Characteristics of Induced/Triggered Earthquakes during the Startup Phase of the Guy–Greenbrier Earthquake Sequence in North–Central Arkansas

ABSTRACT Between August 2010 and June 2011, an intense sequence of induced earthquakes occurred along the Guy–Greenbrier fault in central Arkansas due to fluid injection at nearby waste disposal wells. A previous study by Horton (2012), limited to ∼1000 earthquakes having M D >∼2.0, illuminated the ∼13  km fault. We present an updated catalog of 17,395 earthquakes that is complete between 0≤ M L ≤4.4 between August 2010 and 20 October 2010, with earthquakes located using an updated 1D velocity model for the region. The inclusion of the small‐magnitude events reveals that seismicity starts below the SRE injection well a month earlier than estimated using only M D >2 events. During this period of time, the seismicity migrated from north to south, enhancing the resolution of three joined sections that form the northern ∼7.3  km portion of the fault, which plunges southward. The seismogenic zone covers the lower portion of the Paleozoic sedimentary layers and extends into the crystalline Precambrian basement (∼3  km z M L >3 events constrained within the basement. A b ‐value of 1.01 was obtained for the updated catalog during this period, with the b ‐value varying between 1.37 and 0.72 for different clusters of events. The seismicity pattern at depth is coincident with structural geologic features observed within the Fayetteville Shale (at ∼1500  m depth).