COULOMB STRESS ANALYSIS OF THE PAWNEE TRIPLE JUNCTION AND THE 2016 5.8MW RUPTURE ALONG THE SOONER LAKE FAULT

Induced seismicity has been identified as a major concern in areas of hydrocarbon production, subsurface carbon sequestration, and enhanced geothermal systems, among others. In Oklahoma, the frequency of earthquakes with a magnitude of 3.0 or greater surged from just 2 per year in 2009 to 579 in 2014, peaking at 903 in 2015 before decreasing to 194 by 2018 and 16 in 2023. Wastewater injection was widely regarded as a significant contributor to the dramatic rise in seismic activity across the state. Most of the seismic activity has been located in the north-central portion of the state. An area of interest is the Pawnee Triple Junction (PTJ) in North Central Oklahoma, which consists of the Sooner Lake Fault (SLF), the Stillwater Fault (SWF), and a newly identified fault zone informally named the Northeast Trending Fault Zone (NEFZ). This region was the site of Oklahoma’s largest recorded earthquake—a magnitude 5.8 tremor in 2016—along the SLF. One hypothesis is that aseismic slip along the NEFZ, resulting from wastewater injection, triggered the rupture along the SLF. In order to investigate stress interactions in the vicinity of the PTJ, a Coulomb stress analysis is being conducted with a goal of assessing the stress transfer related to aseismic slip along the NEFZ. Geophysical techniques are being employed in this analysis, utilizing previously collected seismic data from the Oklahoma Geological Survey to better identify fault geometries and complexity. Software such as ArcGIS Pro, Coulomb modeling in MATLAB, and Fault Slip Potential 2.0 are being used in the study to better understand the interplay of stress and seismicity in the region. The results of the analysis will; quantify the amount of slip required along the NEFZ to load the SLF enough to trigger fault slip, and to assess the time-dependent aftershock distribution after slip along the SLF. These findings will offer crucial insights into the underlying factors that triggered this significant earthquake and help better explain the observed aftershock pattern in the area.