In recent years, numerous small earthquakes have occurred near the town of Pecos in West Texas; however, when this activity began and whether it was caused by increased petroleum industry activity has been uncertain because prior to 2017 there were few permanent seismograph stations in the region. We identify and locate earthquakes using data recorded since 2000 at TXAR, a sensitive 10-station seismic array situated about 240 km south of Pecos. We thus show that in 2007, one earthquake occurred near Pecos, in 2009 several more occurred, and subsequently, activity has increased considerably, with more than 2000 events identified in 2017. A time-of-day and year-by-year analysis identifies geographic areas in West Texas where events are likely to be natural earthquakes and quarry blasts. However, for the Pecos events, annual seismicity rates increase along with annual volumes of petroleum production and fluid waste disposal, suggesting a causal link. Analysis of seismograms collected by the EarthScope Transportable Array indicates that the 2009 earthquakes had focal depths of 4.0-5.2 km below sea level, within or just below strata where petroleum is produced and/or wastewater is injected. The largest earthquake to date had magnitude M L 3.7, but the recent high activity rates suggest that greater magnitudes may be possible. For the years 2000-2017, we provide a catalog of 10,753 epicenters of seismic events recorded at TXAR.

No abstract

The rate of seismicity in the hydrocarbon‐producing Fort Worth Basin of north‐central Texas, which underlies the Dallas–Fort Worth metropolitan area, increased markedly from 2008 through 2015, coinciding spatiotemporally with injection of 2 billion barrels of wastewater into deep aquifers. Although the rate of seismicity has declined with injection rates, some earthquake sequences remained active in 2018 and new clusters have developed. Most of this seismicity occurred away from regionally mapped faults, challenging efforts to constrain the continuing hazards of injection‐induced seismicity in the basin. Here, we present detailed new models of potentially seismogenic faults and the stress field, which we use to build a probabilistic assessment of fault‐slip potential. Our new fault map, based on reflection seismic data, tens of thousands of well logs, and outcrop characterization, includes 251 basement‐rooted normal faults that strike dominantly north‐northeast, several of which extend under populated areas. The updated stress map indicates a relatively consistent north‐northeast–south‐southwest azimuth of the maximum horizontal principal stress over seismically active parts of the basin, with a transition from strike‐slip faulting in the north to normal faulting in the southeast. Based on these new data, our probabilistic analysis shows that a majority of the total trace length of the mapped faults have slip potential that is equal to or higher than that of the faults that have already hosted injection‐induced earthquake sequences. We conclude that most faults in the system are highly sensitive to reactivation, and we postulate that many faults are still unidentified. Ongoing injection operations in the region should be conducted with these understandings in mind.

The Jurassic to Cretaceous sedimentary rocks of the Surat Basin in southeast Queensland host a significant volume of coal seam gas resources. Consequently, knowledge of the in situ stress is important for coal permeability enhancement and wellbore stability. Using wireline log data and direct stress measurements, we have calculated stress orientations from 36 wells and stress magnitudes from 7 wells across the Surat Basin. Our results reveal a relationship between high tectonic stress and proximity to structures within the underlying “basement” rocks. The influence of tectonic stresses is diminished with depth in areas with thicker sedimentary cover that are relatively far from the basement structures. We suggest that this relationship is due to the redistribution of in situ stresses around areas where basement is shallower and where basement structures, such as the Leichhardt‐Burunga Fault System, are present. This behavior is explained by a lower rigidity in the thickest basin cover, which reduces the ability to maintain higher tectonic stress. Over the entire Surat Basin, a significant amount of variability in in situ stress orientation is observed. The authors attribute this stress variability to complex plate boundary interactions on the northern and eastern margins of the Indo‐Australian Plate.