Discerning Between Natural and Induced Seismicity by Using Questionnaires Designed to Evaluate Proposals of Induced Earthquakes: Application to the Reno and Kakwa Earthquake Sequences, Northwestern Alberta

The Alberta Geological Survey conducts comprehensive analyses of earthquake sequences to determine whether seismic clusters are of natural origin or induced by anthropogenic activities. These assessments are primarily guided by the criteria established by Davis and Frohlich (1993), which have been widely applied in identifying cases of induced seismicity in Alberta. However, more recent questionnaires were developed to better discern the nature of an earthquake sequence, addressing some of the limitations in the Davis and Frohlich (1993) criteria, including the issues posed by ambiguous and uncertain data. In this study, two questionnaires—Verdon et al. (2019) and Foulger et al. (2023)—were implemented to distinguish between natural and induced seismicity in two case studies: the Reno seismic cluster in the Peace River region and the Kakwa seismic cluster south of Grande Prairie. The feasibility of these questionnaires as effective tools to distinguish between industrially induced seismicity and natural earthquakes was evaluated by analyzing the available information for these two cases across two different time periods: using available information up to November 2022 and March 2023 for the Reno seismic cluster and using available information up to July 2022 and August 2023 for the Kakwa seismic cluster. This approach highlights the evolution in determining the origin of seismicity (whether natural or induced), driven by incorporating additional data and observations over time. For the seismic cluster near Reno, both questionnaires yielded ambiguous results using the information available up to November 2022. However, with acquisition of updated data up to March 2023, the results of both questionnaires became substantially inclined towards an induced seismicity origin. On the other hand, for the Kakwa seismic cluster, both questionnaire results consistently showed a strong inclination towards an induced seismicity origin, using available information up to July 2022 and August 2023.
These questionnaires are one of the multiple tools that a seismologist should use in the determination of natural and induced seismicity; a clear understanding of the regional geology and the physical processes that led to the earthquakes is critical. The relevance of such questionnaires depends on the reliability of the input parameters and the evaluation of the interpreter conducting the assessment; as such, they should be taken as an initial guide for evaluating induced seismicity while acknowledging their limitations and uncertainties.