Seismic Swarm S20240203.2 Near Prague, Oklahoma: Geological Context and Initial Event Analysis

Seismic swarm S20240203.2 began at 05:24 on 3 February 2024, centered 8 km northwest of Prague, Oklahoma. Activity continued until 09:37 on 17 March 2024, registering 2,981 earthquakes across 1,036 hours and 13 minutes. The swarm occurred within the stable continental interior of central Oklahoma, a region underlain by Precambrian basement rocks of the Southern Oklahoma Aulacogen and overlying Paleozoic sedimentary sequences. The area lies near the Nemaha Uplift and associated fault systems, including segments of the Wilzetta Fault Zone, where natural seismicity is low but induced events have increased since the early 2000s due to wastewater injection from oil and gas operations.

Central Oklahoma has experienced notable seismic episodes linked to fluid injection into the Arbuckle Group and other deep formations. The 2011 Prague sequence, which included a magnitude 5.7 mainshock, remains the most significant historical event in the immediate vicinity and demonstrated how pore-pressure changes can reactivate ancient basement faults. Since 1 January 2000, only three swarms have been recorded in the Prague area prior to 2024: single swarms in 2011, 2020, and 2023. These episodes underscore the episodic nature of induced seismicity in the region, where clusters typically last days to weeks and are dominated by events shallower than 8 km.

Analysis of the first 100 events of swarm S20240203.2 reveals a classic swarm signature: an initial large event followed by a dense sequence of smaller aftershocks without a clear mainshock-aftershock decay pattern. The sequence opened with a magnitude 5.0 earthquake at 3 km depth at 05:24:28 on 3 February. Subsequent events ranged from magnitude 0.4 to 3.4, with the majority occurring between 4 km and 7 km depth. Early activity featured frequent events of magnitude 1.0–2.0, interspersed with occasional larger shocks such as magnitude 3.4 at 06:32:59, magnitude 3.0 at 08:19:34, magnitude 3.2 at 09:16:42, and magnitude 2.9 at 11:21:58. Depths remained consistently shallow, rarely exceeding 7 km, consistent with injection-related triggering in the shallow basement.

Temporal distribution showed high rates in the first several hours, with dozens of events per hour initially, gradually declining while maintaining elevated levels for days. Magnitudes clustered below 2.0, yet the presence of multiple events above magnitude 2.5 within the first day indicates sustained stress release along a limited fault patch. Depths showed minor variation, with many early events at 5–6 km transitioning to slightly shallower or deeper locations as the swarm evolved.

This swarm fits the established pattern of induced seismicity in Oklahoma, where fluid migration along pre-existing faults produces prolonged clusters rather than isolated large earthquakes. Continued monitoring remains essential given the region’s history of injection-related activity.

References
SeismoSight internal swarm catalog S20240203.2
USGS Earthquake Catalog (queried for Prague, Oklahoma, 2000–2024)
Oklahoma Geological Survey induced seismicity reports (2023 update)