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Comment on "How will induced seismicity in Oklahoma respond to decreased saltwater injection rates?" by C. Langenbruch and M. D. Zoback.

ABSTRACT: The state of Oklahoma has experienced an unprecedented increase in earthquake activity since 2009, likely driven by large-scale wastewater injection operations. Statewide injection rates peaked in early 2015 and steadily decreased thereafter, approximately coinciding with collapsing oil prices and regulatory action. If seismic activity is primarily driven by fluid injection, a noticeable seismogenic response to the decrease in injection rates is expected. Langenbruch and Zoback suggest that "the probability of potentially damaging larger events, should significantly decrease by the end of 2016 and approach historic levels within a few years." We agree that the rate of small earthquakes has decreased toward the second half of 2016. However, their specific predictions about seismic hazard require reexamination. We test the influence of the model parameters of Langenbruch and Zoback based on fits to observed seismicity distributions. The results suggest that a range of realistic aftershock decay rates and b values can lead to an increase in moderate earthquake probabilities from 37 to 80% in 2017 without any further alteration to the model. In addition, the observation that all four M ≥ 5 earthquakes to date occurred when injection rates were below the triggering threshold of Langenbruch and Zoback challenges the applicability of the model for the most societally significant events.

SUBMITTER: Goebel THW

PROVIDER: S-EPMC5550223 | biostudies-other | 2017 Aug

REPOSITORIES: biostudies-other

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Project description:PurposeTo determine whether there is a difference in the risk of endophthalmitis after an intravitreal steroid injection compared with an anti-vascular endothelial growth factor (VEGF) agent injection.DesignRetrospective cohort study.ParticipantsA total of 75,249 beneficiaries in a large national US medical claims database representing 406 380 intravitreal injections.MethodsData were searched for all intravitreal injections (Current Procedural Terminology 67028) performed between 2003 and 2012. Cohorts were created on the basis of injections using anti-VEGF agents (bevacizumab, ranibizumab, aflibercept, and pegaptanib) and intraocular steroids (triamcinolone and dexamethasone). Endophthalmitis was defined as having a new endophthalmitis diagnosis (International Classification of Diseases 9th Revision 360.0x) and a "tap-and-inject" procedure (Current Procedural Terminology 67015, 67025), a vitrectomy (67036), or an intravitreal antibiotic injection on the same day, between 1 and 14 days post-injection. Exclusion occurred for any history of endophthalmitis, <6 months in the plan, or <1 month follow-up. The main outcome measure was the odds of endophthalmitis using logistic regression while controlling for injection-associated diagnosis, age, race, and gender.ResultsA total of 387,714 anti-VEGF injections and 18 666 steroid intravitreal injections were performed and followed by 73 (rate=0.019% or 1/5283 anti-VEGF injections) and 24 (rate=0.13% or 1/778 steroid injections) cases of endophthalmitis, respectively. After controlling for diagnosis, age, race, and gender, the odds ratio (OR) for endophthalmitis occurring was 6.92 (95% confidence interval, 3.54-13.52, P<0.001) times higher post-steroid injection compared with anti-VEGF injections.ConclusionsThe rate of endophthalmitis post-intravitreal steroid injection in a national cohort was 0.13% (1/778 injections). This rate conferred a significantly increased OR of 6.92 for endophthalmitis compared with anti-VEGF agents.

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Comment on "How will induced seismicity in Oklahoma respond to decreased saltwater injection rates?" by C. Langenbruch and M. D. Zoback.

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