Local Earthquakes in the Dallas-Ft. Worth Region

Local Earthquakes in the Dallas-Ft. Worth Region Map of DFW airport, showing location of earthquakes located by the temporary network (yellow triangles), tops and bottom of producing gas wells (white and red circles), and SWD wells (blue squares). The mean of the DFW earthquake location estimates using a linear velocity model is less than a kilometer from the bottom of the south SWD well.
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Injection or removal of fluids in the shallow crust can trigger earthquakes. In October 2008 and May 2009, small earthquakes occurred which were felt by numerous Dallas-Fort Worth (DFW) residents. PASSCAL provided six, three-component broadband seismographs that were operated for two months following the October 2008 earthquakes. Preliminary analysis of these data and regional seismic data [Frohlich et al., 2010] demonstrates that: (1) Between 30 October 2008 and 31 December 2009, approximately 180 earthquakes occurred with probable hypocenters on or near DFW airport property; (2) Eleven of these were locatable by the local network and had hypocenters with focal depths of ~4.4 km situated along a 1.1 km SW-NE line near the south boundary of the DFW airport (Figure); (3) These hypocenters were situated approximately 500 m from a 4.2 km deep saltwater disposal (SWD) well where injection began on 12 September 2008, seven weeks before the first earthquake; (4) The hypocenters and the SWD well were situated near a mapped NE-SW trending subsurface fault, oriented such that slip along this fault was consistent with regional tectonic stresses; and (5) No evidence was found that drilling, hydrofracture, or natural gas production caused the earthquakes. The timing and proximity to the SWD well suggests that fluid injection at the SWD well may have induced the earthquakes. In June 2009, residents of Cleburne, TX, felt a second series of small earthquakes 60 miles south of DFW. Ten seismograph stations were deployed. Preliminary analysis of these data indicates that small earthquakes continued near Cleburne until at least November 2009, and that they also occurred near a SWD well. Following the felt earthquakes local and national news media called attention to the possible relationship between the earthquakes and the ongoing development of natural gas in the Fort Worth Basin. Even though the largest
of the earthquakes had a magnitude of only M3.3, and they seemed unrelated to hydraulic fracturing, groups opposed to the development of tight gas shales considered them as evidence supporting their position. As noted in the Wall Street Journal, “the quake concerns come at a sensitive time for the industry, which is battling proposed legislation in Congress that would more heavily regulate hydraulic fracturing.”
</p><p>References
</p><p>Frohlich, C., E. Potter, C. Hayward, and B. Stump, Dallas-Fort Worth earthquakes coincident with activity associated with natural gas production, Leading Edge, 29, 270-275, 2010.</p>

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