Injection-Induced Seismicity and Fault-Slip Potential in the Fort Worth Basin, Texas

The rate of seismicity in the hydrocarbon-producing FortWorth 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. Supplemental Content: Tabulation of data used for the interpretation of S-Hmax in the Fort Worth basin.