Ground Motion and Hazard from Induced Seismicity
Gail Atkinson, Western University
Induced seismicity significantly increases seismic hazard in low-to-moderate seismicity regions. In the central U.S., induced-seismicity sources are mostly wastewater disposal wells, whereas in western Canada much of the seismicity is associated with hydraulic fracturing. In either case, the hazard can be modeled by treating the activity as an added seismic source zone in the context of a probabilistic seismic hazard analysis (PSHA); for a future source, the hazard is conditioned on the probability of activation. In this presentation, PSHA concepts for induced-seismicity hazards are overviewed and an example is presented. The induced-seismicity hazard depends on the activation probability, the b-value of the initiated sequence, the ground-motion prediction equations, Mmin and Mmax. Uncertainty in the value of the key parameters implies large uncertainty (more than an order of magnitude) in the likelihood of strong shaking.
The ground-motion prediction equations (GMPEs) are a key element in any hazard evaluation. Most GMPEs developed for natural events do not have appropriate near-distance scaling for induced events, as the focus for their development (and thus their functional form) was tuned for larger, deeper events. The most important issues for induced-seismicity GMPEs are the stress drop and how it scales with focal depth, and depends on whether the event is a mainshock or aftershock, as well as the near-distance saturation behavior for ground motion from small-to-moderate events. Recent studies are used to constrain these parameters and show their implications for ground motions from induced events.
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In this webinar, you will learn about: