Abstract

North Texas started experiencing earthquakes in 2008, which increased in magnitude and frequency from 2011 through mid–2015. Wastewater injection through salt water disposal wells has been tied to inducing these earthquakes. Injection has continued to present day; however, the earthquake occurrence has nearly stopped since mid–2015. Seismologists struggle to explain why earthquakes are associated with some faults and not others in the region. They have focused mainly on the pore-pressure component on induced earthquakes. A recent paper suggests that there is a fluid component that appears to impact the frequency, magnitude, and location of the induced earthquakes. However, millions of gallons of wastewater are being injected in the Fort Worth Basin (FWB) of Texas.

The theory presented here has to do with the structures at the Ordovician Ellenburger Formation level and underlying top of basement level. They outcrop northwest of Austin in Central Texas and structurally dip to the northeast with the deepest point located under the Dallas–Fort Worth (DFW) area. The faults associated with the larger magnitude earthquakes are located where the Ellenburger is near and at its deepest point. Within the Ellenburger, the highest formation pressures are under the DFW area. Here the Ellenburger Formation pressure is also enhanced by the wastewater being injected. Injected fluids will flow from high pressure to lower pressure zones. The injected fluid migration from NE to SW, in an updip direction, provides the lubrication to those structurally updip faults and could explain the lack of seismicity at those faults. The high fault-slip potential faults of the DFW/Venus area are not lubricated by the injected fluids and subject to environmental conditions that appear to impact earthquake frequency and magnitude. By adding a fluid component to the analysis, a better understanding of the timing and pattern of earthquakes is possible and could be relevant to current hydraulic fracturing practices.