Rupture Process of the Mw 5.8 Pawnee, Oklahoma, Earthquake from Sentinel-1 InSAR and Seismological Data

Since 2009, Oklahoma has experienced a soar in induced seismicity, a side effect of extensive saltwater injection into subsurface sedimentary rocks. The seismic hazard entailed by these regional-scale injection operations is, however, difficult to assess. The 3 September 2016 M-w 5.8 Pawnee earthquake is the largest since the increase of seismic activity. The event was preceded by an m(b) 3.2 foreshock two days prior, and changes in injection rates have been reported on wastewater disposal wells located less than 10 km from the epicenter, suggesting that the earthquake may have been induced. Using Sentinel-1 spaceborne interferometric synthetic aperture radar, we unambiguously show that the earthquake produced peak-to-peak line-of-sight displacement of 3 cm at the surface. Kinematic inversion of geodetic and seismological data shows that the main seismic rupture occurred between a depth of 4 and 9 km, over a length of 8 km, with slip reaching at least 40 cm. The causative fault is entirely buried within the Precambrian basement, that is, well beneath the Paleozoic sedimentary pile where injection is taking place. Potentially seismogenic faults in the basement of Oklahoma being poorly known, the risk of M-w >= 6 events triggered by fluid injection remains an open question.