maintained by SeismoSight indicate only one prior swarm in the immediate vicinity since 2000, occurring in 2013. That earlier sequence similarly featured low-to-moderate magnitudes and shallow focal depths, underscoring the episodic nature of induced activity in the region.

Current understanding attributes such swarms to pore-pressure diffusion along basement faults following wastewater disposal. Depths of 5–7 km place events within the crystalline basement, where critically stressed faults respond rapidly to small pressure changes. Monitoring by the Oklahoma Geological Survey and USGS continues to track these patterns, informing regulatory adjustments to injection volumes.

The 2021 swarm reinforces the link between anthropogenic fluid management and seismic hazard in central Oklahoma. Continued surveillance remains essential for distinguishing induced sequences from background tectonic activity and for refining mitigation strategies.

References

USGS Earthquake Catalog
Oklahoma Geological Survey Annual Seismicity Reports
SeismoSight Internal Swarm Database