Seismic Swarm Analysis: Coalson Draw, Texas, November 2023

The S20231108.1 earthquake swarm was recorded in Coalson Draw, Texas, beginning at 15:19 on 7 November 2023 and concluding at 08:30 on 9 November 2023. Over this 41-hour, 11-minute period, 142 events were registered. Analysis of the first 100 events reveals a rapid onset of activity, with magnitudes ranging from 0.5 to 5.2 and focal depths predominantly between 4 km and 8 km. The sequence featured an initial cluster of small events followed by a peak magnitude 5.2 shock on 8 November at 10:27:49, accompanied by several events above magnitude 3.0 within minutes. Subsequent activity showed a gradual decline in both frequency and magnitude, with most later events below magnitude 2.5. Depths remained consistent in the shallow crustal range, indicating a localized source zone. Coalson Draw lies within the Permian Basin of West Texas, a large sedimentary province characterized by thick Paleozoic carbonate and clastic sequences overlying Precambrian basement. The basin hosts numerous normal and strike-slip faults that can be reactivated by changes in pore pressure. Regional geology includes the Delaware Basin sub-province, where Devonian through Permian strata reach thicknesses exceeding 3 km. Historical seismicity in this area has increased notably since the expansion of unconventional hydrocarbon production, consistent with patterns of induced seismicity driven by wastewater injection into deep disposal wells. Since 1 January 2000, four swarms have occurred in the immediate region. One swarm took place in 2022, while three occurred in 2023, highlighting a recent uptick in clustered activity. The November 2023 swarm fits within this pattern of episodic, shallow seismicity. The temporal distribution of the first 100 events shows the majority occurring within the first 12 hours after the initial shock, with magnitudes clustering between 1.5 and 2.5. Depths averaged approximately 6 km, suggesting rupture along a shallow fault segment. No events exceeded magnitude 5.2, and the sequence lacked a clear aftershock decay typical of larger tectonic mainshocks, reinforcing its swarm-like character.

References

SeismoSight internal swarm classification S20231108.1 USGS Earthquake Catalog (historical regional data) Texas Bureau of Economic Geology, Permian Basin tectonic framework reports