Surface Deformation of North-Central Oklahoma Related to the 2016 Mw 5.8 Pawnee Earthquake from SAR Interferometry Time Series

The 3 September 2016 M-w 5.8 Pawnee earthquake shook a large area of north-central Oklahoma and was the largest instrumentally recorded earthquake in the state. We processed Synthetic Aperture Radar (SAR) from the Copernicus Sentinel-1A and Sentinel-1B and Canadian RADARSAT-2 satellites with interferometric SAR analysis for the area of north-central Oklahoma that surrounds Pawnee. The interferograms do not show phase discontinuities that would indicate surface ruptures during the earthquake. Individual interferograms have substantial atmospheric noise caused by variations in radar propagation delays due to tropospheric water vapor, so we performed a time-series analysis of the Sentinel-1 stack to obtain a more accurate estimate of the ground deformation in the coseismic time interval and the time variation of deformation before and after the earthquake. The time-series fit for a step function at the time of the Pawnee shows about 3 cm peak-to-peak amplitude of the coseismic surface deformation in the radar line of sight with a spatial pattern that is consistent with fault slip on a plane trending east-southeast. This fault, which we call the Sooner Lake fault, is parallel to the west-northwest nodal plane of the U.S. Geological Survey National Earthquake Information Center moment tensor solution. We model the fault plane by fitting hypoDD-relocated aftershocks aligned in the same trend. Our preferred slip model on this assumed fault plane, allowing only strike-slip motion, has no slip shallower than 2.3 km depth, an area of moderate slip extending 7 km along strike between 2.3 and 4.5 km depth (which could be due to aftershocks and afterslip), and larger slip between 4.5 and 14 km depth extending about 12 km along strike. The large slip below the 4.5 km depth of our relocated hypocenter indicates that the coseismic rupture propagated down-dip. The time-series results do not show significant deformation before or after the earthquake above the high atmospheric noise level within about 40 km of the earthquake rupture.