Rupture Model of the 2016 M5.8 Pawnee Earthquake From Regional and Teleseismic Waveforms: Potential Influence of Pore Pressure Perturbations on Rupture Dynamics

Date: 4/26/2019

Time: 06:00 PM

Room: Fifth Avenue

The 2016 M5.8 earthquake near Pawnee, Oklahoma is the largest induced earthquake in Oklahoma and is the largest earthquake induced by wastewater injection in the U.S. We invert regional and teleseismic waveforms and compute apparent source time functions to produce a finite-fault model of earthquake rupture. Use of aftershocks as empirical Green's functions allows us to use 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 pore fluids. The rupture model indicates that earthquake rupture occurred in three stages and was confined to disconnected 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 commenced on the deeper part of the fault (>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. Slip on the deeper part of the fault occurred beneath most of the aftershocks and at greater depths than the vast majority of regional seismicity. Shallow slip largely occurred within zones where previous pore pressure modeling indicates greater perturbations. The correspondence of slip patches on the shallow part of the fault and pore pressure perturbations, as well as the inference of deeper rupture for the M5.8 earthquake than for regional events, suggests a unique rupture process, which may be explained by the influence of perturbed pore pressures. 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.

Presenting Author: Morgan P. Moschetti

Authors