title: Causal factors for seismicity near Azle, Texas.
abstract: In November 2013, a series of earthquakes began along a mapped ancient fault system near Azle, Texas. Here we assess whether it is plausible that human activity caused these earthquakes. Analysis of both lake and groundwater variations near Azle shows that no significant stress changes were associated with the shallow water table before or during the earthquake sequence. In contrast, pore-pressure models demonstrate that a combination of brine production and wastewater injection near the fault generated subsurface pressures sufficient to induce earthquakes on near-critically stressed faults. On the basis of modelling results and the absence of historical earthquakes near Azle, brine production combined with wastewater disposal represent the most likely cause of recent seismicity near Azle. For assessing the earthquake cause, our research underscores the necessity of monitoring subsurface wastewater formation pressures and monitoring earthquakes having magnitudes of ∼M2 and greater. Currently, monitoring at these levels is not standard across Texas or the United States.
authors.affiliation: Huffington Department of Earth Sciences, Southern Methodist University, Dallas, Texas 75275, USA.
authors.forename: Matthew J
authors.initials: MJ
authors.lastname: Hornbach
authors.affiliation: Huffington Department of Earth Sciences, Southern Methodist University, Dallas, Texas 75275, USA.
authors.forename: Heather R
authors.initials: HR
authors.lastname: DeShon
authors.affiliation: USA Geological Survey, 345 Middlefield Road, MS977, Menlo Park, California 94025, USA.
authors.forename: William L
authors.initials: WL
authors.lastname: Ellsworth
authors.affiliation: Huffington Department of Earth Sciences, Southern Methodist University, Dallas, Texas 75275, USA.
authors.forename: Brian W
authors.initials: BW
authors.lastname: Stump
authors.affiliation: Huffington Department of Earth Sciences, Southern Methodist University, Dallas, Texas 75275, USA.
authors.forename: Chris
authors.initials: C
authors.lastname: Hayward
authors.affiliation: Institute for Geophysics, The University of Texas at Austin, Austin, Texas 78758-4445, USA.
authors.forename: Cliff
authors.initials: C
authors.lastname: Frohlich
authors.affiliation: Huffington Department of Earth Sciences, Southern Methodist University, Dallas, Texas 75275, USA.
authors.forename: Harrison R
authors.initials: HR
authors.lastname: Oldham
authors.affiliation: Department of Petroleum and Geosystems Engineering, The University of Texas at Austin, Austin, Texas 78712-2100, USA.
authors.forename: Jon E
authors.initials: JE
authors.lastname: Olson
authors.affiliation: Huffington Department of Earth Sciences, Southern Methodist University, Dallas, Texas 75275, USA.
authors.forename: M Beatrice
authors.initials: MB
authors.lastname: Magnani
authors.affiliation: Huffington Department of Earth Sciences, Southern Methodist University, Dallas, Texas 75275, USA.
authors.forename: Casey
authors.initials: C
authors.lastname: Brokaw
authors.affiliation: USA Geological Survey, 345 Middlefield Road, MS977, Menlo Park, California 94025, USA.
authors.forename: James H
authors.initials: JH
authors.lastname: Luetgert