Pore Pressure Threshold and Fault Slip Potential for Induced Earthquakes in the Dallas‐Fort Worth Area of North Central Texas

Earthquakes were induced in the Fort Worth Basin from 2008 through 2020 by increase in pore pressure from injection of oilfield wastewater (SWD). In this region and elsewhere, a missing link in understanding the mechanics of causation has been a lack of comprehensive models of pore pressure evolution (ΔPp) from SWD. We integrate detailed earthquake catalogs, ΔPp, and probabilistic fault slip potential (FSP) and find that faults near large‐scale SWD operations became unstable early, when ΔPp reached ∼0.31 MPa and FSP reached 0.24. Faults farther from SWD became unstable later, when FSP reached 0.17 and at much smaller ΔPp. Earthquake sequences reactivated with mean ΔPp of ∼0.05 MPa. The response of faults shows strong variability, with many remaining stable at higher ΔPp and few that became seismogenic at smaller changes. As ΔPp spread regionally, an ever‐increasing number of faults were impacted and the most sensitive became unstable. Increases in subsurface fluid pressure following years of deep disposal of oilfield wastewater are widely accepted to have caused earthquakes from 2008 through 2020 in the Fort Worth Basin (FWB) of north‐central Texas, underlying the population centers of the Dallas‐Fort Worth metropolitan area, were caused by increases in subsurface fluid pressure following years of deep disposal of oilfield wastewater. No earthquakes were reported in the area prior to 2008. Increasing the fluid pressure in subsurface reservoirs containing faults can cause the faults to become unstable and slip, producing earthquakes. A missing link to understanding the cause of these earthquakes is not knowing how much the fluid pressures have increased, and which geographic areas have been affected. This research combines several lines of evidence to show how the fluid pressure from deep injection increased over time and space leading to the increase in earthquakes. The changes in fluid pressure that made the faults unstable is surprisingly low, the subsurface region affected by the pressure change is large, and the natural sensitivity of the faults has significant variability. This work provides a critical component to understanding the specific conditions leading to induced seismicity in the FWB, which can be applied to similar cases elsewhere. Onset of induced earthquakes in the Fort Worth Basin occurred with pore pressure increases of ∼0.01–0.36 MPa from wastewater injectionPore pressure increase in the slip potential of the seismogenic faults indicates that the instability threshold is 17%–24% for this systemSlip potential of faults that became seismogenic is similar to those that have not ruptured, indicating inherent differences in sensitivity Onset of induced earthquakes in the Fort Worth Basin occurred with pore pressure increases of ∼0.01–0.36 MPa from wastewater injection Pore pressure increase in the slip potential of the seismogenic faults indicates that the instability threshold is 17%–24% for this system Slip potential of faults that became seismogenic is similar to those that have not ruptured, indicating inherent differences in sensitivity