CHARACTERIZATION OF NEWLY REACTIVATED FAULTING AND POTENTIAL SHAKING HAZARD TO NATIONAL STRATEGIC INFRASTRUCTURE NEAR CUSHING OKLAHOMA (Invited Presentation)

The sharp increase in seismicity over a broad region of central Oklahoma has raised concern regarding the source of the activity and its potential hazard to local communities and critical energy industry infrastructure. A total of 45 moderate-sized earthquakes (Mw > 4.0) occurred in Oklahoma in 2014 and 2015. Six of these struck south of Cushing, Oklahoma, near the largest crude oil storage facility in the world. The Oklahoma Corporation Commission (OCC) took actions to limit wastewater disposal based on concern over the shaking hazard posed to this national strategic infrastructure.

In this study we review efforts to monitor and characterize two earthquake sequences near Cushing Oklahoma in October 2014 and October 2015. We apply a multiple-event relocation method to precisely identify the location and depth of reactivated faulting and determine regional moment tensor (RMT) source parameters for the largest and best-recorded earthquakes. Combined analysis of the spatial distribution of earthquakes and RMT focal mechanisms indicate reactivation of two previously unmapped left-lateral strike-slip faults in the shallow crystalline basement. Furthermore, Coulomb failure stress change calculations (ΔCFS), incorporating the relocated seismicity and slip distribution determined from RMTs, suggest that the Wilzetta-Whitetail fault zone south of Cushing, Oklahoma, could produce a large, damaging earthquake comparable to the 2011 Prague Oklahoma Mw 5.6 event. We use the USGS PAGER system to model the shaking distribution and amplitude for an Mw 5.6 earthquake on the newly identified Cushing fault. The scenario earthquake could potentially cause very strong shaking levels (MMI VII-VIII) in the epicentral region. Results from this study are necessary first order observations required to assess the potential hazards of individual faults in Oklahoma.