Rupture Model of the 2016 M5.8 Pawnee Induced Earthquake

Morgan P. Moschetti, Stephen Hartzell, & Robert B. Herrmann

Published August 8, 2018, SCEC Contribution #8342, 2018 SCEC Annual Meeting Poster #088

The 2016 M5.8 earthquake near Pawnee, Oklahoma is the largest induced earthquake in Oklahoma and is the largest wastewater-injection-induced earthquake the in the U.S. We invert regional and teleseismic waveforms to produce a rupture model of the time-evolution of coseismic slip. Use of empirical Green's functions for modeling the regional wave propagation allows us to invert waveforms to higher frequencies (0.5-3 Hz) than previous slip models, providing additional information about the evolution of the earthquake rupture and its potential interaction with injection related pore pressure perturbations. The rupture model indicates that slip was largely confined to two-shallow and deep-slip patches. Rupture initiated near 5 km depth, with initial rupture towards the surface and confined within the shallow slip patch. About 1 s into the rupture, our model indicates that slip initiated at a greater depth (z>8 km). About one third of the moment of the earthquake rupture occurred at this greater depth. The relation of coseismic slip to the region of pore pressure perturbation is of great interest for understanding the magnitudes of induced-earthquakes. In particular, some models of maximum magnitude for induced earthquakes assume that earthquakes will be limited to the region where pore pressures are perturbed by industrial activities. The observation that rupture can initiate and propagate outside of regions of pore-pressure perturbation implies that the magnitude of an induced earthquake is not controlled by injection operations. Comparison of the slip model with inferred distributions of pore pressure (from previous coupled hydrologic-geomechanical modeling efforts; Barbour et al., 2017) and with aftershock distributions suggests that the Pawnee earthquake ruptured beyond the zone of perturbed pore pressure influenced by wastewater injection. This observation is consistent with recent numerical modeling work and has important consequences for forecasting the size of and hazards associated with injection-induced earthquakes.

Key Words
Induced seismicity, source modeling

Citation
Moschetti, M. P., Hartzell, S., & Herrmann, R. B. (2018, 08). Rupture Model of the 2016 M5.8 Pawnee Induced Earthquake. Poster Presentation at 2018 SCEC Annual Meeting.

Related Projects & Working Groups
Seismology