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Local Earthquakes in the Dallas-Ft. Worth Region
Brian Stump (Southern Methodist University), Cliff Frohlich (University of Texas at Austin), Chris Hayward (Southern
Methodist University), Eric Potter (University of Texas at Austin)
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.”
References
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.
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.
2010 IRIS Core Programs Proposal | Volume II | Earthquake Source Studies | II-51