Seismic Swarm Near Arcadia, Oklahoma: January 2024 Analysis

A seismic swarm designated S20240113.1 occurred 5 km west of Arcadia, Oklahoma, from 03:37 on 13 January 2024 to 04:18 on 15 January 2024. In 48 hours and 40 minutes, 53 earthquakes were recorded. This marks the second such swarm in the region since 2000, following one in 2013.

The sequence began with a magnitude 3.1 event at 6 km depth, followed rapidly by the swarm's largest shock of magnitude 4.2 at the same depth. Subsequent activity included a magnitude 4.1 event later on 13 January at 6 km depth. Magnitudes ranged from 0.6 to 4.2, with the majority between 0.8 and 2.6. Focal depths clustered tightly between 5 km and 7 km, consistent with shallow crustal faulting.

Events showed a typical swarm pattern: an initial energetic phase with the two largest shocks within the first 12 hours, followed by a prolonged decay of smaller tremors. Activity extended across 13–15 January, with isolated events on 14 January reaching magnitude 2.8. Depths remained stable, indicating a confined source volume.

Oklahoma lies within the stable continental interior of the central United States, underlain by Precambrian basement rocks of the Midcontinent Rift System and overlying Paleozoic sedimentary layers. The Arcadia area sits near the Nemaha Uplift and associated fault zones that accommodate minor tectonic strain. While natural seismicity is low, the state has experienced a sharp rise in earthquake rates since the early 2000s, primarily linked to wastewater injection from oil and gas operations that increases pore pressure on pre-existing faults.

The January 2024 swarm fits this regional context of induced or triggered seismicity. Depths of 5–7 km align with the crystalline basement where many injection-related events nucleate. Historical data indicate that swarms, rather than isolated mainshock-aftershock sequences, characterize much of Oklahoma’s recent activity.

This event underscores the value of dense seismic monitoring for distinguishing natural from anthropogenic signals in intraplate settings. Continued observation will help refine understanding of fault behavior in the region.

References
USGS Earthquake Catalog
Oklahoma Geological Survey Annual Seismicity Reports
SeismoSight internal swarm classification database