Hydraulic Fracturing, Fault System Architecture, and the Details of Anthropogenic Earthquakes in the Post-Pennsylvanian Delaware Basin of West Texas

Abstract Since about 2009, oil and gas production activities in the Delaware Basin of West Texas and southeast New Mexico have caused a rapid increase in rates of seismicity. This seismicity has been driven primarily by pore fluid pressure increases caused by subsurface injection of both waste saltwater and hydraulic fracturing fluids. High-quality teleseismic monitoring shows that earthquakes have been concentrated in previously dormant fault systems. The analysis of the timing of earthquake occurrence and magnitudes in two southern Delaware Basin fault systems indicates that continuous versus sporadic seismic energy release corresponds with continuous versus sporadic hydraulic fracturing and saltwater disposal activities proximal to the faults, respectively. Treating earthquake magnitudes as a proxy for fault displacement reveals that fault reactivation occurs in patterns that resemble segmented faults both hard and soft linked and that this distribution is likely a faithful representation of the fundamental architecture of the reactivated fault and not simply a function of pore pressure perturbation. The spatial distribution of earthquake magnitudes in the two fault systems illuminates the strong control that preexisting fault system architecture exerts on fault reactivation. Larger earthquakes tend to occur in larger, likely hard linked, fault segments. This suggests that a priori knowledge of a fault system’s architecture can provide some degree of predictability for induced seismicity.