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Abstract:
An earthquake sequence in western Canada exhibits resurgent aftershocks, possibly in response to persistent, post-mainshock saltwater disposal. Here, we reduce uncertainty in mainshock source parameters with joint inference of interferometric synthetic aperture radar and seismic waveform data, showing that the mainshock nucleated at about 5-km depth, propagating up-dip toward the injection source, and arresting at about 2-km depth. With precise hypocenter relocations and Bayesian inference, we reveal that four subparallel faults were reactivated, likely part of a regional, basement-rooted graben system. The reactivated faults appear to be truncated by a conjugate fault that is misoriented for slip in the present-day stress regime. The nearest saltwater disposal well targets a permeable Devonian reef in direct contact with Precambrian basement, atop a ridge-like uplift. Our observations show that a fault system can be activated more than a decade after saltwater disposal initiation, and continued disposal may lead to a resurgence of seismicity.
