Seismic Swarm Analysis: Western Texas, January 2023

A seismic swarm designated S20230125.1 occurred in western Texas between 15:06 UTC on 24 January 2023 and 10:09 UTC on 27 January 2023. Over 67 hours and 2 minutes, the sequence produced 55 earthquakes. Magnitudes ranged from -0.1 to 2.9, with the largest event recorded at 20:14 UTC on 24 January. Focal depths remained shallow, between 1 km and 8 km, consistent with activity in the upper crust of the region.

The sequence began with a magnitude 2.0 event at 6 km depth. Subsequent events clustered tightly in both time and space, showing a typical swarm pattern of numerous small shocks without a single dominant mainshock-aftershock decay. Activity peaked during the first evening, with multiple events above magnitude 2.0 occurring within hours. The swarm then gradually declined, ending with a magnitude 2.1 event at 6 km depth on 27 January.

Western Texas lies within the Permian Basin, a major sedimentary province characterized by thick Paleozoic strata overlying Precambrian basement. The basin has experienced increased seismicity since the mid-2000s, largely attributed to fluid injection associated with hydrocarbon production. Wastewater disposal wells, which increase pore pressure along pre-existing faults, represent the primary mechanism for induced events in this area. Depths recorded during the swarm align with the typical range for injection-induced earthquakes in the Delaware and Midland sub-basins.

Historical records indicate sparse natural seismicity in western Texas prior to widespread oil-field development. Since 2000, only two swarms have been documented in the region according to SeismoSight internal classification: one in 2022 and the current 2023 sequence. This low background rate underscores the episodic nature of recent activity and its correlation with industrial operations rather than tectonic loading.

The 2023 swarm exhibited several diagnostic features of induced seismicity, including rapid onset, shallow hypocenters, and a high proportion of events below magnitude 2.0. Such patterns differ from tectonic mainshock-aftershock sequences, which generally display clearer magnitude-frequency distributions and greater depth variation. Continued monitoring by regional networks remains essential for distinguishing natural from anthropogenic contributions in the Permian Basin.

References

• United States Geological Survey Earthquake Catalog
• Texas Bureau of Economic Geology, Seismic Monitoring Reports
• SeismoSight internal swarm classification database