Abstract

We utilize quantitative risk assessment (QRA) to calculate the conditional probability of slip on mapped faults in response to injection-related increases in pore pressure in north-central Oklahoma (USA) where widespread injection of produced saltwater has triggered thousands of small to medium-sized earthquakes in the past 7 yr. The conditional probability incorporates the uncertainty in each Mohr-Coulomb parameter (stress tensor, pore pressure, coefficient of friction, and fault orientation) through QRA. The result is a cumulative distribution function of the pore pressure required to cause slip on each fault segment. The results can be used to assess the probability of induced slip on a known fault from a given injection-related pore pressure increase. After dividing north-central Oklahoma into six study areas, we invert earthquake focal plane mechanisms in each area to constrain the orientation and relative magnitude of the principal stresses. The QRA identifies the potential for slip on the fault that produced the M 5.6 Prague earthquake in 2011 and the northeastern extension of a mapped fault associated with the M 5.1 Fairview earthquake sequence that occurred in early 2016, and, had the 289°-striking fault of the September 2016 M 5.8 Pawnee event been mapped, it would have been identified as potentially active.

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