INVESTIGATION OF FAULTING PROCESSES OF TWO M5 EARTHQUAKE SEQUENCES IN OKLAHOMA

Abstract

I investigate the stress interaction inside different earthquake clusters to better understand the factors that might drive and control seismicity. I examine a catalog of 6226 events that have been relocated using the GrowClust method. The relocated earthquakes show that the Prague earthquake sequence occurred on a number of anastomosing faults, I also find that the fault propagates up into the Arbuckle formation and shows a pattern that mimics observed structure in the Hunton formation. I then examine the stress drop of the Prague earthquake sequence and find a median stress drop of 2.21 MPa, with low stress drop occurring in the shallow region of 1.8 to 3 km, as well as higher overall stress drops located on the fault activated by the aftershock. I then examine the Pawnee cluster, specifically within the Watchorn, Labette, and Sooner Lake fault systems and the effect of precursory activities on the September 3, 2016 M5.8 Pawnee earthquake. I obtain fault plane solutions for earthquakes with sufficient azimuthal coverage using the HASH algorithm, and then performed Coulomb stress analysis on both seismogenic faults and individual nodal planes. Our results found that the three M≥3.0 foreshocks exerted a cumulative Coulomb stress change increase of 68 to 198 kPa at the mainshock hypocenter and promoted failure for most aftershocks within 2 km of the mainshock. The Coulomb stress change of 500 kPa exerted by the mainshock also promoted failure for most aftershocks within the conjugate fault system. The combined results of these studies suggest that earthquake interaction should be fully considered in hazard assessment for induced seismicity.