Magnetotelluric Imaging Suggests Minimal Downward Saline Fluid Migration in the Region of the Largest‐Known Injection‐Induced Earthquake, Oklahoma

Abstract Regions of intra‐sedimentary fluid injections, such as wastewater disposal, CO 2 storage, and enhanced geothermal systems, commonly record near‐ and far‐field basement‐hosted earthquakes, highlighting complex fluid migration pathways and triggering mechanisms. Here, we present results from a rapid‐response magnetotelluric geophysical survey of the 2016 M w 5.8 Pawnee, Oklahoma earthquake epicenter region, the largest recorded injection‐induced event, that aimed to illuminate the fluid migration pathways from the sedimentary Arbuckle carbonate injection zones into the intrabasement hypocentral zones. Intriguingly, our resistivity model reveals a broadly resistive seismogenic basement, relatively conductive shallow basement and Arbuckle intervals, overlain by discontinuous but highly conductive post‐Arbuckle units. Porosity estimates indicate extremely low (2 km depths, contrasting with intermediate porosity in the fractured top‐basement and Arbuckle unit, and highly porous (10%–30%) post‐Arbuckle sequences. Arbuckle‐to‐basement fracture distribution in core samples shows a prominent decrease in fracture intensities across the basement‐sedimentary interface, representing a fluid flow barrier, and greater intensities in the Upper‐Arbuckle and deeper basement levels. These observations present new evidence suggesting large‐scale confinement of injected saline fluids to flow units within the Arbuckle, and potentially significant lateral dissipation of the fluids than previously thought. The results support a remote triggering model for the 2016 event and provide useful insights for understanding seismic triggering in similar fluid‐injection settings.