Seismic Swarm S20240926.1 Near Toyah, Texas

Seismic swarm S20240926.1 occurred approximately 40 km northwest of Toyah in Reeves County, Texas, within the Delaware Basin portion of the Permian Basin. The sequence began at 10:20 on 25 September 2024 and concluded at 06:30 on 27 September 2024, spanning 44 hours and 10 minutes. During this interval, 31 earthquakes were recorded, with magnitudes ranging from 1.4 to 3.8 and focal depths consistently between 5 and 8 km.

The swarm exhibited a gradual buildup followed by its most energetic phase on 26 September. Early events on 25 September included several shocks of magnitude 2.0–2.5, clustered between 17:00 and 22:00 local time. Peak activity occurred overnight into 26 September, highlighted by a magnitude 3.2 event at 22:17 on 25 September, a magnitude 3.7 shock at 02:22 on 26 September, and the largest event of the sequence, magnitude 3.8, at 07:56 on 26 September. Subsequent events declined steadily, with the final recorded shock of magnitude 1.4 at 06:30 on 27 September. Depths remained shallow throughout, averaging near 6 km, consistent with the sedimentary column overlying crystalline basement in this region.

The Permian Basin formed during the late Paleozoic as a foreland basin associated with the Ouachita orogeny. Its stratigraphic column comprises thick Pennsylvanian–Permian carbonates, sandstones, and evaporites, including the extensive salt layers of the Salado and Castile formations. Pre-existing normal and strike-slip faults, inherited from ancestral tectonic phases, provide pathways for fluid migration and potential reactivation. Historical records indicate that natural seismicity in West Texas was low prior to extensive hydrocarbon development; however, the basin has experienced a marked rise in earthquake rates since the expansion of horizontal drilling and wastewater disposal operations beginning in the early 2000s.

Internal classification data from SeismoSight document 13 swarms in the broader study area since 1 January 2000. Annual counts show a clear uptick: one swarm in 2022, seven in 2023, and five in 2024 through the end of September. This temporal pattern aligns with increased volumes of produced water reinjection across the Delaware Basin, where disposal wells commonly target intervals between 1 and 3 km depth. The shallow focal depths observed in swarm S20240926.1 fall within the range where pore-pressure perturbations from injection are most effective at inducing slip on critically stressed faults.

No damage or felt reports beyond instrumental detection were associated with this swarm, reflecting the modest magnitudes involved. Continued monitoring remains essential given the ongoing industrial activity and the demonstrated capacity for swarm-style sequences in this geological setting.

References

• USGS Earthquake Catalog
• Texas Bureau of Economic Geology, Permian Basin Studies
• SeismoSight internal swarm classification records