On September 1, 2016 a Mw 5.8 earthquake struck the Pawnee area of north central Oklahoma. The rupture occurred in a region of complex fault interactions at 4 -6 km depth, along a previously unmapped fault called the Sooner Lake Fault. Seismic studies suggest this fault is a near vertical (70-90 degree dip), left lateral strike-slip fault. Despite broad agreement between activities related to hydrocarbon production and induced seismicity, we do not fully understand the linkages between injection, subsurface fluid migration, and pressure build-up along faults. Not every injection well is associated with seismicity, and not every fault in a newly seismic region is reactivated by oil and gas production activities. This study deployed magnetotelluric (MT) instruments to better understand the relationship between induced seismicity and waste water injection. The MT data was acquired across 18 MT stations along a profile line perpendicular to the geoelectric strike of the Sooner Lake Fault. This data was imported into the WingLink software with which an inversion was carried out to image the rupture zone. The resulting MT cross-section clearly imaged an upper layer of conductive sediments and a conductive wedge associated with the rupture zone of the Sooner Lake Fault within the resistive basement. The ~4 km wide base of this conductive wedge is found at ~12 km depth and tappers out upward to a depth of ~6 km. The hypocenters of the earthquakes coincide with the tip of this conductive wedge.Geolog
