Earthquake swarms of complex seismotectonic features in West Texas, USA.

As part of the intraplate tectonic regime within the continental US, the seismicity rate in Texas is expected to be low. However, the seismicity rate in West Texas has steadily increased since 2009, and significantly accelerated since 2020 with the Texas Seismological Network (TexNet) reporting (http://catalog.texnet.beg.utexas.edu) 49 M≥4 earthquakes (all after 2020) and 3 M≥5 earthquakes (all after 2022).

Two of the largest of these events, M5.4 (2022-11-16, 21:32:44 UTC) and M5.2 (2023-11-08, 10:27:49 UTC) are part of the Coalson Draw sequence, and very close to each other (separated by <3km epicentral distance). They occur in the shallower part of seismicity defining a complex seismogenic structure apparently spanning ~5 km in depth and stretching across the basin-basement interface at about 5 km depth. Using a multi-scale precise, probabilistic location algorithm (NonLinLoc-SSST-coherence) and waveform moment tensor inversion, we resolve the complex seismogenic structure as composed of a series of possibly linked, approximately east-west normal faulting systems with varying but sub-parallel fault geometries.

Only ~11km to the northwest of the Coalson Draw sequence, the earlier M4.9 (2020-03-26, 15:16:27 UTC) Mentone earthquake sequence includes the first M4+ events to occur in the Delaware Basin. In contrast to the Coalson Draw sequence, all available source mechanisms for the Mentone sequence are similar while relocated seismicity forms a WSW-ENE trending, steeply south dipping plane over a depth interval of ~2 km around or above the basement, suggesting a relatively simple and uniform fault geometry.