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Discriminating Natural and Injection-Induced Earthquakes in the Presence of Uncertainty: A Case Study in Alberta, Canada

Description: 

Ever since Davis and Frohlich proposed criteria for recognizing injection-induced earthquakes, three decades ago, the question of whether a particular earthquake (or earthquake sequence) was natural or induced has continued to present controversies and challenges for seismologists. Factors that are usually considered include spatiotemporal correlation with injection operations, location of known faults, prior levels of seismicity activity, modelled stress changes at the hypocenter, existence of permeable pathways, focal depth and source mechanism. A recent proposed scheme uses a questionnaire to assess both the likelihood that an event was induced as well as the strength of the available evidence. A sequence of seismicity in northern Alberta, Canada on 2022-11-30 produced a M5.3 mainshock, with several significant foreshocks and extensive aftershocks. Determination of whether this sequence was induced or natural highlights many of the challenges in discriminating natural from injection-induced events; although the immediate epicentral region has been historically quiescent, inferred natural and induced seismicity have been observed at distances > 20 km; published fault maps are inconsistent in this area; estimated hypocenter locations exhibit a range of depths, with the shallowest placing the hypocentre near the top of Precambrian basement; and sporadic fluid injections have occurred at various depths within the epicentral region, some of which is ongoing. This presentation reviews and compiles available data for this event, applying several recent schemes to evaluate if the sequence was natural or induced.

Session: Advances in Characterizing Seismic Hazard and Forecasting Risk in Hydrocarbon Systems

Type: Oral

Date: 4/18/2023

Presentation Time: 02:15 PM (local time)

Presenting Author: David W. Eaton

Student Presenter: No

Invited Presentation: 

Authors