Observations of static Coulomb stress triggering of the November 2011M5.7 Oklahoma earthquake sequence

Abstract In November 2011, aM5.0 earthquake occurred less than a day before aM5.7 earthquake near Prague, Oklahoma, which may have promoted failure of the mainshock and thousands of aftershocks along the Wilzetta fault, including aM5.0 aftershock. TheM5.0 foreshock occurred in close proximity to active fluid injection wells; fluid injection can cause a buildup of pore fluid pressure, decrease the fault strength, and may induce earthquakes.Keranen et al. [ ] links theM5.0 foreshock with fluid injection, but the relationship between the foreshock and successive events has not been investigated. Here we examine the role of coseismic Coulomb stress transfer on earthquakes that follow theM5.0 foreshock, including theM5.7 mainshock. We resolve the static Coulomb stress change onto the focal mechanism nodal plane that is most consistent with the rupture geometry of the threeM ≥ 5.0 earthquakes, as well as specified receiver fault planes that reflect the regional stress orientation. We find that Coulomb stress is increased, e.g., fault failure is promoted, on the nodal planes of ~60% of the events that have focal mechanism solutions, and more specifically, that theM5.0 foreshock promoted failure on the rupture plane of theM5.7 mainshock. We test our results over a range of effective coefficient of friction values. Hence, we argue that theM5.0 foreshock, induced by fluid injection, potentially triggered a cascading failure of earthquakes along the complex Wilzetta fault system.